Reduced resorption of cortical bone in mice with induced osteopetrosis.

Two groups of syngeneic radiation chimaeras were established, the reconstitution being with spleen from osteopetrotic mice on the one hand and normal bone marrow on the other. Induced osteopetrosis in the former was evident radiologically not only as metaphyseal opacity but as unduly dense cortices compared with the latter, particularly terminally after 16-18 months. The radiological impressions were confirmed by measurement of cortical thickness in both longitudinal and transverse sections of undecalcified femoral shafts. Measurements were made with a Quantimet-720 System-30 Image Analyser. Terminally the differences were highly significant. One concludes that defective osteoclasts of osteopetrotic mice derived from haematopoietic stem cells fail to resorb not only primitive woven bone but also cortical laminar bone.