The factor-of-risk biomechanical approach predicts hip fracture in men and women: the Framingham Study

We examined the relation between a biomechanical measure, factor-of-risk, and hip fracture risk in 1,100 men and women from the Framingham Study and found that it predicted hip fracture (men, ORs of 1.8; women, 1.2-1.4). Alternative methods of predicting hip fracture are needed since 50% of adults who fracture do not have osteoporosis by bone mineral density (BMD) measurements. One method, factor-of-risk (I broken vertical bar), computes the ratio of force on the hip in a fall to femoral strength. We examined the relation between I broken vertical bar and hip fracture in 1,100 subjects from the Framingham Study with measured hip BMD, along with weight, height, and age, collected in 1988-1989. We estimated both peak and attenuated force applied to the hip in a sideways fall from standing height, where attenuated force incorporated cushioning effects of trochanteric soft tissue. Femoral strength was estimated from femoral neck BMD, using cadaveric femoral strength data. Sex-specific, age-adjusted survival models were used to calculate hazard ratios (HR) and 95% confidence intervals for the relation between I broken vertical bar (peak), I broken vertical bar (attenuated), and their components with hip fracture. In 425 men and 675 women (mean age, 76 years), 136 hip fractures occurred over median follow-up of 11.3 years. Factor-of-risk, I broken vertical bar, was associated with increased age-adjusted risk for hip fracture. One standard deviation increase in I broken vertical bar (peak) and I broken vertical bar (attenuated) was associated with HR of 1.88 and 1.78 in men and 1.23 and 1.41 in women, respectively. Examining components of I broken vertical bar, in women, we found fall force and soft tissue thickness were predictive of hip fracture independent of femoral strength (was estimated from BMD). Thus, both I broken vertical bar (peak) and I broken vertical bar (attenuated) predict hip fracture in men and women. These findings suggest additional studies of I broken vertical bar predicting hip fracture using direct measurements of trochanteric soft tissue.