Department of Veterans Affairs Journal of Rehabilitation Research and Development Vol . 32 No . 4, November 1995 Pages 373–378
CLINICAL REPORT
The Effect of Prosthetic Alignment on Relative Limb Loading in Persons with Trans-tibial Amputation : A Preliminary Report Michael S . Pinzur, MD; William Cox, MD ; James Kaiser, CPO ; Ted Morris, MS; Avinash Patwardhan, PhD ; Lori Vrbos, RN The Department of Orthopaedic Surgery, Loyola University Medical Center, Maywood, IL 60153; The Rehabilitation Engineering Center, Edward Hines, Jr . VA Hospital, Hines, IL 60141; Scheck & Siress Orthotics & Prosthetics, Inc ., Oak Park, IL 60302
Abstract—The prosthetic sockets of 14 independent persons with unilateral trans-tibial (BK) amputation were mounted on an adjustable alignment pylon . Vertical ground reaction forces were recorded in neutral prosthetic alignment and in 10° of prosthetic socket varus, valgus, flexion, and extension. Stance phase time, peak vertical ground reaction force, and impulse were all found to be increased on the sound limb when compared to the amputated residual limb . Significant differences were found in stance phase time and peak vertical ground reaction force when comparing malaligned with neutrally aligned prosthetic limbs . Significant differences were also seen in impulse between neutrally aligned and malaligned prosthetic limbs . The results suggest that prosthetic malalignment in persons with trans-tibial amputation leads to increased loading of the contralateral limb.
INTRODUCTION Sound prosthetic alignment has historically been stressed to enhance residual limb comfort and maximize walking capabilities in persons with lower extremity amputation . Little is understood regarding the relationship between the amputation residual limb and the contralateral remaining sound limb. Clinical and objective scientific data substantiate the observation that unilateral amputees transfer load to their sound limb to a relatively greater degree than to their amputated residual limb (1-3) . When surveyed, persons with unilateral lower extremity amputation experience pain in their non-amputated limb at a rate of between 19 and 71 percent (2,4,5) . Further studies have reported asymmetric gait patterns, altered biomechanical load, and decreased tolerance to the generalized level of deformity, when compared to persons without amputation (2-10). The purpose of this preliminary study was to investigate the relationship between prosthetic alignment and relative load on the amputated residual limb and on the contralateral remaining sound extremity.
Key words : below-knee amputation, gait analysis, ground reaction force, stance phase time.
This material is based upon work supported by the Rehabilitation Research and Development Programs, Department of Veterans Affairs, Washington, DC. Drs. Pinzur and Patwardhan, and Mr . Morris, are affiliated with the Rehabilitation Engineering Center Department of Edward Hines, Jr . VA Hospital, Hines, IL ; Drs . Pinzur, Cox, and Patwardhan and Ms . Vrbos are affiliated with the Department of Orthopaedic Surgery, Loyola University Medical Center, Maywood, IL ; Mr. Kaiser is with Scheck & Siress Orthotics & Prosthetics, Inc ., Oak Park, IL. Address all correspondence and requests for reprints to : Michael S . Pinzur, MD, Department of Orthopaedic Surgery, Loyola University Medical Center, 2160 South First Avenue, Maywood, IL 60153;
[email protected] .
METHODS Fourteen persons with unilateral trans-tibial (BK) amputation, 12 men and 2 women ranging in age from 373
374 Journal of Rehabilitation Research and Development Vol .32 No . 4 1995
25 to 74 years (mean 45 years), participated in the study . A total of 13 patients underwent amputation secondary to traumatic injury, while 1 patient underwent surgery due to peripheral vascular disease . All subjects meeting the entry criteria were asked to participate . In order to insure sufficient ambulatory potential to complete the series of experiments, the following criteria for inclusion were selected: 1. 2. 3. 4. 5. 6.
7. 8.
A weight change of less than 10 pounds during the year preceeding participation in the study Subjects required to be independent community ambulators for a period of 12 months Subjects involved in the study not allowed to use assistive devices for walking Residual limb length between 12 cm and 15 cm No residual limb soft tissue envelope deficiencies, or adherent scar tissue between skin and bone The present amputation was a primary amputation, without any previous amputations that required surgical revision Patients had their present prosthetic device for a minimum of 1 year Subjects wore an endoskeletal prosthetic system allowing the investigators to use their own prosthetic socket during testing.
Patients were excluded if they had any complaints of "phantom limb," or localized residual limb pain. Before the fouttal testing was initiated, each of the subjects was asked to walk a minimum of five times at a self-selected comfortable walking speed on the walkway to become comfortable with the testing procedure . During this period of acclimation, each of the subjects adjusted his or her starting points in order to take one step with each foot in, or near, the center of each of the dual force platforms . All of the subjects underwent initial dynamic prosthetic alignment, that is, the positioning of the prosthetic socket in relation to the prosthetic foot during walking, by the same experienced Certified Prosthetist (2,9–11) . The prosthetic socket of each of the subjects was mounted on an adjustable pylon with a new SACH (solid ankle, cushioned heel) foot (Figure 1). Gait analysis was performed on all subjects utilizing two AMTI Biomechanical Force platfotuts (Advanced Mechanical Technologies, Inc .) . These devices were mounted in a free-standing walkway measuring 11 m. The analyses were performed in the following positions of dynamic prosthetic alignment : 1) neutral ; 2) 10° varus (adduction) ; 3) 10° valgus (abduction) ; 4) 10°
Figure 1. Prosthetic socket mounted on an adjustable alignment pylon and SACH foot.
flexion; and 5) 10° extension . None of the subjects were able to maintain adequate walking balance when the malalignment was set at 15° of malalignment . After recording data for neutral prosthetic alignment, three random trials in 10° of prosthetic socket varus, valgus, flexion, and extension were accomplished . To enhance the internal validity of the study, the order of malalignment positions was randomized using a table of random numbers .
