Evaluation of early pelvic Fracture risk after rotational acetabular osteotomy: Finite element analysis of pelvic stress distribution

Background: This study evaluated stress distribution across the entire pelvis following rotational acetabular osteotomy (RAO) for osteoarthritis secondary to acetabular dysplasia using finite element analysis (FEA). Additionally, we aimed to elucidate the mechanisms underlying postoperative posterior column and inferior pubic ramus fractures, which are recognized complications of RAO. Methods: FEA was conducted based on the computed tomography (CT) images of a 26-year-old female patient who developed a posterior column fracture following RAO. Three pelvic models were constructed: preoperative, immediately postoperative, and 1 year postoperatively, in which osseous union was achieved between the rotated fragment and the ilium; however, the osteotomy site at the superior pubic ramus resulted in nonunion. Additionally, a Union model, simulating the continuity of the superior pubic ramus in both postoperative stages, was created for comparison with the Nonunion model. A load of 500 N was applied in a sitting position, with the von Mises stress distribution and element failure patterns analyzed. Results: In the Nonunion model, von Mises stress at the inferior pubic ramus was approximately 3.6 times higher immediately after surgery than preoperatively (43.0 MPa) and approximately 2.6 times higher than in the Union model. Similarly, the stress in the posterior column increased approximately 5.1-fold (53.9 MPa) immediately postoperatively in the Nonunion model, which was approximately 3.2 times higher (34.2 MPa) than in the Union model. Furthermore, element failure was observed in areas where stress exceeded 30 MPa, with a high incidence of failure in the immediate postoperative Nonunion model. Conclusion: Early post-RAO fractures of the posterior column and inferior pubic ramus are significantly influenced by the continuity of the superior pubic ramus. Notably, even before weight-bearing begins, the presence of a gap at the pubic osteotomy site immediately after RAO may substantially elevate fracture risk.