The Effect of Morphological Variations at the Human Ankle and Hip Joints on their Biomechanical Function

The morphology of the articular surfaces of bones and the insertion sites of ligaments crossing anatomical human joints were reported to vary greatly amongst individuals. These morphological variations could be the main cause for the observed large variations in the joint mechanical function. The goal of this study is to explore the causal relationship between the joint morphology and mechanics in two specific joints- ankle and hip joint. To achieve this goal, six experimentally validated numerical models of the ankle joint complex, were developed from morphological data, obtained from magnetic resonance images of six cadaveric lower limbs and six numerical models of hip joints were developed from morphological data obtained from computer tomographic scans of six healthy hip joints. The morphology of the bone is systematically varied and the resulting mechanical function such as range of motion of the joint, flexibility of the joint and forces in the ligaments are compared with the change in morphology. Since all models used identical material properties and were subjected to identical loads and boundary conditions, it was concluded that the observed variations in mechanical behavior of the joint were due to variations in morphology. The results suggested that the morphological variations could be the main cause for the large variations observed in joint mechanics and could influence the mechanical consequences of ligament injuries and surgical procedures such as joint fusion and joint replacement.