DISTRACTION BONE HEALING

Bone formation by distraction was studied using three different experi mental models: (1) Physeal distraction of the sheep radius was perform ed in 20 animals. (2) Distraction after osteotomy of the radius was ca rried out in 39 sheep. (3) Mandibular distraction after osteotomy was performed in 17 sheep. Formation of the organic matrix and osteogenesi s were studied by radiographic, histologic, and biochemical methods as well as by electron microscopy. The mode of osteogenesis was essentia lly similar in all of these distraction models. Bone formation was pre ceded by organization of the collagenous matrix in the distraction are a. In the beginning of the distraction, the gap was composed of a hete rogenous cell population, with large polymorphic fibroblastlike cells. The cells in the central part differentiated into fibroblasts, which remained functionally active as long as distraction proceeded. During physeal distraction, bone formed from the epiphyseal and metaphyseal s ides as well as from the surrounding perichondrium. Also, in osteotomy distraction of both tubular bone and mandible, bone formed centripeta lly from the osteotomized bone ends toward the center of the gap. The organic matrix was composed almost solely of Type I collagen the earli est stages, suggesting that the mode of osteogenesis differs from bone repair by fracture callus. The structure of the distracted segment wa s mainly lamellar trabecular. Corticalization of the lengthened bone s egment occurred gradually after several months.