Analysis of sit-stand-sit movements in adults with rheumatic...

Analysis of sit-stand-sit movements in adults with rheumatic arthritis

Inge Van den Herrewegen

Promotoren: prof. Malcolm Forward, assoc. prof. Lanie Gutierrez-Farewik Begeleider: ph.d. Eva Broström

Masterproef ingediend tot het behalen van de academische graad van Master in de ingenieurswetenschappen: biomedische ingenieurstechnieken

Vakgroep Civiele techniek Voorzitter: prof. dr. ir. Julien De Rouck Faculteit Ingenieurswetenschappen Academiejaar 2009-2010

Prologue & Acknowledgements

This thesis is the final piece of two years in which I discovered biomedical engineering. It came

to me as a very interesting field, not to say it was in fact a relief to see engineering being used

“for good purposes”.

Writing the thesis in Stockholm (instead of Gent) was a big surplus for me. The experience of

studying abroad is a great experience, and it is a challenge to find, write and finish a thesis on my

own. Ofcourse, this thesis wouldn´t have been possible without the help of my two Swedish

supervisors Lanie Guterriez-Farewik and Eva Broström, leading me the way and always prepared to

answer my questions. The assistance of Anna-Clara Esbjörnsson is also much appreciated. My

supervisor at the UGent Malcolm Forward, although far away, deserves my genuine thanks for his

willingness.

I give permission to make this master dissertation available for consultation and to copy parts of this

master dissertation for personal use. In the case of any other use, the limitations of the copyright

have to be respected, in particular with regard to the obligation to state expressly the source when

quoting results from this master dissertation.

Inge Van den Herrewegen 23/06/2010

Overview

This thesis is made by Inge Van den Herrewegen as final piece of the master biomedical engineering

at Universiteit Gent (UG), Belgium. It is written in the context of an Erasmus program with kungliga

tekniska högskolan (KTH), and in cooperation with Karolinska Hospital in Stockholm, Sweden.

Supervisors are Malcolm Forward for UG, Lanie Gutierrez-Farewik for KTH, and Eva Broström for

Karolinska.

This thesis describes chair rising and descending in patients with rheumatoid arthritis (RA) and in a

control group. Subjects (11 RAs and 9 controls) performed 10 sit-stand-sit (SSS) cycles as fast as

possible, and kinematics and kinetics of the first and last cycle were acquired. The aim is to identify

SSS strategy used by RAs. A trunk-first strategy is hypothesized, with characteristics extensive trunk

flexion, higher hip and lower knee moment, longer rising time, and distinct forward/upward center

of mass (CoM) motion. The momentum-transfer strategy (MomTra) is defined as the normative SSS,

mixing forward and upward CoM motion, and distinction between touch&rise and sit&rise was

made. Subjects with RA showed generally more sit&rise behavior and a higher trunk flexion. Two

strategies other than the normal MomTra were distinguished. 6 Patients performed the closely

related “momentum-transfer with higher trunk flexion” (MomTra-TFl), moving also simultaneously

forward and upward after lift-off, but using higher trunk flexion to achieve this momentum-transfer.

The hypothesized trunk-first strategy was found in the remaining 4 patients. They flexed the trunk

extensively then rose nearly vertically. This is defined “distinct-momentum strategy” (DistMom). The

key biomechanical components to identify and distinguish MomTra, MomTra-TFl and DistMom

strategies were CoM motion, trunk flexion and SSS cycle time.

Key words: motion analysis, sit-stand-sit, rheumatoid arthritis, movement strategies, trunk flexion,

center of mass

Analysis of sit-stand-sit movements in adults with rheumatic arthritis


Supervisors: Lanie Gutierrez-Farewik, Eva Broström, Malcolm Forward

Abstract -This thesis describes chair rising and descending in patients with rheumatic arthritis (RAs) and in a control group. The aim is to identify sit-stand-sit (SSS) strategy used by RAs. A trunk-first strategy is hypothesized. The normal SSS is defined as the momentum-transfer strategy (MomTra), with distinction between touch&rise and sit&rise. Two strategies were found in the RAs: “MomTra with higher trunk flexion” (MomTra -TFl), and “distinct-momentum” (DistMom). The last corresponded to the hypothesis. Strategies were mainly distinguished by CoM motion, trunk flexion and SSS cycle time.

I. INTRODUCTION

This thesis investigates daily activities chair rising and descending in a Time-Stand test (TST). Research about rising on its own defined the normal rising strategy as momentum-transfer (MT). Forward momentum is generated from the start of forward trunk motion (Ts) till the buttocks leave the chair at lift-off (T L). Lifting from the chair transfers this forward momentum of the upper body to forward and upward momentum of the total body. Finally all joints extend vertically from Te. The elderly is found to prefer a trunk-first strategy. Elevation only starts after higher trunk flexion, bringing the center of mass (CoM) over the base of support, taking more time. Less momentum transfer takes places: horizontal and vertical component of the CoM motion are more distinct. Kinetics show a lower knee but higher hip moment.

Descending begins with stooping (the subject buckling into stooped position (Tst)), then the actual descending phase starts when the center of mass (CoM) accelerates downwards. All joints flex till seat contact (Tc), after which weight is transferred to the seat during seat loading, ending at Tsit. No descending strategy has been defined.

RA is an inflammatory d isease associated with joint destruction, disability and pain. It is hypothesized that subjects suffering from RA will perform SSS using a trunk-first strategy, with characteristics as found in the elderly (figure 1).

Figure 1: The trunk-first hypothesis.

II. METHODS

The testing involved 11 adults with RA and a control group (9 subjects). The subject were instructed to perform 10 SSS cycles as quick as possible, rising again as soon as the weight is fully on the chair. Only first and last SSS cycle of the TST were used for further analysis. The events Ts,Tl,Te,Tup,Tst,Tc and Ts it were used to describe the SSS cycle (figure 3). The instruction gives freedom of choice between rising after totally sitting with extension of the trunk (“sit&rise”), or directly as soon as the chair is touched (“touch&rise”) (figure 2).

A conventional biomechanical model, common in gait analysis, was used (Plug-in-Gait, Vicon). Subjects wore reflective markers defining 13 body segments. The analysis yielded mainly normalized thorax, hip, knee and CoM graphs & parameters. The Mann-Whitney U test was used with p<0.05. Trunk-first hypothesis, skipping the momentum-transfer, is translated in short CoM curves and a big parameter value.

Figure 2: Two different ways of performing TST.

Figure 3: The 7 events in the SSS cycle.

III. RESULTS

Normal SSS cycle— the normative SSS cycle as observed in the first cycle of the control group was established, and referred to as momentum-transfer SSS (MomTra). Average time for first cycle was 1.94s, fairly divided between rising and descending. Last cycle showed little fluctuations (“hopping”) in knee flexion during sitting: tired subjects let themselves “fall” on the chair. Sitting phase shortened, resulting in smaller SSS time (1.63s). Kinematic characteristics of sit&rise were higher trunk flexion and hopping during sitting phases.

Characteristics of RA patients— patients showed higher trunk flexion, more knee valgus, higher hip and lower knee moment, but these were not significant. RA characteristics protruded significantly more in last than in first cycle, implying tiredness. Patients hopped less, and preferred sit&rise above touch&rise: they performed SSS more careful.

Strategies of RA patients— On basis of the CoM curves, two RA groups were distinguished (figure 4). “Distinct-Momentum strategy” (DistMom) has shorter and thicker CoM curves than normal, reflecting the expected trunk-first behavior. The total opposite behavior, with CoM curves longer and thinner than control curves, is defined as the new strategy “Momentum-Transfer with higher trunk flexion” (MomTra-TFl). CoM parameter value was 22 resp 12 with p=0.02. Kinematics confirmed this distinction (figure 5). DistMom showed a higher trunk flexion (p=0.04) and a 80 ms longer rising phase (p=0.1). DistMom characteristics appeared already in sitting stages, while MomTra-TFl distinguished only at TL and Tc.

MomTra-TFl is close to the normal MomTra (figure 5), but distinguished in CoM motion (p=0.1) and SSS cycle time (1.95s compared to 1.65s; p=0.28). Trunk flexion and knee valgus were non-significantly higher around Tl and Tc.

Figure 1: CoM curves (last cycle) reflecting for x>0 the forward during upward motion of controls (gray) and patients (dots). RA curves are split in two groups RA DistMom (small dots) and RA MomTra-TFl (big dots). Their averages are shown.

Figure 2: Kinematic characteristics of RA DistMom and RA MomTra-TFl: comparison of controls, DistMom. and MomTra-TFl strategies on thoraxangles, hipangles and knee var/val angles.

I. DISCUSSION

Three strategies to perform sit-stand-sit were distinguished. The key biomechanical components found to identify the three strategies were CoM motion, trunk flexion and rising time (figure 6). The normative SSS cycle MomTra as executed by the control group, showed the mixed forward-upward rising phase of MT. DistMom flexed the trunk extensively then rose nearly vertically. Characteristics corresponded to the trunk-first hypothesis: higher trunk flexion and distinct forward/upward CoM were significant; longer rising time was nearly significant. Due to partial moment acquisition failure and small group sizes, no results exist for the moments, but they are expected to follow also trunk-first strategy, being higher in the hip and lower in the knee. RA MomTra-TFl didn´t agree with our trunk-first hypothesis and was closer to the normative SSS, but used higher trunk flexion to achieve the momentum-transfer. Characteristics showed in a non-significant way in higher trunk flexion and longer SSS time, and CoM forward-upward motion overlapped nearly significantly more (p=0.1).

Subject typifications nor the difference touch&rise /sit&rise could explain the variations in strategies: explanation remains for continued investigation.

Figure 3: Distinguishment of RA strategies between each other and with the normal: MomTra (gray), DistMom (orange), MomTra-TFl (yellow). Differences occur on three pillars: max trunk flexion, CoM forward-upward overlap and SSS cycle time. Arrows represent worth mention differences.

II. CONCLUSIONS

Normative kinematics and kinetics for the standard SSS cycle were established, and called MomTra after its similarity with the RIS strategy MT. Patients with RA deviated from this using the closely related MomTra-TFl strategy, or the trunk-first strategy DistMom. Main distinguishing parameters were CoM motion, trunk flexion and rising time, being possibly clinically observable biomechanical measures that could be used to identify SSS strategies.

Table of contents

1. Introduction ...................................................................................................................................... 1

1.1. Introduction to motion analysis ................................................................................................ 2

1.1.1. Motion of the human body................................................................................................ 2

1.1.2. Motion analysis .................................................................................................................. 3

1.1.3. Motion analysis equipment ............................................................................................... 6

1.2. Introduction to chair rising and descending, &relation to rheumatoid arthritis ...................... 9

1.2.1. Rising/descending movement ........................................................................................... 9

1.2.2. Rising/descending strategies ........................................................................................... 14

1.2.3. Rheumatoid arthritis and its influence on SSS ................................................................. 18

1.2.4. Study aims and specific hypothesis ................................................................................. 19

2. Materials & Methods ...................................................................................................................... 21

2.1. Subjects & test procedure ....................................................................................................... 21

2.2. Data processing ....................................................................................................................... 22

2.3. Identification of SSS cycles and events .................................................................................... 23

2.4. Analyzing .................................................................................................................................. 26

2.4.1. CoM analysis .................................................................................................................... 27

2.4.2. Statistical analysis ............................................................................................................ 28

2.4.3. Performing comparative analyses ................................................................................... 28

3. Results ............................................................................................................................................. 30

3.1. General results ......................................................................................................................... 30

3.1.1. Events & phases ............................................................................................................... 30

3.1.2. Features in general graphs .............................................................................................. 34

3.1.3. Comparison with last cycle for controls .......................................................................... 35

3.2. RAs versus Controls ................................................................................................................. 37

3.2.1. Characteristics of RAs ...................................................................................................... 37

3.2.2. Sit&rise as RA strategy ..................................................................................................... 39

3.2.3. More subtle RA strategies .............................................................................................. 42

3.2.4. Conclusion regarding RAs <-> Controls ............................................................................ 43

3.2.5. Testing the trunk-first hypothesis: CoM motion ............................................................. 44

3.2.6. Conclusion: final distinction between controls, RA DistMom and RA MomTra-TFl ........ 47

4. Discussion ........................................................................................................................................ 48

4.1. The normative SSS cycle ......................................................................................................... 48

4.2. Characteristics of RAs .............................................................................................................. 50

4.3. Strategies of RAs ...................................................................................................................... 51

4.4. Trustworthiness of the data .................................................................................................... 53

4.4.1. Moments .......................................................................................................................... 53

4.4.2. Small groups and significance .......................................................................................... 54

4.4.3. Graph analysis .................................................................................................................. 54

4.4.4. First or last cycle? ............................................................................................................ 54

4.4.5. RIS <-> SSS Cycle times .................................................................................................... 55

4.4.6. Accuracy of tym-txm ........................................................................................................ 55

4.4.7. Knee valgus ..................................................................................................................... 55

4.5. Future perspectives ................................................................................................................. 56

APPENDIX .............................................................................................................................................. 57

ATTACHMENTS ...................................................................................................................................... 83

REFERENCES ........................................................................................................................................... 85

Table of abbreviations

Abbreviation Explanation

SSS Sit-Stand-Sit

TST Time-Stand Test

STS Sit-to-Stand

RIS Rising

DESC Descending

GRF Ground reaction force

CoM Center of Mass

RA Rheumatoid Arthritis

MomTra Momentum-transfer

DistMom Distinct-momentum

MomTra-TFl Momentum-transfer with

higher trunk flexion

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1. Introduction

A very practical indication of joint problems such as in rheumatoid arthritis is difficulties in moving, and more specifically in the important daily activities (for example, walking, stair climbing, chair rising...). These are important because even small dysfunctions may cause a big decrease of quality in daily life. Examining a patient’s’ way of performing a daily activity is thus useful for purposes of diagnosis of the severity and impact of the disease. Walking is by far the most investigated (using the techniques of gait analysis). This thesis though, will focus on chair rising and descending. Performed on average 4 times an hour, this is a main daily activity [46]. But it is also a very aggravating movement for knee and hip, which makes it a good indicator of problems in these joints. According to pain and limitations, the patient will adapt their rising/descending strategy. In clinical practice, rising from a chair is already a common test, but unlike in gait analysis, the tests are still performed “on sight” i.e. using skills of observation: whereby the examiner judges the compensatory maneuvers just by watching the test. This thesis aims to assess the adapted motion more qualitatively, by means of motion analysis. This approach will include measurement of the movement of the body in space (kinematics) and the forces producing these movements (kinetics). One special aspect of the kinematics is the movement of the center of mass (CoM) of the body, because those data create more insight concerning stability.

As a conclusion, this thesis will use motion analysis to examine chair rising and descending in two subject groups: a reference group to establish a normative data set, and a group of patients with rheumatoid arthritis to search for a compensatory strategy.

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1.1. Introduction to motion analysis 1.1.1. Motion of the human body

The human body moves thanks to flexible bone connections: a general synovial joint connects two bones in a moveable way (figure 1). The joint surface is covered with cartilage (more specifically hyaline cartilage), which is very important in the joint: it is a much softer material than bone, and can move with little‐to‐no friction when in contact with the opposing surface. Secondly, cartilage has a certain shock‐absorbing nature, because of its ability to hold water molecules well. Furthermore, the synovial membrane together with the cartilage, forms a cavity for the synovial fluid, which serves as the joint cushion. The joint stability is established by its shape, and by surrounding ligaments and muscles [29].

The joints of interest in this thesis, hip and knee, are such synovial joints. The hip joint connects the femoral head (the ball‐formed end of the thigh bone) with the acetabulum (the socket of the pelvis) (figure 2). It is a simple ball‐and‐socket joint, allowing for a wild range of rotation and movement, somewhat limited by five ligaments. The main hip motion is flexion‐extension from 15° retroflexion till 125° anteflexion [41]. The knee joint is a slightly more complex joint, made up of three bones: the femur, tibia, and the patella (kneecap) (figure 3). The knee is a very important weight‐bearing joint in the body, and is stabilized by 4 ligaments. Furthermore, there are 2 menisci between the cartilage surfaces of the femur and tibia: they are shock absorbers that help to center the knee joint during activity and to minimize the amount of stress on the articular cartilage. The combination of the menisci and the surface cartilage in the knee produces a nearly frictionless gliding surface. The knee is an incredible joint: strong, flexible, and very tough. Its main motion is flexion till 130° [32,35].

The muscles surrounding a joint produce together the joint moment, causing the movements of the segments. Muscle actions can thus be seen as a set of moments acting about a joint. Hip and knee joint moments are positive in extension. According to Doorenbosch and coworkers, the main muscles creating the moment for joint flexion during rising from a chair are gluteus maximum, biceps femoris caput longum, Rectus femoris, Gastrocnemius, soleus, and tibialis anterior [15].

Figure 1: a general synovial joint [33]

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Figure 2: the hip joint [34] Figure 3: the knee joint [35]

1.1.2. Motion analysis 1.1.2.1. What and how of motion analysis

“Analyzing a motion” provides kinematics (positions, velocities and accelerations of body parts), and kinetics (joint moments). These data are gathered by what is called full motion analysis, which can be done in different ways, but in its ‘completeness’ it should include a motion tracking system (MTS) for the kinematics, combined with a ground reaction force plate (GRFplate) to compute the kinetics (figure 4). This is the most common way and was, used by some 70% of the studies concerning chair rising [23]. Other ways exist also (e.g. Music and co‐workers researched body mounted accelerometers and gyroscopes. These are cheaper, portable and less time‐consuming), but are less accurate [46]. To link the gathered data to reality, a body model is applied.

The MTS (motion tracking system) can be either a pure video analysis that uses mathematical image processing, or the more accurate optical tracking system using retro‐reflective markers, which is widely used in clinical practice and commercially available in shape of the Vicon or ExpertVision systems [28]. The retro‐reflective markers are placed on palpable bony points on the body, (landmarks) which serve to calculate the segment and joint center positions. Conventional marker placements were earlier developed for analysis of gait, and Galli and coworkers showed that these are appropriate for chair rising analysis too [12].

A multi‐segment human body model approximates the human kinematics & kinetics from the gathered MTS and GRF plate data. Different body models exist: the 7‐segment linked model is used quite often (reducing the whole upper body as the HAT=hat‐arms‐trunk segment [46]), but the whole‐body model is more accurate. Created by Davis, this model was developed for gait analysis but is perfectly usable in chair rise analysis too [45]. It represents the body consisting of 15 rigid bodies (‘segments’) connected by joints: two feet, shanks, thighs, hands, lower and upper arms, and one pelvis, thorax and head (figure 5). The movements of the segments are generally described in Euler angles and are dictated by the 3 rotational degrees

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of freedom of the joints. Joints can transfer inter‐segmental forces, and the actions of the muscles and ligaments around the joint are modeled as inter‐segmental moments.

