성견 하악골 상행지 수직 골절단술후 조기 기능시의 골치유에 관한 연구

Abstract

This investigation is an experimental study of the bone healing and remodeling process after Vertical Ramus Osteotomy(abbreviated as VRO) with early mobilization in adult dogs. Nineteen dogs were divided into three groups. Normal Control Group(N=2) was free of surgery. Experimental Group I(n=5) received only VRO without any intentional movements of distal fragments, and Experimental Group II(n=12) got VRO and backward driving of distal fragments. Animals were killed serially and the operated sites were reviewed grossly and histopathologically after the plain radiographs and Magnetic Resonance Images(abbreviated as MRI) were taken. The obtained results are as follows : 1. The early bone healing after VRO occurred mainly by the fusion of endosteal and subperiosteal calluses, and osteoinduced calluses from the cortices of fragments in intramembranous bone formation process. And the cartilagmous bone formations, which were considered to be associated with early functional movements of the mandible, were evident at the Junction of these calluses. 2. The overlapping cortices of each fragment were fused by the osteoinduced calluses after decreased mobility of fragments mainly achieved by the subperiosteal calluses at the lateral and posterior part of pterygomasseteric sling. 3. Osteocytes in the cortices of fragments were dead by ischemia and the marrow tissues were predominantly replaced by fibrous tissues in early stages. Active revascularization in the cortex and formation of new bone in the marrow, seen as the cancellous bones, were observed almost simultaneously and they were maintained until the 8th week when bone unions were confirmed. 4. Morphology of the mandible was changed by remodeling of the bone with reattachments of adjacent muscles after the 8th week. Callus in the gap was changed more and more into the compact bone after the 8th week, which united the proximal and distal fragments securely. 5. Low or iso-signal intensity at the cortex of fragments in early stages of MRI was being increased from the 4th week till the 12th week after VRO. The marrow spaces had high signal intensities on the T2-weighted images in early stages, but they returned to normal T1 and T2 high signals after the 12th week. 6. Signal intensities of the interfragmentary gap were high at the early stages and were gradually decreased to low signals at the 24th week. Atrophy of the masseter muscles with the high signal spots suggesting the increased vascularity was seen from the 2nd week, but the recovery of muscular volume with disappearance of high signal spots were also observed after the 8th week. In summary, the overlapped fragments made by VRO were completely healed by true bony union in adult dogs, even though they had cortex to cortex overlapping and early mobilizations had been allowed. Development of caelluses through the intramembranous bone formation, and the cartilaginous bone formations at the union of them wre mainly involved in the early bone healing. Direct communication of the marrows of the both segments was not found in this investigation, and more advanced study will be needed to explain the details of the fate of bony union after VRO.