Risk factors for hip fracture in women with high BMD: EPIDOS study

Hip fractures are common among older women. At the present time, major efforts are being made to identify women with low bone mineral density (BMD). However, more than half of hip fractures occur in women who would not classically be considered osteoporotic by BMD. This study aimed to identify factors associated with hip fracture in women with high BMDs. A total of 7598 French women aged over 74 participated in the EPIDOS study and had BMD measured by dual energy X-ray absorptiometry. Analysis was carried out comparing women with and without hip fractures over more than 3 years of follow-up. The participants were divided into three groups based on femoral neck BMD, so as to have equal numbers in each group (cut-off points=0.601 g/cm², and 0.683 g/cm²). Multiple risk factors thought to be associated with hip fracture were tested in the high and low BMD groups to search for those whose effect was stronger in the high BMD group. Age adjusted Cox regression was used. Results for continuous variables are reported per standard deviation change. Positive interaction between higher BMD, hip fracture and the following factors were found: age (P<0.01), ultrasound attenuation (P<0.05), urinary deoxypyridinoline (DPD) (P<0.05), left quadriceps strength (P<0.05) and right and left foot coordination (P<0.05). The following factors had a larger hazards ratio in those in the upper third of BMD than the low and were statistically significant: femoral neck BMD, nulliparity, age, ultrasound attenuation and speed, prior fracture, urinary deoxypyridinoline, left grip strength and foot coordination. Multiple factors appear to be more strongly associated with hip fractures in women with high BMD than low. They appear to cluster as factors that may relate to bone turnover and architecture and others which are more subtle measures of left-sided coordination.