Figure 5: complete motion analysis includes a motion tracking system and a GRF plate. They are translated into joint kinematics and kinetics using a body model.

The output of the MTS is the marker positions, basically points in space. Davis’ multi‐segment body model comprises these markers into segments (3 markers define together 1 segment), defining the orientation of segmentally‐embedded coordinate systems and instantaneous joint center locations (figure 6). Finally, angles between segments are calculated from these [45]. The most important of these final angles are thorax, hip, knee and ankle angles (figure 7). These can be single and double differentiated by weighted least squares numerical differentiation to obtain velocities and accelerations. The center of mass (CoM) is computed from the kinematic data, summing all contributions of each of the separate body segments [6]. The kinetics, net 3D joint moments Mx,My,Mz, are computed from the combination of kinematic and force plate data by application of Newtons second law and Euler’s equations of motion with the inverse dynamic method [12,2,18,19]. The equations are solved starting at the foot (on which the known GRF acts) and proceeding from segment to segment. On each segment i connected by joint kl with segments k and l, intersegmental forces Fki and Fli, intersegmental moments Mki and Mli, and gravitational force representing the weight of the segment mi, have to be considered for calculation of the joint moments (box 1). A first impression of a joint moment can be obtained by multiplying the reaction force vector with the distance from the joint to that vector (figure 8). This includes errors, since inertial and gravitational effects are neglected.

Figure 4: visualisation of the 15‐ segment whole body model

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Figure 7: segment coordinate systems and joint center locations determined from the marker position data (only lower body shown) [45]

Figure 8: approximation of the hip joint moment by multiplying the GRF (red

arrow) with the distance to the joint (gray arrow)

(1) Fki + Fli + Fei + mi.g = mi.ai (2) rki x Fki + rli x Fli + rei x Fei + ri x mi.g + Mki + Mli = ri x mi.ai + d/dt(Ii.ωi) (3) = (2) ‐ ri x (1) : Rki x Fki + Rli x Fli + Rei x Fei + Mki + Mli = d/dt(Ii.ωi)

Box 1: (1) and (2) are the equations of motion to be applied on each segment. In these, the positions are relative to some stationary reference point O. In solving the inverse dynamics , the previous equations

applied to a seperate segment are taken relative to the CoM of that segment (ri), which is moving. This gives a third equation (3). Writing out (1) and (3) for all segments will give sequentially all joint forces and

moments.

Figure 6: main angles calculated from

segment positions

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1.1.2.2. Errors & assumptions

Leardini and co and Music and co investigated the impact of errors on the complete motion analysis (figure 9). Errors are introduced due to the marker‐based definition of the segments: the markers on the body surface are assumed to reflect the motion of the underlying bones, neglecting soft tissue deformation. Especially at the thigh this deformation can be significant, inducing an error of around 30 mm in the allocation of the hip joint center. Variables in the sagittal plane are less affected by this, with the error in the motion of the shank of 10 mm in translation and 8° in rotation [24]. Especially during rising motion, a false valgus position of the knee might be observed due to a small misplacement of knee markers. More errors are introduced by the simplicities of the body model: segments are assumed to be rigid bodies with their masses concentrated in their CoM, and are connected by only one joint (which isn’t the case e.g. for the ankle joint being a combination of many articulations); joints are modeled as ideal pin joints with no added friction during rotation. The errors introduced by all these assumptions are acceptable [46]. Furthermore, the model doesn´t count the chair as point of interaction with the environment.

Figure 9: errors are introduced in the complete motion analysis due to marker placement and body model

approximation

1.1.3. Motion analysis equipment

Equipment includes infra‐red cameras to assess the kinematics, and force plates to assess kinetics.

The cameras are distributed over the edges of the calibration volume, not facing one other directly. They send out pulses of infra‐red light, which is reflected by retro‐reflective markers donned on the subjects. This reflected light is captured again by sensors mounted on the cameras (figure 10). The cameras are calibrated statically (putting a marked L‐frame at the force plate corner to establish origin and axes orientation) and dynamically (waving a small marked rod in the calibration volume). Each camera, recording a certain 2D view in which some marker are moving, distinguishes the markers from the noise by a process called spot‐searching: for every reflection, the camera generates a grayscale blob, with certain intensity depending on the strength of the reflection. If the grayscale blob is circular and the pixel intensity is brightest at the center, the camera subjects it to a circularity threshold to decide whether it is a marker or not. The distinction is possible due to the much stronger and particularly shaped reflection of a marker, compared to everything else the infrared signal encounters [26]. Each of the optoelectronic cameras records a 2D view, simultaneously at 100 Hz; information from all the cameras is required to reconstruct the 3D markers positions.

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Ehara and co tested a 6‐camera reconstruction system and showed an error of around 0.9 mm, depending on the field of camera view and the resolution of the cameras (a marker can be ignored due to partial occlusion or merging with other markers).

The ground reaction force (GRF) plates serve to measure the external forces and moments. The vertical Fz is the most important showing vertical acceleration/deceleration, but also the antero‐posterior Fy is very useful (since it reflects forward momentum generation), as is the left‐right Fx (showing asymmetry in the motion). Kralj and coworkers state that the acquired moments can be ignored by assuming that the foot doesn’t exert a torque on the force plate [10]. The GRF plate in the Vicon system is basically a load transducer, working with strain gauge load cells, converting the load to a change in resistance (figure 11). This change is measured by a Wheatstone bridge (figure 12), which gives a small voltage output (millivolts). 6 Such Wheatstone bridges are combined in one force plate, giving 6 output voltages. These are sent to a high‐gain amplifier and finally to an A/D converter. The digitized signals are linked to respectively Fx, Fy and Fz (components of the reaction force), and Mx,My and Mz (moment components) by the calibration matrix C (figure 13). The force plate with strain gauge load cells can be a very accurate measurement device, but there is one drawback: when abrupt load changes occur, every load cell is subjected to "ringing" and an oscillating data pattern is observed. This originates from the spring‐like deforming behavior of load cells, exhibiting vibrations at its natural frequency. All data should afterwards be passed through a low‐pass filter (e.g. 2nd order Butterworth filter) to get rid of the noise (it removes high frequency components and thus produces smoother data).

Figure 11: strain gauge [42]: their deformation due to force corresponds with a change in resistance

Figure 10: position tracking of a reflective marker

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Figure 13: The calibration matrix C, calculating the force and moment inputs to the platform (Fj) based on the

platform outputs voltages (Vi). The matrix can be simplified by using only the diagonal terms, since they actually represent the conversion load‐voltage, and the others represent only the cross talk between the transducers [44].

Figure 12: full wheatstone bridge, connecting four active strain gauges, measuring the change in resistance. This is the most sensitive and most accurate kind of bridge. Applying the stable excitation

voltage, the alternate two terminals of the bridge are balanced according to the principle of a Wheatstone bridge (V = 0). When then a load appears, small mechanical strains will subtly change the resistance of the bridge arms, and the bridge will become unbalanced. This results in a signal output,

related to the stress value.

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1.2. Introduction to chair rising and descending & relation to rheumatoid arthritis

1.2.1. Rising/descending movement

This thesis focuses on the Time‐Stands‐Test (TST), consisting of 10 Sit‐Stand‐Sit (SSS) cycles performed as quickly as possible. As far as is known, no research from a biomechanical point of view has been performed on the TST specifically. Though, rising as a test on its own (STS = Sit‐To‐Stand) has been analyzed thoroughly since the 1990’s [15,16,12,10,7]. Furthermore, STS doesn’t differ significantly from the rising part of the SSS movement [7], which makes its findings and definitions valuable also this study on the TST. Descending to a chair is generally considered as clinically less important and thus noticeably less analyzed: only two studies include a descending analysis [10,7].

Their most important findings are summarized in the following paragraph.

1.2.1.1. Main features

STS activity is, in mechanical terms, one of the most demanding daily activities. An STS movement requires a bigger peak joint moment, yields a higher peak hip joint pressure, and requires greater muscle strength than most other daily activities like walking, jogging and stair climbing [2]. The exact values of maximum joint moments depend on the applied strategy (and thus on the patient), but the sum of the peak hip and knee moments is found to be the same regardless of strategy. According to Yoshioka and coworkers, in order to perform a STS task, max knee + hip joint moment must be 1.53 Nm/kg [18]. Furthermore, STS requires coordination of several muscle groups, with special requirements on balance [46]. According to Hirschfeld and coworkers, weight transfer during STS is induced already during sitting by forces exerted by buttocks and feet. The buttocks create here the isometric rising forces (forward acceleration), while the feet perform mainly damping control before seat‐off. The CoM moves forward then upward: its horizontal component arises from forward rotation of trunk while its vertical component is due to extension of the hips and legs [54]. Kerr and coworkers as well as Kralj and coworkers found that descending is performed more slowly than rising [7,10]. This longer descending time is mostly due to more caution, demanded by the deceleration of the body mass working against gravity. Also subjects might employ a slower movement in descending because of lack of visual information, making them unsure about the location of the endpoint.

The rising/descending motion described above, is the one found in most healthy individuals. Scarborough and coworkers called it MT (“momentum‐transfer” strategy). According to Vannozzi and coworkers and Yoshioka and coworkers, it is considered as the strategy which holds an optimally coordinated use [8,18]. In other words, the most common way of rising/descending is also the most efficient one.

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1.2.1.2. Division in phases

In gait analysis, a division of the common movement into phases is performed (divided into stance phase and swing phase, and each further divided into sub‐phases), and this division is widely accepted. For chair rising/descending though, there is no standard classification. Schenkman and co‐workers and Kralj and co‐workers have made some attempts to define the rising [6,10] and descending [10] movement. The two components RIS (rising) and DESC (descending) are visualized in figure 15.

Figure 14: visualisation of chair rising (up) and descending (down) [7]. The length between the figures represents roughly the timing, showing a slightly longer descending phase.

‐ RIS ‐ The main events distinguishable during STS can be defined using two different approaches: Schenkman and co‐workers bases the event definitions mainly on kinematic data [6], Kralj and co‐workers on force platform data [10]. In several studies a pressure‐sensitive seat switch is also used to define the lift‐off event very accurately, then this event can be used as a point for the synchronization of various result curves [15,12]. No matter which defining method is applied, all studies agree on the definition of 5 main events during STS as follows: start of STS (Ts), Lift‐off (TL), start of extension (T45%), upright position (Tup) and Tquiet standing (table 1). Ts, TL and Tup are the most distinguishable ones. Based on those main events, the STS movement is divided in phases. No standard division exists, but Schenkman and Kralj agreed on the main division into 3 mechanically distinct phases [6,10] (figure 15, table 2). Starting in the seated position at Ts, the momentum‐generation phase begins with the first trunk flexion. This phase generates the initial horizontal upper‐body momentum for rising by flexion of the trunk and pelvis. At TL, the Momentum‐transfer phase starts. The initial horizontal momentum of the upper body (the trunk moving forward) is transferred to horizontal and vertical momentum of the total body (lifting from the chair). In this phase, maximum hip and thorax flexion and maximum hip and knee moments occur. Momentum‐transfer ends at T45%, and the extension phase begins. The body rises only in a vertical direction now, extending all joints simultaneously. Quiet standing is only reached after more seconds (often assigned as a 4th phase, the ‘stabilization phase’).The movement can be divided further by including vertical

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acceleration‐deceleration of the body. Vertical acceleration starts at ‘start of seat unloading’, a moment distinguishable by a fast increase in Fz (due to redistribution of body mass and vertical acceleration). Vertical acceleration goes into deceleration at T45%, which in its turn lasts logically till upright position.

Table 1: main events during STS Ts, Tl and Tup are very important and accurate. Quiet standing is a more arbitrary time. T45%, the start of extension, , takes place at around 45% of the STS movement cycle, at max ankle angle [6] or end of vertical acceleration [10]. Both studies define it independently, and it is only a coincidence that both occur at 45% of the STS cycle. More info about the comparison between both is given in attachments A definition of T45%, an attempt to show that the times are indeed comparable although from different studies.

MAIN EVENTS force platform data Motion analysis data Seat switch START OF STS (Ts)

Fast increase in Fy (due to generation of forward momentum)

Noticeable start of trunk flexion

LIFT‐OFF (Tl) Fy is at its maximum first instant when angular velocity of hip angle is 0 rad/s

Seat switch off

Start of extension (T45%)

max ankle dorsiflexion OR End of vertical acceleration

UPRIGHT POSITION (Tup)

All joints fully extended OR No more hip angular velocity

Quiet standing

Fz converges to equal BM

Figure 15: Phases in STS

Table 2: Phases in STS

One more feature is associated with the characterization of motion: states of equilibrium. These depend on 1) whether the body is moving or not and 2) the relative place of the body´s center of mass (CoM) and the point of application of the ground reaction force (center of

momentum‐generation

Ts momentum‐transferTL extensionT45% Tup

PHASES Start End Description Stability

I Momentum‐generation Ts Tl Hip flexion while still seated Inherent stability II Momentum‐transfer Tl T45% Rising from the chair Dynamic stability III Extension T45% Tup Extension of the body Quasi‐static stability

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pressure CoP). Three different states exist [6]: static, quasi‐static and dynamic equilibrium. When the body is not moving, it is said to be in static equilibrium. This implies directly that the CoP is the vertical projection of the CoM. A body that is moving but only through positions of static equilibrium is called inherent stable. Quasi‐static equilibrium occurs when the CoP and projected CoM are nearly coincident. A moving body is said to be in dynamic equilibrium, since the CoP is far from the projected CoM. A static body would fall in this situation, but a moving body can traverse these positions. All three of these states occur in the STS movement [6]. In the momentum‐generation phase, the CoM is over the base of support (the chair), so the body is inherent stable. The presence of kinetic energy in the momentum‐transfer phase implies that the CoM is not directly over the CoP: the body relies on dynamic stability. This is considered the most challenging phase: the joint moments reach their maximum just after the buttocks lose contact with the chair. Finally the CoM projection quickly approaches the CoP, satisfying (at the beginning of the extension phase) the criterion for quasi‐static stability (table 2).

‐ DESC ‐ The sitting down movement is analogous to standing up, and therefore Kralj and co‐workers and Kerr and co‐workers defined the events and phases in a logical reversed order [10,7]. They both used ‐as in rising‐ another definition, but the defined phases match more or less. The main events are the start of descending (Td), stooping posture (Tst), sitting position (Tsit) and Tquiet sitting (table 3). Using these events, three phases are again defined (figure 16, table 4). Stooping phase begins at Td, and ends at Tst. The subject generates an impulse for moving the body weight backwards to the seat, more precisely the subject buckles into a stooped position (figure 17). This stooped position is a posture essentially never observed during quiet stance: the forces and positions of normal quiet stance are said to be destabilized [7]. At Tst, descending phase begins. The body segments accelerate into flexion (thus GRFz < body weight), then slow down (thus GRFz > body weight) but keep flexing till the chair is touched. Seat loading, from Tc, till Tsit, transfers the body weight to the seat, and the hip angle decreases again. Quiet sitting is only reached after several more seconds (often assigned as a 4th descending phase, the ‘stabilization phase’). The descending movement can be further divided by including vertical acceleration‐deceleration. Vertical acceleration begins at Tst and deceleration begins in the middle of the descending phase. Vertical deceleration ends logically with the sitting position. The three states of stability are again present: quasi‐static during stooping, dynamic during descending and inherent stable during seat loading (table 4).

Table 3: main events in descending.

MAIN EVENTS force platform data (10) Motion analysis data (7) Seat switch START OF DESCENDING (Td)

change in Fy (to go to stooped posture)

Hip joint starts to flex

Stooping posture (Tst = T15%)

change in Fz (due to start downward acceleration)

SEAT‐CONTACT (Tc)

Hip angle is maximum

Seat switch off

SITTING POSITION (Tsit)

Fy is minimum Trunk angular velocity is 0

Quiet sitting Fluctuations in Fy decrease

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Figure 16: phases in descending

Table 4: phases in descending

Figure 17: sketch of stooped position

1.2.1.3. Standardization of the testing procedure

No standardization exists for the restrictions, parameters and instructions during chair rising/descending tests. With regard to the initial sitting position, most studies use a chair height of 0.40m (according to the British Standards Institute) [2,18], or an adjustable height depending on the knee (80% knee height [6], tibial plateau height [8], “to achieve a comfortable position” [10&12]). The feet are mostly positioned to create a vertical tibia orientation. During rising, the arms can be kept immobile (crossed over the chest) in order not to influence the CoM and prevent covering of the lower limb markers in instrumented motion analysis; on the other hand, letting the arms move freely gives a more correct image of the applied subject strategy. The same dilemma exists concerning timing: studies attempted to use forcing methods (e.g. following the beat of a metronome [6, 53]), or instructions (e.g. “as fast as you can” [36]) to control timing; mostly it is preferred to let subjects perform at a velocity of their own choice [10,7,49,15,16].

These different testing procedures affect the chosen strategy, especially the initial sitting position [23,36,37] and timing [20,23,36].The consequences of testing procedure choice affect the kinematics as well the kinetics (figure 19). Janssen and co‐workers wrote a review investigating the importance of chair height, concluding that it is critical to control the initial position of the subject: a higher chair leads to lower moments at the knee and hip [23]. Linden and co‐workers and Brunt and co‐workers made similar remarks for foot position and ankle angle [36, 37]: putting the feet more anterior (knee more extended) locates the GRF further from the hip joint and thus leads to higher hip moments. Furthermore, this position creates a

stoopingTup descendingTst seat loadingTc Tsit

PHASES Start End Description Stability

I Stooping Td Tst Upright to stooped posture Quasi‐static stability II Descending Tst Tc Descending Dynamic stability III Seat loading Tc Tsit Weight transfer to seat Inherently stable

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potential for instability. Advancing or elevating only one leg partly excludes this leg and the closest leg will compensate resulting in higher moments in that leg. In the free position, subjects will automatically place their non‐affected foot furthest back [11]. Concerning timing, according to Janssen and co‐workers, letting subjects choose their own pace is the optimal way to capture the most natural pattern and task time, which is a useful indication of the subject’s’ performance. In a slowly performed STS the subject puts the CoM closer to the CoP by putting the legs closer to the seat, and leans the trunk forward, thus requiring nearly no forward momentum generation. Faster standing up can be considered more as a DVR (dominant vertical rise) movement, with increasing the peak vertical momentum of the CoM and earlier activated extensor muscles [16,20,23,36].

