Temporal Inﬂ uences of Functional Knee Bracing on … functional knee braces (FKBs) are widely...

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Brian Campbell is with Bowling Green State University Kinesiology Division in Bowling Green, Ohio 43403. Email: [email protected]. James Yaggie and Daniel Cipriani are with the Depart-ment of Exercise and Nutritional Sciences at San Diego State University, San Diego, CA 92182.

Temporal Infl uences of Functional Knee Bracing on Torque Production of

the Lower Extremity

Brian Campbell, James Yaggie, and Daniel Cipriani

Context: Functional knee braces (FKB) are used prophylactically and in reha-bilitation to aide in the functional stability of the knee. Objective: To determine if alterations in select lower extremity moments persist throughout a one hour period in healthy individuals. Design: 2X5 repeated measures design. Setting: Biomechanics Laboratory. Subjects: Twenty subjects (14 male and 6 female, mean age 26.5±7 yrs; height 172.4±13 cm; weight 78.6±9 kg), separated into braced (B) and no brace (NB) groups. Intervention: A one-hour exercise program divided into three 20 minute increments. Main Outcome Measures: Synchronized three-dimensional kinematic and kinetic data were collected at 20-minute increments to assess the effect of the FKB on select lower extremity moments and vertical ground reaction forces. Results: Increase in hip moment and a decrease in knee moment were noted immediately after brace application and appeared to persist throughout a one hour bout of exercise. Conclusions: The FKB and the exercise intervention caused decreases in knee joint moments and increases in hip joint moments. Key Words: joint moments, ground reaction forces, bracing

Today, functional knee braces (FKBs) are widely used in the prevention, maintenance, and rehabilitation of anterior cruciate ligament (ACL) injuries and have been shown to have a potential protective effect on the ACL immediately after donning the brace.1-5 The use of FKBs have been an integral part of standard knee rehabilitation protocols in an effort to create a functionally stable knee via tactile infl uence.3,6 These braces are not only used post-operatively, but often pre-opera-tively in an effort to avoid surgery.7 Additionally, FKBs are used as a protective appliance for those that have injured or reconstructed knee structures.

Mechanically, the FKB is thought to protect the joint by preventing terminal extension of the knee and controlling the anterior translation of the tibia11, typically checked by the ACL. Previous research has shown when individuals with damaged or newly reconstructed ACL apply a FKB, there is an increase in extensor torques at the hip and ankle during walking.1 This suggests the occurrence of a corresponding decrease in extensor torques at the knee. These changes are characteristics of what

J Sport Rehabil. 2006,15, 216-227 © 2006 Human Kinetics, Inc.

Temporal Infl uence of FKB on Torque Production 217

is often referred to as an ACL defi cient gait pattern or quadriceps avoidance gait.8 DeVita et al2 also found that healthy subjects walked with an increase of 14.3% and 5.1% in hip and ankle torque, respectively, immediately following the applica-tion of the FKB; however, no changes in knee torque were noted.2 Further, during running tasks, hip extensor torque increased while knee extensor torque remained unchanged. The investigators attributed these changes to proprioceptive and tactile infl uences. In addition, a pilot study revealed that a healthy individual running with a FKB experienced reduced extensor torque at the knee while there was an increase in extensor torque at the hip joint.9 That study was followed by work by Devita, Hunter, and Skelly investigating the effects of a FKB on the biomechan-ics of running in subjects with previous ACL injury.10 Interestingly, the FKB did not appear to have any affect on the kinetic variables of the ACL injured subjects. Although these changes have been shown to occur in healthy individuals2,9 wear-ing an FKB, it is still not understood if these gait alterations persist over time. The presence of gait aberrations at the hip, knee, and ankle following the application of a FKB, regardless of knee “health,” begs the question of temporal infl uences of the proprioceptive infl uences.

