Women and men with hip fractures have a longer femoral neck moment arm and greater impact load in a sideways fall
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In a case control study, we report that women and men with hip fractures have a longer moment arm of the force applied on the proximal femur during a sideways fall, a structural feature that may contribute to fracture risk. The impact load and its direction during a sideways fall onto the greater trochanter are partly determined by the geometry of the proximal femur. We hypothesized that the hip geometry in elderly with hip fractures produces a greater impact on the hip during a sideways fall.
We studied 41 female (77.2 ± 9.9 years) and 22 male (76.2 ± 12.1 years) patients with hip fractures and 40 female (85.7 ± 6.0 years) and 17 male (84.3 ± 10.1 years) controls. Hip geometry was analyzed on the nonfracture hip in patients and left hip in controls using dual-energy X-ray absorptiometry.
There was no difference in areal bone mineral density (aBMD), hip axis length, femoral neck axis length, or neck-shaft angle between cases and controls. However, the moment arm of the force on the hip during a sideways fall was 7.3% and 9.5% longer resulting in 5.6% and 9.1% greater moment in such a fall in female and male cases relative to their respective controls independent of height and weight (all p < 0.056). In multivariate logistic regression analysis, only the moment arm length in a sideways fall was associated with increased risk of hip fracture in females (odds ratio = 1.91, 95%CI: 1.14–3.20 for each SD increase in moment arm length of sideways fall, p = 0.02) and males (odds ratio = 2.69, 95% CI, 1.19–6.09, p = 0.01).
A longer moment arm in the sideways fall increases the resultant force applied to the hip predisposing to hip fracture.
KeywordsFracture Hip Hip axis length Moment arm length Sideways fall
Conflicts of interest
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