Adjusting Hip Fracture Probability in Men and Women Using Hip Axis Length: the Manitoba Bone Density Database

Most studies report that longer hip axis length (HAL) is associated with increased hip fracture risk in women, but comparable data in men are sparse. Using a registry of all dual-energy X-ray absorptiometry (DXA) results for Manitoba, Canada, we identified 4738 men and 50,420 women aged 40 yr and older with baseline hip DXA results, HAL measurements, and Fracture Risk Assessment Tool (FRAX) hip fracture probability computed with femoral neck bone mineral density (BMD). Population-based health service records were assessed for a subsequent hospitalization with a primary diagnosis of hip fracture. During mean 6.2 yr of follow-up, 70 men and 1020 women developed incident hip fractures. Mean HAL was significantly greater in those with vs without incident hip fractures (men 123.0 ± 7.6 vs 121.3 ± 7.4 mm, p = 0.050; women 106.9 ± 6.2 vs 104.6 ± 6.2 mm, p < 0.001). When adjusted for age and femoral neck BMD, each millimeter increase in HAL increased hip fracture risk by 3.6% in men (p = 0.022) and 4.6% in women (p < 0.001); this association was unaffected by sex (p value for interaction = 0.477). When adjusted for log-transformed FRAX hip fracture probability, each millimeter increase in HAL increased hip fracture risk by 3.4% in men (p = 0.031) and 4.8% in women (p < 0.001); this association was again unaffected by sex (p interaction = 0.409). A bilinear adjustment applicable to both men and women was developed: relative increase in hip fracture probability 4.7% for every millimeter that HAL is above the sex-specific average, relative decrease in hip fracture probability 3.8% for every millimeter that HAL is below the sex-specific average. We concluded that greater DXA-derived HAL is associated with increased incident hip fracture risk in both men and women, and this risk is independent of BMD and FRAX probability.