[Osteoclastic resorption of trabeculae in osteoporotic femoral head: a scanning electron microscopic study]

Osteoclastic resorption was studied by scanning electron microscopy on the trabeculae of femoral heads collected from 7 cases of aged women at an average age of 72.4 years, who underwent endoprosthetic replacement for intracapsular fracture of femoral neck. Femoral head trabeculae from 3 young adults killed in traffic accident served as control. The trabeculae of the femoral head formed round or roundish arch structure. The columnar trabeculae of the femoral head in the aged women showed overt osteoclastic resorption, manifesting thinning, tapering and perforation. The icicle-like trabeculae then became rounded, lost height and eventually turned into a small tubercle. As a result, the inter-trabecular space enlarged markedly. Under high magnification, on the trabeculae could be discerned oval, narrow oval or spindle-shaped Howship lacunae, which were various in size, depth and content, but all revealed punch-out edge. Around the lacunae the collagen fibril lamella normally covering the quiscient bone surface became resorbed sooner or later. During bone resorption, the inorganic component of the bone matrix were first dissolved and resorbed leaving behind rough and irregular collagen fibrils; nevertheless, the collagen might be degraded and resorbed first with residual inorganic crystals and irregular bone nodules. Then emerged in the Howship lacunae and surrounding area newly formed collagen fibrils and bone tissue, signifying reversal and new bone formation phases following the the bone resorption phase. In the aged women, however, this phenomenon was rather infrequently encountered, thereby leaving the bone turnover always in a negative balance state.