Cartilage and labrum mechanics in the normal and pathomorphologic human hip.

摘要

While the healthy hip provides decades of pain free articulation, the cartilage and labrum may degenerate during the process of osteoarthritis (OA). Most hip OA is caused by subtle pathomorphologies, including acetabular dysplasia and acetabular retroversion. The link between pathomorphology and OA is thought to be mechanical, but the mechanics have not been quantified. The aim of this dissertation was to provide insight into the pathogenesis of hip OA via finite element (FE) modeling. The objectives were two-fold: to validate a subject-specific modeling protocol for a series of specimens and assess the effects of assumptions on model predictions, and to use the modeling protocol to evaluate soft tissue mechanics in pathomorphologic hips in comparison to normal hips. For the first objective, FE predictions of contact stress and contact area were directly validated for five cadaveric specimens, and the specimen- and region-specific hyperelastic material behavior of cartilage was determined. FE predictions of contact stress and contact area were in good agreement with experimental results, and were relatively insensitive to the assumed cartilage constitutive model. There were distinct regional differences in the hyperelastic material behavior of human hip cartilage, with stiffer lateral than medial cartilage and stiffer acetabular than femoral cartilage. In order to investigate the mechanical link between pathomorphology and hip OA, FE models of ten hips with normal morphology, ten hips with acetabular dysplasia and ten hips with acetabular retroversion were generated. FE models of dysplastic acetabula demonstrated the importance of the acetabular labrum in load support in the dysplastic hip. FE models of retroverted acetabula demonstrated distinct superomedial contact patterns in comparison to distributed contact patterns in the normal hip. Finally, the effects of cartilage constitutive model on predictions of transchondral maximum shear stress and first principal strain were evaluated. In contrast to contact stress and contact area, maximum shear stress and first principal strain were sensitive to the cartilage constitutive model. Overall, this dissertation provides novel insights into the contact mechanics of pathomorphologic hips that may be important in the pathogenesis of OA, as well as the technical foundation for studies evaluating additional mechanical variables in the human hip.