transtibial_prosthetics_1.pdf

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Tome 1

( Socket Design )

Trans-tibial

Prosthetics

Course Work Manual

ICRC

( INTERNATIONAL COMMITTEE OF THE RED CROSS )


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Trans-tibial Prosthetics

INDEX

Section Pages

1 Biomechanic Principles for PTB Socket Design 2

2 Surface Anatomy Of Lower Extremity 11

3 Patient Assessment 16

4 Measurements & Casting Techniques 30

5 Cast Modification 51


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SECTION - 1

BIOMECHANICS PRINCIPLES FOR

THE PATELLAR TENDON BEARING

(PTB)

SOCKET DESIGN.


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BIOMECHANICS OF SOCKET FIT

Comfort, stability and function of a prosthesis are achieved primarily by the

application of certain biomechanical principles. In the past, the application of these

principles has been based upon clinical experience and trial and error. In more recent

years, the contributions of a number of investigators have provided a clearer

understanding of some of these biomechanical factors. The purpose of this chapter

is to relate selected biomechanical principles to socket shape of the below-knee

prosthesis, with special reference to the patellar-tendon-bearing below knee

prosthesis.

Pressure as a Determinant of Comfort

The magnitude of pressure between the stump and socket is one of the major

determinants of comfort in a prosthesis. Pressure is directly proportional to the force

applied and inversely proportional to the area over which it is applied. This is

expressed in the formula P=F/A, in which P represents the average pressure, and F

and A represent, respectively, the applied force and the area over which the force is

applied.

P=F/A

The force F is expressed in kilogram and represent the weight the patient is bearing

on the prosthesis. The area is expressed in square centimetres and represent the

surface applied by the socket on the stump.

To minimize discomfort, it is important to avoid excessive pressure on the stump.

There are two way to reduce the pressure. First you can reduce the amount of force

apply on the stump by reducing the weight. Second you can increase the area over

which the force is applied. To reduce the force exercised on the stump by theprosthesis you must use external means such as a thigh corset, crutches or other

similar means. To increase the area, you must use all the possible bearing surface

of the stump. Although for the first approach, it is easy to do, it is rather cumbersome

and does defeat the ultimate means of the prosthesis to make the patient as

autonomous and functional as possible. As for the second approach, in practice it is

not that simple because the relative firmness or softness of the tissues of the stump

are not uniform. As well, some areas of the stump tolerate pressure quite well, while

other areas are relatively sensitive to pressure. However, both of these factors can be

accommodated by appropriate design of the contours and shape of the socket.


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To start with a general concept, consider Figure 1.3, which represents a heavy bar

resting on a cube. The pressure on top of the cube is equal to the weight of the bar

divided by the area of the cubes upper surface. Figure 1.4 shows the same bar being

supported, not only on the original cube, but by two additional cubes identical to the

original and at equal distances from it.

Socket Contours and Shape Related to Pressure Distribution

Figures 1.1 and 1.2 show top views of contours of the socket walls of two different

types of below-knee prosthesis. Figure 1.1 is derived from a PTB socket, whileFigure 1.2 is derived from a type of socket that was fitted before the PTB socket

came into general use. Although the socket periphery of Figure 1.1 conforms more

closely to that of the below-knee stump than is the case with the PTB socket, the PTB

socket is generally the more effective of the two from the standpoint of comfort and

function. It is important to understand the reasons for this and, in general, to

understand the principles that relate socket contours and shape to pressure

distribution.

Fig. 1.1 Fig. 1.2

Fig. 1.3 Fig. 1.4


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In this case the pressure on the middle cube will be only one-third as great as in

Figure 1.3, since the supporting area is three times as great. These two examples

illustrate the application of a basic principle in prosthetic fitting, and that is to utilize

as much area of the stump as possible to distribute the force applied by the socket tothe stump.

By cutting a slot, or relief, in the steel bar, as shown in the middle diagram of Figure

1.5, a more even distribution of pressure would be obtained, in spite of the

differences in relative firmness of the steel and rubber cubes. However, if the rubber

cubes were very soft, the relief alone might not be enough to produce the desired

distribution. To illustrate, suppose the steel bar had a mass of 200 kg and the rubber

cubes were so soft that a mass of 15 kg compressed them so that the steel bar came

to rest firmly on a steel cube in the middle. Then the steel cube would have to supporta mass of 170 kg as opposed to the 15 kg supported by each of the rubber cubes.

Accommodating for Differences in Relative Firmness

In most cases, various areas of the stump will differ in relative firmness. If an object

in fitting is to distribute pressure evenly over these areas in spite of different degrees

of firmness of the tissues, then modifications of socket contour with respect to the

stump become necessary. The next series of illustrations demonstrates the principles

involved.

If the cubes in Figure 1.4 had the same dimensions, but differed in their relative

firmness, the pressure would not be distributed evenly. For example, if the middle

cube were made of steel and the other two were made of soft rubber, the steel cube

would support most of the load.

The load distribution could be improved by cutting a deeper relief in the steel bar.

Since this might weaken the bar, an alternative solution might be used. Instead of

making the relief deeper, two build-ups could be added to the bar, as shown in

Figure 1.6. If the relief were cut to the proper depth and build-ups of the properthickness were applied, an even distribution of pressure would be obtained.

Fig. 1.5


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Now apply this to a prosthesis. The diagram in Figure 1.7 is a schematic

representation of a stump that is essentially circular in cross-section, encased in a

socket that accurately matches the periphery of the stump. If the stump were of

uniform firmness, the stump-socket pressure would also be uniform. The diagram in

Figure 1.8 is similar to Figure 1.7, except that the stump is not of uniform firmness.

The areas indicated by the letter F are relatively firm, while softer areas are

indicated by the letter S. This, of course, is a schematic diagram.

If the socket were shaped to match the stump accurately, the pressure on the stump

would not be evenly distributed. The firm areas Fig 1.8 designated by F would

take relatively more of the load, while the soft areas designated by S would take

relatively less. A more even distribution of pressure could be obtained by purposely

modifying the socket to make reliefs in the socket over the firm areas and bulge the

socket inward over the soft areas, as shown in the diagram in Figure 1.9.

Fig. 1.6 Fig. 1.7

Fig. 1.8 Fig. 1.9


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Accommodating for Different Tolerance to Pressure

The same strategy described above, namely that of utilizing reliefs and inward

contours in the socket, can be used to compensate for different tolerance to pressure

of the various areas of the stump. In this case the purpose is different. Instead of

producing an even distribution of pressure, the objective is to produce a selective

loading of the tissues so that more of the weight will be supported by the pressure-

tolerant areas and less weight will remain on the pressure- sensitive areas.

