Women and men with hip fractures have a longer femoral neck moment arm and greater impact load in a sideways fall

Osteoporos Int. 2009 Jul;20(7):1151-6. doi: 10.1007/s00198-008-0768-y. Epub 2008 Oct 18.


Introduction: 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.

Methods: 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.

Results: 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).

Conclusions: A longer moment arm in the sideways fall increases the resultant force applied to the hip predisposing to hip fracture.

MeSH terms

  • Absorptiometry, Photon / methods
  • Accidental Falls*
  • Aged
  • Aged, 80 and over
  • Biomechanical Phenomena
  • Bone Density
  • Bone Diseases, Metabolic / epidemiology
  • Case-Control Studies
  • Female
  • Femur / anatomy & histology
  • Femur / diagnostic imaging
  • Femur Neck / anatomy & histology*
  • Femur Neck / diagnostic imaging
  • Hip Fractures / etiology
  • Hip Fractures / pathology*
  • Hip Joint / anatomy & histology*
  • Hip Joint / diagnostic imaging
  • Humans
  • Male
  • Middle Aged
  • Osteoporosis / epidemiology
  • Pelvic Bones / anatomy & histology
  • Pelvic Bones / diagnostic imaging
  • Pressure / adverse effects
  • Risk Factors
  • Stress, Mechanical
  • Victoria / epidemiology