Trans-femoral amputee gait: socket-pelvis constraints and compensation strategies

The paper deals with the identification of motor strategies adopted by trans-femoral amputees to compensate for the constraints of hip motion induced by the interference of the socket with the pelvis and, particularly, with the ischial tuberosity. A group of 11 subjects with trans-femoral amputation, three of whom wore two different prostheses, giving a sample size of 14 cases, were studied by gait-analysis protocols: the present paper focuses on the pelvis-thigh kinematics at foot strike. The results showed that, at the prosthetic side, the hip is significantly less flexed and less extended, respectively, at the ipsilateral and contralateral foot strike. Moreover, the pelvis is significantly more anterior tilted at sound foot strike. The anterior step length showed a decreased sound limb anterior step in 12 out of 14 cases. The authors interpret these results as a combination of mechanical constraints and compensatory actions: the reduced prosthetic hip extension is determined by the mechanical constraint involved in the pelvis-socket interference; and the increased pelvis tilt and sound hip flexion occurring at the same time are compensating strategies, adopted by the amputees, in order to obtain a functional step length and symmetrical thigh inclinations. Those factors determine a gait pattern which is functional, only slightly slower than normal gait, and without any perceivable alterations. On the other hand, the authors show that the increased pelvis tilting necessarily overloads the lumbar tract of the spine and may be related to the frequent occurrence of low-back pain in amputee subjects, despite the positive functional gait recovery.