To illustrate, the three cubes in Figure 1.10 have the same dimensions and the same

degree of firmness. Assume that the cube in the middle is pressure-sensitive and the

other two cubes are pressure-tolerant. The objective is to load the end cubes

selectively so that less weight will remain to be supported by the middle cube. If aheavy bar were placed on the cubes, as shown in Figure 1.10, the same amount of

weight would be borne by each cube. This is not what is wanted. By cutting a relief

in the steel bar, as shown in Figure 1.11, a more desirable weight distribution can be

obtained. If the relief alone is not sufficient, build-ups may be added, as shown in

Figure 1.12. By making the reliefs and build-ups of proper dimensions, almost any

proportional distribution of weight on the three cubes can be obtained even to the

point of completely unloading the middle cube.

Fig. 1.10

Fig. 1.12Fig. 1.11


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The application of this principle can now be illustrated. Figure 1.l3 is a schematic

diagram of a stump of uniform firmness, encased in a socket. The socket has reliefs

over the pressure-sensitive areas, which are designated by S, and inward contours

over the pressure- tolerant areas, which are designated by T. The inward bulges

over the pressure tolerant areas will cause the tissues in these locations to sustain a

relatively large portion of the load, leaving a smaller part of the load to be borne by

the sensitive areas. The reliefs in the socket will assist further in reducing the

pressure sensitive areas.

Sockets of both below knee and above knee prostheses are usually designed to apply

the biomechanical principles illustrated above. By incorporating appropriate reliefs

and contours, sockets can be shaped to accommodate differing degrees of firmness

of the stump and different tolerances to pressure.

The typical patellar-tendon-bearing prosthesis for the below knee amputee has an

inward protuberance that fits under the patellar tendon and a snug contour that fits

under the medial flare of the tibia. The posterior wall bulges inward slightly, and

the lateral wall is shaped to provide firm pressure on the lateral distal half of the

stump. Reliefs in the socket are usually provided for pressure-sensitive areas at the

anterior distal aspect of the stump, over the crest of the tibia and over the head of

the fibula.


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Effect of Relative Inclination of Supporting Surface

Pressures on the stump are greatly influenced by the relative inclination of the

supporting surfaces that are in contact with the stump.

In applying this principle, it can be seen that a horizontal supporting surface in a

socket is preferable to a steeply inclined supporting surface. In the socket of a below

knee prosthesis, except for the Symes amputation, a horizontal surface to which a

major part of the load can be applied is not available. While the bottom of the socket

for a mid-leg amputation may be approximately horizontal, the end of the stump can

hardly tolerate pressure, let alone heavy loading. If the below knee stump is fitted in

a socket in which the steeply inclined walls provide the major supporting surface, it

is usually necessary to support part of the weight by means of a thigh corset becauseof the excessive pressure that would be generated if all the necessary supporting

force had to be applied to the stump by the socket walls. The thigh corset transmits

part of the load via the side bars and knee joints to the shank of the prosthesis, with

a corresponding reduction in the amount of the weight that must be supported by the

socket in contact with the stump.

The thigh corset is somewhat bulky

and tends to produce atrophy of the

thigh. By fitting the stump in slight

initial flexion and by purposelymodifying the contour of the socket by

making an inward bulge to fit under the

area of the patellar tendon, an effective

weight bearing area is made available,

as shown in Figure 1.14. While this

area is not horizontal, it is much less

steeply inclined than the other support-

ing areas of the socket wall. The

corresponding reduction of the loadthat must be supported by the steep

walls of the socket makes it possible, in

most cases, to dispense with the thigh

corset and to suspend this type of

prosthesis with a supracondylar wedge

or, less efficient, with a strap.

Fig. 1.14


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Although the supporting area of the patellar tendon is less steeply inclined than the

other supporting areas, it still has a downward and backwards slope. The stump,

supported on this area tends to slide downward and backward. To prevent this, an

anteriorly-directed counter-force is required. The anteriorly-directed counter-force

is applied by the posterior wall of the prosthesis. The posterior wall should be

relatively high to provide as much area as possible over which to distribute the

counter-force, but it must not be so high that it interferes with sitting comfort. It is

not enough for the posterior wall to match the posterior aspect of the stump. The

posterior wall of the socket must be flattened, or even have an inward bulge, so that

the tissues with which it is in contact are under some initial compression. If this was

not done, the stump would tend to slide downward and backward until the tissues on

the posterior aspect of the stump were compressed sufficiently to provide a counter-

force to arrest the motion. Also, the bony surfaces on each side of the posterioraspect of the stump would bear too much pressure.

A well contour of the socket in the area of the medial flare of the tibia can provide

an effective weight bearing area. To maintain the stump on the inclined surface, a

counter-force must be supplied by the lateral wall of the socket to the lateral aspect

of the stump. The major part of this counter-force will be applied to the distal half

or distal third of the stump.

Total Contact Sockets

The socket of the PTB prosthesis is designed to provide total contact with the stump.

Prior to the development of the PTB prosthesis, a majority of trans-tibial sockets did

not provide contact of the socket with the end of the stump. From a biomechanical

standpoint, the total contact design is generally preferable because it offers the

following advantages:

1. It helps to prevent oedema and aids venous return. This is the most important

advantage. In the intact limb, the pumping action of the muscles is an important

factor in moving venous blood back toward the heart. In the amputated limb thisimportant pumping action is reduced. There is a tendency for oedema to develop in

the dependent stump unless pressure is applied to the entire stump.

2. The total contact socket provides greater area over which to distribute the load.

Even though the load supported by the end of a mid-leg or mid-thigh stump is not

great, it does decrease to some extent the load that must be borne by the other areas

of the stump.

3. Because it is in contact with a greater area of the stump, the total contact socket

probably provides better sensory feedback to the wearer.


