Repair of bone grafts. A vital microscopic and histological investigation in the rabbit.

Using a vital microscopic method--the titanium chamber--it has been possible for the first time to dynamically follow the healing patterns in ortotopical cancellous and cortical bone grafts. Cancellous grafts healed by an initial strong osteogenetic phase without previous resorption of pre-existing bone trabeculae. Cortical grafts occasionally also healed primarily with osteogenesis, however rapidly followd by a dominant resorptive phase. A second and much stronger osteogenetic phase followed 60 days or more after grafting. Lamellated bone was as a rule preceded by woven bone of which two different types are described. Woven bone observed before grafting became lamellated afterwards which might be taken as an indication of survival of grafted woven bone. Numerous Howships lacunae, giving the bone a wavy appearance, were seen at resorption of bone trabeculae. In dense bone creeping substitution was observed. The cutter heads moved with an estimated rate of 30--40 microns a day. The resorption canals were later replaced by new bone formation. Vascular penetration rate in a cancellous graft was calculated to maximum 0.2--0.4 mm/day and in a cortical graft in pre-existing vascular canals to maximum 0.15--0.30 mm/day. A sufficient amount of vessels--about the same vascular density as before grafting--was necessary for bone remodelling to occur.