Mechanical work adaptations of above-knee amputee ambulation

Objective: To quantify the muscular adaptations of above-knee amputee patients' ambulation using an experimental and modeling approach. Design: Nonrandomized controlled study. Setting: A referral center for treatment of veterans with amputation. Subjects: Eight normal ambulators and 8 nondysvascular above-knee amputee subjects wearing the same lightweight prostheses were studied with a gait analysis system, walking at self-selected speeds. Main Outcome Measures: Using an inverse dynamics linked segment model, the mechanical torque, power output, and work done were calculated at the hip, knee, and ankle joints. Results: The mean concentric ankle plantarflexor work done was much greater for the normal subjects compared to the prosthetic limb in pushoff (25.2 ± 3.7J vs 4.9 ± 2.1J), but greatest for the intact limb of the amputee subjects (34.2 ± 6.6J). Also, the concentric hip extensor work done in early stance was greater for the intact limb of the amputee subjects than for normal subjects (9.9 ± 5.5J vs 3.6 ± 2.6J), presumably compensating for the coincident decreased pushoff of the prosthetic limb. Other compensatory mechanisms are also discussed. Conclusions: Increased joint torques and power outputs of the amputee subjects' intact limb compared to normal ambulation may be viewed as providing additional gait progression and upright stance during parts of the gait cycle when the amputated limb lacks needed active muscle support.