Therefore, the purpose of this study was to determine if alterations in gait following application of a FKB persist over a one-hour period of exercise in healthy, college age individuals. It was hypothesized that there would be an initial decrease in knee extensor moment coupled by a subsequent increase in hip and ankle extensor moments along with a decrease in vertical ground reaction force (VGRF) in the braced condition. Further, these initial alterations would decline as the individuals became familiar with the tactile sensation of the FKB during the exercise protocol.

MethodsDesign

A 2�5 factorial design with repeated measures (brace � time) was utilized. Sub-ject sample size was estimated a priori by calculating effect size of the previous literature.

Subjects

Approval for this investigation was granted by the universityʼs human subjects review board. Twenty healthy volunteers (14 male and 6 female, mean age = 26.5 ± 7 years, height = 172.4 ± 13 cm and weight = 78.6 ± 9 kg) were screened to assure age appropriateness, health status, and freedom from lower extremity pathologies within two years prior to the investigation. Participants reviewed and completed a health history questionnaire and all informed consent documents prior to inception of the protocol. Subjects were then randomly assigned into a braced (B; n = 10) or no braced group (NB; n = 10).

Instrumentation and Equipment

The DonJoy Legend™ FKB (dj Orthopedic, Vista, CA; Figure 1) was selected due to its popularity in the marketplace and its use in recent, relevant literature.11-14

218 Campbell, Yaggie, and Ciprian

Multiple braces were procured to assure proper fi t as indicated by manufacturerʼs guidelines.

The design of the study warranted the use of several integrated technologies to address the research question (Figure 2). Two photocells (Micro Switch, Free-port, Ill) were used to monitor the subjectʼs jogging velocity during each of their gait trials. Prior to the testing, the subjects performed fi ve practice jogging trials to determine a comfortable jogging pace. A 5% window above and below their self selected jogging pace was calculated. Acceptable jogging trials needed to fall within the defi ned window to be considered for data analysis.

An AMTI force platform (Advance Mechanical Technologies Inc. Model # OR6-5-1, Watertown, Mass) was used to collect ground reaction forces and add to the input for joint moment calculations. Force plate data were sampled at 960 Hz.

Six Falcon Motion Analysis cameras (Santa Rosa, Cal), sampling at 60Hz, were integrated with Eva Hi-RES software to obtain the kinematic data during the multiple gait cycles. Orthotrak 4.2 (Santa Rosa, Cal) was used to calculate the kinetic values generated by the subjects during the jogging gait trials. All data were time matched using an external trigger.

Protocol

Each subject performed a multitrial jogging gait analysis, consisting of 10 bouts, to establish a baseline for kinetic and kinematic measures. The subjects in the B group were then fi tted with an FKB with the factory installed 10° extension stop. All braces were fi tted by the principal investigator according to the manufacturerʼs guidelines. After fi tting, each subject completed a series of jogging trials to establish immediate post brace measures. Subjects from both groups then performed fi ve minutes of lower extremity stretching followed by a one-hour exercise protocol.

Figure 1—DonJoy Legend FKB.


The exercise protocol consisted of various multidirectional activities that would be included in a typical athletic workout regimen.

The exercise protocol, illustrated in Table 1, was subdivided in three 20-minute bouts made up of exercise and rest. At each 20-minute increment, additional jog-ging gait trials were performed. The NB group performed the identical protocol, with the exception of the application of the brace.

Figure 2—Schematic of applied biomechanics laboratory layout.


Data Analysis

Successful trials were averaged in the Multiple Trial Module of Orthotrak and then exported to a spreadsheet to obtain the desired mid-stance numerical values. This was repeated for each subject at each time point. Previous research by DeVita et al identifi ed torque, work, and power alterations as they occurred specifi cally at mid-stance.1-2 Therefore, this investigation focused on the occurrence of these changes in kinetic data, specifi cally, at mid-stance. Mid-stance was identifi ed at the point at which the anterior/posterior ground reaction force curve was equal to zero. The kinetic values of mid-stance were then extracted for further analysis.

