Microdamage accumulation in the femoral head and its association with subchondral insufficiency fractures: A retrospective study.

Introduction: Subchondral insufficiency fracture (SIF) of the femoral head typically occurs in older adults with compromised bone quality and often progresses to rapidly destructive coxarthropathy. However, the etiology of SIF remains poorly understood. We examined associations among spinopelvic alignment, pelvic tilt, and microdamage accumulation in the femoral head in patients with SIF compared with osteoarthritis (OA) secondary to hip dysplasia and cadaveric controls. Materials and methods: We analyzed eight SIF patients, ten OA patients, and nine cadaveric controls. All patients underwent total hip arthroplasty. Radiological evaluation included lumbar lordosis angle (LLA), sacral slope (SS), and pelvic tilt angles (PA) in standing and supine positions. Histomorphological assessment focused on a 5 × 5-mm cancellous bone area beneath the joint surface. Results: The SIF group exhibited significantly lower LLA and SS, as well as a greater difference between standing and supine PA compared with the OA group, indicating increased posterior pelvic tilt. Histomorphologic analysis revealed reduced trabecular bone volume and greater crack length in SIF compared with OA. Crack surface density was significantly higher in both SIF and OA groups than in controls. Conclusion: SIF patients demonstrated greater posterior pelvic tilt and lower LLA compared with OA. Histologically, SIF showed lower trabecular bone volume and longer microcracks. These data suggest the nature of the microdamage, not just the amount of the microdamage, is important to skeletal fragility. Our findings underscore the importance of assessing both spinopelvic alignment and bone quality when evaluating patients at risk for SIF.