Abstract:
This paper describes a significant enhancement to an existing finite element (FE) model of total hip arthroplasty (THA) dislocation by incorporating an anatomically and mechanically realistic representation of the hip joint capsule. Previous "hardware-only" models tended to underestimate in-vivo stability. To improve the model's clinical fidelity, researchers added 3D bone structures derived from CT scans and a hip capsule represented by eight distinct sectors, each meshed with hexahedral continuum elements. Each capsule sector was assigned experimentally-derived, large-deformation (hyperelastic) material properties. The model is capable of simulating complex multi-body contact, including the capsule wrapping around the implant and bone during motion. To demonstrate the capsule's contribution to biomechanical stability, the model simulated a dislocation-prone "low sit-to-stand" maneuver. The key output metric was the resisting moment generated by the hip as a function of flexion angle. In the hardware-only model, significant resistance occurred only after the implant components began to impinge. In contrast, the capsule-enhanced model showed a substantial resisting moment from the very beginning of the motion due to progressive capsule tautening. This soft-tissue resistance resulted in a 3.6-fold increase in overall construct stability and also reduced peak stresses on the implant's polyethylene liner by up to 50%. This enhanced model provides a more objective tool for studying how implant design and surgical techniques, such as the extent of capsule repair, influence the risk of dislocation.
