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 moment of inertia of the prosthetic limb of people with unilateral, transtibial amputations to match the mass and moment of inertia of the intact limb improves 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 prosthesis loading conditions.

SETTING: University research laboratory.

SUBJECTS: Six ambulatory individuals with unilateral, transtibial amputations.

INTERVENTIONS: Subjects walked at 1.34 m/sec under three prosthetic limb loading conditions: (1) no added load; (2) loading that produced a match of prosthetic 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 closely matched to the intact limb, step length, swing time, and stance time became less symmetrical. Energy cost for the 100% load condition was significantly greater (6% to 7%) than the baseline and 50% conditions.

CONCLUSIONS: The loading configuration required to produce a match in the moments of inertia of the prosthetic and intact lower legs resulted in greater gait asymmetry and higher energy cost.