Walking symmetry and energy cost in persons with unilateral transtibial amputations: Matching prosthetic and intact limb inertial properties

Objectives: To investigate the hypothesis that increasing the mass and mome nt of inertia of the prosthetic limb of people with unilateral, transtibial amputations to match the mass and moment of inertia of the intact limb imp roves walking symmetry without increasing energy cost. Design: Gait symmetry and metabolic energy cost of walking for six subjects with unilateral, transtibial amputations were evaluated under three prosth esis loading conditions. Setting: University research laboratory. Subjects: Six ambulatory individuals with unilateral, transtibial amputatio ns. Interventions: Subjects walked at 1.34m/sec under three prosthetic limb loa ding conditions: (1) no added load; (2) loading that produced a match of pr osthetic shank and foot mass and moment of inertia with those of the intact limb (100% load); and (3) a load that was half that of the 100% condition (50% load). Main Outcome Measures: Step length, swing time, stance time, and metabolic energy expenditure. Results: As mass and moment of inertia of the prosthetic limb became more c losely matched to the intact limb, step length, swing time, and stance time became less symmetrical. Energy cost for the 100% load condition was signi ficantly greater (6% to 7%) than the baseline and 50% conditions. Conclusions: The loading configuration required to produce a match in the m oments of inertia of the prosthetic and intact lower legs resulted in great er gait asymmetry and higher energy cost.