Hip morphology and bone mineral density are associated with hip fracture type in elderly Japanese patients

Femoral neck fractures and trochanteric fractures have distinct biomechanical mechanisms, but the anatomical determinants of fracture type remain incompletely understood. We compared proximal femoral morphology, acetabular morphology, and bone mineral density between fracture types in elderly Japanese patients and evaluated factors associated with fracture type.

This retrospective study included 194 surgically treated patients (77 trochanteric fractures and 117 femoral neck fractures) between April 2022 and March 2024. Standardized radiographs and computed tomography reconstructions aligned with the femoral neck axis were used to measure proximal femoral geometry (neck-shaft angle, femoral offset, femoral neck width, and hip axis length) and acetabular parameters (center-edge angle and Sharp angle). Height-adjusted hip axis length was calculated as hip axis length divided by body height. Areal bone mineral density was measured by dual-energy X-ray absorptiometry. Binary logistic regression was used to identify factors associated with fracture type, and receiver operating characteristic analysis was performed to evaluate discriminatory performance.

Patients with trochanteric fractures were older and shorter than those with femoral neck fractures (p = 0.006 and p = 0.031, respectively). Areal bone mineral density was significantly lower in patients with trochanteric fractures (p < 0.001). Acetabular morphology differed between groups, with greater acetabular coverage, as suggested by the center-edge and Sharp angles in trochanteric fractures. Absolute hip axis length did not differ; however, height-adjusted hip axis length was modestly but significantly greater in trochanteric fractures (p = 0.023). Other proximal femoral parameters were comparable. Receiver operating characteristic analysis demonstrated limited discriminatory ability for individual variables, whereas a combined model showed modest improvement.

These findings suggest that hip fracture type reflects the combined influence of systemic bone fragility and hip morphology. Although the discriminatory performance of individual parameters was limited, these findings may improve the mechanistic understanding of fracture patterns in elderly Japanese patients.