The Functional Roles of Muscles, Passive Prostheses, and Powered Prostheses During Sloped Walking in People With a Transtibial Amputation

Abstract

Sloped walking is challenging for individuals with transtibial amputation (TTA) due to the functional loss of the ankle plantarflexors. Prostheses that actively generate ankle power may help to restore this lost function. The purpose of this study was to use musculoskeletal modeling and simulation to quantify the mechanical power delivered to body segments by passive and powered prostheses and the remaining muscles in the amputated and intact legs during sloped walking. We generated walking simulations from experimental kinematic and kinetic data on slopes of 0, ±3 deg and ±6 deg in eight people with a TTA using powered and passive prostheses and eight nonamputees. Consistent with our hypothesis, the amputated leg hamstrings generated more power to both legs on uphill slopes in comparison with nonamputees, which may have implications for fatigue or overuse injuries. The amputated leg knee extensors delivered less power to the trunk on downhill slopes (effect size (ES) ≥ 1.35, p ≤ 0.02), which may be due to muscle weakness or socket instability. The power delivered to the trunk from the powered and passive prostheses was not significantly different (p > 0.05), However, using the powered prosthesis on uphill slopes reduced the contributions from the amputated leg hamstrings in all segments (ES ≥ 0.46, p ≤ 0.003), suggesting that added ankle power reduces the need for the hamstrings to compensate for lost ankle muscle function. Neither prosthesis replaced gastrocnemius function to absorb power from the trunk and deliver it to the leg on all slopes.

Figures

Fig. 1

Comparison of the mean (±standard deviation) processed EMG signals from each muscle group (shaded area) and the mean (±standard deviation) of the processed muscle excitations in the simulations for individuals with TTA using both prostheses (upper and lower bounds indicated by solid lines). Discontinuities in the simulation traces are a result of the gait cycle normalization we used for visualization purposes to be consistent across people with left and right leg amputations. The discontinuities reflect the end points of full gait cycle simulations and do not affect the results.

Fig. 2

Comparison of the mean (±standard deviation) processed EMG signals from each muscle group (shaded area) and the mean (±standard deviation) of the processed muscle excitations in the simulations for nonamputees (upper and lower bounds indicated by solid lines)

Fig. 3

Mean (±standard deviation across all trials) power delivered to the trunk, ipsilateral leg, and contralateral leg by the hamstrings in the intact, amputated, and average nonamputee leg during stance at slopes of 0 deg, ±3 deg, and ±6 deg. Values are normalized by segment mass. Significant differences are indicated between intact and amputated leg (L), passive-elastic and powered prostheses (P), and compared to nonamputees (N), with p-values <0.001 indicated by “*.” Individuals with TTA relied more heavily on the hamstrings compared to nonamputees, but use of a powered prosthesis reduced this hamstring compensation compared to use of a passive-elastic prosthesis.

Fig. 4

Average power delivered to the trunk, ipsilateral leg, and contralateral leg by the hamstrings muscles in the intact, amputated and average nonamputee leg during stance (0–60% gait cycle) at slopes of 0 deg, ±3 deg, and ±6 deg. Values are normalized by segment mass. Use of a powered prosthesis reduced hamstrings compensations in the amputated leg compared to using a passive prosthesis, primarily during midstance (approximately 20–50% prosthetic leg gait cycle).

Fig. 5

Mean (± standard deviation across all trials) power delivered to the trunk and ipsilateral leg by the rectus femoris in the intact, amputated, and nonamputee leg during stance at slopes of 0 deg, ±3 deg, and ±6 deg. Significant differences are indicated between intact and amputated leg (L), passive and powered prosthesis (P), and compared to nonamputees (N), with p-values <0.001 indicated by “*.” Values are normalized by segment mass. The amputated leg rectus femoris transferred less power from the leg to the trunk at −6 deg compared to nonamputees.

Fig. 6

The left column gives the mean (±standard deviation across all trials) power delivered to the trunk and ipsilateral leg by the passive and powered prostheses compared to the summed contributions of all ankle muscles in the intact and nonamputee legs. Thus, these plots compare the functional roles of each prosthesis and the biological ankle. The middle and right columns compare the passive and powered prostheses (same values as in left column) to the soleus and gastrocnemius of the intact and nonamputee legs. Values are normalized by segment mass. Significant differences are indicated between intact and amputated leg (L), passive, and powered prosthesis (P) and compared to nonamputees (N), with p-values <0.001 indicated by “*.”

Fig. 7

Average power delivered to the trunk, ipsilateral leg, and contralateral leg by the powered and passive prostheses compared to the soleus, gastrocnemius, and sum of all ankle muscles in the nonamputee leg during stance (0–60% gait cycle) at slopes of 0 deg, ±3 deg, and ±6 deg. Values are normalized by segment mass.

Fig. 8

Mean (±standard deviation) knee flexion angle during stance for nonamputees (shaded area) and the amputated leg of individuals with TTA using both prostheses (lines indicate mean and upper and lower bounds of one standard deviation). There was large variation in knee angle across participants with an amputation, which may partially explain the large variability in segment power generated by the muscles of the amputated leg.