Statistical Analysis

Intraclass correlation coeffi cients were calculated to examine the internal con-sistency of the GRF data across bracing condition. In order to test for the initial effects of wearing the brace on hip, knee, and ankle joint moments and vertical ground reaction forces (VGRF), multivariate and univariate ANOVAs were run for the measures obtained from those trials when the brace was being worn by the B group. In order to test for the effects of exercise on the joint moments and VGRFʼs, as well as the continuing effects of the knee brace, two-way MANOVA with repeated measures for each dependent variable was completed. The brace

Table 1 Exercise Protocol

Activity Time (min)

Lower extremity stretching 5Jog around 175 m indoor track 2Stationary bike 2Rest 1Backward running 1High knee running 1Rest 2Figure eight running 1High knee running 1Rest 1Backward running 1Ladder runs 1Rest 1Carioca to the right 1Carioca to the left 1Rest 1Jog around 175 m indoor track 2Total 250

Note. All activities were performed at a self selected pace. Lower extremity stretching consisted of various self selected lower extremity stretches. With the exception of the jog around the track and the stationary bike, all other activities were performed on a 20 m marked course within an indoor gymnasium.


condition (B and NB) served as the second factor. Main effects were further ana-lyzed using independent samples T-test. Level of statistical signifi cance was set at P < .05 for all comparisons. The statistical analysis was performed using the SPSS 11.0 for Windows package (SPSS Inc., Chicago, Ill).

Results

Reliability of Scores

Intraclass correlation coeffi cients (ICCs) for the GRF values for the B and NB conditions were .8221 and .9305, respectively. Coeffi cients for joint moment values were for the B and NB conditions were .9508 and .9669, respectively.

Joint Extension Moments at Mid-stance

Figure 3 illustrates the means and standard deviations for the hip, knee, and ankle joint moments at T2 for the B (H = 2.09 ± .48, K = .45 ± .43, A = 2.79 ± .33) and the NB (H = 1.61 ± .19, K = 1.40 ± .31, A = 2.67 ± .14) groups, respectively. In addition, independent sample T-tests revealed that there were signifi cantly greater hip moments (P = .012) and signifi cantly reduced knee moments (P = .000) imme-diately following brace application (T2), while the ankle joint moments were unaffected.

Hip

Figure 4 illustrates the means and standard deviations for the extension moments occurring at the hip for the B (T1 = 1.98 ± .65, T2 = 2.09 ± .48, T3 = 1.93 ± .29, T4 = 1.80 ± .24, T5 = 1.58 ± .45) group and the NB (T1 = 1.74 ± .64, T2 = 1.61 ± .19, T3 = 1.45 ± .09, T4 = 1.38 ± .22, T5 = 1.44 ± .37) group across time points 1-5.

Figure 3—Means (± SD) of hip, knee, and ankle moments immediately following brace application (T2). Note. Hip moments signifi cantly greater in the B group. Knee moments signifi cantly reduced in the B group. (P < .05)


Hip extension moments were then analyzed for the repeated measures for each of the fi ve time points. There was no signifi cant interaction between time period and brace condition. There was a signifi cant main effect for time (P = .003), stating that there was a signifi cant difference in hip extension moment over time when both groups were considered together. Pairwise comparisons revealed a signifi cant decrease in hip moments from T1 to T4 (P = .022), T1 to T5 (P = .005), T2 to T3 (P = .016), T2 to T4 (P = .000) and T2 to T5 (P = .002). There was also a main effect for condition (P = .007) revealing that the B group experienced signifi cantly greater hip moments than the NB at T2, T3, and T4.