Figure 18: Differences in testing procedure have consequences on kinematics and kinetics.

1.2.2. Rising/descending strategies

The normal movement just described (momentum‐transfer strategy or MT [16]), is not possible for every individual. Subjects with functional limitations are found to use a compensatory strategy, adapting their motion to reflect their abilities. Limited range of motion (ROM), joint pain, muscle weakness and poor coordination alter the kinematics and kinetics [4,12,15,16,17,25,38,48,49,50]. These studies cover examples of MT‐deviations due to e.g. age, obesity, arthrosis and arthritis. For the elderly, Scarborough and coworkers defined the deviating characteristics in a strategy called ETF (extensive trunk flexion) [16]. The same characteristics return in several of the other studies. Doorenbosch and co‐workers examined the kinetics and kinematics of this strategy and called it FSTS (sit‐to‐stand with full trunk flexion) [15].

1.2.2.1. An artificial trunk‐first strategy: definition of FSTS [15]

Doorenbosch and co‐workers instructed healthy subjects to perform twice STS: once naturally, once whilst “first bending fully the trunk”. A side from the normal strategy MT (here called NSTS or normal sit‐to‐stand), a second strategy FSTS was defined: sit‐to‐stand with full trunk flexion. The main characteristics of FSTS yielded higher hip angles, and significantly higher hip but lower knee joint moments. No deviation of knee angle occured (figure 20).

The instructed large trunk flexion in FSTS brings the CoM close to the CoP before lift‐off, which drastically reduces the need for forward momentum generation. The movement can thus be

chair hight

higher lower hip and knee moments

foot position

more posterior lower moments

arms free influence CoM motion

timing faster less trunk flexion

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executed much slower (>2s), and totally in quasi‐static equilibrium. The momentum‐transfer phase is consequently skipped, whereas the extension phase is quite similar to normal (only more hip extension necessary). Elevation of the body thus only starts after the upper body “rolled” forward, bringing the CoM over the base of support (figure 19). These features result in a lower knee but higher hip moment (figure 20). Just after lift‐off (being the moment that max moments occur), the hip joint is further but the knee joint is closer to the GRF line of action in FSTS. This implies thus bigger hip but smaller knee joint moments in full trunk flexion strategy. The decrease in distance to the knee joint for instance, was in this example about 4 cm, corresponding with a net moment decrease of 0.2 Nm/kg for each leg. Knee and hip moments are found to be complementary. The ankle moment stands independently, being more related to the CoP location. Investigating ankle moment is only useful when compared to the CoP location.

Figure 19: altered kinematics (above: hip and knee angle) and kinetics (under: hip and knee moment) in FSTS (dotted line) compared to NSTS (full line). The vertical line represents lift‐off: maximum angles and momenta

occur just after this moment.

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1.2.2.2. Strategy of the elderly: definition of ETF [16]

FSTS is an artificial strategy, but its characteristics return naturally in subjects with limitations. Scarborough and coworkers defined different strategies for elder subjects (figure 21). Compared to MT, ETF strategy includes again a more extensive trunk flexion, no change in knee angle, and the kinetics are altered with a bigger hip and lower knee moment. The extensive trunk flexion while seated brings the CoM closer to the CoP at TL, reducing the momentum‐transfer phase severely. This implies that nearly the whole motion is performed in quasi‐static stability (table 5). Papa and coworkers, who focused also on elder persons with functional limitations, found the same characteristics (although they did not define it as being a strategy) [50]. Extra findings were a higher horizontal CoM velocity before accelerating upwards (thus higher horizontal momentum), and lower coordination effort necessary to achieve balance.

Scarborough and co‐workers also mention a third strategy, DVR (“dominant vertical rise”). One could see it as an exaggeration of MT or the opposite of ETF, in which the trunk is nearly not flexed at all. It is mainly distinguishable by a knee torque larger than normal (table 5). Since this report will focus on patients with knee problems, this strategy is not relevant.

Figure 20: visualisation of hip and knee moment in NSTS and FSTS. The lenght of the blue and purple line represent respectivily hip and knee moment,

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Figure 21: visualisation of the strategies in the elderly [16]: MT (a), ETF (b), DVR (c)

1.2.2.3. Strategies due to other limitations

Su FC and co‐workers, and Farquhar and co‐workers analyzed subjects with osteoarthritis after total knee arthroplasty [25,49]. They focus mainly on the differences between left and right, but also found more trunk flexion, a larger hip but smaller knee moment and a higher CoM horizontal velocity.

Epifanio and coworkers made the only rising analysis including subjects with rheumatoid arthritis (RA) [13]. The study was more of an illustration of the use of waveforms for graph analysis (FPCA‐method) than really dissecting RA strategies. Their small analysis showed that RA leads to a higher trunk flexion and a smaller knee moment during rising.

1.2.2.4. The most efficient strategy

Yoshioka and co‐workers investigated the most efficient rising strategy from a pure mechanical point of view [18]. Depending on which moment to minimize, different ‘optimal strategies’ exist (figure 22). The strategy minimizing the sum of all joint moments is considered as the normal strategy MT. Minimizing knee moment leads to altered kinetics with a higher trunk flexion at TL.

Figure 22: visualisation of rising strategies minimizing knee moment (up) and hip‐knee‐ankle moments (down)

Table 5: summary of the characteristics of ETF and DVR [16]

Characteristics of ETF (and DVR) compared to MT

ETF DVR

Ankle and knee angle = = Trunk angle 12° more 10° less Ankle and hip moment 1%BW more 1%BW less Knee moment 0.5%BW less 1%BW more CoM: forward momentum 0.03/s more 0.01/s less CoM – CoP distance at TL closer further stability Quasi‐ static Dynamic Total STS time 0.5s longer =

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1.2.3. Rheumatoid arthritis and its influence on SSS

1.2.3.1. What is rheumatoid arthritis?

Rheumatoid arthritis (RA) is an inflammatory disease associated with joint destruction, disability and pain [52]. This leads to chronic and symmetrical problems, with activity that comes and goes. Mainly the joints of the extremities (arms and legs), and especially wrist and fingers are affected. RA is particularly devastating in joints of the lower body, since they can be rendered incapable of withstanding the stresses of weight bearing. The exact cause of RA is still unknown; genetic factors, environmental factors and life style are the most risk factors.

1.2.3.2. Practical symptoms

There is no single test for Rheumatoid Arthritis, and the diagnosis is based on several criteria. Usually, ACR classification criteria for RA are applied, where 4 out of 7 criteria have to be fulfilled. The symptoms vary, but most patients develop a progressive disease leading to pain, joint destruction and disability. The joint gets inflamed, limiting joint mobility (smaller ROM, “stiffness of the joints”) and causing pain. As a result of less weight bearing due to the pain, muscles begin to show some atrophy and ligaments become more lax [51]. Table 6 illustrates how the main joints of the lower body are affected, which could have an influence on SSS test performance.

Table 6: possible influence of RA to alter SSS motion: symptoms in the lower body joints. Forefoot and knee problems are observed in earlier stadia than ankle and hip problems.

Practical symptoms of RA

Forefoot (MTP) limited ROM [40] Ankle limited ROM especially in plantar flexion Knee pain at the utmost positions

limited ROM in flexion and extension (more in flexion) bigger ROM varus/valgus [48]

Hip limited ROM in flexion

1.2.3.3. Consequences of RA symptoms for SSS

RA patients will probably develop their own compensatory rising mechanism, adapted to their limited ROM and joint pain. Allin and co‐workers predict initial foot advancement due to limited knee flexion and smaller ankle dorsiflexion angle [11]. According to Epifanio and co‐workers, subjects with limited knee extension show some final persistent knee flexion [13]. Pain in a joint will result in lower moments in that joint [25], and Savelberg and co‐workers found that muscle weakness around the knee induces a rising motion with increased trunk flexion [17].

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1.2.4. Study aims and specific hypothesis

The overall aim of this thesis is to determine functional outcome such as chair rising and descending among persons with Rheumatoid Arthritis. This is achieved by comparing the biomechanical quality of movement during sit‐stand‐sit (SSS) between RA patients and healthy controls. A template is created to implement the sit‐stand‐sit test in clinical practice at Karolinska hospital.

This thesis tries to find specific SSS strategies used by patients with RA. No so‐called “typical RA‐strategy” has been defined as we know. Furthermore, previous studies mostly included just rising but not the combination with descending in a time‐stand test.

Specific hypothesis

Looking at all previous mentioned results, the same features seem to return. The features occurring in FSTS (as artificial strategy) and ETF (observed in the elderly), together with the results from the two studies concerning osteoarthritis and the few RA‐characteristics found in the FPCA‐study, fit all in the same pattern (box 2). This pattern is called “trunk‐first strategy”, and it exhibits mainly four characteristics (figure 23). As the name implies, more trunk flexion occurs. Concerning kinetics, there a larger hip moment but a lower knee moment is involved. The CoM moves longer horizontally resulting in a bigger forward momentum. The CoM position is closer to the CoP at TL, inducing a quasi‐static stability during nearly the whole rising motion. CoM motion is divided into two more distinguishable stages: first forward, then upward. This is referred to as momentum‐distinct instead of momentum‐transfer. Rising motion is performed slower.

Our hypothesis is that subjects suffering from RA will exhibit a similar trunk‐first strategy.

Figure 23: characteristics of the trunk‐first strategy

AnglesHip & thorax: more flexion

Knee: no change

MomentsHip: biggerKnee: lower

CoM closer to CoP at TL=> momentum‐distinct instead of

momentum‐transfer

Rising timelonger

trunk‐first strategy

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Box 2: Assembly of “the trunk‐first strategy”. Several studies show the same characteristics.

(a) The features of ETF are exactly the same as found in the artificial FSTS (only less pronounced). They are the main characteristics of the trunk‐first movement.

(b) Also the results of osteoarthritis studies show similarities (table 6).

Table 7: trunk‐first characteristics in studies involving osteoarthritic subjects

Reference [25] [49] More trunk flexion Higher hip moment Smaller knee moment Higher CoM horizontal velocity

(c) A higher trunk flexion and a smaller knee moment during rising were observed in the small

study involving subjects with RA. (d) Minimizing the knee moment results in a strategy with higher trunk flexion and higher hip

moment

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2. Materials & Methods

2.1. Subjects & test procedure

A consecutive series of patients with RA were invited to participate in the study during the period of 2007‐2009. Inclusion criteria were independent ambulation of 12 m and joint activities in lower extremities. Eleven adults with RA, 3 men and 9 women, mean age 59.3 years (SD 14.1) range 35‐74 participated in the study. A control group in approximately the same age span as the subjects was recruited from colleagues, friends and acquaintances. The control group consisted of 9 healthy adults, 2 men and 7 women, mean age 52 years (SD 14.6) range 37‐75, with no known history of orthopaedic surgery in the lower limbs or neurological signs. There was no significant difference between the entire groups or between gender with respect to age, weight and height (tables 8 resp 9). Participation was voluntarily and ethical approval was obtained from Karolinska University Hospitals Ethics Committee.

The subject was seated on a chair (height 0.40m without back or arm supports). The chair was positioned in front of the two ground reaction force plates (figure 24). The instruction of the time‐stand test was to “rise and sit down on the chair, 10 times in a row as quick as possible”. Starting in seated position, 10 Sit‐Stand‐Sit cycles were thus sequentially performed.

A conventional biomechanical model was used as common in gait analysis (Plug‐in‐Gait, Vicon) [45]. This included 34 retro‐reflective markers. Subjects donned the markers based on established anatomical landmarks, creating a model of 13 body segments: head, trunk, upper arms, lower arms, pelvis, thighs, shanks, and feet (see Attachments B: marker positions). Antropometric data were measured for identification of joint center and joint axis (table 10).

The data were collected with a 3D motion analysis system (Vicon, Oxford UK) at the motion laboratory at Karolinska University hospital. Two regular video cameras recorded the movement (frontal and sagittal view), and 8 opto‐electronic cameras collected the marker data. Each motion analysis camera collected 2D positions of the markers at 100 Hz. Ground reaction force data was collected with 2 force platforms (Kistler, Winterthur Switzerland) at 1000 Hz.

Figure 24: sketch of the test arrangement

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Table 8: comparison between patient and control group showing average +‐standard deviation

Characteristics patients / controls

RA Controls

Age (yrs) 59,3 +‐ 14.1 52 +‐14.6

Gender 8 F, 3 M 7 F, 2 M

Height (m) 1.64 +‐0.1 1,68 +‐0.1

Weight (kg) 67,5 +‐11 70.1 +‐12

disease duration (yrs) 8,4 +‐7

Table 9: comparison between genders showing average +‐ stdev

Characteristics between genders

female male

Age (yrs) 55.7+‐ 14.4 57.3+‐16

Height (m) 1.62 +‐0.07 1.79+‐0.08

Weight (kg) 64.6 +‐9.7 81.2 +‐7.1

Table 10: antropometric measurements General measurements Body Mass

Height Upper body Shoulder offset

Elbow width Wrist width Hand thickness

Lower body Leg length Knee width Ankle width

2.2. Data processing

Figure 25: software and instrumentation used for motion analysis

Figure 25 shows the data flow. Workstation served as the control interface for Vicon, and processed also the captured data: it combines the image data from the cameras with the calibration data to reconstruct the 3D motion data (figure 26). For analysis, data were visualized in Polygon, a processing software that Vicon has especially developed for biomechanical visualization and reporting [26].

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Data processing is done using a combination of Workstation and Bodybuilder to transform the raw 2D data coming from the cameras, to usable 3D marker position data linked to a body model. The software (Workstation) reconstructs 2D marker position from the 8 cameras into 3D marker positions, using the camera calibration files. During marker and segment identification, extra markers were occasionally used to prevent losing data from missing marker trajectories. Longer marker gaps were filled with the help of redundant (i.e., more than 3) markers on the trunk, head, and occasionally pelvis. The missing marker trajectories could be filled in using its relationship to the other markers on that segment. Finally, all marker data were filtered with a Woltring filter with an MSE value of 15 to reduce the noise.

Figure 26: visualization of the collected data

Left: the 2D‐data collected from 8 cameras on different positions. Right: the 2D data are assembled to the 3D marker positions. Also GRFs (yellow) are simultaneously collected.

2.3. Identification of SSS cycles and events

Figure 27: the 7 events in the SSS cycle. Ts, Tup and Tsit are defined on visual marker motion; TL,

The most important events in one sit‐stand‐sit cycle (start, standing, end) were defined by visual inspection of the 3D marker data. Since SSS cycles are repeated after each other, the instances of the start of standing up (Ts) and end of sitting down (Tsit) were identical, and were defined on the turning point of the trunk (i.e. RBAK marker). Upright position (Tup) was defined on the basis of the pelvis turning point, moreover when the pelvismarkers (SACR, LASI, RASI) start to rotate or translate backwards (table 11). Beside these visually distinguishable events, based on previous research four more events are defined: TL, Te, Tst and Tc. The SSS cycle is thus divided as shown in figure 27. Ts initiates the momentum‐generation phase, which ends when the subject rises from the chair at lift‐off TL, defined as the first maximum occurring in the hip angle curve. This induces also the start of the momentum‐transfer phase, ending at ‘start of extension’ Te. Te is defined as the moment maximum ankle dorsiflexion angle occurs.

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Tup holds the end of extension, and sequentially all joints start to flex again. This flexing, still without downward acceleration of the body, is called stooping. Stooping posture is reached at Tst, defined on the GRF curve as a change in Fz. This is mentioned here for purposes of completeness, but since our GRF data were not reliable, no calculations were performed for this thesis in Tst.. After stooping, the actual descending phase starts, and ends when the subject makes contact with the seat at Tc. This occurs simultaneously with the second maximum in the hip flexion curve. The final phase is seat loading, ending at Tsit. This is summarized in tables 12 and 13, and figure 28.

Table 11: definition of the considered time interval

Start of standing up = Ts Upright position = Tup End of sitting down = Tsit

RBAK marker starts to move forward

Pelvismarkers (SACR, LASI, RASI) start to rotate or translate backwards

RBAK marker starts to move forward

Table 12 : main events in the SSS cycle. The description explains the use, while the definition shows the practical implementation.

MAIN EVENTS

DESCRIPTION DEFINITION

Ts START OF SSS Trunk starts to move forward Visual in workstation: Marker RBAK moves

TL LIFT‐OFF Subject rises from the chair On hip curve: Max hip angle

Te START OF EXTENSION End of upward acceleration On ankle curve: max ankle dorsiflexion angle

Tup UPRIGHT POSITION Turning point between rising and descending

Visual in workstation: pelvismarkers change direction

Tst STOOPED POSTURE Start downward acceleration (On GRF curve: change in Fz)

Tc SEAT CONTACT Subject touches the chair again On hip curve: Max hip angle

Tsit SITTING POSITION Basically same as Ts: Turning point of trunk

Visual in workstation: RBAK changes direction

Table 13: phases in the SSS cycle.

PHASE START

END DESCRIPTION

I MOMENTUM‐GENERATION

Ts TL Hip flexion while seated

II MOMENTUM‐TRANSFER TL Te Rising from the chair III EXTENSION Te Tup Final extension of the body to upright position IV STOOPING Tup Tst Initial flexion of the body into stooped posture V DESCENDING Tst Tc Descending & moving backward to the chair VI SEAT LOADING Tc Tsit Weight transfer to the seat

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Figure 28: definition of main events: Ts and Tsit on thorax markers, Tup on pelvis markers; TL and TC on hip curve,

Te on ankle curve, Tst on GRFz curve.

Construction of the sit‐stand‐sit template in Polygon

Since TST is a new test not yet implemented in clinical practise, a new template has to be developed to assess quickly results for each patient. It creates angle and moment graphs of the chosen subject, superposed on the average standard deviation of the control group. The template to be used is shown in attachments C.

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2.4. Analyzing

Only first and last SSS cycles of the TST (or one before last if the last was poorly collected) were included in further analysis. The data were analyzed and compared both on an individual basis and as a group. This was performed in two steps: visually by examining the graphs (table 14), and statistically by comparing certain parameters (table 15). All graphs and parameters were assessed through the polygon template, except for those concerning the center of mass (CoM).

Table 14: 4 kinematic, 2 kinetic and 2 center of mass graphs were looked at.

PARAMETER

Kinematic graphs Trunk flexion angleHip flexion angle Knee flexion angle Knee var/val angle

Kinetic graphs Hip momentKnee moment

CoM graphs CoMy versus CoMxCoMx and CoMy versus time

Table 15: 4 kinematic, 6 temporal, 6 kinetic, 3 cycle time and 2 center of mass parameters were identified and analyzed.

