ASSESSMENT OF BONE-FORMATION DURING OSTEONEOGENESIS - A CANINE MODEL

Distraction osteoneogenesis, callotasis, has been demonstrated to be a n effective means of lengthening long bones. A variation of ilizarov's technique produces a transport disk from one cut surface of bone with in a defect and advances the disk to the opposite surface to close the defect. This process, previously described by Costantino et al. (Arch Otolaryngol Head Neck Surg 1990; 116:535-45), demonstrated bone forma tion within the distraction site. The precise mechanism of bone format ion has not yet been described for the mandible. Four conditioned beag les were studied, with one control dog maintained in neutral fixation and three dogs distracted at 0.25 mm every 8 hours. A two-cm defect wa s closed, and dogs were kept in fixation for 1 week after closure, aft er which they were killed. Three sites were evaluated: (1) the distrac tion seam, (2) the interface of the cortical and distracted bone, and (3) the cortexes at the closed defect. Each site was bisected, and one half was decalcified for immunohistochemical and hematoxylin and eosi n pathologic evaluation. The vascular basement membrane was labeled fo r laminin and type IV collagen. Both of these substances demonstrate t he differentiation of the vascular matrix component predisposing prima ry bone formation. Labels were intense at the distraction seam where i ntense angiogenesis occurred. No hyalin cartilage was observed at the distraction site, which indicates that the fixation was stable and tha t ossification occurred primarily without intermediate callous formati on. This model demonstrated that osteoclasts within the canine model p roduce bone through primary bone formation within an angiogenic matrix rich in basement membrane laminin and type IV collagen. Likewise, bon e is species specific in mineral composition for dog mandible, Underst anding the formation and composition of distracted bone is essential f or understanding application of this technique within the clinical set ting.