Humans ambulate with bipedal gait and the ankle-foot system is imperative for efficient and symmetrical gait. Individuals with lower-limb amputation lose the anklefoot system and must rely on prostheses to ambulate. Prosthetic systems have traditionally been designed to mimic select aspects of the natural ankle-foot complex, such as roll-over shape and the late-stance ankle power burst. However, as prosthetic users still do not reach the same level of function as individuals without amputation it is clear that there is room for improvement in current prosthetic systems. In other words, there may be other aspects or features of lower limb mechanics during gait that could hold the key to enabling meaningful improvements in prosthesis design to be achieved. In particular, recent research has identified important, and somewhat surprising, features of the natural shank’s segmental kinematics and kinetics that may be useful as design criteria for future prosthetic systems. However, before advancements can be made in the designs of prosthetic systems, we must understand the shank segmental kinematics and kinetics during the gait of users with current prosthetic ankle-foot systems. Thus the aim of this study was to characterize the segmental kinematics and kinetics of the residual shank in prosthetic gait and compare to typical gait.

Shank segmental kinematics and kinetics in overground gait were analyzed for four individuals with unilateral transtibial amputation who used the same energy-storing-and-returning prosthetic ankle-foot system. The kinematic results revealed that the proximal shank remained horizontal throughout stance in prosthetic gait, similar to typical gait, despite the prosthetic users’ lack of active plantar flexion. Kinetic results showed that power flowed into the shank from more proximal segments at the moment of push-off on the prosthetic side, as opposed to typical gait and on the intact side where power flowed out of the proximal shank. In addition, the velocity of the proximal shank was higher at push-off on the prosthetic side compared to the intact side or typical gait. These results indicate that, to compensate for the lack of active push-off in the prosthesis, these prosthetic users use more proximal structures to lift the foot off the ground in late stance, instead of actively pushing it off. Analysis of spatiotemporal parameters revealed a shorter stance time and longer step length on the prosthetic side, where, presumably, the prosthetic users terminate the stance phase early to avoid the lowering and downward acceleration of the proximal shank. These results give better insight into the shortcomings of current prosthetic ankle-foot systems and provide design criteria that may be used to improve the design of prosthetic ankle-foot systems and resulting gait function of the prosthetic user.