Kinematic parameters (Degrees)

Max trunk flexion RIS & DESCMax hip angle RIS & DESC

Temporal parameters (% SSS cycle)

Timing max tr fl RIS & DESCTiming max hip angle RIS & DESC Timing start knee ext RIS & DESC

Kinetic parameters (Nm/kg)

Max knee ext moment RIS & DESCMax knee var/val moment RIS & DESCMax hip fl moment RIS & DESC

Cycle time parameters (s)

SSS cycle time TOTSSS cycle time RIS SSS cycle time DESC

CoM parameters(% SSS cycle)

Tym‐Txm RIS & DESC

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2.4.1. CoM analysis

CoM x‐ and y‐components were normalized on heigt, and two kinds of graphs are constructed: “CoMy versus CoMx”, and “CoMx and CoMy versus time”.

CoMy versus CoMx represents directly the CoM movement. By shifting this curve so that the starting point on the x‐axis is for each subject its lowest y‐value, x=0 corresponds to the moment that the upward motion starts. This shows the overlap of forward and upward CoM motion better, excluding the influence of the x offset value. The trunk‐first hypothesis is translated visually in these curves: using a trunk‐first strategy means not moving forward anymore once upward motion has started, and will thus result in shorter curves (figure 29).

Superimposing CoMx and CoMy versus time serves merely to construct the parameter Tym‐Txm, representing a measure of the overlap of forward and upward CoM motion. Tym‐Txm is a temporal value, characterizing the interval between the timing of CoMymax and CoMxmax. A trunk‐first motion goes first forward reaching xmax (at txm), then only later going upward to reach ymax (at tym), leaving a big time interval between both maxima (figure 30). The interval is called tym‐txm, and is calculated in both rising and descending. For both last and first trials, two exceltemplates, one for rising and one for descending, compute the respective tym‐txm, by searching for the timing of the maxima in the forward and upward CoM movement. The graphs were examined very carefully to find a good definition for the new parameters that fits them all. For interval RIS, this was not really a problem, but in defining interval DESC some difficulties rose. Looking at all y‐graphs, it appears that the second ymax is not always that clear; sometimes the graph doesn’t even reach a second maximum (appendix extra B: com x,y versus t). Many possibilities to define a good and representative interval have been considered, and in the end a surprisingly good definition has been found, fitting all subjects properly. The starttime for the interval is chosen not as the time when ymax occurs, but as the time when the graph falls 4 % under its max value.

Figure 29: Visual representation of the trunk‐first hypothesis in CoMy versus CoMx curves

Momentumtransfer (blue curve)

Trunkfirst (purple curve)

Together x and y motion Separately x and y motion

On CoMy versus CoMx: fluently forward+upward

On CoMy versus CoMx: abrupt angle when forward ‐> upward

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2.4.2. Statistical analysis

Descriptive statistics were used to calculate mean and standard deviations. To compare means in age, height and weight between subjects and controls, independent‐Samples T test was used. The differences in TST between subjects and controls were calculated with non‐parametric Mann‐Whitney U test. Data were analyzed in the statistical program, Statistica version 9. Statistical significance was set at p≤0.05.

2.4.3. Performing comparative analyses

Box 3 shows all performed comparisons with the number of subjects involved. First cycle is compared with last cycle, RAs are compared to controls. From these analyses, 5 new groups are constructed and compared again. On basis of trunk flexion during sitting according to the videos, all subjects are divided into two groups: touch&rise (10 subjects) and sit&rise (10 subjects). On basis of the CoMy versus CoMx curves, the RA subjects are divided into two groups: RA DistMom (4 subjects) and RA MomTra‐TFl (6 subjects).

Finally, depending on which analysis is performed, several subjects had to be excluded due to poor data. From the 3D reconstructed videos, visually poor GRF data have been removed (the center of pressure of the GRF vector appeared not under the subjects feet) which leaves only 4 out of 9 controls and 5 out of 11 RAs left for moment analysis. CoM analysis cannot be performed for subjects with segments that couldn’t be processed in workstation due to marker occlusions, occurring in two subjects (1 control and 1 RA).

Figure 30: trunk‐ first hypothesis in the parameter tym‐txm. The graphs are examples from the last trial of a control (left) and of a RA (right). The black arrow shows the interval tym‐txm in rising.

Momentumtransfer Trunkfirst

Together x and y motion Separately x and y motion

Interval tym‐txm: SMALL Interval tym‐txm: BIG

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Box 3: all comparative analysis

A First <‐> last ‐ for the controls:

o main analysis: 9 first <‐> 9 last o moment analysis: 4 first <‐> 4 last

‐ for the RAs o main analysis: 11 first <‐> 11 last o moment analysis: 5 first <‐> 5 last

B Controls <‐> RAs ‐ In first cycle

o main analysis: 9 controls <‐> 11 RAs o moment analysis: 4 controls <‐> 5 RAs o CoM analysis: 8 controls <‐> 10 RAs

‐ In last cycle o main analysis: 9 controls <‐> 11 RAs o moment analysis: 4 controls <‐> 5 RAs o CoM analysis: 8 controls <‐> 10 RAs

C touch&rise <‐> sit&rise ‐ In last cycle

o angle graph analysis: 10 touch&rise’s <‐> 10 sit&rise’s D touch&rise controls <‐> touch&rise RAs

‐ In last cycle o angle graph analysis: 6 touch&rise controls <‐> 4 touch&rise RAs

E sit&rise controls <‐> sit&rise RAs ‐ In last cycle

o angle graph analysis: 2 sit&rise controls <‐> 8 sit&rise RAs F controls <‐> RA DistMom <‐> RA MomTra‐TFl

‐ In first cycle o main and CoM parameter analysis: 9 controls <‐> 4 RA DistMom <‐> 7 RA

MomTra‐TFl ‐ In last cycle

o main and CoM analysis: 9 controls <‐> 4 RA DistMom <‐> 7 RA MomTra‐TFl

‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ main analysis = angle graphs; maxima, timing and cycle time parameter values moment analysis = moment graphs and parameter values CoM analysis = CoM graphs and parameter values

30

3. Results

3.1. Results of the control group

The results reported in this section are the mean curves for the first cycle of the control group. On these, the main events are defined to get more insight in them. Later, distinction will be made with last cycle, and RA subjects.

3.1.1. Events & phases

The average time a healthy subject needed to perform the first SSS cycle of its Time‐Stands‐Test, was 1.94 seconds. This is divided relatively equally between rising (0.94s) and descending (0.98s). These values were used for normalization, and all further values and curves use the normalized time unit %SSScycle. Momentum‐generation and extension phase in rising, and descending and seat loading phase in descending made up the main time of the SSS cycle with phase times from 18 to 27.5%. Momentum‐transfer and stooping phase were two short phases (around 5%). Extension phase took half the time of RIS, while descending phase made up half DESC (Figure 31 and 32). The events are marked on all general graphs (figure 33,34,35).

SSS RIS = 48.5 %SSScycle DESC =51.5 %SSScycle

Momentum‐generation

Momentum‐transfer

Extension Stooping Descending Seat loading

18 %SSScycle

5.5 %SSScycle

25 %SSScycle

4 %SSScycle

27.5 %SSScycle

20 %SSScycle

37 %RIScycle

11.5 %RIScycle

51.5 %RIScycle

7.5 %DESCcycle

53.5 %DESCcycle

39 % DESCcycle

Figure 32: duration of phases in the first cycle of the control group, derived from the event times. The upper row shows which part a phase takes in the whole SSS, the lower row shows which part a phase takes in its

movement (rising or descending).

0 18 23.5 48.5 (52.5) 80 100 %SSS cycle Figure 31: event times in the first cycle of control group, in % SSS cycle time

31

Figure 33: general graphs of thorax (up) and hip (down) angle. Gray represents the standard deviation zone, the blue lines are the main events.

32

Figure 34: General graphs of knee extension (up) and varus/valgus (down) angles. Gray represents the standard deviation zone, the blue lines are the main events.

33

Figure 35: General graphs of knee (up) and hip (down) moments. Gray represents the standard deviation zone, the blue lines are the main events.

34

All curves experience similar behavior: very symmetric around Tup, with on both sides a maximum/minimum. Furthermore, although previous studies defined also Te or Tst as important parameters, the biggest kinematic and kinetic events happen basically around TL and TC. For this, and to facilitate following discussion, a new division into phases is introduced here (table 16). The only events are now Tsit, TR, Tup, and TD. Tsit and Tup remain as defined before. TR and TD are defined as the times at which the maxima/minima occur. They correspond always more or less to TL respectively Tc, but they are different for every curve. These small variations in TR and TD between curves show the order in which different joints reach their maximal motion (table 17). In rising, at the hip starts to extend and the knee starts to turn from valgus to neutral, followed by trunk and finally knee extension. In descending, the knee reaches valgus again first, then the trunk starts to straighten. Around 80ms later, at Tc, hip and knee joints reach their maximum flexion.

3.1.2. Features in graphs of the control group

With the above TR‐TD ‐definitions, the curves of figures 33‐35 are summarized in an ordinarily way (table 18). The thorax and hip shows the same flexion‐extension‐flexion‐extension pattern during SSS. The increase in hip flexion (Tsit‐TR) is due to flexion of the trunk, since the thigh stays horizontal on the seat. The big decrease (TR‐Tup) is a combination of the thigh moving from the horizontal to the vertical position, and trunk extension. The knee starts generally in valgus position, turns to neutral during rising, and back to valgus during descending. Knee extension occurs during rising and flexion during descending. During sitting phases knee flexion remains constant on 87 degrees. Little fluctuations can occur though: the knee first flexes a little more, then less. Videos of subjects exhibiting these fluctuations show that they control their downward motion less. This results in a harder impact on the chair which makes the subject perform a little hop. This “hopping” occurs more often in last than in first trial (people are tired of doing 10 SSS cycles, and do the motion less precise), and more often in

Table 17: TR and TD are close to TL resp TC, though little different for each curve. As such, they show the sequence in which the maximum angles occur. The times are in %SSS cycle; since 1 SSS cycle takes on average 1.94 s, 2% corresponds to 40ms.

Summary of the control curves: timing

Thorax angle Hip angle Knee extension angle

Knee var/val angle

Hip‐ and knee moment

TR 20% (TL+2%) TL Te Tc Tc+6%

TD 74% (Tc‐6%) Tc Tc 70% (Tc‐10%) Tc‐2%

Table 16: Practical events TR and TD. For each curve, “sitting” means now the parts of the curve outside the maxima, “up and down” corresponds to the part in between the maxima.

Sitting till TR Tsit ‐ TR Going UP TR ‐ Tup Going DOWN Tup ‐ TD Sitting from TD TD ‐ Tsit

35

control than the RA group (patients are more careful and have less velocity). The knee, during sitting, appears on average to be in a slight valgus (4°), but with high standard deviation: between subjects the knee position ranges from large valgus (13°) to even slight varus (5°), and can change while still seated. In the upright position the knees are always neutral. TD here is defined by the moment when there is again a high standard deviation around the average curve. Furthermore, joint flexions during SSS correspond with an increase in moment, while extension decreases the internal joint moment. Knee and hip moment correspond in value, with maxima around 0.7 Nm/kg. The standard deviation zone for the hip moment is broader than that for knee moments.

3.1.3. Comparison with last cycle

The above curves represent all the first SSS cycle of the control group. Some differences occur for the last cycle (figure 36, table 20). At first, there is a remarkable difference in SSS cycle time: 1.94s for first, 1.63s for last (p=0.23). The difference arises especially during rising, and is mostly due to the long initiation in the first cycle (the first cycle starts with a nearly straight trunk (10° flexion), last often with a trunk flexion till over 30°). All curves representing a last cycle are from now on normalized to this 1.63s. Secondly, the interval TR‐TD is broader in last cycle. This means practically that the sitting stages shorten during the TST (table 19).

The differences in these curves are not really big though: the Mann‐Whitney U test for first versus last SSS in the control group gave lowest p‐values only around 0.1, thus there is no statistical significance.

Table 19: Parameters representing the main difference between first and last cycle. Both show the shortened sitting stage in last cycle.

parameter First SSS Last SSS p‐value Timing max tr fl RIS 20 16 0.1333 Timing max hip angle RIS 18 14 0.1119

Table 18: summary of the general curves using TR and TD as moments when maxima occur

Summary of the control curves: values and shape

Thorax angle Hip angle Knee extension angle

Knee var/val angle

Hip‐ and knee moment

Sitting till TR Flexion to 32.8°

Flexion to 92° 87 ° 13° valgus to 4°varus

Increase to 700 Nmm/kg

Going UP Extension Extension Extension To neutral Decrease to 0 Going DOWN Flexion Flexion Flexion Away from

neutral Increase to 700 Nmm/kg

Sitting from TD Extension from 29.9°

Extension from 92°

87° + hopping

13° valgus to 4°varus

Decrease

36

Table 20: Summary of figure 36 (curves for last cycle compared to first cycle)

Last cycle compared to

first

Thorax Hip Knee Knee var/val Moments (hip and knee)

Sitting phases

10 ° more flexion

10 ° more flexion

More fluctuations

At Tup 4 ° more extension

More extension

5 ° more extension

TR – TD 5%broader interval

10%broader interval

10%broader interval

At TR 100 Nmm/kg higher

At TD 100 Nmm/kg lower

Figure 36: last cycle (blue) compared with first cycle (cyan) for the controls. From left to right: thorax and hip angles, knee extension and var/val angles, and hip and knee moments.

Conclusions see table 20.

ThoraxAngles10

-55

deg

HipAngles110

-10

deg

KneeAngles110

-10

deg

KneeAngles var/val20

-20

deg

37

3.2. RAs versus Controls 3.2.1. Characteristics of RAs

Characteristics of RAs are best observed by comparing the last SSS cycles of RAs with those of the controls (figure 37,table 21). The main differences are seen on thorax and knee var/val curves. RAs flex their trunk about 6° more at TR and TD (although the difference is not significant, with p=0.14). RAs’ knees are in 4° more valgus than normal.

Table 21: Summary of figure 37 (curves for RAs compared to controls)

RAs compared to controls

Thorax Hip Knee Knee var/val

Knee‐moment

Hip‐moment

Sitting stages

Less

fluctuations More

valgus (4d)

At Tup Bit less

extension (3d)

Bit more extension

(3d)

TR – TD TR‐Tup

interval bit later (2%)

Tup‐TD

interval bit earlier (2%)

At TR, at TD More

flexion (6d)

More valgus (4d)

Bit smaller (50Nmm/kg)

Higher (200Nmm/kg)

Figure 37: Comparison between RAs (darkred) and Controls (cyan, with gray standard deviation zone) for last cycle. From left to right: thorax and hip angles, knee extension and var/val angles, and hip and knee moments.

Conclusions see table 21.

ThoraxAngles10

-55

deg

HipAngles110

-10

deg

KneeAngles110

-10

deg


-20

deg

KneeMoment1500

-1000

Nmm

HipMoment1500

-1000

Nmm

38

Beside extensive trunk flexion and knee valgus, some differences occur in the SSS performed by RAs. The thorax and knee angle curves in figure 7 show small shifts, especially in the rising part. This phenomenon is confirmed (figure 38 and 39): RIS takes 5% more time for RAs. Furthermore, during rising, less time is spent on momentum‐generation, and more on momentum‐transfer. During descending, the opposite happens: the sitting phase takes longer time for RAs (figure 39). Remarkable differences between left and right side are only visible in the moment curves: all RAs have a big L/R‐difference, and only 1 out of 4 controls. Furthermore, the side having the highest hip moment always has the lowest knee moment. Knee and hip moments are in RAs on average 50 Nmm/kg lower respectivily 200 Nmm/kg higher. The maximum hip moment values are 0.3 Nm/kg higher than normal for RAs. On the contrary maximum knee moment is 0.2 Nm/kg lower (table 22). Furthermore, patients with RA suffer visually more from fatigue. This is clear from the p‐values resulting from the comparison first <‐> last trial (table 23): for the RAs the difference is significant (p<0.05) while for the controls the p‐values are >0.1. It means that “RAs get more quickly tired”, adapt their pattern accordingly, making it thus more pronounced in last trial. Finally, remarkable is that RAs don´t need more time to perform an SSS cycle: p‐values for time parameters are consequently higher than 0.4.

SSS for RAs RIS = 48.5+5 %SSScycle DESC =51.5‐5 %SSScycle

Momentum‐generation

Momentum‐transfer

Extension Stooping Descending Seat loading

37‐4.5 %RIScycle

11.5+5.5 %RIScycle

51.5‐1 %RIScycle

7.5‐2 %DESCcycle

53.5‐2 %DESCcycle

39+4 % DESCcycle

Figure 39: duration of phases in the first cycle of the RAs, compared to control group. The numbers in black are for the control group, the added red values represent the differences for RA group.

Table 22: comparison of maximum hip and knee moments occurring during SSS of controls and RAs (Nm/kg). RAs have a higher hip but lower knee moment.

Controls RAs P value Max hip flexion moment RIS 1.08 1.39 0.06 Max hip flexion moment DESC 1.02 1.39 0.11 Max knee extension moment 0.95 0.75 0.17

0 18 23.5 48.5 (52.5) 80 100 %SSS cycle Controls 0 18 26.5 53.5 56 80 100 %SSS cycle RAs

Figure 38: event times in the first cycle of the RAs, compared to the control group, in % SSS cycle time

39

3.2.2. Sit&rise as RA strategy

The subjects were, on the basis of their videos, divided into two groups: “sit&rise” and “touch&rise”. The test instruction was to perform 10 SSS’s as quick as possible, and this has its consequences: some subjects sit first totally on the chair before rising again (“sit&rise tactic”). They mainly let the chair brake their descending phase. Others break the descending themselves before seat‐contact, and rise again as soon as the chair is touched (“touch&rise tactic”). Obviously the second strategy demands a lot more muscle force and coordination (figure 40). The features characterising sit&rise and touch&rise can be explained in a more mathematical way (figure 41, table 24). The main conclusion is that trunk extension during sitting stages is, a lot higher in sit&rise strategy. This translates itself also in the hip angle. The chair breaking the descending during sit&rise has a consequence on the sit&rise knee curves: they show the hopping effect that doesn’t occur in touch&rise. Furthermore, especially at TR and TD the trunk flexes remarkabley more in sit&rise. During sitting, the knee in sit&rise is in more valgus. The difference touch&rise <‐> sit&rise is summarized in figure 42.

