MASS AND MASS-DISTRIBUTION OF BELOW-KNEE PROSTHESES - EFFECT ON GAIT EFFICACY AND SELF-SELECTED WALKING SPEED

Objective: To study mass and mass distribution effect on function of b elow-knee prostheses. Design: Design modifications were done to produc e proximal center of mass location versus distal center of mass locati on variations, and prosthesis weight was modified from 42% to 70% of n ormal limb weight. Work across joints of affected and unaffected extre mities was compared to assess the ability of the prosthesis to substit ute for function loss. Setting: University biomechanics laboratory. Pa rticipants: Fifteen volunteers with below-knee amputations, residual l imb length greater than 8.3cm, but excluding Syme amputations. Interve ntions: Patients walked with all configurations at self-selected walki ng speeds and 120m/min. Main Outcome Measures: Self-selected walking s peed and metabolic efficiency. Work across the joints of affected and unaffected sides was compared. Results: Proximal center of mass locati on produced a more efficient gait. Weight change from 42% to 70% of no rmal bad no significant effect. Mechanical studies show that the prost hesis is a relatively poor substitute for the normal limb. mast work i s done by the nonamputated side. Particularly, the prosthesis failed t o produce effective forward impulses on the body, resulting from push- off and deceleration of the swing leg. Conclusions: For a proximal cen ter of mass, lightweight distal components (eg, feet) should be used; it is questionable whether further expenditure to develop ultralightwe ight prostheses would be cost effective lot level walking. (C) 1998 by the American Congress of Rehabilitation Medicine and the American Aca demy of Physical Medicine and Rehabilitation.