Knee

Figure 5 illustrates the means and standard deviations for the extension moments occurring at the knee for the B (T1 = .97 ± .51, T2 = .45 ± .43, T3 = .62 ± .49, T4 = .50 ± .69, T5 = .49 ± .67) group and the NB (T1 = 1.17 ± .35, T2 = 1.40 ± .31, T3 = 1.19 ± .29, T4 = 1.06 ± .45, T5 = 1.15 ± .77) group across time points 1-5. An interaction effect (brace � time; P = .003) for knee moments was identifi ed. Independent samples T-tests were performed to determine if there was a signifi cant difference between B and NB at each time point. The T-tests revealed that there were signifi cantly less knee moments experienced in the B group during T2 (P = .000), T3 (P = .006), T4 (P = .049), and T5 (P = .028). Paired samples T-tests were also performed for the B and NB groups to see if there were any differences between time points. The paired sample T-test revealed that there was signifi cant reduction in knee moment in the B group from T1 to T2 (P = .001), T1 to T3 (P = .04), T1 to T4 (P = .001) and T1 to T5 (P = .004). As for the NB group, the paired samples T-tests revealed a signifi cant reduction in knee moment from T2 to T4 (P = .026).

Figure 4—Means (± SD) of hip extension moments at T1 - T5. Note. Main effect for time: Signifi cant decrease in hip moments, †) signifi cantly different from T1, ‡) signifi cantly dif-ferent from T2. Main effect for condition: Signifi cantly greater hip moments in the B group at θ) T2, T3 and T4. (P < .05)


Ankle

Figure 6 illustrates the means and standard deviations for the plantarfl exion moments occurring at the ankle for the B (T1 = 2.66 ± .31, T2 = 2.79 ± .33, T3 = 2.97 ± .46, T4 = 2.90 ± .58, T5 = 2.83 ± .47) group and the NB (T1 = 2.80 ± .86, T2 = 2.67 ± .14, T3 = 2.70 ± .25, T4 = 2.59 ± .26, T5 = 2.61 ± .32) group across time points 1-5. Ankle plantarfl exion moments did not change signifi cantly with the inclusion of exercise. There was no interaction effect and no main effects for brace condition or for time.

Vertical Ground Reaction Forces at Mid-Stance

Figure 7 illustrates the means and standard deviations for the mid-stance vertical ground reaction forces for the B (T1 = 2.25 ± .21, T2 = 2.18 ± .19, T3 = 2.24 ± .24, T4 = 2.16 ± .23, T5 = 2.14 ± .23) group and the NB (T1 = 2.49 ± .65, T2 = 2.28 ± .14, T3 = 2.24 ± .17, T4 = 2.31 ± .23, T5 = 2.24 ± .23) group across time points 1-5.

There was no interaction between the brace condition and time. Finally, there were no signifi cant differences found for the subjects in vertical GRF over time, following any bout of exercise. Thus, neither exercise nor brace condition do not appear to have an effect on vertical GRF.

DiscussionHip, knee and ankle moments at mid-stance were initially evaluated at T2 to deter-mine if the brace had a signifi cant affect on the dependent variables. As indicated

Figure 5—Means (± SD) of knee extension moments at T1 - T5. Signifi cant reduction in knee moment, †) signifi cantly different from T1 in the B group. Signifi cant reduction in knee moment, ‡) signifi cantly different from T2, in the NB group. Signifi cantly reduced knee moments in the B group compared to the NB group at θ) T2, T3, T4, and T5. (P < .05)


in the previous research,1-2 the current study revealed an increase in hip moments and a subsequent decrease in knee moments immediately following brace appli-cation. Thus, the application of the FKB caused a decrease in the knee moment, therefore reducing the stress on the knee joint and potentially shifting the torque production up the kinetic chain to the hip joint. It is speculated that the restriction of movement, and or the “newness” of the brace caused a change in the gait pat-tern, specifi cally during stance that shifted the stress away from the knee and up to the hip immediately after application. Hip, knee, and ankle joint moments were further evaluated throughout a one-hour bout of exercise.