Figure 40: subjects performed TST in two different ways: “touch&rise” rises again as soon as the chair is touched (orange), while “sit&rise” sits first totally on the chair before rising again. The difference is clearly distinguishable

on the videos.

Table 23: comparison between first and last cycle in RAs and controls. RAs as well as controls need in the first cycle a lot more time to prepare for rising (left), but in the RAs, it is a more pronounced difference: lower p‐value (right)

RAs Last<‐>first

Median first

Median last

Timing max tr fl RIS 22 18 Timing max hip angle RIS 18 16

Controls Last<‐>first

Timing max tr fl RIS 20 16 Timing max hip angle RIS 18 14

Significance last<‐>first

P value controls

P value RAs

Timing max tr fl RIS 0.13 0.021

Timing max hip angle RIS 0.11 0.046

40

Figure 41: Average graphs for touch&rise (orange) and sit&rise (yellow) in last SSS cycle. The features

differentiating both strategies are summarized in table 10.

Table 24: Summary of figure 9 (curves for sit&rise compared to touch&rise)

ThoraxAngles10

-55

deg

HipAngles110

-10

deg

KneeAngles110

-10

deg


-20

deg

Sit&rise compared to Touch&rise


Sitting stages 17°less flexion Less flexion Hopping

(fluctuations of 5°)

4° more valgus

Tup

TR – TD 5% smaller interval

5% smaller interval

At TR 6°more flexion 5° more valgus

At TD 6°More flexion 5° more valgus

41

Figure 42: characteristics of touch&rise and sit&rise strategies

The main features in RA curves, , i.e. the higher trunk flexion at TR and TD and higher knee valgus during sitting, are also features characterising sit&rise. Figure 43 shows this correspondance visually by superimposing average RA and sit&rise curves. Indeed, remarkably 7 out of 11 RAs do site&rise. Sit&rise could thus be considered as an RA strategy, then touch&rise is the normal way of perforing the TST. This makes sense: while healthy persons will have no troubles rising directly after descending, RAs having less muscle strenght cant counteract their own descending momentum, and have thus to take the short rest on the chair.

Figure 43: Correspondence between RA (darkred) and sit&rise (orange) curves: both curves nearly coincidence.

The dotted curve is the normal, shown to clarify the correspondance between the other two more.

ThoraxAngles10

-55

deg

KneeAngles20

-20

deg

42

3.2.3. More subtle RA strategies

Comparing RA sit&rise and normal sit&rise reveals subtle differences occuring in RA patients. RAs performing touch&rise do this with constantly more trunk flexion than controls performing touch&rise, during the whole SSS. RAs perform thus the touch&rise strategy more in a trunk‐first way than controls: during sitting stages, thoraxangle is higher from controls, to touch&rise strategy , to touch&rise RA (figure 44, left). A similar remark is made for RAs performing sit&rise: at TR and TD, they flex the thorax more than controls doing sit&rise (figure 44, right).

Figure 44: RA‐control comparison seperatelty for touch&rise (left,orange) and sit&rise (right, yellow) subjects. Table 25 summarizes this. Left: average of 6 controls touch&rise subjects (cyan) and average of 5 RA touch&rise subjects (darkred). For thoraxangles, the general curve is superimposed to mark the difference in trunk flexion while seated. Right: average of 2 controls sit&rise subjects (cyan) and average of 6 RA sit&rise subjects (darkred). Table 25: summary of figure 12 (curves for RAs compared to controls, separately for sit&rise and touch&rise)

ThoraxAngles10

-55

deg

HipAngles*110

-10

deg

KneeAngles**110

-10

deg

KneeAngles*20

-20

deg

ThoraxAngles10

-55

deg

HipAngles110

-10

deg

KneeAngles110

-10

deg


-20

deg

RAs compared to Controls

‐ Touch&rise ‐ Sit&rise


Sitting stages 10° more flexion

10° more flexion

4° more flexion

2° more valgus

Tup 10° more flexion 5° more extension

5° more flexion

10° more extension

TR – TD 10% broader interval

10% Broader interval

At TR

10° more flexion

At TD

10° more flexion

43

3.2.4. Conclusion regarding RAs <‐> Controls

The main purpose was to identify features that arise in RA subjects, compared to a control group. From the graphs and tables made and presented in the pages above, the following conclusions are summarized below.

RAS COMPARED TO CONTROL GROUP

Proof Proof in numbers and graphs

RAs take more time for rising (?)

Time till Tup is bigger; trunk and knee curves are during RIS shifted to the right No significant differences were found for SSS cycle time RIS though

RIS = 48.5+5 %SSScycle p>0.4

RAs experience more fatigue

More difference between parameters for first and last SSS

Parameter P value controls

P value RAs

Timing max tr fl RIS 0.13 0.021

Timing max hip angle RIS 0.11 0.046

Sit&rise is a common strategy for RAs

Some features: ‐ More trunk flexion at TR

and TD ‐ More knee valgus during

sitting

RAs perform sit&rise with a trunk‐first strategy

More trunk flexion at TR and TD than controls doing sit&rise

Cyan: the normal way of performing sit&rise strategy Darkred: RAs doing sit&rise

RAs perform touch&rise in a more extreme way

The features that make touch&rise differ from normal, are the same but more pronounced for RAs

Black dotted: general curve Cyan: the normal way of performing touch&rise strategy Darkred: RAs doing touch&rise

ThoraxAngles10

-55

deg

KneeAngles20

-20

deg

ThoraxAngles10

-55

deg

44

3.2.5. Testing the trunk‐first hypothesis: CoM motion

In the curves showing the CoM motion (figure 45), clear differences occur. The controls data are visibly more regular then the RAs. The RAs though, seem divided into two groups (orange and yellow), with the controls (gray) mainly in between them. Especially in DESC this is clear, with 6 out of 8 controls “in the gap”. The two outliers are one control with an on video distinguishable trunk‐first motion which makes the position of his CoMcurve logic, and one control with extraordinary arm movements making the CoM not trustable. The RA group is split accordingly: the orange curves are the expected trunk‐first behavior, which will be referred to as DistMom “distinct momentum” strategy (4 RAs). The yellow curves distinguish themselves with their more pronounced forward motion during going up: this behavior is seen in 6 RAs and is called MomTra‐TFl, “momentum‐transfer with higher trunk flexion” (table 26). Plotting their average CoMcurves, the difference shows very distinguishable: DistMom strategy CoM curve is short and thick, while MomTra‐TFl strategy has long and thin CoM curves (figure 46).

Table 26: division of the RA subjects in two groups DistMom and MomTra‐TFl

Momentum‐distinct DistMom 4 RA subjects

Momentum‐transfer with higher trunk flexion

MomTra‐TFl 6 RA subjects

Figure 45: The graphs show CoMy versus CoMx (normalized and shifted curves) of all subjects: controls (gray) and RAs (yellow and orange), for last cycle. Up is the whole SSS cycle, under is separately RIS (left) en DESC

45

Figure 46: average CoM motion (CoMy versus CoMx) for controls (gray), RA DistMom (orange) and RA MomTra‐

TFl (yellow).

The main characteristic of the new MomTra‐TFl strategy is its long CoM curve. Since the length of the CoM curve represents infact how much the subject moves still forward during upward motion, this length implies a big overlap of both motions (table 27, up). Besides this mixture of forward and upward motion, MomTra‐TFl has a 5d higher trunk flexion and a 4d higher valgus than normal around the lift‐off and seat‐contact moments TR and TD (figure 47, yellow compared to gray graphs). This higher trunk flexion at TR creates more stability since the CoM is brought closer to the CoP. Thanks to this excess of stability, forward and upward motion can be combined more easy. Finally, MomTra‐TFl takes also more time to perform: SSS cycle time is 1.95s (compared to the normal of 1.65s; p=0.289823).

MomTra‐TFl is distinguished from the other RA strategy DistMom in the first place on ground of CoM motion: short curves and big tym‐txm for DistMom, long curves and small tym‐txm for MomTra‐TFl. The overlap is significantly different in the descending part with p=0.028 (table 27, down). More differences between both RA strategies occur though (figure 47, table 28). Both show bigger trunk flexion than normal, but this is more extreme in DistMom: max trunk flexion rising is 41.5 degrees for DistMom compared to only 32 for MomTra‐TFl; significant with a p‐value of 0.042. Max trunk flexion descending (37.7 <‐> 32 degrees) has p = 0.068. Something similar is visible in knee var/val angles: DistMom strategy holds the most valgus, while MomTra‐TFl is in the middle between these and the normal small valgus. Furthermore, While DistMom features appear in already in sitting stages, MomTra‐TFl distinguishes only at TR and TD. Finally, the interval TR‐TD is delayed in DistMom, but not in MomTra‐TFl strategy. This difference between the two RA strategies has p‐values of 0.1 for timing parameters, and show a delay around 4%SSScycle or 80ms on the hip curve.

46

Figure 47: Characteristics of RA DistMom and RA MomTra‐TFl, and differences between both: comparison of controls (gray), DistMom (orange) and MomTra‐TFl (yellow) strategies on thoraxangles, hipangles and knee

var/val angles.

Table 28: summary of figure 47 (comparison between characteristics of MomDist and MomTra‐TFl RA strategies)

ThoraxAngles10

-50

deg

HipAngles110

-10

deg


-20

deg

DistMom and MomTra‐TFl compared to Controls

Thorax Hip Knee var/val

Sitting stages 10° more flexion

6° more valgus 2° more valgus

Tup 7° more flexion

TR – TD 10% delayed

10% delayed

At TR and TD (compared to sitting stages)

17° more flexion 4° more flexion

4° more flexion

4° more valgus

Table 27: Parameter tym‐txm (in %SSS cycle, representing the overlap between forward and upward CoM motion). A low value means big overlap. Up: comparison MomTra‐TFl to controls . Down: comparison between the two RA strategies.

Overlap of forw and upw motion Controls MomTra‐Tfl p‐value

tym‐txm RIS 17 13 0.14

Overlap of forw and upw motion DistMom MomTra‐Tfl p‐value

tym‐txm RIS 26 13 0.24 tym‐txm DESC 22 12 0.028

47

3.2.6. Conclusion: final distinction between controls, RA DistMom and RA MomTra‐TFl

Controls RA DistMom RA MomTra‐Tfl CoM

Forward <‐> upward

motion more separate Longer forward motion

Thorax

More trunk flexion

always (p=0.075983 at TR)

More trunk flexion at TR,TD

Knee var/val

More valgus during

sitting More valgus at TR,TD

Interval TR‐TD

Controls DistMom MomTra‐Tfl Timing max hip angle DESC 80 90 82

Delayed (p=0.189663) CoM overlap forw<‐>upw motion

Controls DistMom MomTra‐Tfl

tym‐txm RIS 17 26 13 tym‐txm DESC 14 22 12

Further (p=0.018904 in DESC)

Closer (p=0.137639 in RIS)

SSS cycle time

Controls DistMom MomTra‐Tfl

SSS cycle time TOT 1.63 1.65 1.95 Longer (p=0.289823)


-20

deg

48

4. Discussion

An SSS cycle in TST takes generally less than 2 seconds, of which rising and descending take equal time. Depending on how far the sitting motion is completed, two SSS executions exist: touch&rise and sit&rise. The last is seen more often in RA subjects. Furthermore, the hypothesis that RA subjects would use a trunk‐first strategy was partly confirmed: two RA strategies were distinguished, DistMom and MomTra‐TFl, of which the DistMom corresponded with the trunk‐first strategy. This discussion reports salient findings and compares with findings of earlier research. It concludes with some advice for future studies.

4.1. The normative SSS cycle

The standard SSS cycle, being the first cycle in TST, has been analyzed thoroughly in this thesis on basis of 4 angles and 2 moments. Graph shapes, maximum values and timings are hard to compare with previous studies though, for many reasons. Previous research only included rising and descending separately, whereby their curves, times and phases include quiet standing and sitting whereas this is not the case in the current study. Timing values are also hard to compare because the TST is performed “as quick as possible”, while rising studies always preferred subjects to use their own velocity. The presentation of SSS cycles in this thesis can thus be considered as a first set of normative data for SSS.

The SSS cycle shows some typical features (figure 48). Generally, it takes less than 2s, of which rising and descending take equal time. This results in very symmetric curves. Big events are all situated around moments of seat interaction TL and Tc. In rising, at TL the hip starts to extend and the knee starts to turn from valgus to neutral, followed by trunk and finally knee extension. In descending, the knee reaches valgus again first, than the trunk starts to straighten. Around 80ms later, at Tc, hip and knee joints reach their maximum flexion. Furthermore, two normative SSS cycles exist: touch&rise SSS.and sit&rise SSS (figure 49). Touch&Rise is the most difficult, since descending momentum has to be slowed down severely before Tc in order to immediately start rising again. Sit&Rise on the contrary, lets the chair help in breaking, which induces knee fluctuations during sitting phase (hopping). Rising starts only after fully being seated on the chair, reaching a more vertical trunk position.

49

Figure 48: features of the SSS cycle in the TST

Figure 49: the two normative SSS cycles: touch&rise and sit&rise

very symmetric around Tup

average time < 2s

Big events are all situated around TL and TC

“hopping” in last cycle

touch&rise SSS <‐>

sit&rise SSS

50

4.2. Characteristics of RAs

Previous studies agreed that the STS motion for RAs tends towards a trunk‐first strategy, with characteristics of figure 50. Two of these characteristics, i.e. higher thorax flexion and bigger hip moments, are also found in the RAs SSS cycle, but without any significances: observed p‐values are between 0.1 and 0.2. RAs CoM and rising time showed no mentionable difference at all with the normals (figure 51). Besides these two trunk‐first features, some additional RA‐behaviour comes forward in the Time‐Stands‐Test. At first, RAs’ knees are in 4° more valgus than normal (no significance analysis is done for this). Secondly, RAs suffer visually more from fatigue: significances first <‐> last cycle exist (in contrast with the normal SSS which has no first <‐> last significance). RAs adapt their pattern thus more than normal in between first and last cycle. Furthermore, 7 out of 11 RAs chose the sit&rise SSS. Finally, RAs performing Sit&Rise and Touch&rise do this in a more extreme way (more trunk flexion). The difference comes out at Tsit for Touch&rise, while in Sit&rise it occurs at TL (figure 52).

Figure 50: the trunk‐first hypothesis

RAs flex have about 6° more trunk flexion at TR and TD. No change in knee angle occurs

Max hip moment is 0.3 Nm/kg is higher for rising and descending; max knee moment is 0.2 Nm/kg lower

No differences in CoM‐behaviour or length of momentum‐transfer phase

No differences in cycle times

Figure 51: matching RA characteristics to the trunk‐first hypothesis. = found, but with no significance (p‐values 0.1 to 0.2)

= not found

AnglesHip & thorax: more flexion

Knee: no change

MomentsHip: biggerKnee: lower

CoM closer to CoP at TL=> less momentum‐transfer

Rising timelonger

trunk‐first strategy

51

Figure 52: touch&rise and sit&rise performed by RAs (the gray silhouette): RAs perform both with higher trunk flexion, but this occurs at Tsit in Touch&rise, while it occurs only at TL in Sit&rise.

4.3. Strategies of RAs

On ground of the CoM‐behaviour, this SSS study splits the RAs in two groups: RA DistMom and RA MomTra‐TFl. They are significantly different in max trunk flexion during rising (41.5 degrees for DistMom compared to only 32 for MomTra‐TFl), and in overlap forward‐upward motion (nearly only half the overlap existing in MomTra‐TFl occurs in DistMom). SSS rising time is remarkably longer in MomTra‐TFl strategy, but not significantly. Figure 53 summarizes the characteristics of the two RA strategies, compared to the normal momentum‐transfer strategy.

Figure 53: Distinguishment of the two RA strategies between each other and with the normal. Differences occur on three pillars: max trunk flexion, CoM forward‐upward overlap and SSS rising time. Black arrows represent worth mention differences (although only two of them are really significant), gray arrows mean that parameter shows no difference between those strategies.

MomTra (controls)

32d

RA MomTra‐TFl

34dRA DistMom

41d

MomTra (controls)

14

RA MomTra‐TFl

12p = 0.02

RA DistMom

22

MomTra (controls)

0.81s

RA MomTra‐TFl

1.02sRA DistMom

0.92s

Max trunk flexion

CoM forw‐upw

rising time

52

RA DistMom shows some (nearly‐)significant differences with the normal SSS: their trunk is constantly 9 degrees more flexed, and forward and upward CoM motion overlaps much less than normal (figure 54). Also the rising time in DistMom is longer, shown by the shift in TR‐TD interval, although the cycle time parameters show no difference at all. RA DIstMom shows a big correspondance with the trunk‐first strategy! No results exist of the moments since the groups became too small for this, but we expect the joint moments to follow also trunk‐first strategy, being higher in the hip and lower in the knee.

RA MomTra‐TFl shows two trunk‐first features in a non‐significant way (little higher trunk flexion and longer rising time; figure 55). This strategy doesn´t agree thus with our trunk‐first hypothesis and is closer to the normative SSS –hence also the name “momentum‐transfer”. An important difference occurs though, concerning the CoM forward‐upward motion. The CoM moves longer forward, overlapping a lot with upward motion (p=0.1).

Strategies differ in rising time as well as in SSS cycle time. Rising times are 0.81s for controls, 0.92s for DistMom, and 1s for MomTra‐TFl. SSS cycle times are 1.63s for controls, 1.65s for DistMom, and 1.95s for MomTra‐Tfl. DistMom prolongs thus only its rising phase, seen also by a delay in the normalized curve. MomTra‐TFl prolongs both rising and descending; its curve follows the normal without delay. Trunk‐first hypothesized a longer rising time, found in both RA strategies.

RA DistMom flexes the trunk constantly 9d more than normal (p=0.07)

(no moment comparisons anymore due to too less subjects)

Big interval between forward and upward motion timing (p=0.02 in descending)

No difference in cycle times (p=0.9), but the TR‐TD interval is shifted which shows longer rising phase.

Figure 54: matching RA DistMom characteristics to the trunk‐first hypothesis.

= found, with (nearly‐)significance (p‐values < 0.1) = found, but with no significance

53

RA MomTra‐TFl flexes the trunk 2d more than normal (p=0.4) at moments of seat contact

(no moment comparisons anymore due to too less subjects)

THE CONTRARY:

Smaller interval between forward and upward motion timing (p=0.1 in rising)

Rising takes 0.2s longer than for the normal MomTra (p=0.28), but also descending takes longer: total SSS cycle time is higher.

Figure 55: matching RA MomTra‐TFl characteristics to the trunk‐first hypothesis.

