Prosthetic loading during kneeling of persons with transfemoral amputation

Observations in the field of lower limb prosthetic rehabilitation have show n that several transfemoral prostheses show signs of wear on some component s of the knee unit. This is thought to be a result of severe loading develo ped during activities associated with kneeling. Some prostheses may have fa iled due to repetitive action of such loading. In order to determine the na ture and magnitude of the loads developed during kneeling by persons with t ransfemoral amputation, and to investigate the influence of various prosthe tic parameters, an analysis of the results of 162 tests in prosthetic knee hyperflexion was undertaken. The services of four males with amputation wer e enlisted. The measurements involved simultaneous use of two Kistler force platforms, a six-channel strain gauge transducer mounted on the prosthetic shank, and a data acquisition system. The critical loads for this configur ation were found to be the shear force on the knee hinge, the sheer force i mposed by the knee chassis on the shin, and the bending moment tending to h yperflex the knee. These loads ranged from 0.6 to 6.2 kN, 0.9 to 6.7 kN, an d from 18.3 to 155.7 Nm, respectively. To achieve a comfortable kneeling po sition, some prostheses permit foot rotation about the pylon axis of 90 inf inity to allow the shank to be approximately parallel to the ground. Tests were also conducted with the prostheses in this configuration and the most influential prosthetic parameter was found to be the external rotation of t he foot (toe-out angle). During kneeling, it was found that the loading was dependent upon the position of the torso relative to the prosthesis, but l oads were much higher than those developed during level walking.