Transfemoral amputees walking on a rotary hydraulic prosthetic knee mechanism: A preliminary report

Results from multiple instrumented gait analysis trials of seven traumatic transfemoral amputees capable of community ambulation are reviewed. All subjects used a novel rotary hydraulic prosthetic knee offering both stance and swing phase control, in combination with various contemporary prosthetic ankle-foot mechanisms. Unlike previous hydraulic stance and swing units, the Otto Bock 3R80 knee provides stance stability whenever the desired weightbearing load is applied to the prosthesis. The mechanical principles and basic functions of the knee joint are described. Results from three phases of gait studies are presented to identify inter-individual variability and the effect of varying sagittal plane knee alignment and the ankle-foot mechanism selected. Subjective amputee preferences for specific foot devices are presented. The pattern of hip moments on the amputated side during stance phase are characteristic of the individual amputee. However, the magnitude and timing of the hip moments vary considerably between individual amputees. So long as the prosthetic knee remains biomechanically stable, it appears that alignment alterations or the use of varying foot devices have little impact on the hip extension moment. On the other hand, the hip flexion effort required for the amputee to initiate knee flexion in late stance phase is directly related to the linear position of the prosthetic knee in the sagittal plane: the more posterior the knee, the greater the effort needed to begin swing phase. Clinical function of this hydraulic prosthetic knee was considered satisfactory with all tested ankle-foot mechanisms. Transfemoral amputee preference for specific prosthetic feet in this study seemed to be determined by two biomechanical factors: (1) their ability to benefit from the use of a dynamic response foot without compensating with the non-amputated knee, and (2) their ability to generate a hip extension moment on the prosthetic side during the weight acceptance phase of gait.