= found, with (nearly‐)significance (p‐values < 0.1) = found, but with no significance

= not found

4.4. Reliability of the data 4.4.1. Kinematics

The kinematics were calculated by means of a whole‐body linked‐segment model which is shown to have a satisfactory internal validity [35].

4.4.2. Kinetics

Not much kinetic analysis was included in this study. This was due to poor GRF data: the GRF vector appeared sometimes at locations on the force plate that do not relate to foot placement, and a constant gap existed between left and right side (figure 56). Moment data were thus not always reliable. Yoshioka and co‐workers found that the sum of the peak hip and knee moments is 1.53 Nm/kg independent of strategy used [18]. Our results give 1.922 or 2.039 for first or last cycle in unimpaired subjects and 2.254 or 2.148 for the RA subjects.

On the other hand, the video of the subjects was checked and shows no abnormalities, with both feet seeming to stay on the platform. Max moment values gave low p‐values in comparing control to RA group: they determine the difference with RAs. From the main

54

distinguishing parameters for controls <‐> RAs, 2 out of 3 are moment parameters (figure 57). Furthermore, Moment curves are the only ones showing a L/R difference compatible with RAs: all RAs have a big difference between left and right side, and only 1 out of 4 controls.

4.4.3. Small groups and significance

Subjects groups involved in this study were small (20 in total, divided into groups with size up to 5 subjects). It has to be kept in mind that with such small groups it is dangerous to draw firm conclusions that can be extrapolated to a larger population.

4.4.4. Graph analysis

Some very advanced mathematical methods exist for comparing the shape of curves (like PCA [13], principal component analysis, a very good way to distinguish between graphs, but these are very complicated which makes the interpretation hard and has no direct meaning for clinicians), but in this thesis the graphs are judged only by sight. The max values seen on the graphs might differ a bit from the calculated ones since the graphs represent the average but for the parameters the more robust medians were preferred (less sensitive to outliers).

4.4.5. First or last cycle?

Often in comparison results, only the last cycle of the TST is considered. This choice is justified: whenever an analysis was performed for both first and last cycle (e.g. plotting CoM RA/control curves first for first cycle, and secondly for last cycle), the last showed the most distinction. An example is figure 58: in last cycle, a bigger difference is seen. P‐values show the same preference for last cycle: e.g. the most significant p‐value proving distinction between RA DistMom and RA MomTra‐TFl is 0.06 in first, but 0.04 (significant) in last cycle. Subjects get tired, pronouncing strategy characteristics more in last cycle.

.

Figure 57: The 3 parameters showing significant difference for RAs. Two out of three are moment values.

Max knee extension moment

Max trunk flexion RIS

Max hip flexion moment

Figure 56: example of the hip moment curves left (red) and right (green) of one subject. In this case, the red curve seems to have an offset error.

Hip fl/ext Moment1500

-1000

Nmm

55

Figure 58: CoM graph comparison between RAs (red) and controls (gray); left for first, right for last cycle. The right one, last cycle thus, shows more difference.

4.4.6. Cycle times

SSS cycle time parameters show often high p‐values (e.g. in RA‐control), while the graphs and parameters related to timing show a clear difference. Also remarkable is a low p for controls (0.2) but a high p for RAs (>0.5) in first‐last comparison. These strange results might be due to the big standard deviation of the cycle times in the RAs (1.1 to 9.12s) (table 29). Table 29 : min and max values of the timing parameters for the RAs. This shows a very big variation!

MIN & MAX First Last

SSS cycle time TOT 1.1 – 8.4 1‐ 9.12SSS cycle time RIS 0.67 – 3.61 0.51 ‐ 4.52SSS cycle time DESC 0.43 – 4.79 0.6 ‐ 4.6

4.4.7. Accuracy of tym‐txm

The parameter tym‐txm is derived from the superimposed graphs CoMx and CoMy versus time. The big drawback of using a parameter is that it only accounts for the maxima, and not for the shape of the curve –which can be quite important. Appendix extra B (CoM x,y versus t) shows the graphs for all subjects. E.g. one subject starts the forward movement a lot earlier than the upward, but since it takes a while before the x‐curve reaches its absolute maximum, this large interval is badly reflected in the value tym‐txm (figure 59).

Figure 59: CoMx and CoMy curves of one subject. The parameter txm‐tym RIS defined on the fist maxima, represents poorly the early forward motion; the gray arrow would be a better value.

4.4.8. Knee valgus

The knee valgus occurring during sitting stages could be a motion analysis artifact. Verification with knee moment values should be executed to verify the truth.

‐0,050

0,050,1

0,150,2

‐0,05 0 0,05 0,1

y

x

56

4.5. Future perspectives

This thesis shows enough evidence to conclude that the time‐stands‐test deserves further investigation. The division into two RA strategies should be verified with larger groups. The strategies showed no correlation with subject typifications as height, age or disease duration. An analysis including pain in hip and knee joint has not been done yet.

The kinetics were not included in this thesis due to partial data acquisition failure (there were errors of a systematic nature that were also rather random and for which the source was not obvious). The moments could be very interesting to include since they show low p‐values for the RA group. Furthermore, the knee valgus moment would show whether the observed valgus position during patients’ sitting is real. Knowledge of the center of pressure of the ground reaction force would create more insight in the stability states of the motion during the different strategies. This can especially help for better understanding of the MomTra‐TFl strategy.

57

APPENDIX All results, from very useful to nothing‐saying, are summarized in this appendix. The characteristics for each group are first listed, followed by the comparison analysis between groups. Finally, some figures which are used to check the punctuality of the results are listed.

Characteristics per group

This includes the basic statistics for first and last cycle by controls, RAs, RADistMom and RAMomTra‐TFl. For the control group, the average graphs are also shown

Control group

First cycle

Controls, first cycle median min max

lower quartile

upper quartile

Max trunk flexion RIS 32.79196 21 44.8 28.33094 33.25171Max trunk flexion DESC 29.95354 21 47.9 25.76885 38.17259Max hip angle RIS 92.78296 80 96.4 86.57296 95.5607Max hip angle DESC 91.36628 84 101 90.06373 99.33533Timing max tr fl RIS 20 10 30 16 24Timing max tr fl DESC 74 68 88 72 86Timing max hip angle RIS 18 10 28 14 22Timing max hip angle DESC 80 70 82 76 82Timing start knee ext RIS 18 10 36 16 24Timing start knee ext DESC 46 36 54 42 50Max knee ext moment RIS 0.90886 0.7 1.22 0.77024 1.0977Max knee ext moment DESC 0.90663 0.7 0.98 0.79984 0.94562max knee var/val moment RIS 0.19927 0 0.36 0.06638 0.33153max knee var/val moment DESC 0.20584 0.1 0.47 0.09598 0.38284max hip fl moment RIS 1.01308 0.8 1.46 0.8917 1.26374max hip fl moment DESC 1.02676 0.8 1.28 0.893 1.16683SSS cycle time TOT 1.94 1.7 3.23 1.78 2.45SSS cycle time RIS 0.94 0.7 1.34 0.87 1.12SSS cycle time DESC 0.98 0.8 1.89 0.91 1.37

tym‐txm RIS 12 8 16 11 16tym‐txm DESC 10 6 16 9 10

61

Last cycle

Controls, last cycle median min max

lower quartile

upper quartile

Max trunk flexion RIS 33.05693 23.57575 43.9367 25.53702 35.3657Max trunk flexion DESC 29.95354 21.37351 50.6843 26.32068 35.8289Max hip angle RIS 93.08424 82.61965 104.3639 85.59343 97.6379Max hip angle DESC 90.06373 81.26974 106.4457 84.18983 97.652Timing max tr fl RIS 16 12 20 14 18Timing max tr fl DESC 78 70 100 74 100Timing max hip angle RIS 14 10 18 14 16Timing max hip angle DESC 80 74 90 78 84Timing start knee ext RIS 18 12 24 14 20Timing start knee ext DESC 46 38 48 46 48Max knee ext moment RIS 0.95387 0.69961 1.2583 0.82043 1.1124Max knee ext moment DESC 0.78347 0.6997 0.9308 0.71597 0.8828max knee var/val moment RIS 0.26408 0.07407 0.4829 0.12327 0.4193max knee var/val moment DESC 0.21462 0.09177 0.4493 0.11043 0.3747max hip fl moment RIS 1.0855 0.89498 1.2337 0.98122 1.1686max hip fl moment DESC 1.01969 0.74588 1.2441 0.8727 1.142SSS cycle time TOT 1.63 1.27 3.32 1.44 2.46SSS cycle time RIS 0.81 0.61 1.53 0.69 1.11SSS cycle time DESC 0.86 0.66 1.79 0.75 1.3


65

RAs, RA MomDist, RA MomTraTFl groups

First cycle

RAs, first cycle median min max

lower quartile

upper quartile

Max trunk flexion RIS 37.68479 21.58925 88.2679 25.22116 39.4935Max trunk flexion DESC 35.07985 20.29954 91.8683 27.47003 37.6325Max hip angle RIS 91.68416 82.47231 110.7473 86.5067 95.0129Max hip angle DESC 94.23006 76.06306 111.9139 88.76517 101.7701Timing max tr fl RIS 22 16 28 18 28Timing max tr fl DESC 76 66 100 72 94Timing max hip angle RIS 18 12 30 14 24Timing max hip angle DESC 80 74 98 78 86Timing start knee ext RIS 20 12 28 16 24Timing start knee ext DESC 46 40 60 42 52Max knee ext moment RIS 0.78587 0.67209 0.8736 0.75382 0.8675Max knee ext moment DESC 0.87353 0.6876 1.052 0.79865 1.0467max knee var/val moment RIS 0.21531 0.13389 0.7681 0.16541 0.612max knee var/val moment DESC 0.27772 0.04956 0.6131 0.20155 0.4343max hip fl moment RIS 1.4675 1.14011 1.9476 1.29869 1.6095max hip fl moment DESC 1.45213 0.79835 1.509 1.42389 1.4572SSS cycle time TOT 1.88 1.1 8.4 1.51 3.04SSS cycle time RIS 1.01 0.67 3.61 0.75 1.26SSS cycle time DESC 0.97 0.43 4.79 0.74 1.78


RA MomDist, first cycle median min max

lower quartile

upper quartile

Timing max tr fl DESC 100 76 100 76 100Timing max hip angle DESC 86 86 98 86 98


RA MomTra‐TFl, first cycle median min max

lower quartile

upper quartile

Max trunk flexion RIS 41.4678 40.02487 88.3971 40.02487 88.3971Max trunk flexion DESC 37.6983 37.33809 84.0042 37.33809 84.0042



66

Last cycle

RAs, last cycle median min max

lower quartile

upper quartile

Max trunk flexion RIS 37.80329 27.96973 88.3971 29.24553 40.98013Max trunk flexion DESC 33.69862 22.96886 84.0042 28.57728 37.69834Max hip angle RIS 91.49522 80.95683 112.8415 88.16098 99.54083Max hip angle DESC 94.42751 77.31587 106.9941 85.22117 99.12082Timing max tr fl RIS 18 0 28 14 20Timing max tr fl DESC 76 70 100 74 92Timing max hip angle RIS 16 0 20 10 16Timing max hip angle DESC 82 76 100 78 86Timing start knee ext RIS 18 4 26 12 24Timing start knee ext DESC 46 40 52 44 52Max knee ext moment RIS 0.75341 0.67279 0.7978 0.7346 0.77991Max knee ext moment DESC 0.77746 0.65463 0.9248 0.75236 0.85002max knee var/val moment RIS 0.33949 0.15505 0.6429 0.16882 0.50296max knee var/val moment DESC 0.27775 0.06404 0.6727 0.13201 0.3364max hip fl moment RIS 1.39509 1.13494 1.7718 1.14302 1.56235max hip fl moment DESC 1.39344 0.89532 1.6461 1.38702 1.6103SSS cycle time TOT 1.92 1 9.12 1.5 2.59SSS cycle time RIS 1.02 0.51 4.52 0.78 1.26SSS cycle time DESC 0.95 0.6 4.6 0.84 1.18


RA DistMom, last cycle median min max

lower quartile

upper quartile



RA MomTra‐TFl, last cycle median min max

lower quartile

upper quartile

Max trunk flexion RIS 32.37927 27.96973 40.98013 28.55127 38.77037Max trunk flexion DESC 32.34693 26.93689 43.16679 28.57728 34.10983Timing max tr fl DESC 76 70 92 72 84Timing max hip angle DESC 82 76 86 78 86


67

Comparative analysis per group

Comparisons are performed for all the analysis in box.

First <‐> last ‐ for the controls:

o main analysis: 9 first <‐> 9 last o moment analysis: 4 first <‐> 4 last

‐ for the RAs o main analysis: 11 first <‐> 11 last o moment analysis: 5 first <‐> 5 last

Controls <‐> RAs ‐ In first cycle

o main analysis: 9 controls <‐> 11 RAs o moment analysis: 4 controls <‐> 5 RAs o CoM analysis: 8 controls <‐> 10 RAs

‐ In last cycle o main analysis: 9 controls <‐> 11 RAs o moment analysis: 4 controls <‐> 5 RAs o CoM analysis: 8 controls <‐> 10 RAs

C touch&rise <‐> sit&rise ‐ In last cycle

o angle graph analysis: 10 touch&rise’s <‐> 10 sit&rise’s touch&rise controls <‐> touch&rise RAs

‐ In last cycle o angle graph analysis: 6 touch&rise controls <‐> 4 touch&rise RAs

sit&rise controls <‐> sit&rise RAs ‐ In last cycle

o angle graph analysis: 2 sit&rise controls <‐> 8 sit&rise RAs controls <‐> RA DistMom <‐> RA MomTra‐TFl

‐ In first cycle o main and CoM parameter analysis: 9 controls <‐> 4 RA DistMom <‐> 7 RA MomTra‐TFl

‐ In last cycle o main and CoM analysis: 9 controls <‐> 4 RA DistMom <‐> 7 RA MomTra‐TFl

‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ main analysis = angle graphs; maxima, timing and cycle time parameter values moment analysis = moment graphs and parameter values CoM analysis = CoM graphs and parameter values

68

First <> last

For the controls

Last <‐> First (controls) median first median last p‐value Max trunk flexion RIS 32.79196 33.05693 0.757278 Max trunk flexion DESC 29.95354 29.95354 0.964784 Max hip angle RIS 92.78296 93.08424 0.401543 Max hip angle DESC 91.36628 90.06373 0.565993 Timing max tr fl RIS 20 16 0.133321 Timing max tr fl DESC 74 78 0.353838 Timing max hip angle RIS 18 14 0.111962 Timing max hip angle DESC 80 80 0.216374 Timing start knee ext RIS 18 18 0.479929 Timing start knee ext DESC 46 46 0.894626 Max knee ext moment RIS 0.90886 0.95387 1.000000 Max knee ext moment DESC 0.90663 0.78347 0.563703 max knee var/val moment RIS 0.19927 0.26408 0.563703 max knee var/val moment DESC 0.20584 0.21462 1.000000 max hip fl moment RIS 1.01308 1.0855 0.772830 max hip fl moment DESC 1.02676 1.01969 0.772830 SSS cycle time TOT 1.94 1.63 0.233231 SSS cycle time RIS 0.94 0.81 0.269691 SSS cycle time DESC 0.98 0.86 0.269691

last cycle (blue) compared with first cycle (cyan) for the controls

ThoraxAngles10

-55

deg

HipAngles110

-10

deg

KneeAngles110

-10

deg


-20

deg

69

For the RAs

Last <‐> First (RAs) median first median last p‐value Max trunk flexion RIS 37.68479 37.80329 0.645764Max trunk flexion DESC 35.07985 33.69862 0.843832Max hip angle RIS 91.68416 91.49522 0.742666Max hip angle DESC 94.23006 94.42751 0.742666Timing max tr fl RIS 22 18 0.020577Timing max tr fl DESC 76 76 0.643222Timing max hip angle RIS 18 16 0.046119Timing max hip angle DESC 80 82 0.444051Timing start knee ext RIS 20 18 0.370728Timing start knee ext DESC 46 46 0.946998Max knee ext moment RIS 0.78587 0.75341 0.403396Max knee ext moment DESC 0.87353 0.77746 0.296271max knee var/val moment RIS 0.21531 0.33949 1max knee var/val moment DESC 0.27772 0.27775 1max hip fl moment RIS 1.4675 1.39509 0.676104max hip fl moment DESC 1.45213 1.39344 1SSS cycle time TOT 1.88 1.92 1SSS cycle time RIS 1.01 1.02 0.599361SSS cycle time DESC 0.97 0.95 0.915851

Thorax, hip, knee flexion and knee varus/valgus angles, knee and hip moment. Comparison between first (darkred) and last (pink) cycle in RAs.

ThoraxAngles10

-50

deg

HipAngles110

-10

deg

KneeAngles110

-10

deg

KneeAngles var/val 2

-26

deg

KneeMoment1500

-1000

Nmm

HipMoment1808

-673

Nmm

70

Controls <> Ras

In first cycle

RAs <‐> Controls (first cycle) median control median RA p‐value Max trunk flexion RIS 32.79196 37.68479 0.17146Max trunk flexion DESC 29.95354 35.07985 0.59485Max hip angle RIS 92.78296 91.68416 1Max hip angle DESC 91.36628 94.23006 0.81971Timing max tr fl RIS 20 22 0.42503Timing max tr fl DESC 74 76 0.76121Timing max hip angle RIS 18 18 0.73244Timing max hip angle DESC 80 80 0.30506Timing start knee ext RIS 18 20 0.87923Timing start knee ext DESC 46 46 0.73244Max knee ext moment RIS 0.90886 0.78587 0.39127Max knee ext moment DESC 0.90663 0.87353 0.90252max knee var/val moment RIS 0.19927 0.21531 0.39127max knee var/val moment DESC 0.20584 0.27772 0.90252max hip fl moment RIS 1.01308 1.4675 0.06619max hip fl moment DESC 1.02676 1.45213 0.11135SSS cycle time TOT 1.94 1.88 0.59485SSS cycle time RIS 0.94 1.01 0.76121SSS cycle time DESC 0.98 0.97 0.59485

tym‐txm RIS 12 15 0.28632tym‐txm DESC 10 14 0.06889

Thorax, hip, knee flexion and knee varus/valgus angles, knee and hip moment. Comparison between RAs (darkred) and Controls (cyan) for first cycle (conclusion see table)

ThoraxAngles10

-55

deg

HipAngles110

-10

deg

KneeAngles110

-10

deg


-20

deg

71

RAs compared to controls


Sitting till TR More valgus (4d)

Sitting from TD

Bit more flexion (2d)


More valgus (5d)

At Tup Less extension (5d)

Bit less extension (3d)

Bit more extension (3d)

TR – TD Interval slightly shifted to the right (2%)

Interval slightly shifted to the right (2%)

At TR More flexion (10d)


More valgus (5d)

At TD More flexion (4d)

Bit less flexion (2d)

Bit less flexion (3d)

More valgus (3d)

In last cycle

RAs <‐> Controls (last cycle) median control median RA P value Max trunk flexion RIS 33.05693 37.80329 0.14888Max trunk flexion DESC 29.95354 33.69862 0.494125Max hip angle RIS 93.08424 91.49522 1Max hip angle DESC 90.06373 94.42751 1

The graphs show the normalized and shifted CoM motion: CoMy versus CoMx. Controls (gray) and RAs (yellow) for first cycle.