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BELOW KNEE - SURFACE ANATOMY

Bony structures to be identified:

- Femoral condyles

- Femoral epicondyles

- Tibial condyles

- Medial Tibial Plateau

- Adductor Tubercle

- Patella

- Tibial Tuberosity ( tubercle )

- Lateral Tibial Tuberosity- Head of Fibula

- Tibial Crest

- End of Tibia

- End of Fibula

- Medial Tibial Flare

- Tibialis Anterior

Muscles to be identified:

- Tibialis Anterior

- Gastrocnemius

- Quadriceps Femoris

- Patellar Tendon

- Hamstrings

- Biceps Femoris

- Semimembranosus

- Semitendinosus


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LateralFemoral Condyles

Medial Femoral

Condyles

Lateral Femoral Epicondyles

Lateral Tibial condyles

Medial Tibial condyles

- Medial Tibial Plateau

Adductor Tubercle

Patella

Patella

Tibial Tuberosity

( tubercle )

Tibial Tuberosity

( tubercle )

Lateral Tibial

Tuberosity ( tubercle )

Head of FibulaTibial Crest

Distal End of TibiaDistal End of Fibula

Medial Tibial Flare

Patellar Tendon

Bony structures of the below knee stump (anterior-lateral view)

Bony structures of the below knee stump (anterior-medial view)


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Popliteal Fossa

Biceps Femoris

Gastrocnemius

Semitendinosus

Semimembranosus

Hamstrings

Gluteus maximus

Tensor fasciae latae

Gluteal fold

Medial malleolus

Tendo calcaneus

Back of left lower extremity

Soleus

Lateral malleolus

Perona longus & brevis


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SECTION - 3

PATIENT ASSESSMENT


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PATIENT ASSESSMENT

Introduction:

To carefully examine the patients stump is a very important part of the Prosthetists

work. The examination will tell if the patient is ready for treatment or not. Also the

examination will be a factor in deciding what type of prosthesis to prescribe and the

type of special considerations to make.

The importance of keeping carefully a record for each patient cannot be

overemphasized. It help you to be more accurate, and more professional, in your

decisions leading to the fabrication of the prostheses. It is also primordial forreferences when discussing with other rehabilitation members as well as with the

relatives.

Below aredescriptions of different conditions of the stumpthat will be helpful to

record.

Abrasions.

Are caused by rubbing between the prosthesis and the skin. They should not be a

factor in the new fitting. Abrasions may take the form of blisters or raw skin surfaces.

Boils and other skin infections.

Pus-filled infections, with a core of dead tissue, that occur, usually around a hair

root. Medical care may be required before a prosthesis is fitted.

Bone Spurs.

Bony outgrowths, that may often be found by palpation. The most common regionof spur formation is the end of fibula, in below knee stumps.

Bursa.

A sac filled with a thick fluid, it lies under the skin and over bony prominence.

Bursae are located over the patella and around the tendons of the knee. When there

is too much pressure and movement over them, they get bigger, sometimes only for

a short period of time. Bursae may become infected and require medical treatment

or a change in the prosthesis.


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Discoloration.

Often skin which has had too much pressure, has been damaged by bruising or

oedema, has an abnormal colour.Pressure first reddens and then after several weeks, toughens and darkens the skin to

brown.

Bruises causes blue, yellow, green or brown colours. These show that blood is in the

deeper layers of the skin.

Oedema reddens the skin, if it occurs for long periods it results in blue colours and

finally in the case of chronic oedema, brown stains are left. These stains fade slowly

and may disappear.

Colours of the skin is the most useful guide to show areas of pressure, and may

indicate to the Prosthetist that pressures in the socket should be changed.

Oedema.

A collection of fluid in soft tissues of the stump. May be postoperative or may be

caused by a poorly fitting prosthesis. ( e.g. constriction proximally.)

Oedema should be reduced, with an elastic bandage as much as possible before

fitting is done, otherwise the socket becomes loose too soon.

Pressure point.

An area of the stump that is painful when pressure is applied. An example is the area

where the peroneal nerve passes over the lower surface of the fibular head. Such

points usually require relief in the socket.

Scars.

There are two types of scar tissue:

- Atrophic - thin and easily damaged.

- Hypertrophic - Thickened, painful and often stuck to the bone.All scar tissues tend to be inelastic, and care must be taken to make sure that it is not

stretched or rubbed. When stretched it may tear.

When the scar sticks to the bone it may be possible to loosen it by movement and

massage.

If there is no piston action it may be possible to apply constant pressure over a larger

area of scared tissue.

Trigger points.

A sensitive spot on the stump that causes pain even if it is only touched tightly. Oftenconstant pressure can be tolerated.


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Stump shape.

The stump may be described as bulbous, cylindrical or conical.

The conical stump shrinks the least.The bulbous stump shrinks the most in the distal portions. It also may require an

extra build up on your liner in order to make the donning of the socket easier.

Distal padding.

The amount of tissues covering the cut end of the bone may differ very much.

When the cover is thin it is important to be careful when fitting. Stumps with heavy

distal cover should especially be fitted with total contact sockets to reduce the risk

of oedema.

Condition of subcutaneous tissue.

The condition of the tissues underneath the skin will give a guide to tissue shrinkage.

The tissue is pinched lightly between two fingers and if it can be described as heavy,

then more shrinkage can be expected than if it is described as light.

Also the muscles of the stump are used as a guide to rate of atrophy. A large mass of

muscles will start to atrophy very quickly where as firm musculature will take longer

to atrophy.

Pain.

Pain is described by location, degree and sensation experienced. It may be caused by

some condition in a different place from where the patient feels it.

It is important for the Prosthetist to find out if the pain is caused by the prosthesis or

by a condition within the stump.

Condition of the knee joint.

When describing the condition of the knee joint - range of motion, joint stability,

muscle strength, patella and contractures are included. Although the prosthetist has

to look at those conditions, the physical therapist is usually the most apt to perform

the evaluation of the knee.

Range of motion:

If the range of motion is reduced the Prosthetist may either make the socket

brims higher to ensure no extra movement. Or if medically indicated the fit

and alignment may be made to increase the range of movement.Also range of motion of the hip joint may effect the fitting of a prosthesis.


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Joint stability:

Sometimes the knee joint is easily dislocated or very unstable medio-

laterally, as a cause of injury or a congenital condition.Suspension and socket type should be chosen accordingly to the type and

degree of instability.

Muscle strength :

It is important to know how strong the muscles of the knee and hip are in

order to know if the patients weight can be supported, and if the muscles are

strong enough to control the knee.

Patella:

Sometimes the Patella has been removed or it is split. This will only be a

problem if it affects the possibility of weight bearing at the tendon.

Contracture:

It will not be a problem unless it is severe. The aim of the prosthetic fitting

is not to reduce contractures, although in some case, in cooperation with the

physical therapist, it can help to reduce the contracture.

Condition of the cut end of bones:

Usually the fibula is shorter than the tibia. If fibula is longer than tibia, it is usually

very sensitive and care must be taken in fitting.

In some cases the fibula moves with knee flexion, but this should not be a problem

in a good fitting socket.

The tips of the bones may initially be sharp and care must be taken during fitting.


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EXAMINATION OF THE KNEE.

RANGE OF MOTION:

With the patient sitting on a flat firm surface, check the range of motion of the knee

joint.

Normal range of motion:

Flexion 130

Extension 0 - 10

The most common problem with knee range of movement is the knee flexion

contracture ( the knee cannot extend fully ).

