MECHANICS OF AMPUTEE JUMPING – CONSIDERATION FOR LOADING

Abstract

Amputees must develop compensatory mechanisms to overcome the constraints imposed by a mechanical prosthesis. In completing a bilateral countermovement jump, amputees must accommodate the limited ankle dorsiflexion angle and adapt to the limited plantar-flexor moment that occurs at the prosthetic joint. The aim of this research was to determine the loading on the limbs and the joint kinetics adopted by transtibial amputees in order to achieve a jump. Six amputee (AMP) and 10 able-bodied (AB) participants performed maximal vertical jumps on two force plates while kinematic data was recorded using a 9-camera VICON infrared system. The amputees did not jump as high as the AB participants. The AMPs raised the prosthetic heel from the floor to compensate for the restricted motion at the ankle. Consequently, kinematic symmetry was maintained at the knee and the hip. The knee flexion places the prosthetic shank in a more horizontal position. This is a vulnerable position due to the reduced strength in the knee extensors as a consequence of the amputation. In order to reduce the instability and loading at the knee, the maximum propulsive vGRF on the prosthetic side was reduced and the intact limb assumed a dominant role. Until amputees can take the loading on the prosthetic side, it is not recommended that they participate in jumping.