Compensatory mechanisms of transtibial amputees during circular turning.

Turning plays a prominent role in daily living activities and requires the modulation of the ground reaction forces to accelerate the body's center-of-mass along the path of the turn. With the ankle plantarflexors being prominent contributors to the propulsive ground reaction forces, it is not clear how transtibial amputees perform turning tasks without these important muscles. The purpose of this study was to identify the compensatory mechanisms used by transtibial amputees during a simple turning task by analyzing the radial and anterior-posterior ground reaction impulses and sagittal, transverse and coronal joint work of the residual and intact legs. These quantities were analyzed with the residual leg on both the inside and outside of the turn and compared to non-amputees. The analysis showed that amputees and non-amputees use different joint strategies to turn. Amputees rely primarily on sagittal plane hip joint work to turn while non-amputees rely primarily on ankle work in the sagittal plane and hip joint work in the coronal plane. Differences in strategies are most likely due to the minimal power output provided by the passive prosthetic feet used by amputees and perhaps a desire to minimize the risk of falling. Understanding these differences in turning strategies will aid in developing effective rehabilitation therapies and prosthetic devices that improve amputee mobility.