A knee flexion contracture is

measured by measuring the

angle between the midline of

the thigh and the midline of

the stump.


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If there is some medial - lateral looseness, care must be taken to make a socket

that supports the knee medio-laterally, e.g. supracondylar support. Or if the

instability is extremely severe a thigh corset can be added to the prosthesis.

KNEE JOINT STABILITY:

The Medio - Lateral stability ( Collateral ligaments ) is checked by applying valgus

and varus stress to the joint. The patient is sitting with the stump extended.

The medial collateral ligament is loose, if the

knee joint can be opened on the medial

side.

The lateral collateral ligament is loose, if

the knee joint can be opened on the

lateral side.


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KNEE JOINT STABILITY:

The Anterior - Posterior knee stability ( Cruciate ligaments ) is checked when the

patient sitting with a flexed knee.

The Prosthetist pulls the lower leg anteriorly

and if movement is detected the patient has a

loose or torn anterior Cruciate ligament.

If movement is detected when the lower

leg is pushed Posteriorly, the patient has a

loose or torn posterior Cruciate ligament.

The most common problem with anterior - posterior instability is that there is

a tendency for the knee to hyperextend ( extend too much ) This could be helped

by making eithera socket with supra patellar support or if the problem is

severe, adding a thigh corset to the prosthesis.


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MUSCLE STRENGTH:

The patients muscle strength of the knee extensors is checked by asking the patient

to extend the knee while the prosthetist is resisting this movement.

The main knee extensor muscles are:

Quadriceps - Rectus femoris,

Vastus lateralis,

Vastus intermedius,

Vastus medialis.

The strength of the knee flexor muscles is checked by asking the patient to flex the

knee while the prosthetist is resisting this movement.

The main knee flexor muscles are:

Hamstrings - Semimembranosus,

Semitendinosus, Biceps Femoris.

NB. The muscle strength evaluation, as

most of the other tests for the knee and

hip problems, is better done by the

physical therapist.


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EXAMINATION OF THE HIP:

RANGE OF MOTION:

To make an accurate assessment of the hip it is necessary to have the patient lye

down on a couch. This is to avoid any movement of the pelvis, because this

would show a false impression of hip joint movement.

Let the patient lie on his / her back to test for hip adduction, abduction and

flexion as illustrated below. And let the patient lie on the front / stomach to testfor hip extension ( see illustration )


Flexion 130 Extension 30


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The most common problem with range of movement at the hip joint for

amputees is that there is a hip flexion contracture ( the hip is stuck in some

degree of flexion ) This can accurately be measured by using the - Thomas Test

- as described on the following page.


Abduction 45-50 Adduction 20-30


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Thomas Test

The Thomas Test for flexion contracture of the hip.

With the hip flexed, the lumbar spine flattens

and the pelvis is stabilized. Further flexion can

only originate in the hip joint.

A fixed flexion contracture is caractherized by

the inability to extend the leg straight without

arching the thoracic spine.

The extend of a flexion contracture can be de-

termined by estimating the angle between the

table and the patients leg.


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MUSCLE STRENGTH:

Strength of hip flexion muscles is tested by having the patient sit on a firm surface.He / she flexes the hip ( lift the thigh up on the seat ) while the prosthetist is resisting

the movement and assessing the strength.

The main hip flexor muscles are:

Iliopsoas.

Strength of hip extensor muscles is tested by having the patient lie on a firm

surface, lifting the leg a little and then extending it ( moving the thigh away from the

couch ) while the prosthetist is resisting the movement and assessing the muscle

strength.

The main hip extension muscle is:

Gluteus Maximus.


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MUSCLE STRENGTH:

Strength of hip abduction musclesis tested by having the patient lie on the

side lifting the leg to be tested up from the couch, the prosthetist resists this

movement and assesses muscle strength.

The main hip abductor muscle is:

Gluteus Medius.

Strength of hip adduction musclesis tested by letting the patient lie on the

back adducting both legs while the prosthetist resists the movement.

The main hip adductor muscles are:

Adductor Longus,

Adductor Brevis,

Adductor Magnus.


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SECTION - 4

MEASUREMENTS

&

CASTING TECHNICS


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MEASUREMENT & CASTING TECHNIQUES

FITTING AIDS

Fitting aids may include a tracing of the stump, record of circumference, length and

diameter measurements of the stump and sound shank, some angular measurements

of the stump, and most important of all a plaster cast.

STUMP MEASUREMENTS

The measurements can be of two or three dimensions. Although the stump is a

volumetric mass of three dimensions, in practice we are recording mainly two

dimensions measurements. The cast is a three dimensions measurement. This is why

the measurements will never be as accurate as a well applied cast. Their accuracy

depends on the condition of subcutaneous tissue, musculature, size of stump, and the

skill and experience of the prosthetist with regard to how much tension to apply on

the measuring tape. However, measurements are useful as a reference for later.

Two dimensions measurements

Linear measurements: Circumferences, diameters and length or height

(See Measurements Assessment Chart )

Angular measurements: Usually for contracture of the stump.

Circumferential:

Although it is a common practice to take the circumference at mid patellar level, it

is awkward to use that measurement as a reference on the positive mould. Thepostero-proximal reconstruction on the cast render impossible to keep the tape

perpendicular to the longitudinal axis of the stump. Plus we have a severe

modification at the PTB level. It is more practical to take this first circumference 2,5

cm below the mid PTB. This way there is no interference when referring to it on the

mould and it is just below the deep indentation of the PTB.


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Diameters

-The following measurements are needed to aid in modification of the plaster cast:

1) At the patellar tendon level - an AP measurement taken from mid-tendon to the

popliteal region between the medial and lateral hamstrings. This should be taken

with the knee in 10 - 15 degrees flexion. Here you can take two diameters, one

without pressure and one with firm compression. This way it helps you to judge the

value of the force used. The difference between those two diameters should be

around 1.2 to 1.5 cm.

2) Just above the femoral condyles - an M-L measurement to be used for the

supracondylar suspension. This supracondylar measure should be made as tight astolerable.

* If you are making a suprapatellar socket, you can take the A-P measurements at that

level.

3) At the patellar level - an M-L

measurement of the femoral condyle,

to its widest point. Usually taken

without compression. If there are soft

tissue, the tissue should be compressed

to about half of its thickness.

4) Optional. You can take the M-L

measurements from the flare of the

tibial condyle to just superior to the

head of the fibula.

Diameter measurements of the normal shank are useful for cosmetic shaping of the

prosthesis.