Figure 6—Means (± SD) of ankle plantar fl exion moments at T1 - T5. No signifi cant dif-ferences observed over time. (P < .05)

Figure 7—Means (± SD) of vertical ground reaction forces at T1 - T5. No signifi cant differences observed over time. (P < .05)


A signifi cant main effect for time was revealed in the hip moments. This sug-gests that as exercise persisted, there was a signifi cant decrease in hip moments, regardless of brace condition. It is possible that as the subjects became more fatigued, they performed the trials in a more erect position and or with less hip fl exion, which would reduce the hip extension moments. In addition, there was also a signifi cant main effect for condition regarding the hip moments, reveal-ing a signifi cantly greater hip moment experienced in the B group, specifi cally at T2, T3, and T4. This also implies that the reduction in knee joint torque must cause a shift in torque production to an alternate joint given the similar VGRF characteristics of the trials. Therefore, the hip joint is the most likely joint to manage the stress.

Analysis of the knee joint moments revealed that the B group experienced signifi cantly reduced moments during T2 through T5 when compared to the NB group. The signifi cant difference found between groups at T2 (immediate post brace application) is somewhat contrary to the results of DeVita et al.2 Specifi cally, these investigators found that there was no difference in knee torque between groups; however, the work performed at the knee joint in healthy individuals decreased immediately after brace application. Our knee joint torque fi ndings along with the work of DeVita et al2 suggest that the FKB appears to be reducing the stress on the knee joint and shifting the forces away from the knee to other areas of the body, namely the hip joint. It is possible that the proprioceptive infl uence that the brace offers causes the individual to adopt a quadriceps avoidance gait pattern, thereby reducing knee joint torque during the stance phase. By reducing the torque experienced by the knee joint during stance, it is likely the stress experienced by the ligamentous structures is also reduced. The results further reveal that there were signifi cantly reduced knee moments in the B group during T2 through T5 when compared to T1. Once the FKB was applied, there was an immediate reduction of knee joint moment which persisted throughout a 1-hour period of exercise. T1 is the time point where no brace was used, and the subsequent points of assessment (T2 – T5) were performed with the FKB applied.

The active quadriceps anteriorly translates the tibia on the femur, which tends to antagonize the ACL. Although this study did not observe how the FKB affected the muscle activity, we can assume that the alteration in the gait characteristics may have been generated by changes in muscle fi ring patterns caused by the FKB. It is possible that because of the FKB, the quadriceps were not recruited as much in order to perform knee extension, which may further lead to the ligaments experiencing greater forces. Osternig and Robertson5 found that specifi c knee and ankle fl exors and extensors were highly sensitive to prophylactic knee bracing. In their study, 67%-83% of all braced versus nonbraced comparisons for the selected knee and ankle musculature produced signifi cant differences. Of those they found that 73% resulted in signifi cant reductions in muscle activity while wearing the knee brace.

Analysis of the knee joint moments in the NB group revealed an interesting decrease in knee moment from T2 to T4. It is possible that although this group was not wearing a knee brace, the participants began to experience some level of fatigue, induced by the performance of the exercise protocol. Although fatigue was not measured, it may have infl uenced some subjects to adopt an affected gait pattern, thus reducing knee extensor moments late in the protocol.


Ankle moments were not signifi cantly affected by either condition or time. This is similar to what DeVita et al2 found during jogging trials of healthy individuals immediately after FKB application. Given that the foot/ankle complex has initial contact with the ground, initiating the closed-chain motion, the hip is most likely to account for the torque changes. Furthermore, motor programming of such gross motor activities may involve more dominant, proximal muscles to modify changes in gait and therefore does not infl uence the more distal joints.

Vertical ground reaction forces were not found to be signifi cant by condition or time. Our fi ndings are contrary to Knutzen et al, stating that brace conditions had greater vertical and anterior/posterior ground reaction forces during the con-tact phase.15 The current study investigated the effects of a FKB while jogging at a self selected pace. If the jogging pace of the trials was increased or decreased away from the self selection, the GRFʼs may have been signifi cantly infl uenced. Although the GRFʼs factor into the joint moment calculations, it is possible that the differences in joint moments that were evident may have been due to muscle activation differences or even kinematic differences caused by the brace. It is pos-sible that further differences in joint moments may have been visible if the GRFs were signifi cantly affected by the speed of the jogging trials.

