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Loading response challenges the limb with the dual demands of accepting rapidly moving body weight to both absorb the shock of floor contact and create a stable limb over which the body can advance. Delay in achieving foot flat contact with the floor causes a prolonged period of heel only support and results in an unstable base of support for those persons with transtibial amputations. The purpose of this study was to identify mechanical causes of instability during weight acceptance with three different prosthetic foot designs, Single Axis, Seattle Lightfoot, and Flex Foot. Ten male individuals with transtibial amputations were tested on three separate occasions wearing each prosthetic foot. A comparison group of ten individuals without transtibial amputations was also examined. Mean free walking speed was significantly slower for those with transtibial amputations regardless of the prosthetic foot worn (p < 0:05). Contralateral toe off times were significantly later for each prosthetic foot (p < 0:01). The timing of peak knee flexion was found to be significantly later than normal for each prosthetic foot (p < 0:01). To minimize the impact of initial floor contact, persons with an intact limb used rapid plantar flexion, followed by a slower lowering of the foot to the floor. Dorsiflexion then stimulated knee flexion and foot flat. Two altered functions were found for all three prosthetic feet, reduced knee flexion and prolonged heel only support. Diminished knee flexion reflected delayed dorsiflexion and tibial advancement as a result of the cushioned heel. Lateness in reaching foot flat was also found. To improve the walking abilities of those persons with transtibial amputations, prosthetic foot designs need to incorporate mechanisms which promote early foot flat while preserving limb stability.

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The purpose of this study was to test the hypothesis that the magnitude and timing of peak foot pronation would be predictive of the magnitude and timing of peak rotation of tibia and femur. Thirty subjects who demonstrated a wide range of pronation participated. Three-dimensional kinematics of the foot, tibia, and femur segments were recorded during self-selected free walking trials using a six-camera VICON motion analysis system. Regression analysis demonstrated that the magnitude and timing of peak pronation was not predictive of the magnitude and timing of tibial and femoral rotation. The lack of a relationship between peak foot pronation and the rotation of the tibia and femur is contrary to the clinical hypothesis that increased pronation results in greater lower extremity rotation. It would seem, therefore, that the relationship between foot pronation and rotation of the lower extremity segments should be assessed on a patient-by-patient basis.

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