Optimizing Stem Length in Conversion Hip Arthroplasty: An Expanded Finite Element Analysis

Background/Objectives: Stress concentration around distal screw-removal holes confers a major risk for periprosthetic fractures following conversion total hip arthroplasty (cTHA) for intertrochanteric femoral fractures. Optimal stem-selection criteria and guidelines for cTHA can improve clinical outcomes. We determined the influence of cementless stem length on stress distribution around distal screw-removal holes. Methods: For finite element analysis, institutional data from preoperative CT scans of contralateral femurs of patients who underwent THA were used. To replicate the post-nail-removal state, we used 3D registration of Standard Triangulated Language data of the intramedullary nail as an unused material to simulate distal screw-removal holes, located 135 mm from the proximal end of the intramedullary nail. Cementless stems of 130, 140, 150, and 160 mm were individually registered using STL data, and cTHA models were constructed accordingly. Using simulations under load conditions representing normal walking and stair climbing, the mean and maximum equivalent stress values around the distal screw-removal holes were calculated. Repeated-measures ANOVA with Bonferroni correction was used for multiple comparisons. Results: Compared to the 130-mm stem, the 150-mm and 160-mm stems similarly reduced the maximum equivalent stress around distal screw-removal holes, although the 140-mm stem showed no significant difference with other stems. Conclusions: A ≥150-mm stem length reliably mitigates stress concentration around distal screw-removal holes post-cTHA, is the optimal choice for balancing effectiveness and risk of complications, and may contribute to improved long-term clinical outcomes. This study provides practical evidence for stem selection in cTHA and offers valuable insights for future treatment guidelines.