Bone fractures only when it is loaded beyond its strength. The purpose of this study was to determine the association of femoral strength, as estimated by finite element (FE) analysis of DXA scans, with incident hip fracture. This prospective case-cohort study included a random sample of 500 men and 170 incident hip fracture cases (16 in the random sample) during a mean±SD follow-up of 7.7±2.2 yrs from the MrOS study (n=5957 community-dwelling men ≧65 yr of age). We analyzed the baseline DXA scans of the hip using a validated plane-stress, linear-elastic FE model of the proximal femur and derived the femoral strength during a sideways fall. We derived an estimated strength intervention threshold of 4263 N corresponding to the FN BMD T-score=−2.5. Cox regression accounting for the case-cohort design assessed the association of the femoral strength with hip fracture. Compared with the non-fracture group, the intra- and extra-capsular fracture (IC and EC) groups had significantly (p<0.0001) lower FN BMD (0.79±0.12 v. IC 0.67±0.11 & EC 0.65±0.10 g/cm2), TR BMD (0.76±0.12 v. 0.68±0.11 & 0.62±0.10) and TH BMD (0.96±0.13 v. 0.84±0.13 & 0.79±0.11) as well as FE strength (5704±1175 v. 4658±935 & 4726±1048 N). The FE strength was significantly (P<0.05) associated with both IC and EC fractures, the age-BMI-adjusted hazard ratio (HR) per SD decrease of the FE strength was 3.49 (95% CI 2.305.31) and 3.25 (1.925.52) for IC and EC fracture, respectively. The association was still significant (p<0.05) for IC fractures after further adjustment for FN, TR and TH BMDs, the HR being 1.93 (1.173.20), 3.01 (1.924.73) and 2.41 (95% CI 1.533.79) respectively. The association with IC fracture was as strong as FN BMD (Harrells C index for the strength 0.79 v. FN BMD 0.79) and stronger than TR and TH BMDs (0.76 and 0.78). Sensitivities (specificities) for IC fracture prediction were higher with the strength threshold than the FN BMD T-score threshold: 0.36 (0.92) v. 0.29 (0.96), whereas using either of both thresholds improved prediction further (sensitivity 0.45, specificity 0.90). This is the first time that an estimate of strength from DXA has been used to predict hip fracture in men and the results suggest that the strength estimate provides predictive ability for IC fracture in addition to hip BMD but not for EC fracture in older men.
Disclosure: The authors declared no competing interests. This analysis was supported by the Arthritis Research UK The MrOS Study is supported by National Institutes of Health funding under the following grant numbers: U01 AR45580, U01 AR45614, U01 AR45632, U01 AR45647, U01 AR45654, U01 AR45583, U01 AR052234, U01 AG18197, U01 AG027810, and UL1 RR024140.