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 ( pinteraction = 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.