ConclusionsCollectively, these data regarding joint moments indicate that the brace may have a protective effect on the knee during mid-stance jogging trials in healthy individu-als. A decrease in moment at the knee during mid-stance was found, and it appears that the force and moments were further transmitted to the hip joint. Although not assessed in the current study, the reduction in the extension moment at the knee and subsequent increases at the hip may be partially attributed to changes in muscle fi ring patterns as previously mentioned in the literature.12

Future RecommendationsFuture investigation could examine lower extremity kinetics during different gait conditions. Perhaps an increase in the velocity of jogging/running gait would fur-ther alter the characteristics of gait when wearing an FKB. Furthermore, a more distancing temporal analyses may also elucidate these gait modifi cations during activity. The use of short time increments between assessments would provide a clearer picture of the effects of FKB usage on torque values. In addition, the use of a subject pool with a history of ACL injury or trauma would further lend to the applicability of these data in sport and recreational settings. It would also be interesting to observe the infl uence of these braces on muscle fi ring patterns, which may also shed light on some of the potential causes for these shifts in torque production among joints.

References 1. DeVita P, Lassiter T, Hortobagyi T, Torry M. Functional knee brace effects during

walking in patients with anterior cruciate ligament reconstruction. Am J Sports Med. 1998;26(6):778-784.


2. DeVita P, Torry M, Glover KL, Speroni DL. A functional knee brace alters joint torque power patterns during walking and running. J Biomech. 1996;29(5):583-588.

3. Nelson KA. The use of knee braces during rehabilitation. Clin Sports Med. 1990;9(4):799-811.

4. Cook FF, Tibone JE, Redfern FC. A dynamic analysis of a functional brace for anterior cruciate ligament insuffi ciency. Am J Sports Med. 1989;17(4):519-524.

5. Osternig LR, Robertson RN. Effects of prophylactic knee bracing on lower extremity joint position and muscle activation during running. Am J Sports Med. 1993;21(5):733-737.

6. Sforzo GA, Chen N, Gold CA, Frye PA. The effect of prophylactic knee bracing on performance. Med Sci Sports Exerc. 1989; 21:3:254-257.

7. Wirth MA, DeLee JC. The history and classifi cation of knee braces. Clin Sports Med. 1990;9:731-741.

8. Timoney JM, Inman WS, Quesada PM, Sharkey PF, Barrack RL, Skinner HB, Alexander AH. Return of normal gait patterns after anterior cruciate ligament reconstruction. Am J Sports Med. 1993;21:6:887-889.

9. DeVita P, Skelly WA. Intrasubject variability of lower extremity joint moments of force during the stance phase of running. Hum Move Sci. 1990;9:99-115.

10. DeVita P, Hunter PB, Skelly WA. Effects of a functional knee brace on the biomechan-ics of running. Med Sci Sports Exerc. 1992;24(7):797-806.

11. Wu KH, Ng YF, Mak FT. Effects of knee bracing on the functional performance of patients with anterior cruciate ligament reconstruction. Arch Phys Med Rehabil. 2001;82:282-285.

12. Ramsey DK, Wretenberg PF, Lamontagne M, Nemeth G. Electromyographic and biomechanic analysis of anterior cruciate ligament defi ciency and functional knee bracing. Clin Biomechanics. 2003;18(1):28-34.

13. Greene DL, Hamson KR, Bay RC, Bryce CD. Effects of protective knee bracing on speed and agility. Am J Sports Med. 2000;28(4):453-459.

14. Warming T, Jorgensen U. The effect of bracing on extension strength in patients with ACL insuffi ciency. Scand J Med Sci Sports. 1998;8(1):14-19.

15. Knutzen KM, Bates BT, Schot P, Hamill J. A biomechanical analysis of two functional knee braces. Med Sci Sport Exerc. 1987;19:303-309.

Temporal Inﬂ uences of Functional Knee Bracing on … functional knee braces (FKBs) are widely...

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