Functional anatomy and biomechanics of the hip joint capsule

Abstract

Joint preserving surgery seeks to correct joint pathology and prevent osteoarthritis from developing. Access to the joint is made difficult by the strong capsular ligaments which surround the joint. To perform joint preserving surgery, these ligaments must be cut to gain access. While tissue anatomy and biomechanics of the hip are well described, the chosen surgical approach continue to be debated. An understanding of the functional anatomy of the capsule is required to practice effective joint preserving surgery. This thesis investigates the functional anatomy of the hip capsule, its capacity to stabilise the hip joint, and management during hip surgery. Computational simulations were performed to quantify the stabilising contributions of the capsule. The capsule had the ability to prevent edge loading by moving the joint reaction force 0.8° inbound per Nm of internal capsular restraint in a dislocation prone position. Subsequently, a deeper understanding of the fibrous structures that comprise the capsule was characterised using a methodology that combines multi-axial testing and digital image correlation. The capsule was mechanically heterogeneous and the location and directions of 7 ligamentous structures including the zona orbicularis were detected. Following this, the effect capsular release on joint exposure and joint torque was investigated for hip resurfacing via the direct anterior approach. Adequate exposure of both proximal femur and acetabulum can be delivered with minimal torque in some cases by preserving the mid substance of the ischiofemoral ligament. This research demonstrates the protective mechanism of the capsule and its ability to maintain contact force between the femoral head and acetabulum. A deeper understanding of the fibrous network and the locations of all fibrous structures is essential for surgeons undertaking joint preserving surgery. While patient-specific factors may necessitate additional capsular releases during surgery, capsular repair is recommended during surgery to reduce adverse loading scenarios.