Geometric and mechanical modelling of the human locomotor system

A critical review of studies related to the modelling of the human locomotor system is given. Kinematic and dynamic modelling and analysis of the pelvis-leg apparatus as an ensemble of four rigid body segments are described. Experiments were performed on two patients with custom-made instrumented massive proximal femoral prostheses implanted after tumour resection. Telemetered axial forces transmitted along the prostheses, together with kinematic, force plate and electromyographic data, were recorded synchronously during level walking, single and double leg stance, and isometric tests of the hip muscles. A sagittal plane model of the locomotor system, with an anatomical model of the knee joint, was developed from an existing model and used for a comparative study of methods for the calculation of the internal forces. A three-dimensional computer graphics-based animated model of the locomotor system was developed, with the hip as a ball-and-socket joint, the knee as a parallel spatial mechanism and the ankle as a two-hinge complex. Thirty-four muscles or muscle groups were included. A method for the determination of the orientation of multi-joint systems from surface markers was developed to take account of measurement errors including skin movement artefacts. Both the 2D and 3D models of the locomotor system were evaluated and validated quantitatively with the telemetered femoral axial forces. It is concluded that (a) a significant part of the bending moments along limbs are transmitted by a combination of tensile forces in muscles and compressive forces in bones so that moments transmitted by the bones are much less than the limb moments, (b) bi-articular muscles play a major role in modulating forces in bones, (c) appropriate simulation of muscle forces is important in experimental or theoretical studies of load transmission along bones, (d) computer graphics-based modelling and animation are important tools in bridging the gap between clinical users and biomechanists.