Fig. 4.1


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Lengths

-The three most important length measurements are as follows:

1) Length of stump - taken from the tibial plateau, or the axis of rotation of the knee

(adductor tubercle), to the most distal aspect of the stump.

2) Length of tibia - taken from the tibial plateau to the distal end of the tibia.

3) The mid PTB of the normal shank or the knee centre - taken from the axis of

rotation of the knee (adductor tubercle) to the floor, barefoot. The amputee should

be in a seated position, with foot flat on the floor and knee flexed at 90 degrees.

Angular

For the BK prostheses, we take mainly the degrees of flexum (contracture in flexion)

of the stump if there is such a contracture.

Length and circumference measurements are taken of the sound foot. Heel height is

recorded. The firmness of the prosthetic heel is determined by the patients weight

and activity level.

Other measurements worth of taking are measurements of the prosthesis the patient

is actually wearing, particularly the AP and the M-L of the socket.

*When you are taking measurements, try to always use reference points you can

easily relocate at any time. Keep the same approach and always use the same tools.


38/6436

Before taking the measurements, sit the amputee on a firm bench or table, just as you

would do for taking the cast. His thigh supported, the back of his knee approximately10 cm from the edge of the table, and the knee is 15 to 20 degrees of flexion. The

midline of the thigh on the amputated side is perpendicular to the front edge of the

table (Figs. 4.3 & 4.4).

A moistened cast sock is pulled over the amputees stump. If the patients stump is

very hairy, spread vegetable oil or other lubricant over the stump. This will avoid the

unpleasant experience of peeling the hair while removing the cast later. (Do not used

industrial lubricant for machinery or car to avoid allergy reaction.) Care must be

taken to avoid posterior displacement of the tissue at the distal end of the stump. Anytension or stress on the suture line and anterior aspect of the tibia is undesirable. An

elastic strap, which passes around the amputees pelvis is clamped to the superior

medial and lateral sides of the sock as shown in Figure 4.2.

Check the fit by pinching a fold in the sock, pulling it away from the stump, and

releasing. It should snap back to the stump. The cast sock should be fitted snugly and

should not move during the measurement and the casting.

Procedure for Measurements

Material needed:

Tape measure, callipers, meter stick, goniometer.

Indelible pencil, a pen and measurements charts.

Thin cast sock

Two meters length of elastic webbing

Two harness clamps

20 knee- flexion angle template

Using the measure chart provided take all the measures carefully filling in all the

boxes.The sections marked Personal Data and Manufacturing details are equally important

since they will communicate your decisions to the workshop or technician who will

manufacture the limb.

Pay special attention to the area recording socket position. Measure and record any

deformities. These will allow the accurate bench alignment (initial alignment) of the

socket at a later stage.


39/6437

A good stump sock is the basis of a good cast, sound measurements and the tracing

if needed.

1/ It controls the soft tissue holding it in place.2/ It gives a place to write marks over the stump, and later, allows the references

marks to be transferred on the positive mould.

10cm

Fig. 4.3 Fig. 4.4

Fig. 4.2


40/6438

Circumferences

Before taking the circumferences, use an indelible pencil and mark on the sock the

exact location for those measurements. Also you may as well draw all the reference

marks on the stump (see casting reference marks).

When taking the circumference measurements, you must make sure that the

measuring flexible tape is perpendicular to the longitudinal axis of the stump.

*If you must provide a thigh corset with the prostheses, You must take the thighcircumferences as indicated on the form. The first thigh circumference is

immediately above the patella. The other one should be as proximal to the groin as

you are planning to terminate the corset.

Diameters

Make sure you are using the calliper properly to avoid inducing errors of reading .

*The diameters of the thigh should also be taken if you have to provide a thigh corset.

Lengths

When you take the lengths, make sure the stick is always parallel to the longitudinal

axis of the segment you are measuring.

Angle

Only if there is flexion contracture of the stump or the hip.

The Sound Leg Measures will determine the accuracy of the set up of the leg prior

to fitting and the cosmetic appearance of the leg.

The old prostheses measurements can be taken at another moment, but should not be

forgotten.

All measures, except for the supracondylar ML diameter and the AP diameter at the

PTB level, should be taken without deforming the soft tissue with the tape measure,

or callipers.Accurate and repeatable measures are essential.


41/6439

Tracing.

Tracing of the stump contours can

be taken just before the cast or themeasurements. The amputee is

sitting in the same position as for

measurements or casting, with the

casting sock in place. Position a

sheet of paper or a cardboard under

the stump and draw the contours of

the stump. Mark some reference

points on the tracing and on the sock

with the indelible pencil.

To avoid any distortion of the shape

of the stump, you must:

1- Make sure you are not widening

the form by pressing the cardboard

on the back of the stump;

2- Hold the tracing pencil

perpendicular to the paper at alltime.

The most important tracing is the

one in the frontal plane, i.e. view

from the front. But you can also take

one from the coronal plane, i.e. side

way.

After the cast is done, using the reference measurements, correct the tracing and cutit out. Verify on the stump of the patient if it is appropriate. Later on you can use the

tracing to verify the correctness of your cast during the modifications.

This approach is particularly important for beginner. In practice, it is so common

to loose the shape of the stump while taking the cast or modifying it.

We used to make a tracing of the sound leg both from the front and from the side.

Although it can be helpful for the final shaping of the prosthesis, it is rather

cumbersome to carry this big sheet of paper around. If you really need that kind of

accuracy for the cosmetic, the use of polaroid picture is less cumbersome and as

efficient. If the latter is not available, try to have the patient present when you sculptthe leg. This way, you can compare before finishing the prosthesis.

Fig. 4.5


42/6440

BELOW KNEE CASTING PROCEDURE

Aims

The aim of fitting a good BK socket is to achieve comfortable total contact. At the

same time carrying most of the patients weight on the areas of the stump which can

tolerate pressure and protecting the areas which cannot.

Presently, the plaster cast is still the most common way used to achieve this goal. If

well carried out the rectification process that will follows will be much easier and the

final fit of the socket will be good.

Materials required.Material for the measurements plus the following:

1. 2 to 3 rolls of plaster bandage; 15 or 20 cm

2. Elastic bandage.

3. Grease.

4. Scissors and cast cutter if required.

Casting Technique

Cast wrapping of the amputees stump for the fabrication of a socket is the most

important part in the procedure of fitting and constructing a prosthesis for the trans-

tibial amputee. There is no substitute for this procedure, or for skilful, experienced

hands. A cast well taken will require little modification of the positive plaster , and

thus reduce any chance of error.

The importance of a well taken cast cannot be overemphasized. The best possible

adjustments and alignment will never overcome the problems created by a poorly

fitting socket. A well fitting socket is the foundation of success, and it does start witha well taken cast.

