Trabecular bone volume and microdamage accumulation in the femoral heads of women with and without femoral neck fractures.

Repetitive loading causes fragility and microdamage accumulation in the skeleton, but it is not clear whether microcracks accumulate with age in the human skeleton, or whether older women with femoral neck fractures have more microdamage than older women without fracture. This study tested the hypotheses that: (1) microcracks accumulate in the femoral head with age; and (2) older women with femoral neck fractures have significantly more microcracks than similar aged women without fractures. Nonosteoarthritic femoral heads from 9 young (16-66 years) and 12 old (73-88 years) female cadavers and those from 7 females with femoral neck fractures (56-90 years) were dissected. Midfrontal slabs were block stained with 1% basic fuchsin and 150-microm-thick specimens were measured histomorphometrically. Percent trabecular bone area (TbxAr) significantly decreased in older and fractured subjects compared with young subjects (p < or = 0.05). Microcrack density (CrxDn) was significantly higher in women older than 70 years compared with those younger than 70 (p = 0.005; Spearman's r = 0.41, p = 0.032), but was not different between older women with and without fractures. Osteocyte lacunar density (OtxDn) was significantly less in old and fractured subjects compared with young subjects (p < or = 0.01), and inversely correlated to crack density (r = -0.49, p = 0.011). CrxDn was higher in women with low TbxAr (Spearman's r = -0.56; p = 0.004), and varied inversely with OtxDn (Spearman's r = -0.47; p = 0.014). This is consistent with the idea that cracks accumulate more rapidly in women with low bone density. It is also consistent with the idea that the osteocyte network detects microcracks, and signals for their repair.