Osteopetrosis complicated with femoral subtrochanteric pathological fracture with numerous microcracks observed in the femoral cortex: A case report

The histopathology of osteopetrosis, a dysfunction of osteoclasts, remains unknown. We surveyed the histopathology of a case of late-onset osteopetrosis using bone histomorphometry. A 77-year-old man sustained a left pathological femoral fracture in the subtrochanteric site after a fall from the standing position. Based on plain radiographic findings, the patient was diagnosed with autosomal-dominant late-onset osteopetrosis. After open reduction and internal fixation, late surgical-site infection occurred at 8 weeks postoperatively. The femoral head was resected through the subtrochanteric site to reduce the infection. Numerous bulk staining-positive microcracks were detected in the cortical bone from the resected specimen. Osteopetrosis was speculated to cause osteoclast dysfunction by inhibiting bone remodeling in the osteon of the cortical bone at the fracture site. Furthermore, osteocytes could not function as a repair system for microcracks, resulting in the retention of numerous microcracks. This phenomenon may have induced pathological fracture.