Histological evaluation of human bone tissue one year after distraction.

Distraction osteogenesis is a technique of bone lengthening and remodelling. It has become increasingly popular after 1992 when McCarty showed first cases of hypoplastic mandibles treated in this way. Authors report the histological results of the biopsy of osteogenic tissue obtained one year after distraction of the mandible performed in a young patient suffering from bilateral congenital anchilosis of the ATM, with microgenia and II Class sec. Angle, 1st Div. malocclusion. Biopsy included the distracted area and an adjacent part of the original bone. The specimen was cut in order to obtain a three-dimentional inspection of the regenerated bone in the direction of its distraction. Main results are reported. In the upper (crestal) margin and along the buccal and lingual surface, a cortical layer has been formed. The inner portion of the newly formed bone consists of cancellous bone, with interdigitating, mostly plate-like trabeculae. The density of the cancellous bone increases from the distal and mesial ends towards the center of the distracted area, and at the same time the bone architecture becomes more irregular. This indicates, that the structure of the bone formed in the earlier period of distraction is more determined by the tensile forces and becomes more randomly oriented in the later stages of the procedures. In the perifery, the trabeculae consist of a central core of initially formed bone. This core includes strands of dence fibrous tissue that are incorporated into the newly formed bone. These strands can be traced to the junction between old and new bone, where they are anchored in a broad cement line at the junction between the two bone matrixs. Ongoing, trabecular remodeling replaces this more primitive matrix compartment by mature lamellar bone. In the middle zone, the architecture of the new bone becomes more irregular, and the tissue has not fully matured jet. This is suggested by the presence of some fibrocartilaginous islands, fully surrounded by bone. Most of the fibrocartilage is already calcified or undergoes mineralization, and will soon be substituted by bone via endochondral ossification. It has to be stressed, however, that bone union is obtained in all the sections examined. The remodelling activity too is higher in the center of the distracted area and results in a continous substitution by mature lamellar bone. All these activities are accompanied by a rich vascularization, and are also reflected by numerous osteoclastic resorption and concomitant formation sites, as indicated by numerous osteoblast, osteoid seams and freshly mineralized bone. In summary, histological examinations confirms that both the quantity, as well the quality of the bone formed in the distracted area has reached a density and degree of maturation that should allow full weight-bearing.