72

Timing max tr fl RIS 16 18 0.470449Timing max tr fl DESC 78 76 0.849361Timing max hip angle RIS 14 16 0.93944Timing max hip angle DESC 80 82 0.470449Timing start knee ext RIS 18 18 0.93944Timing start knee ext DESC 46 46 0.704043Max knee ext moment RIS 0.95387 0.75341 0.177911Max knee ext moment DESC 0.78347 0.77746 0.902523max knee var/val moment RIS 0.26408 0.33949 0.713303max knee var/val moment DESC 0.21462 0.27775 0.902523max hip fl moment RIS 1.0855 1.39509 0.066193max hip fl moment DESC 1.01969 1.39344 0.111348SSS cycle time TOT 1.63 1.92 0.494125SSS cycle time RIS 0.81 1.02 0.403318SSS cycle time DESC 0.86 0.95 0.775052

tym‐txm RIS 17 15 0.656854tym‐txm RIS 14 15 0.593955

Thorax, hip, knee flexion and knee varus/valgus angles, knee and hip moment. Comparison between RAs (darkred) and Controls (cyan) for last cycle (conclusion see table)

ThoraxAngles10

-55

deg

HipAngles110

-10

deg

KneeAngles110

-10

deg


-20

deg

KneeMoment1500

-1000

Nmm

HipMoment1500

-1000

Nmm

73

Touch&Rise <> Sit&rise

ThoraxAngles10

-55

deg

HipAngles110

-10

deg

KneeAngles110

-10

deg


-20

deg

The graphs show the normalized and shifted CoM motion: CoMy versus CoMx. Controls (gray) and RAs (yellow and orange) for last cycle.

74

Touch&Rise controls <> Touch&Rise RAs

Sit&Rise controls <> Sit&Rise RAs

ThoraxAngles10

-55

deg

HipAngles*110

-10

deg

KneeAngles**110

-10

deg

KneeAngles*20

-20

deg

ThoraxAngles10

-55

deg

HipAngles110

-10

deg

KneeAngles110

-10

deg


-20

deg

75

Controls <> RA DistMom <> RA MomTraTFl

In first cycle

RA DistMom <‐> RA MomTra‐TFl median RA DistMom median RA MomTra‐TFl Pvalue Timing max tr fl DESC 100 75 0.11061Timing max hip angle DESC 86 79 0.06825


In last cycle

RA DistMom <‐> Controls median control median DistMom P value Max trunk flexion RIS 33.05693 40.74635 0.075983Max trunk flexion DESC 29.95354 37.51822 0.396066Max hip angle RIS 93.08424 99.29102 0.699676Max hip angle DESC 90.06373 94.41512 0.816961Timing max tr fl RIS 16 19.00000 0.537094Timing max tr fl DESC 78 89.00000 0.487454Timing max hip angle RIS 14 14.00000 0.938503Timing max hip angle DESC 80 90.00000 0.189663Timing start knee ext RIS 18 17.00000 1.000000Timing start knee ext DESC 46 49.00000 0.487454SSS cycle time TOT 1.63 1.65000 0.938503SSS cycle time RIS 0.81 0.92500 0.938503SSS cycle time DESC 0.86 0.85000 1.000000


RA MomTra‐TFl <‐> Controls median control median MomTra‐Tfl p value Max trunk flexion RIS 33.05693 32.37927 0.458719 Max trunk flexion DESC 29.95354 32.34693 0.750824 Max hip angle RIS 93.08424 91.49522 0.832339 Max hip angle DESC 90.06373 94.42751 0.915700 Timing max tr fl RIS 16 18.00000 0.596628 Timing max tr fl DESC 78 76.00000 0.427263 Timing max hip angle RIS 14 16.00000 0.915700 Timing max hip angle DESC 80 82.00000 0.957791 Timing start knee ext RIS 18 18.00000 0.873845 Timing start knee ext DESC 46 46.00000 1.000000

76

SSS cycle time TOT 1.63 1.95000 0.289823 SSS cycle time RIS 0.81 1.02000 0.289823 SSS cycle time DESC 0.86 0.97000 0.672000

tym‐txm RIS 17 13 0.137639 tym‐txm DESC 14 12 0.561276

RA DistMom <‐> RA MomTra‐TFl median RA DistMom median RA MomTra‐TFl Pvalue Max trunk flexion RIS 41.4678 32.37927 0.040239Max trunk flexion DESC 37.6983 32.34693 0.068248Timing max tr fl DESC 100 76 0.110613Timing max hip angle DESC 98 82 0.171461


77

Controls (gray) <‐> RA DistMom (orange) <‐> RA MomTra‐TFl in last cycle: thorax, hip and knee var/val angles and xyCom motion.

ThoraxAngles10

-50

deg

HipAngles110

-10

deg


-20

deg

78

Extra

Checking the parameterdata

Check of the resulting values for controls (up) and RAs (down). This is a quick way to remark abnormal data and double check on them.

79

CoM x,y versus t

CoMx (blue) and CoMy (red) in time (%SSS). All subjects, devided into Controls (left), RA DistMom (middle) and RA MomTra‐TFl (right) for last cycle. Looking at these graphs, realize that only the maxima matter. For instance, the x‐curves (blue) seem to come in two shapes: flat and close to 0, or starting negatively with positive maxima, covering a big range. This difference is not at all important though: it arises from the different test interpretations sit&rise and touch&rise. Because the graphs are constructed from the normalized ánd shifted CoMdata, the far starting x‐position from the touch&go´s is translated into the x‐curve shifted vertically down. The considered time interval is not influenced by the shifting.

80

Individual graphs: remarks

83

ATTACHMENTS All figures and tables of less importance are listed below here

ATTACHMENT A Definition of T45%

ATTACHMENT B Marker positions

Pelvis SACR LASI,RASI

Trunk C7 T10 CLAV STRN RBAK

Legs (thigh+shank+foot)

LTHI,RTHI LKNE,RKNE LTIB,RTIB LANK,RANK LTOE,RTOE (LHEE,RHEE)

Head LFHD,RFHD LBHD,RBHD

Arms (upper+lower+hand)

LSHO,RSHO LELB,RELB LWRA,RWRALWRB,RWRB LFIN,RFIN

(6)

Data provided: time of event

Recalculation to lift‐off = 0% Extension = 100%

Lift‐off 0.93 s 0%

Max ankle dorsiflexion

1.27 s (1.27‐0.93)/(2.21‐0.93) = 27%

extension 2.21 s 100%

Comparison of (6), defining max ankle dorsiflexion as occurring on 1.27s, and (10), defining end of body acceleration as occurring on 45% of the rising cycle. Using the clearly defined interval between lift‐off and extension events in both experiments, they occur respectively at 27 and 28%

(10)

Data provided: percentage in the total cycle

Recalculation to lift‐off = 0% Extension = 100%

Lift‐off 34% 0% End of acceleration (dFz/dt min)

45% (45‐73)/(73‐34) = 28%

84

ATTACHMENT C Polygon SSS template

Left is the template in polygon constructed to retrieve easily results from the SSS tests; right explains the template. All what is green are links, which show the individual subject curves superposed on the normal average when clicked; such a screenshot for the ‘main angles’ is shown. Patient name: Personal number: Exam date: Performed by:

Video 10x Sit-Stand-Sit Frontal Sagittal

Report Text report

3D gait analysis Right = green and Left = red. Control value +/- one standard deviation = grey SSS cycle 1 ('first'): Video Kinematics:

Main angles All Angles Angle velocities CoM

Kinetics: !Control GRF Moments

SSS cycle at the end ('last'): Video Kinematics:

Main Angles All Angles Angle velocities CoM

Kinetics: !Control GRF Moments

Time and moment values

=> export to excel!

General information

Regular videos Empty file where therapists can enter their conclusions

DATA PRESENTATION FOR FIRST AND LAST CYCLE OF THE TST

3D‐reconstructed video Kinematics:

‐ Main angles: thorax, knee, hip, ankle angles in sagittal plane

‐ All angles: thorax, knee, hip, ankle angles in

sagittal, frontal and transverse plane ‐ Angle velocities: thorax, knee, hip, ankle

velocities in sagittal plane ‐ CoM: CoM movement upwards,forwards

Kinetics: ‐ Control GRF: control the GRF graphs to be

sure that the GRF data are ok ‐ Moments: knee, hip moment in sagittal plane

and knee moment in frontal plane TIME AND MOMENT VALUES

These are computed in our excel template

85

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1

Analyse van de sit-stand-sit beweging in volwassenen met reumatische artritis


Begeleiders: Malcolm Forward, Lanie Gutierrez-Farewik, Eva Broström

Abstract –Deze thesis beschrijft het opstaan van en gaan zitten

op een stoel in patienten met reumatische arthritis (RA) en een controle groep. Subjecten (11 patienten en 9 controlepersonen) voerden 10 sit-stand-sit (SSS) cycli zo snel mogelijk na elkaar uit, en kinematica en kinetic van de eerste en laatste cyclus werden verzameld. Het doel is SSS strategien te identificeren die worden aangewend door patienten met RA. Een trunk-first strategie wordt vooropgesteld als hypothese, met karakteristieken extensieve romp flexie, groter heup- en kleiner kniemoment, langere stijgtijd, en een meer distincte voorwaarts/opwaartse center of mass (CoM) beweging. De momentum-transfer strategie (MomTra) is gedefinieerd als de normatieve SSS, die voorwaarts en opwaartse CoM beweging mengt. Een onderscheid wordt gemaakt tussen touch&rise en sit&rise. Patienten met RA vertonen in het algemeen meer sit&rise gedrag en een grotere rompflexie. Naast de normale MomTra strategie worden twee RA strategieën onderscheden. Zes subjecten met RA voeren de gelijkaardige “momentum-transfer with higher trunk flexion” (MomTra-TFl) uit, waarin ook na lift-off simultaan voorwaarts en opwaarts wordt bewogen, maar meer romp flexie wordt gebruikt om deze momentum-transfer te verkrijgen. De gehypothiseerde trunk-first strategie werd geobserveerd in de overige vier patienten. Zij bogen extensief de romp waarna ze bijna verticaal opwaarts van de stoel rezen. Dit werd de “distinct-momentum” (DistMom) strategie genoemd. De biomechanische sleutelcomponenten om de MomTra, MomTra-TFl and DistMom strategieën te identificeren en onderscheiden, zijn CoM beweging, rompflexie en SSS cyclus tijd.

Sleutelwoorden: bewegingsanalyse, sit-stand-sit, reumatische

arthritis, bewegingsstrategie, sit&rise, distinct-momentum, momentum-transfer with higher trunk flexion

I. INTRODUCTIE Opstaan en gaan zitten (samengenomen in de sit-stand-sit

(SSS) beweging) zijn sleutelcomponenten van functionele mobiliteit met een gemiddelde frequentie van 4 keer per uur [1] en een grote belasting voor knie- en heupgewricht [2]. Patienten met reumatische artritis (RA) worden verwacht problemen te ondervinden in SSS en passen hun strategie aan, door pijnlijke gewrichten en limitaties in hun range of motion. Clinici zouden de behandeling voor SSS mobiliteit in patienten met RA kunnen verbeteren door, gebaseerd de geobserveerde bewegingsstrategie, te bepalen welke spieren en gewrichten vermoedelijk beschadigd zijn. Deze thesis identificeert de verschillen tussen SSS strategieën van patienten met RA.

De SSS cyclus werd geanalyseerd als deel van de Time-Stand test (TST), bestaande uit 10 SSS cycli zo snel mogelijk na elkaar uitgevoerd. Naar onze kennis is er nog geen

biomechanische analyse uitgevoerd hiervoor. Opstaan van een stoel als aparte beweging (RIS) is wel al uitvoerig onderzocht vanaf de jaren ’90 [3,4,5,6,7]; gaan zitten (DESC) werd maar in twee studies opgenomen [6,7]. Over het algemeen worden beide verdeeld in drie hooffases. Voorwaarts momentum wordt gegenereerd vanaf de start van voorwaarste rompbeweging (Ts) tot het zitvlak de stoel verlaat op lift-off (TL). Het verlaten van de stoel brengt het voorwaarts momentum van het bovenlichaam over naar voorwaarts en opwaarts momentum voor het hele lichaam. Start van extensie (Te) vindt plaats wanneer het lichaam puur vertikaal stijgt en alle gewrichten simultaan worden gestrekt. DESC begint met stooping (het subject buigt naar gestupeerde positie (Tst)), waarna de echte dalingsfase start door neerwaarste versnelling van de CoM. Alle gewrichten buigen totaan stoelcontact (Tc). Het gewicht wordt overgebracht naar de stoel tijdens seat loading, eindigend op Tsit.

De ideale strategie voor opstaan van een stoel werd de momentum-transfer strategy (MT) genaamd, en wordt gebruikt door valide personen van alle leeftijden [4,8,9]. Tijdens MT, in een lange momentum-transfer fase creëert het voorwaarts momentum tijdens het zitten een opwaarts en blijvend voorwaarts momentum tijden het opstaan. Dit verschijnt als een vlotte CoM beweging en vraagt om coördinatie van verschillende spiergroepen, met speciale aandacht voor de balans [1]. Testpersonen met functionele limitaties die niet in staat zijn om MT uit te voeren, zullen een compensatiestrategie ontwikkelen die hun bekwaamheden reflecteert [3,4,5,10,11,12,13,14,15,16]. Gelimiteerde range of motion, gewrichtspijn, spierzwakte en povere coördinatie beïnvloeden de kinematica en kinetica van hun beweging. Voor de oudere generatie definieerden Scarborough and co-workers de “extensive trunk flexion strategy” (ETF) [4], en Doorenbosch and coworkers onderzochten de biomechanische aspecten hiervan [3]. In ETF, ook distinct-momentum of trunk-first strategie genaamd [16], buigt het subject de romp meer extensief op het moment dat de stoel wordt verlaten (TL). Elevatie van het lichaam start alleen nadat het bovenlichaam als het ware naar voren rolt en zo de CoM over het steunpunt brengt. Dit creëert meer stabiliteit tijdens de beweging en verlaagt het nodige coördinatievermogen om balans te verkrijgen. Er grijpt minder momentum transfer plaats: de horizontale en vertical component van de CoM beweging zijn meer gescheiden. Dit induceert een tragere stijgfase (>2s). De kinetica tonen dat een kleiner moment in de knie plaatvindt, maar er wordt daarentegen een groter moment in de heup geobserveerd. ETF is de optimale strategie om intern kniegewrichtmoment te reduceren en om te compenseren voor spierzwakte rond de knie [9,11].

2

RA is een inflammatoire ziekte geassocieerd met gewrichts–vernietiging, -invaliditeit en -pijn [20]. De impact van RA op de beweging van het opstaan van een stoel is nog niet grondig onderzocht; een kleine studie vond enkele kenmerken als een grotere rompflexie en een kleiner kniemoment [17]. Symptomen van RA als gewrichtspijn, gelimiteerde range of motion en spierzwakte zouden SSS strategie aanpassen [18]. Naar onze kennis is er nog geen zogenaamde “typische RA-strategie” gedefineerd geworden. Onze hypothese is dat subjecten lijdend aan RA een trunk-first strategie zullen vertonen, met karakteristieken zoals die geobserveerd in oudere personen (figure 1).

Figure 1: De trunk-first hypothese. Patienten worden verwacht tijdens opstaan deze 4 trunk-first karakteristieken te vertonen: meer rompflexie, groter heup- en lager kniemoment, langzamere stijgfase, en een meer disticte voorwaarts/opwaartse CoM beweging.

II. METHODE

A. De test 11 patienten met RA werden betrokken in de test, 3 mannen

en 9 vrouwen in de leeftijd van 35 tot 74 jaar. De criteria tot toelating waren een onafhankelijke ambulatie van 12 m en reumatische artritisactiviteit in de gewrichten van het onderlichaam. Een controlegroep van 9 personen in ongeveer dezelfde leeftijdgroep werd samengesteld, bestaande uit 2 mannen en 7 vrouwen (table 1). De testen werden uitgevoerd en data verzameld in het Karolinska Universiteitshospitaal in Stockholm. Deelname was vrijwillig en de ethische goedkeuring was verkregen via het Karolinska ethisch committee. De proefpersonen werden geïnstructeerd zo snel mogelijk 10 opeenvolgende SSS cycli uit te voeren, terug opstaand van zodra hun gewicht op de stoel rustte. De instructie liet elk persoon de vrijheid van keuze om op te staan, of terug na volledig te gaan zitten met rompextensie (“sit&rise”), of direct van zodra de stoel werd aangeraakt (“touch&rise”) (figure 2). De stoel was 0.40m hoog en zonder rug- of armleuning om afduwen van andere oppervlakken dan de grond en het zitvlak te vermijden.

Table 1: vergelijking tussen patienten controlegroep: gemiddelde +- standaard afwijking.

Characteristic Patients with RA

Controls

Gender (F,M) 8 F, 3 M 7 F, 2 M Age (yrs) 59,3 +- 14.1 52 +- 14.6 Height (m) 1.64 +- 0.1 1,68 +- 0.1 Weight (kg) 67,5 +- 11 70.1 +- 12 Disease duration (yrs) 8,4 +- 7

Figure 2: Twee manieren om de TST uit te voeren: “touch&rise”, onmiddelijk opstaan van zodra de stoel is aangeraakt, en “sit&rise”, eerst volledig op de stoel gaan zitten voor terug op te staan. Het verschil is op zicht onderscheidbaar.

