Optimising stem selection for conversion total hip arthroplasty following femoral trochanteric fracture surgery: an exploratory study using thermoelastic stress analysis

PURPOSE: To evaluate the effect of the stem length on femoral stress distribution, using thermoelastic stress analysis (TSA) to provide insights into optimal stem selection for conversion to total hip arthroplasty (cTHA) following femoral trochanteric fracture. METHODS: 6 simulated femurs were prepared via intramedullary nailing followed by implant removal to construct a post-explantation model. A screw hole was replicated 135 mm distal to the apex of the greater trochanter. Following femoral neck osteotomy, cTHA models were constructed using either a quadrangular taper collared standard or long stem. TSA was conducted under vertical loading, measuring the maximum change in the sum of principal stresses around the screw hole. The stress-reducing effects of both stems were compared using the Wilcoxon signed-rank test. RESULTS: Maximum stress around the screw hole decreased after stem insertion, with a greater reduction in the long stem group. The median maximum stress at the distal screw hole measured 11.2 and 8.42 MPa laterally and -14.6 and -12.3 MPa medially for the standard and long stem, respectively. The long stem significantly reduced stress in both regions. CONCLUSIONS: Stem insertion alleviated stress concentration, with long stem offering greater relief. The long stem effectively redistributed stress, providing valuable insights for optimising stem selection and reducing postoperative fracture risk.