Effect of the lateral rotators on load transfer in the human hip joint revealed by mechanical analysis.

A deeper understanding of load transfer in the human hip joint is of great importance as there is strong evidence that the mechanical loading of the hip has a major effect on the onset and progression of osteoarthritis. In this work, a biomechanical model of the human hip joint is developed which takes the lateral rotators into account. On the basis of a two-dimensional analysis of the human hip joint, the dependencies of the hip joint reaction force and its angle to the vertical are derived. The dependencies can be given as explicit equations. In addition, a numerical finite element analysis has been set up to calculate the contact pressure distribution on the femoral head. The results of this study are not subject-specific and are intended to show qualitative results and relationships of the load transfer behavior. The results of this two-dimensional study show that the lateral rotators have a significant effect on the contact pressure distribution in the human hip joint. Activated lateral rotators shift the maximum contact pressure in the medial direction and the contact pressure at the lateral edge of the contact area is significantly reduced. The results are validated by comparison to results in the literature and subsequently discussed. The results give additional insight into the load transfer behavior of the human hip joint and might be of relevance to investigations on the development of conservative therapies for osteoarthritic hips.