Femoral structure and stiffness in patients with femoral neck fracture

Bone morphological characteristics may relate to the risk of hip fracture. We applied finite element modeling to radiologic data for two groups of wom en in vivo to address two questions: (a) Do individuals who have just susta ined a femoral neck fracture exhibit reduced three-dimensional structural s tiffness? and (b) Are victims of hip fracture disproportionately more susce ptible to loads sustained in a fall than to stance-type loads? Ten white wo men (age: 64-76 years) who had just sustained a femoral neck fracture and 1 8 female volunteers (age: 65-76 years), matched as groups for race, age, an d body mass index, were evaluated. From quantitative computed tomography sc ans, femoral morphometric and volumetric cancellous density measurements we re obtained and a finite element model was constructed. Two load conditions were simulated: single-stance phase and lateral fall. Global stiffness val ues were determined for each model. The cancellous bone density was signifi cantly lower at the femoral neck and the femoral neck and head diameters we re 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 sign ificantly between the groups for either load condition. An apparently linea r relationship was found for stiffness at stance load compared with stiffne ss at fall load (r = 0.84, p < 0.001), and slopes did not differ significan tly between the groups. Although cancellous density was reduced at the frac ture site in patients with femoral neck fractures, this did not result in a reduction in the pre dieted bone stiffness. Previous studies have establis hed 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 de pendent on issues such as the risk of falling and fall biomechanics than on the structural characteristics of bone.