Effects of inertial properties of transfemoral prosthesis on leg swing motion during stair ascent

Stair ascent, especially the step-over-step gait, is a difficult motor task for people with transfemoral amputation. Our previous study demonstrated the effects of foot placement on the leg swing of able-bodied subjects. The study examined stair ascent with full-foot contact (FFC) and half-foot contact (HFC) as ambulation strategies. The results suggested that HFC causes the leg swing to have a greater inertial motion than FFC, as well as the applicability of the stair ascent strategy for transfemoral amputees with transfemoral prostheses without a motorized prosthetic knee joint. The present study investigated the effects of the inertial properties of a transfemoral prosthesis on leg motion during the stair ascent swing phase in simulation trials. The joint moment at the hip became smaller than that of an able-bodied subject. The peak values of the horizontal and vertical components of the joint reaction force were approximately the same as those of an able-bodied subject. These results suggest that a transfemoral prosthesis leg swing can be achieved with similar or smaller kinetic demand at the hip joint when half-foot contact on the stair steps is used as a stair ascent strategy. The mass had the largest effect of the inertial properties on the variability of the simulated kinetic parameters. The results of the present study may enhance prosthesis design with regard to the inertial properties and usability.