Femoral structure and stiffness in patients with femoral neck fracture

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Abstract
Bone morphological characteristics may relate to the risk of hip fracture. We applied finite element modeling to radiologic data for two groups of women in vivo to address two questions: (a) Do individuals who have just sustained a femoral neck fracture exhibit reduced three-dimensional structural stiffness? and (b) Are victims of hip fracture disproportionately more susceptible to loads sustained in a fall than to stance-type loads? Ten white women (age: 64–76 years) who had just sustained a femoral neck fracture and 18 female volunteers (age: 65–76 years), matched as groups for race, age, and body mass index, were evaluated, From quantitative computed tomography scans, femoral morphometric and volumetric cancellous density measurements were obtained and a finite element model was constructed. Two load conditions were simulated: single-stance phase and lateral fall. Global stiffness values were determined for each model. The cancellous bone density was significantly lower at the femoral neck and the femoral neck and head diameters were significantly larger in the women in the fracture group than in those in the control group. The stiffness of the proximal femur did not differ significantly between the groups for either load condition. An apparently linear relationship was found for stiffness at stance load compared with stiffness at fall load (r = 0.84, p < 0.001), and slopes did not differ significantly between the groups. Although cancellous density was reduced at the fracture site in patients with femoral neck fractures, this did not result in a reduction in the predicted bone stiffness. Previous studies have established a very strong relationship between the stiffness and strength of bone. Since these modeling methods were thoroughly validated ex vivo, we conclude that although decreased bone density at the femoral neck may predict where fracture initiates, the risk of hip fracture per se may be more strongly dependent on issues such as the risk of falling and fall biomechanics than on the structural characteristics of bone.