Direct Measurement of 3D Force and Moment on Lower-Limb Osseointegrated Fixation

Occasional mechanical failures is a concern for transfemoral amputees using osseointegrated fixation. Understanding the true load applied on osseointegrated fixation is one important step in solving this problem. Conventionally, the load magnitude can be calculated based on the motion of the prosthesis and the ground reaction forces measured by a force plate using inverse dynamics. However, this approach allowed only one or two walking steps to be measured and errors are compounded when involving more than one joint above the ankle. In this study, the load applied on the lower-limb osseointegrated fixation was directly measured with a load transducer. Twelve transfemoral amputees fitted with a fixation and their usual prosthesis (knee and foot) were assessed during approximately 51±12 normal walking steps in straight line. Three-dimensional force and moment local extremas and patterns at the fixation along a gait cycle were displayed. Step-to-step variability of each subject was low. This tends to validate gait laboratory-based studies focusing on one or two steps. High subject-to-subject variability was demonstrated. This could be due to the wide variety of components, alignments and anthropometric characteristics within the tested population.