375 CLINICAL REPORT : Prosthetic Alignment for Trans-tibial Amputees
Stance phase time was employed as a measure of walking stability . Peak vertical ground reaction force was used as a measure of maximum limb loading. Impulse, or the force applied to the limb during the period of limb loading, was measured by calculating the area under the vertical ground reaction force curve from initial floor contact (i.e., heel strike to toe-off) . It was also used as a dynamic measure of total loading of the limb . The data were collected at 120 Hz and subsequently processed off-line to obtain two three-dimensional ground reaction force vectors . Additionally, stance phase time and vertical ground reaction force results were computed from the processed data (Figure 2). Medial-lateral, fore-aft, and torque ground reaction forces—valuable measures of the shearing forces on the limbs—were recorded, but their values were so small when compared to the vertical ground reaction force that a comparison was not justified. Data Analysis A descriptive analysis was performed on the raw data for summarization and to obtain measures of central tendency and dispersion (Tables 1-4) . The data were also reviewed for the presence of outliers.
Required statistical assumptions were found to be met, including homogeneity of the variance/covariance matrices (Cochran's p=0 .02). The level of significance was set at 0 .05. A multivariate analysis of variance (MANOVA) was performed as an omnibus test . Post hoc univariate F-tests were subsequently performed on all dependent variables.
RESULTS Overall, statistically significant differences were observed between stance phase time, peak vertical ground reaction force, and impulse in all subjects when comparing amputated and sound limbs (MANOVA W.lambda F=27 .09, p=0 .0000) . There were no significant differences in the three gait parameters when comparing neutral prosthetic alignment with the four positions of intentional prosthetic malalignment (MANOVA W.lambda F=0 .73, p=0 .7248 : Tables 2-4). There was no significant interaction noted (p=0 .7248). When we compared impulse (i .e., total dynamic loading), we found significantly increased loading with all positions of prosthetic malalignment, with prosthetic socket varus (adduction) and extension producing greater discrepancies than valgus (abduction) or flexion; however, this was not statistically significant (p=0 .49).
Table 1. Descriptive data with univariate comparisons. Variable
BK Mean ± SD
SL Mean ± SD
Significance
Peak Force (Newtons)
792 .76±12.3
865 .37 ± 15 .6
F=30 .26 p=0 .0000*
Impulse (nanoseconds)
468 .93 ± 7 .62
538 .57±10 .9
F=66 .03 p=0 .0000*
Stance Time (seconds)
0 .824±0.080
0 .877±0 .100
F=36 .93 p=0 .0000*
Table 3. Alignment as a function of impulse (F=0 .85, p=0.4933). Variable
Mean ± SEM
Neutral 10° Varus (Adduction) 10° Valgus (Abduction) 10° Flexion 10° Extension
497 .10 495 .90 515 .00 511 .49 499 .24
± 9 .58 ± 9 .58 ± 9 .58 ± 9 .58 ± 9 .58
*BK = trans tibial amputation; SL = sound limb .
Table 4. Alignment as a function of peak force (F=0 .50, p=0 .7333).
Alignment as a function of stance phase time (F=0 .27, p=0 .8951).
Variable
Mean ± SEM
Variable
Neutral 10° Varus (Adduction) 10° Valgus (Abduction) 10° Flexion 10° Extension
828 .83 ± 14.75 831 .90±14.75 817 .88 ± 14.75 821 .76±14.75 844 .94±14.75
Neutral 10° Varus (Adduction) 10° Valgus (Abduction) 10° Flexion 10° Extension
Table 2.
Mean ± SEM 0 .8343 ±9 .84 0 .8340±9 .84 0 .8746±9 .84 0 .8698±9 .84 0 .8414±9 .84
376 Journal of Rehabilitation Research and Development Vol .32 No . 4 1995
Vertical component of the ground reaction force of the prosthetic limb 1000 900 800 700 600
NEUTRAL ALIGNMENT
E it
500
10 DEGREE FLEXION
z
400
10 DEGREE FLEXION 10 DEGREE VARUS
300
10 DEGREE VALGUS
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BODY WEIGHT
100 0 -100 0.0
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1000 900 800 700 600 z
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500 400
10 DEGREE FLEXION 10 DEGREE FLEXION 10 DEGREE VARUS
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100 0 -100 0.0
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.4
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Figure 2. Vertical ground reaction force tracings in the neutral and altered prosthetic alignments for the amputated limb (2a), and the sound contralateral limb (2b) . The dotted line on each curve represents the subject's body weight in Newtons . Note the asymmetry of the curves, the increased peak, and total forces on the sound limb, and the increased magnitude of those forces with the altered prosthetic alignments.
377 CLINICAL REPORT: Prosthetic Alignment for Trans-tibial Amputees
DISCUSSION Clinical experience has suggested that prosthetic malalignment would decrease overall walking stability. The subjects in this study were sufficiently good prosthetic walkers that they were able to compensate for the malalignment of their prostheses over a short length (11 m) of walking in the controlled environment of a Gait Analysis Laboratory . All had a significant increase in the total dynamic loading of their residual limbs during the period of the study when their prostheses were malaligned. If a small amount of prosthetic malalignment increases residual limb loading during the short duration of the study period, what would be the long-term effect of walking with a malaligned prosthetic limb? The results of this study agree with the commonly held clinical notion that optimal prosthetic alignment does promote steady and comfortable walking with a lower extremity prosthesis . Conversely, prosthetic malalignment may well lead to instability, discomfort, increased limb loading, and tissue breakdown when applied over a long period of time .
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