Intracapsular hip fracture and the region-specific loss of cortical bone: Analysis by peripheral quantitative computed tomography

Generalized bone loss within the femoral neck accounts for only 15% of the increase in intracapsular hip fracture risk between the ages of 60 and 80 y ears. Conventional histology has shown that there is no difference in cance llous bone area between cases of intracapsular fracture and age and sex-mat ched controls. Rather, a loss of cortical bone thickness and increased poro sity is the key feature with the greatest change occurring in those regions maximally loaded during a fall (the inferoanterior [IA] to superoposterior [SP] axis). We have now reexamined this finding using peripheral quantitat ive computed tomography (pQCT) to analyze cortical and cancellous bone area s, density, and mass in a different set of ex vivo biopsy specimens from ca ses of intracapsular hip fracture (female, n = 16, aged 69-92 years) and po stmortem specimens (female, n = 15, aged 58-95 years; male, n = 11, aged 56 -86 years). Within-neck location was standardized by using locations at whi ch the ratio of maximum to minimum external diameters was 1.4 and at more p roximal locations. Cortical widths were analyzed using 72 radial profiles f rom the center of area of each of the gray level images using a full-width/ half-maximum algorithm. In both male and female controls, cancellous bone m ass increased toward the femoral head and the rate of change was gender ind ependent. Cancellous bone mass was similar in cases and controls at all loc ations. Overall, cortical bone mass was significantly lower in the fracture cases (by 25%; p < 0.001) because of significant reductions in both estima ted cortical area and density. These differences persisted at locations tha t are more proximal. The mean cortical width in the cases was significantly lower in the IA (22.2%;p = 0.002) and inferior regions (19%;p < 0.001), Th e SP region was the thinnest in both cases and controls. These data confirm that a key feature in the etiology of intracapsular hip fracture is the si te-specific loss of cortical bone, which is concentrated in those regions m aximally loaded during a fall on the greater trochanter. An important impli cation of this work is that the pathogenesis of bone loss leading to hip fr acture must be by a mechanism that varies in its effect according to locati on within the femoral neck. Key candidate mechanisms would include those in volving locally reduced mechanical loading. This study also suggests that t he development of noninvasive methodologies for analyzing the thickness and estimated densities of critical cortical regions of the femoral neck could improve detection of those at risk of hip fracture.