Compensatory mechanisms in below-knee amputee gait in response to increasing steady-state walking speeds.

Compensatory mechanisms in below-knee amputee gait are necessary due to the functional loss of the ankle muscles, especially at higher walking speeds when the mechanical energetic demands of walking are greater. The objective of this study was to examine amputee anterior/posterior (A/P) ground reaction force (GRF) impulses and joint kinetics across a wide range of steady-state walking speeds to further understand the compensatory mechanisms used by below-knee amputees. We hypothesized that amputees would rely more on their intact leg to generate greater propulsion relative to the residual leg, which would result in greater GRF asymmetry between legs as walking speed increased. Amputee and control subject kinematic and kinetic data were collected during overground walking at four different speeds. Group (n=14) average amputee data showed no significant differences in braking or propulsive GRF impulse ratios, except the propulsive ratio at 0.9 m/s, indicating that the subjects maintained their initial levels of GRF asymmetry when walking faster. Therefore, our hypothesis was not supported (i.e., walking faster does not increase GRF loading asymmetry). The primary compensatory mechanism was greater positive residual leg hip joint power and work in early stance, which led to increased propulsion from the residual leg as walking speed increased. In addition, amputees had reduced residual leg positive knee work in early stance, suggesting increased output from the biarticular hamstrings. Thus, increasing residual leg hip extensor strength and output may be a useful mechanism to reduce GRF loading asymmetry between the intact and residual legs.

The effect of foot and ankle prosthetic components on braking and propulsive impulses during transtibial amputee gait.

OBJECTIVE: To assess the influence of energy storage and return (ESAR) prosthetic feet and multi-axis ankles on ground reaction forces and loading asymmetry between lower limbs in transtibial amputees. DESIGN: Subjects wore 2 different prosthetic feet with and without a multi-axis ankle and were analyzed using a blind repeated-measures multivariate analysis-of-variance design. SETTING: Gait analysis laboratory. PARTICIPANTS: Fifteen healthy unilateral transtibial amputees (>55 y) who had an amputation at least 1 year before testing because of vascular disorders. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: The anteroposterior ground reaction force impulse, peak ground reaction forces, and braking and propulsion impulse duration were analyzed as subjects walked at a self-selected speed while wearing each of the 4 foot-ankle prosthesis combinations. Statistical analyses were used to determine if there was a significant foot, ankle, or foot-ankle interaction effect on the outcome measures for each foot (P<.05). RESULTS: Amputees generated a significantly greater propulsive impulse with the residual leg when wearing a multi-axis ankle with the ESAR and non-ESAR foot, which improved the propulsive symmetry between the residual and intact legs. There was no prosthetic foot effect on these measures. There were no significant differences in the peak residual-leg braking or propulsive ground reaction forces or the impulse durations due to the prosthetic foot, ankle, or foot-ankle interactions, although an increase in the propulsive impulse duration approached significance (P=.062) with a multi-axis ankle. CONCLUSIONS: These results suggest that amputee gait may improve with the prescription of multi-axis ankles that allow for greater propulsive impulses by the residual leg, which improve the loading symmetry between legs.