*We have chosen to describe a casting technique for the PTB SCSP (Patellar

Tendon Bearing Supra Condylar Supra Patellar) over the regular conventional

PTB tibial prostheses. In the context of the ICRC working with soft Alvelux insert

and polypropylene, the PTBSC and the PTB SCSP are probably the most efficient

way to make a BK socket with adequate suspension while providing decent stability

of the knee. The supracondylar wedge suspension is far superior to the use of

supracondylar strap. It does keep the pistonning action of the prostheses to a

minimum. Furthermore, it reduced the need for a waist belt. Finally, it gives enough

medio lateral stability that only a few amputees do require a thigh corset.


43/6441

CASTING PROCEDURE

The casting technique we will be describing is known as a two parts cast for the PTB

SCSP. The reason we choose this two parts approach over the one step, is mainly

because it is much easier to control all the different details of the casting. This is

particularly important for the beginner. The one step casting method, although

faster, has just too many details to be controlled at once for a beginner. Also, the two

parts approach cast is easier to remove from the patient. Finally, the cast remains

more intact, i.e. without losing its initial shape, while being removed.

Just after taken the measurements, the amputee is still seated on a firm bench or

table, with his thigh supported, the back of his knee approximately 10 cm (Fig. 4.6)

from the edge of the table, and the knee is 20 degrees (Fig.4.8) of flexion. During theentire wrapping sequence, the knee joint should be held in position of 20 of flexion

so as to emphasize bony prominences, aid in the definition of the patellar tendon,

and assist in locating the hamstring tendons.

You can use a 20 template to position the stump and instruct the patient to hold this

attitude with minimum muscle tension.

Before starting, make sure you have the material and tools required for the casting.

Position yourself in front of the stump and sit lower than the amputee. This will help

you to obtain a better cast.

20

10cm

Fig. 4.8

Fig. 4.6 Fig.4.7


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Reference marks:

A. Outline of the patella.

B. Middle of the patellar tendon mark with a horizontal line midway between the

distal pole of the patella and the superior border of the tibial tubercle.

C. Outline the head of the fibula.

D. Anterior border of the tibia (tibial crest).

E. Medial border of the tibia.

F. Outline the anterior distal end of the tibia.

G. Outline the distal end of the fibula.

H. The inferior border of the medial flare of the tibial condyle.

I. The inferior border of the lateral flare of the tibial condyle.

J. The femoral epicondyles

In addition, marks should outline any areas of the stump that require special

treatment because of prominence, sensitivity, or other reasons.

Pay particular attention to:

-The outside borders of the medial and lateral hamstring tendons;

-The anterior prominences of the lateral and medial tibial condyles;

-An unusually prominent tibial tubercle;

-Bone spurs,

-Adherent scars, neuromata, and any other sensitive areas.

When accurate stump marks have been made we are ready for the cast.

Fig. 4.9

a

b

f

ci

d

g

j

h

e


45/6443

CASTING STAGE

1/ Using a 15 or 20 cm plaster bandagethe stump is wrapped carefully.Some

prosthetists begin the wrapping proximally while others prefer to start distally.

Elasticized plaster bandage (10 cm width) would be preferable as it conforms more

readily to the stump.As this is not available, we can later compensate by using an

elastic bandage over the cast.The upper edge of the bandage should be positioned

1 to 2 cm over the lower edge of the patella. If you go any higher, it will be difficult

later to get an accurate moulding of the supracondylar.

2/ Wrap the bandage firmly around the stump at right angle to the longitudinal axis,

until the plaster is three layers thick. Firm, even tension must be maintained so that

the triangular shape of the anterior aspect of the stump is retained, and the loose fleshis not pulled posteriorly with the bandage.

3/ Proceed to wrap the cast down the stump eventually taking in the distal end. A

good technique, at this point, is to use the figure 8 approach.

4/ The cast should not be so tight as to cause rucks and lines.

At all times during the wrapping care should be given to the smoothing and moulding

of the cast.

Because ICRC is not using elastic plaster bandage, the use of an elastic bandage

over the plaster bandage is an excellent way to compress the cast and to obtain a

more accurate mould. The elastic bandage can be reused over and over, as long as

you wash it after using it. You can even pull a stockinet over the cast in order to keep

your elastic bandage cleaner.

5/ The plaster wrap is worked

with both hands. Smooth the

plaster over the surface of the

stump by moving the hand fromanterior to posterior around the

stump, and from distal to

proximal. Mould the plaster

around bony prominences so that

they are clearly defined, but

avoid to overwork it as the plaster

begins to harden. Theprosthetist

should avoid making any sharp

indentations with his/her fingers

in the plaster wrap.Fig. 4.10


46/6444

As mentioned previously, the knee joint must be maintained in 20 of flexion

throughout the casting procedure. The prosthetist should check this repeatedly and

instruct the amputee to hold this position with a minimum of muscular tension.

Contraction of stump musculature can distort the wrap cast.

6/ As the plaster begins to set position the thumbs on either sides of the patellar

tendon as shown in the diagram and press in firmly. The thumbs must be at a 45

angle to the long axis of the tibia. Be sure to bend the interphalangeal joints of the

thumbs so that only the thumb tips touch the wrap, as shown in Figure 4.11. Be

careful not to impinge on the inferior border of the patella nor on the anterior

proeminences of the tibial condyles.

Wrap the 3rd, 4th, and 5th fingers around the stump so that thetips of the fingersapply moderate pressure in the centre of the popliteal area. If there is doubt about

location of the tendon, use the stump-length measurement taken in Step 5 as a check.

Remember, all that must be done before the plaster has too hardened.

S em i tendin osus tendo n

S em im em bran osus tendo n

G rac i l i s t endo n

S a r tor ius ten don

B iceps fem ori s t en don

P a te l la r t end on

Fig.4.11


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The upper (3rd) finger should be approximately 1.2 centimetres distal to the thumbs

(Fig. 4.12). Be sure the finger tips are centred in the poplitealarea and that the

hamstring tendons are not compressed.

The remaining finger (index or 2nd) extends on each side of the wrap and helps to

resist any tendency toward mediolateral bulging (Fig. 4.13).

You should press hard enough to get a good identification of the spots yet not too

much as to enlarge the M-L of the stump. Good care should be taken to keep the M-

L of the cast as close as possible to the M-L of the stump.

1.2cm

Fig.4.12 Fig.4.13


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49/6447

With the cast removed and corrected we are now ready to fill and continue on to Cast

Modification.

