Stress Analysis in Conversion Total Hip Arthroplasty: A Finite Element Analysis on Stem Length and Distal Screw Hole.

Proximal femoral fractures are particularly common in older adults, and cases requiring conversion to total hip arthroplasty may arise because of treatment failure or osteoarthritis. Fractures around the distal screw removal holes can be problematic. This study aimed to analyze the relationship between stem length and femoral stress distribution to determine the optimal stem length. A finite element analysis simulation was conducted using pre-existing femoral computed tomography data, an intramedullary nail, and three types of stems of varying lengths. Loads simulating normal walking and stair climbing were applied, and the average and maximum equivalent stresses were measured on both the medial and lateral sides of the distal screw removal hole for each stem length. Statistical analysis was then performed to evaluate the stress distributions. The average stress around the distal screw removal hole tended to decrease as stem length increased. The maximum stress was significantly lower with the 160-mm stem, which provides a 40-mm bridging length, compared to the 120-mm and 130-mm stems, where the stem tip aligned with or only slightly extended past the distal screw removal hole (bridging lengths of 0 mm and 10 mm, respectively). In conversion hip total arthroplasty following proximal femoral fractures, using a sufficiently long stem can help avoid stress concentration around the distal screw removal hole, thereby potentially reducing the risk of periprosthetic fractures.