Arthritis & Rheumatism, Volume 60,
October 2009 Abstract Supplement

The 2009 ACR/ARHP Annual Scientific Meeting
Philadelphia October 16-21, 2009.


A Biomechanical Approach Predicts Hip Fracture Independent of Bone Mineral Density (BMD) in Women: The Framingham Osteoporosis Study

Dufour1,  Alyssa B., Roberts2,  Benjamin, Kiel3,  Douglas P., Bouxsein2,  Mary L., Hannan3,  Marian T.

IFAR, Boston, MA
BIDMC, Boston, MA
Hebrew SeniorLife & Harvard Medical School, Boston, MA

Purpose:

Hip fractures are disabling events for older persons. Studies have identified low BMD as a major risk factor, yet up to half of those suffering a hip fracture do not have low BMD; thus, alternative methods of assessing fracture risk are needed. One such method is the biomechanical Factor-of-Risk (F), defined as the ratio of force applied to the hip from a sideways fall to femoral bone strength. We examined the relation between F and risk of hip fracture in men and women of the population-based Framingham Study.

Method:

Subjects included 1100 Framingham Original Cohort members who had hip BMD scans (LUNAR DPA) in 1988–89 (baseline). Body weight, height (used to calculate BMI (kg/m2)) and age were measured at baseline. Incident hip fractures were ascertained and confirmed by interview and review of medical records through 12/31/05. We calculated F in two ways: using the ratio of either the estimated peak force or the attenuated (atten) force applied to the hip in a sideways fall from standing height divided by the femoral strength. Peak force (N) was calculated from height (m) and weight (kg). The attenuated force incorporated the cushioning effect of trochanteric soft tissue thickness (mm), as estimated by BMI, using published sex-specific regressions. Femoral strength (N) was estimated from femoral neck BMD, using a relation derived from published cadaveric femoral strength testing. Sex-specific crude, age- and BMD-adjusted Cox Proportional Hazards regressions were used to calculate hazard ratios (HR) and 95% confidence intervals (CI) for the relation between hip fracture risk and both Fpeak and Fatten.

Results:

In the 425 men and 675 women (mean age 76 yrs) mean BMI was 26.8 kg/m2. Median follow-up was 11.3 yrs and 155 hip fractures occurred (28 in men). Fpeak and Fatten were associated with increased risk of hip fracture, adjusting for age (Table). A 1 SD increase in Fpeak was associated with a HR of 1.88 in men and 1.23 in women. Similarly, for Fatten, the HR for hip fracture was 1.78 in men and 1.41 in women. After adding BMD to the model, Fatten remained predictive of hip fracture in women. In men, we could not adjust for BMD due to collinearity with F.

Conclusion:

In summary, both Fpeak and Fatten predict subsequent hip fracture in men and women. In women, we showed for the first time that Fatten predicts hip fracture independent of hip BMD. These findings provide strong rationale for additional studies testing the ability of this biomechanical approach to predict hip fracture.

Table. Adjusted hip fracture hazard ratios (95% CI) in men and women for a 1 standard deviation (SD) increase.

ModelMenWomen
Age-adjusted  
Factor-of-Riskpeak1.88 (1.38, 2.55)1.23 (1.10, 1.37)
Factor-of-Riskattenuated1.78 (1.30, 2.44)1.41 (1.26,1.58)
Age- and BMD-adjusted  
Factor-of-Riskpeak–*0.80 (0.51, 1.27)
Factor-of-Riskattenuated–*1.20 (1.01, 1.41)
* In men, Factor-of-Riskpeak and Factor-of-Riskattenuated were collinear with BMD. Therefore, we were unable to examine this association.

To cite this abstract, please use the following information:
Dufour, Alyssa B., Roberts, Benjamin, Kiel, Douglas P., Bouxsein, Mary L., Hannan, Marian T.; A Biomechanical Approach Predicts Hip Fracture Independent of Bone Mineral Density (BMD) in Women: The Framingham Osteoporosis Study [abstract]. Arthritis Rheum 2009;60 Suppl 10 :558
DOI: 10.1002/art.25638

Abstract Supplement

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