Before filling the cast, it is helpful to place it in the sandbox so that the plumb line

is vertical and the cast is in five to seven degrees of knee flexion. In this way, when

the plaster positive is poured and the negative wrap removed, the mandrel will take

the place of the plumb line as a reference. This will be extremely important later

when you will be modifying the cast. It will help you to see the cast in the proper

alignment, and to make the modifications at their proper location. .

When the plaster has hardened and cooled, the wrap is cut posteriorly in the centre

to avoid damage to the positive in critical areas marked with indelible ink. The

indelible markings will have transferred from the stockinette to the plaster negative

and then to the plaster positive, and will act as a guide in the modification procedure

(see Fig. 4.15). Remember that it is possible for the marks to have moved. With your

finger, palpate the cast to identify the bony areas. Remark the reference points if

need to.

Fig.4.14

F i n g e r spos i t ion

SC S PS e c t i o n

B as icc a s t

A N T E R IO R M E D IA L


50/6448

Fig.4.15


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52/6450

Another approach for taking a BK cast is standing up.

Fig.4.18


53/6451

SECTION - 5

CAST MODIFICATION


54/6452

CAST MODIFICATION

No matter how skilfully the mould was taken, further modifications are alwaysnecessary. The object of these modifications is to increase socket contact pressures

in weight bearing areas and decrease contact pressures in pressure sensitive areas.

Wherever greater weight bearing pressures are desired, plaster is removed from the

positive, and where relief is desired, the cast is built up with plaster.

It must be understood and constantly borne in mind that every square centimetre of

stump surface available for loading should be utilized, however small it seems. For

this reason, over-buildup must be avoided. Over-buildup will negate the bridging

effect created around that area and will often result in an unstable socket. Total

contact will be lost, shear forces between the stump and socket will be increased, and

oedema pockets will be created.

Excessive undercutting of the cast in areas traditionally thought of as good weight

bearing areas can also have ill effects. One must not forget that between the socket

and strong, firm patellar tendon, for example, there is skin. Pressure sensitive areas

may be in contact with the socket surface during loading as long as weight-bearing

or pressure is avoided.

The following description of the cast modification technique can only be used as aguide owing to the highly individual nature of the patients and their conditions.

Tools and other requirements:

1) Indelible pencil;

2) Knife, approximately 15 cm with narrow and flexible blade;

3) Scarpas knife;

4) Surform rasp blade (flat, half round and round);

5) Wire screen;

6) Spatulas;

7) 1/2 tacks with hammer or stapler;8) Plaster container.

The positive cast is held in the vice by the mandrel. Before starting the

modifications, remove all the excess plaster, ridges and unnatural bumps, and shape

the proximal edge of the lateral and the medial supracondylar wall. All transferred

indelible ink marks should be darkened if necessary. Using both finger and eyes, try

to see if your references marks have not moved during the casting process. If they did

move, redraw them to the appropriate area.

It is extremely important for you to be viewing the cast in the proper alignment

during the modification process.


55/6453

The posterior trim line is defined by taking a line perpendicular to the mandrel (i.e.

parallel to the floor) from the mid-patellar tendon shelf straight across to the

posterior wall. It must be kept in mind that the cast is in 5 - 7 degrees of knee flexion

with respect to the mandrel. It is important to keep the posterior wall as high aspossible, especially with a shorter stump. However, there is also the amputees

comfort to consider; bulging of tissue when the amputee is seated is undesirable and

can be avoided.

Note: if necessary, the medial corner of the posterior brim may be slightly lowered

for the more prominent hamstring.

Then record all the measurements, diameters and circumferences, of the cast. Com-

paring your measurements, it should help you to judge and make the appropriate

modifications. Compare the cast measurements with the stump measurements. Thisshould help you to determine the intensity of your modification. It is part of the

prosthesis conception. The modifications is not something you do automatically,

all alike for every cast. Every patient is individual and requires a custom made

socket.

Using the midline and the reference

marks, use your template to see if the

form of your cast coincides with the

form of the stump. During the whole

modification process, you can refer toyour template in order to check if you

are not moving too far away from the

initial shape.

Starting with the M-L at the femoral

condyle, rectify the cast to bring it to

your initial M-L measurement. Remove

some plaster as well on the lateral side

as on the medial side. Notice that for awell taken cast, the difference between

those two M-L shouldnt be bigger than

3 mm. If the cast is more than 3 mm

wider than the measurements, given

your measurements were well taken, the

cast was poorly done. If the cast M-L

is smaller, it is possible your measure-

ments were taken too loosely.

Please when correcting the M-L, respect the shape of the femoral condyles. There

shouldnt be flat or concave surface on the cast in those areas. Firmcontact in thisarea is essential to aid in mediolateral stability.

Fig.5.1


56/6454

Then we move unto the supracondylar area. Use an external calliper to measure the

M-L for that area. After comparing the measurements, you may find you have to

remove up to 2 cm of plaster. Start digging on the medial side with a curve knife

(Scarpa knife). Because of the morphology of that area, it can be well indented in acrescent-like form. This way you are creating the space to later mould a thick wedge,

which will serve for the suspension of the prosthesis. When removing the plaster,

respect the form of the femoral condyle, staying as close as possible to the condyle

without touching it. Always make a nice flaring out proximally.

Laterally, on the opposite side, you can remove few mm of plaster with a semi

round Surform blade. You can slightly dig in. The tendon for the Tensor of the

Fascia Lata can be compressed on a large surface but not on a narrow one. Remem-

ber it is a counter pressure to assist the suspension of the wedge on the medial side.

Because there is often a large tissue mass just above the femoral condyles, when a

P.T.S socket is used, care must be taken to ensure supportive contact without im-

pinging on that tissue. Therefore, the proximal edge of a P.T.S socket must be flared

out gradually. After which you can start the regular modifications as for any PTB

socket.

Anterior Surface of the Cast.

The patellar tendon area is modified between the lower border of the patella and the

tibial tubercle to a depth of 5 to 10 mm. The depth of the shelf will depend on howwell the cast was moulded when it was applied to the stump, the AP diameter

measurement taken, condition of the skin, and the shape of the tendon, whether with

round edges or square ones. As for the width of the PTB, it can be up to 2.5 cm. If

you are using a soft insert rather than a hard socket, it can even be slightly wider.

It was believed you had to build up right under the PTB indentation. It has been

proven that there is a gap inside the socket even without building up that area.

Therefore, to improve stability, you should remove some plaster from that area,

down to the proeminence of the tibial tubercle. You just follow the shape of the tibiain that area. Just make sure you always maintain a convex shape. Avoid any concave

sculpting in that area. The cutaway should gradually flare into the relief areas. Only

when this area is extremely sensitive (bursitis or else), you do have to avoid

removing plaster. Exceptionally, in few extreme cases, you may have to add some

plaster on the cast.

