Structure of the femoral neck in hip fracture: Cortical bone loss in the inferoanterior to superoposterior axis

Although bone mass is a contributory risk factor for hip fracture, its dist ribution about the femoral neck is also important, Femoral neck biopsies we re obtained from 13 females with intracapsular hip fracture (fracture: mean age 74.3 +/- 2.3 years [SEM]) and 19 cadaveric samples (control: 9 males a nd 10 females 79.4 +/- 1.7 years) and the areas of cortical and cancellous bone were quantitated in octants, In the control group, although males had larger bones than females, the proportions of cortical and cancellous bone were not different (p > 0.05) between the genders, The total amount of bone , as a proportion of bone + marrow, was significantly reduced in the fractu res compared with the female controls (%Tt.Ar: fracture 27.83 +/- 1.18, fem ale control 33.62 +/- 1.47; p = 0.0054), Reductions in cortical bone area o ccurred in all regions but particularly in the inferior, inferoanterior, an d anterior octants (p < 0.05), There were no differences between cases and controls in the regional amount of cancellous bone (all regions, p > 0.178) , Marked reductions in mean cortical bone width between the fracture and fe male control group occurred in the anterior, inferoanterior (31%), and supe roposterior (25%) regions. Representing cortical widths as simple Fourier f unctions of the angle about the center of area (R(2)adj = 0.79) showed in t he cases that there was preservation of the cortical bone in the inferior r egion, with the proportional loss of cortical bone being greatest in the in feroanterior and superoposterior regions. It is concluded that loss of cort ical, rather than cancellous, bone predominates in cases of femoral neck fr acture. This loss occurs primarily along the inferoanterior to superoposter ior axis. As this axis bears the greatest strain during a fall, it is hypot hesized that specific thinning of the cortex in these regions leads to an e xaggerated propensity to fracture in those so affected, above that resultin g from an equivalent general decrease in bone mass.