B. Analyze Een conventioneel biomechanisch model dat alledaags

wordt aangewend in gait analyse, werd aangewend (Plug-in-Gait, Vicon) [19]. Subjecten werden voorzien van reflectieve markers op anatomisch vaste plaatsen, waaruit een model van 15 segmenten werd gecreëered: hoofd, romp, bovenarmen, onderarmen, handen, bekken, bovenbenen, onderbenen, en voeten. Om dataverlies door verdwijnende marker trajektories te voorkomen, werden occasioneel extra markers gebruikt: lange markerhiaten werden gevuld met hulp van overbodige (i.e. meer dan 3) markers op romp, hoofd en bekken. De instrumentatie bestond uit twee gewone video cameras om de beweging op te nemen, 8 opto-electronische cameras (Vicon MX40) voor de kinematica, en twee krachtplaten (Kistler) voor de kinetica. Alleen de eerste en laatste cyclus van de TST (of de voorlaatste als de laatste pover was opgenomen) werden opgenomen in de analyze. Thorax, heup, knie en CoM grafieken werden visueel vergeleken (table 2), en een statistische analyze werd uitgevoerd op enkele parameters m.b.v. Statistica version 9 (table 3). Statistische significantie van de Mann-Whitney U test werd vastgelegd op p<0.05. CoM grafieken en parameters waren speciaal inbegrepen om de trunk-first hypothese te testen. De grafieken, y- versus x-component (CoMy versus CoMx), werden verschoven naar links zodat ze voor x>0 alleen het deel voorstellen waar opwaartse beweging plaatsvindt. De MT strategie voor opstaan van een stoel, zowel voorwaarts als opwaarts bewegend tijdens de momentum-transfer fase, resulteert dus in een langere grafiek. De trunk-first hypothese (die de momentum-transfer overslaat) wordt vertaald in kortere CoM grafieken. De CoM parameter Tym-Txm representeert het voorwaarts-opwaarts onderscheid in een waarde. Hij wordt berekend als het interval tussen de timing van CoMymax en CoMxmax. De trunk-first hypothese, waarin CoMymax laat in de bewegin voorkomt, wordt dan vertaald in een grote waarde voor Tym-Txm. In de RA groep worden dus een kortere grafiek en grotere Tym-Txm-waarde verwacht.

Analyzes werden uitgevoerd voor het vergelijken van de laatste met de eerste cyclus, RA groep met controlegroep, en sit&rise met touch&rise. Op basis van de CoM grafieken werden twee groepen gedestileerd uit de patientengroep (DistMom (4 subjecten) and MomTra-TFl (6 subjecten)), en deze werden elk apart geanalyseerd. Enkele testpersonen werden uitgesloten van de CoM respectievelijk moment analyzes door onherstelbaar verdwenen markers (1 control, 1

3

RA) respectievelijk slechte opnames van reactiekrachten (5 controls and 6 RAs).

C. De SSS cyclus De gebeurtenissen Ts,Tl,Te,Tup,Tst,Tc en Tsit beschrijven de

SSS cyclus (figure 3). Ts en Tsit, in principe dezelfde gebeurtenissen, werden gedefinieerd op het zwenkpunt van een romp marker, terwijl Tup gedefinieerd is op het bekkens’ zwenkmoment. De ogenblikken van interactie met de stoel, TL voor RIS en TC voor DESC, werden gedefinieerd als de maxima op de heupgrafiek. Het eerste maximum op de enkelgrafiek bepaalt Te, en de eerste verandering na Tup in vertikale reactiekracht geeft Tst. De SSS cyclus tijd werd berekend van Ts tot Tsit, en alle tijdswaarden werden genormaliseerd op dit interval.

Figure 3: De 7 gebeurtenissen in de SSS cyclus. Ts, Tup en Tsit zijn gedefineerd op visuele marker beweging (zwenkpunten van romp en bekken). TL en Tc zijn momenten van max heupflexie. Te vindt plaats op max enkel dorsiflexie. De eerste verandering in Fz na Tup bepaalt Tst.

Table 2: Geanalyseerde grafieken: 4 hoeken, 2 momenten, en de CoM. Rechts: de belangrijkste hoekdefinities.

Kinematic graphs

Trunk flexion angle Hip flexion angle Knee flexion angle Knee var/val angle

Kinetic graphs

Hip moment Knee moment

CoM graphs CoMy versus CoMx CoMx and CoMy versus time

Table 3: Geanalyseerde parameters: 4 kinematische, 6 tijds-, 6 kinetische, 3 cyclus tijd and 2 CoM variablen.

Kinematic parameters (Degrees)

Max trunk flexion RIS & DESC Max hip angle RIS & DESC

Temporal parameters (% SSS cycle)

Timing max tr fl RIS & DESC Timing max hip angle RIS & DESC Timing start knee ext RIS & DESC

Kinetic parameters (Nm/kg)

Max knee ext moment RIS & DESC Max knee var/val moment RIS & DESC Max hip fl moment RIS & DESC

Cycle time parameters (s)

SSS cycle time TOT SSS cycle time RIS SSS cycle time DESC

CoM parameters (% SSS cycle)

Tym-Txm RIS & DESC

III. RESULTATEN

A. De normale SSS cyclus: MomTra De normale SSS cyclus zoals geobserveerd in de eerste

cyclus van de controlegroep wordt de momentum-transfer SSS (MomTra) genaamd. De gemiddelde cyclustijd was 1.94s, eerlijk verdeeld tussen RIS (0.94s) and DESC (0.98s). Alle grafieken ervaarden een gelijkaardig gedrag: heel symmetrisch rondom Tup, met aan beide zijden een maximum rond TL and Tc (figure 4). Er vonden geen grote veranderingen op Te of Tst plaats in thorax-, heup- en kniehoeken. Tijdens het zitten boog de romp, knie buiging bleef constant, en knie varus/valgus positie varieerde onder personen van grote valgus tot kleine varus. Op TL begon de heup zich te strekken en ging de knie van valgus naar neutral, gevolgd door extensie van de romp en als laatse de knie. In het gaan zitten bereikte de knie eerst terug valgus positie waarna dan de romp zich rechtte. Ongeveer 80ms later, op Tc, bereikten heup en kniegewrichten hun maximale flexie.

De laatste cyclus neemt minder tijd in beslag (1.63s), voornamelijk door verkortte zitfases. Knie flexie ondervond kleine fluctuaties tijdens het zitten, een fenomeen dat werd gedefinieerd als “hopping”: door moeheid controleerden de testpersonen hun neergaande fase minden in de laatste cyclus, waardoor de impact op de stoel bij het gaan zitten harder aankwam. Kinematica en kinetica in de laatste cyclus waren niet significant verschillend van de eerste.

B. Sit&rise versus touch&rise 10 Subjecten bleken touch&rise SSS cycli uit te voeren, 10

de minder belastende sit&rise. Kinematische karakteristieken van sit&rise waren meer flexie van de romp en hopping gedurende zitfases (figure 5).

Figure 4: kinematica van de eerste cyclus uitgevoerd door de controlegroep: thorax, heup, knie flexie en valgus hoeken (genormaliseerd op een SSS cyclus tijd van 1.94s).

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Figure 5: Gemiddelde grafieken –hoek(deg) versus tijd (%)- voor touch&rise en sit&rise in de laatste SSS cyclus. Sit&rise toont meer rompflexie en hopping gedurende zitfases.

C. Kenmerken van patienten met RA Karakteristieken van patienten met RA resulteerden uit de

vergelijking van de laatste cyclussen van patient- met controlegroep. RA groep voerde een 6° grotere rompflexie op Tl and Tc, en een 4° grotere knievalgus uit dan normaal. Maximaal heup moment was 0.3 Nm/kg groter, maximaal knie moment 0.2 Nm/kg kleiner. De verschillen waren niet significant. Wel significant was de verandering die plaatsvond tussen eerste en laatste cyclus: RA karakteristieken komen meer uit op het einde van de TST, een teken van moeheid (table 4). Patienten, trager en voorzichtiger, hopten minder. Zeven van de elf patienten deden sit&rise. Sit&rise kan dus worden beschouwd als een RA strategie, dan is touch&rise de normale manier om een TST uit te voeren. Het apart beschouwen van beide strategieën toonde dat patienten in touch&rise meer rompflexie dan normaal gedurende de hele SSS aanwenden, terwijl ze in sit&rise alleen op TL and Tc de romp meer buigen (figure 6).

Table 4: Vergelijking tussen eerste en laatste cyclus in patienten controlegroep: tijdsparameters voor max romp en heup hoek tijdens RIS toonden dat de zitfase korter is in de laatste cyclus, zowel voor patienten als controlepersonen (linker kolom). Voor de patienten, dit verschil is meer geprononceerd met lagere p-waarden (rechterkolommen). Patienten passen dus hun strategie meer aan door moeheid in de laatste cycles.

Comparison first last in controls and

RAs

First last - Controls - RAs

p-value controls

p-value RAs

Timing max tr fl RIS (%SSScycle)

22 18 20 16

0.13 0.02

Timing max hip fl RIS (%SSScycle)

18 16 18 14

0.11 0.04

ThoraxAngles10

-55

deg

Figure 6: Vergelijking en visualisatie van thoraxhoeken, alleen subjecten die touch&rise (links) / sit&rise (rechts) deden inbegrepen. Links: patienten (donkerrood) buigen de romp constant meer dan de normale touch&rise beweging (cyaan). De algemene controlegrafiek (zwarte stippellijn) is supergeponeerd om de touch&rise grafieken beter te situeren. Rechts: patienten (donkerrood) buigen de romp meer op TL en TC dan normale sit&rise (cyaan). Visualisatie: het grijze silhouette is de patient, zwart de controlepersoon.

D. Strategieën van RA patienten Op basis van de CoM grafieken, werd de RA groep in twee

gesplitst (figure 7). De “Distinct-Momentum strategie” (DistMom) had kortere en dikkere CoM grafieken dan normaal, wat het verwachtte trunk-first gedrag reflecteert (4 patienten). De zes overige patienten toonden het totaal tegengestelde gedrag, met langere en dunnere CoM grafieken dan de controlepersonen: deze nieuwe strategie werd gedefinieerd als “Momentum-Transfer with higher trunk flexion” (MomTra-TFl). Tym-txm bevestigde deze opdeling met waarden van 26 voor DistMom, 17 voor controlegroep en 13 voor MomTra-TFl. Het verschil tussen DistMom and MomTra-TFl was significant met p=0.028. De kinematica toonden significant verschil in maximale rompflexie: 41.5° voor DistMom vergeleken met 32° voor MomTra-TFl (p=0.042). DistMom karakteristieken verschenen al in zitfases, terwijl MomTra-TFl zich alleen op TL and Tc onderscheed van de normale cyclus (figure 8). Tijdsparameters van de twee RA strategieën hadden p-waarden rond 0.1, duidend op een in DistMom 80 ms langer durende zitfase vooraleer de patient opwaarts beweegt.

MomTra-TFl was meer gerelateerd aan de normale MomTra strategie, maar met een SSS cyclus (zowel RIS als DESC) die remarkabel langer duurde (1.95s vergeleken met 1.63s; p=0.28). De CoM werd dichterbij het steunpunt gebracht waardoor meer stabiliteit werd gecreeerd; dankzij deze overvloed aan stabiliteit konden voorwaarts en opwaartse bewegingen makkelijker worden gecombineerd. Kinematisch gezien toonde MomTra-TFl 5° meer rompflexie en a 4° meer valgus dan normaal rond TL en Tc (figure 8).

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Figure 7: (a) individuele CoM grafieken (laatste cyclus) voor de controlegroep (grijs) en patienten met RA (onderbroken zwart). Voor x>0 reflecteren CoM grafieken de voorwaartse beweging gedurende opwaartse beweging. Op basis van hun uitgestrekheid in x-richting werden de RA grafieken in twee groepen RA DistMom (stippellijn) and RA MomTra-TFl (streepjeslijn). (b) De gemiddelde grafieken voor DistMom, controle- en MomTra-TFl groepen.

Figure 8: Gemiddelde grafieken -hoeken (deg) versus tijd (%)- voor controle-, RA MomTra-TFl en RA DistMom groep in laatste SSS cyclus. Karakteristieken van DistMom and MomTra-TFl strategieën tonen zich romp, heup, en knie valgus grafieken.

IV. DISCUSSIE Er warden drie strategieën onderscheden om sit-stand-sit uit

te voeren. De normatieve SSS cyclus MomTra zoals uitgevoerd door de controlegroep toonde dezelfde voorwaarts-opwaartse stijgfase als de ideale MT. DistMom

werd geobserveerd in 4 patienten, waarin de romp extensief wordt gebogen en dan een bijna verticale stijging plaatsvindt, wat correspondeert met de trunk.first hypothese. De overige patienten voerden MomTra-TFl uit, met een mix van voorwaartse en opwaartse CoM beweging, maar om deze momentum-transfer te verkrijgen wordt meer rompflexie dan normaal aangewend. De biomechanische sleutelcomponenten om de drie strategieën te identificeren waren CoM beweging, rompflexie, en SSS cyclus tijd (figure 9).

De standaard SSS cyclus MomTra (figure 10) nam minder dan 2s tijd in beslag, eerlijk verdeeld tussen RIS en DESC resulterend in symmetrische grafieken. Grote gebeurtenissen waren allemaal gesitueerd rond stoel-af en stoel-op. De laatste cyclus van de TST verschilde van de eerste in een kortere zitfase en meer aanwezigheid van hopping, en toonde beter RA kenmerken. Er bestaan twee normale SSS cycli: touch&rise SSS en sit&rise SSS. Touch&rise is de meest belastende waarin de persoon zelf zijn neerwaartse beweging moet afremmen om daarna onmiddelijk weer op te staan. RA patienten met minder spierkracht kunnen hun eigen neerwaarts momentum niet tegenwerken en voeren meer sit&rise uit, waarin de stoel de neerwaartse beweging remt. Men kan zich afvragen of de keuze tussen touch&rise en sit&rise strategie puur een kwestie van kunnen is: de TST instructie zou misverstaan kunnen zijn zodat sit&rise wordt gedaan ookal kunnen ze touch&rise aan, of sit&rise kan worden vermeden uit angst voor achterover vallen.

Patienten met RA toonden over het algemeen 4° meer valgus dan normaal. Dit zou een artifact door misplaatsing van markers kunnen zijn, en er zijn te weinig kinetische data aanwezig om de valgus observatie te checken. Patienten leden meer onder moeheid dan de controlegroep, hun strategie meer aanpassend in de laatste cyclus. Twee RA strategieën werden gedefinieerd, RA DistMom en RA MomTra-TFl, met significante verschillen in maximale romp flexie gedurende opstaan (41.5° voor DistMom, 32° voor MomTra-TFl), en in overlap voorwaarts-opwaartse beweging (maar half de overlap van MomTra-TFl was in DistMom). Een SSS cyclus duurde opmerkelijk langer in MomTra-TFl strategie, maar niet significant.

RA DistMom ondersteunde de trunk-first hypothese (figure 11). De romp was constant 9° meer gebogen, en voorwaarts en opwaartse CoM beweging was meer distinct dan normaal, beide bijna significant (p around 0.1). Er bestaan geen resultaten voor de kinetica door te kleine de groepen, maar we verwachten dat de hypothese gevolgd wordt, zijnde een groter moment in de heup en kleiner in de knie. RA MomTra-TFl volgde de trunk-first hypothese niet en geleek meer op de normale SSS. Verschillen met de normale toonden zich op niet-significante wijze in een grotere rompflexie en langere SSS cyclus tijd, en bijna significant (p=0.1) in de CoM beweging: het lichaam beweegt lang voorwaarts, ook tijdens de opwaartste fase.

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Figure 9: Onderscheid tussen RA strategieën onderling en met de normale: vlnr MomTra (grijs), DistMom (oranje), MomTra-TFl (geel). Verschillen verschijnen op drie pillaren: max romp flexie, voorwaarts-opwaartse CoM beweging, en SSS cyclus tijd. De pijlen tonen de noemenswaardige verschillen.

Figure 10: Kenmerken van de standaard SSS MomTra.

9° more (p=0.07)

(no moment comparisons due to too less subjects)

bigger Tym-Txm (p=0.02)

longer rising phase but no difference in cycle times

Figure 11: RS DistMom karakteristieken linken aan trunk-first hypothese. =correspondeert, bijna significant (met p < 0.1). = correspondeert maar zonder significantie

Enkele opmerkingen moeten worden gemaakt. Knie-en heup moment acquisitie mag niet worden betrouwd omdat de verworven kinetica niet overeenkwamen met de bevindingen van Yoshioka and coworkers (som van piek heup en knie momenten in opstaan was 2.039 Nm/kg in plaats van de verwachtte 1.53 Nm/kg). Groepen waren vaak klein, waardoor conclusies moeilijk veilig over te brengen zijn naar de hele populatie. Resultaten worden dus al als vermeldenswaardig beschouwd vanaf p<0.2, zeker als alle ander p-waarden boven 0.5 liggen (zoals voor tijdsparameters). De parameter tym-txm moet met voorzichtigheid worden behandeld omdat de waarde niet altijd de voorwaarts-opwaarts overlapping van de grafieken correct reflecteert.

Subject typificaties als leeftijd, hoogte, gewicht, sekse en duur van de ziekte kon de variaties in SSS strategieën tussen RA patienten niet uitleggen; noch het verschil touch&rise/sit&rise kon dit. Er is geen rekening gehouden met pijn of andere karakteristieken van de reumatische artritis. De vraag “waarom voeren sommige RA patienten de DistMom of MomTra-TFl SSS strategieën uit in plaats van MomTra” blijft open voor verder onderzoek. Toekomstige studies betreffende RA patienten die SSS uitvoeren, worden geadviseerd het gebruik van CoM beweging als classificatiemethode voor SSS strategie te valideren. Waard op te nemen is een goede kinetische analyse.

V. CONCLUSIES Normatieve kinematica en kinetic voor de standaard SSS

cyclus werden verworven, en MomTra genaamd naar de gelijkenis met de RIS strategie MT. Patienten met RA wijken hiervan af door de gerelateerde MomTra-TFl strategie of de trunk-first strategie DistMom. De hoofdkenmerken ter onderscheiding zijn CoM beweging, rompflexie en SSS cyclustijd. Dit zijn klinisch observeerbare biomechanische grootheden die kunnen worden gebruikt om SSS strategieën te identificeren.

VI. DANKWOORD Deze thesis was niet mogelijk geweest zonder de hulp van

mijn twee zweedse begeleiders Lanie Guterriez-Farewik en Eva Broström, die mij de weg hebben geleid en altijd bereid waren mijn vragen te beantwoorden. De hulp van Anna-Clara Esbjörnsson is ook ten zeerste geapprecieerd. Mijn begeleider aan de Ugent Malcolm Forward, hoewel verweg, verdient mijn welgemeende dank voor zijn bereidwilligheid en opoffering van zijn weekend voor deze thesis.

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