It was also believed that you do not remove plaster from the patella. Experience

show that in most cases you can remove few millimetres, up to 6 mm, on the lower

part of the patella. This does prevent to have the usual gap between the socket and

the stump in that area, therefore improving the cosmetic of the prostheses.


57/6455

Fig.5.2


58/6456

Fig.5.3


59/6457

The antero-medial surface of the tibia is then modified to within 1 cm of the crest of

the tibia. Beginning from the medial tibial flare to within 2 cm of the distal aspect of

the tibia, the cast is cut away to a depth of approximately 3 - 5 mm, depending again

on how the plaster wrap was moulded.

The anteriolateral aspect of the cast is modified, along the lateral border of the tibia,

close but not touching the crest, between the anterior lateral prominence of the tibial

plateau and to within 2 cm of the most distal aspect of the tibia to a depth 5 - 8 mm.

Avoid sharp concave digging. It is too uncomfortable and often painful for the

amputee.

Medial Aspect

The flare of the medial tibial condyle is a very important weight bearing area. It must

be kept in mind that with a soft insert, the medial flare will be compressing the soft

material during weight bearing. Therefore, when using a soft insert, you can be more

aggressive in the removing of plaster for that area. Please, maintain the contour of

the tibial flare. Locate the template (Fig. 5.4 ) at the medial midline of the model

using the indication marks as a reference. Depending on how much soft tissue there

is on the individual stump, and on how well the negative plaster was moulded, 3 - 7

mm of plaster is removed from the flare.

The M-L measurement (Fig.5.6, medial tibial flare to just superior to the head of the

fibula) should be used as a reference. The reduced area should be blended in

smoothly with the antero-medial surface.

Fig.5.5Fig.5.4 Fig. 5.6


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Lateral Aspect

To ensure good counterpressure for the medial tibial flare, there must be definite

contact pressure at the stump-socket interface of the lateral wall. It is necessary to

maintain mediolateral stability during loading. In most cases, however, the lateral

wall of the amputees stump is far from ideal for this purpose, owing to the presence

of the head and distal cut end of the fibula. Extreme care must be taken not to

impinge on these areas. The shaft of the fibula is the only suitable area to use for

providing the necessary stabilizing counterpressure. Approximately 3 - 9 mm of

plaster may be removed from the cast between the head and distal end of the fibula.

Since a certain amount of sinking into the socket will take place during gait, care

must be taken to provide sufficient relief for the head of the fibula. Modificationshould start approximately 2 cm distal to the fibular head and end about 1.5 cm

proximal to the cut end of the fibula.

Once again, the shorter the amputees stump, the less area is available on the lateral

wall to achieve mediolateral stability. To avoid a higher concentration of pressure

that is desired, the P.T.S type socket can be an adequate solution. An excellent way

to improve the medio-latera1 stability of the socket.

Posterior Aspect

The posterior surface of the amputees stump is the only area without any bony

prominences, and here plaster can be removed to reduce the circumferential

measurements. However, the hamstring areas must not be cut away, nor should the

distal posterior region of the cast. Any reduction of the latter area could cause

pulling of the tissue over the distal end of the amputees stump. Over-reduction of

the distal posterior region of the cast is often the cause of skin breakdown at the distal

anterior aspect of the tibia.

The popliteal area is reduced until the measurement corresponds to the AP diameter

taken previously. You can even remove few extra mm, up to 3 mm, to compensate

for the compressibility of the soft insert. The deepest part of the popliteal

counterpressure should be at the level of the PTB. Avoid making a walnut shape

bulge. The best result, for comfort and correct pressure distribution is when the

gastrocnemius depression is not deeper than 6 mm. Favourable loading areas should

gradually blend in with relief areas, so that sudden build-upsand reductions are

avoided.


61/6459

The cast can now be smoothed off with wire screen in those areas which have been

reduced. With a steel brush, rough the areas where you will be adding plaster. Run

water over the cast before adding plaster.

It is helpful to drive tacks or staples into the centre of each relief area so that the

length of tack left exposed is equal to the amount of relief desired.

The buildup for the flared posterior brim is best constructed by driving several tacks

halfway into the cast along the predetermined posterior brim line. A large quantity

of thick plaster mix is placed just superior to the brim line. Holding a tongue

depressor horizontally at the posterior shelf level, the plaster is scooped downward

in a short radius-curve with the long edge of the tongue depressor. This flare is then

blended in with the medial and lateral walls. This flare will serve to prevent tissuebunching during knee flexion and will allow flexion to occur with reasonable

comfort.

Fig.5.7


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Modify sensitive area build-ups.

As a rule, 2 to 3 mm is sufficient, with the

exception of the most distal anterior aspect

of the tibia and perhaps the head of the fibula

Fibula head.

Add plaster build up, 3-5 mm thick over apex

and at least 6 mm distal to the lower border of

the head of the fibula. Also extend the apex

of the buildup posterior to the true

anatomical apex.

Anterior distal tibia

Add plaster buildup 5 mm thick over the

most prominent area. Extend the buildup

over the lateral border of the distal end of the

tibia.It is also wise to build up the distal end

of the tibia, 0.3 to 0.7 cm, depending on the

amount of total contact possible with the

individual amputee.

If the fibula is longer than the tibia, and protrudes beyond the main body of the

stump, add 6 mm of plaster over the area which protrudes.

Over buildup must be avoided, and any buildup that is applied should be blended

gradually into the other areas. Keep in mind that a mould that is properly trimmed

around pressure-sensitive areas will in fact create relief pockets without losing firm

contact and socket stability.

Total contact is of utmost importance, as it provides containment of the tissue,

feedback and improved circulation, and, generally, increases the surface area of the

stump-socket interface. Care must be taken to prevent excess buildup distally in

order to ensure a total contact fit. While total contact is important, it should not be

mistaken for end bearing. With the wire screen give the cast a smooth finish.

The model is ready for use in fabrication of the socket.

Fig.5.8


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REFERENCES

1. Below Knee Prosthetics, Course Work Manual, National School of Prosthetics &

Orthotics, Phnom Penh, Cambodia.Carson Harte, Anne Henriksen.

2. Clinical Aspects of Lower Extremity Prosthetics, Trans-tibial, Symes and Partial

Foot Amputations, The Canadian Association of Prosthetists and Orthotists.

3. Trait dAnatomie Artistique, Dr. Paul Richer, Inter-Livres

Compiled and edited by Jacques Forget, CCP (Canadian Certified Prosthetist).


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