The Experimental Study Of Bone Replantation In Situ After Excessive Osteotomy Of Mandibular Angle

Objective: Prominent mandibular angle (PMA) is among the most common problems obsessing Asian females, who take an ovoid, reduced, and slender face as their aesthetic standard. With the osteotomy for prominent mandibular angle getting more and more popular in Asian countries, incidences of post-operational complications are surging rapidly. Excessive osteotomy is one of the most serious complications that are irreversible. Patients afflicted with it often demonstrate horse-like face shape, which imposes very serious disturbance on their everyday life. Sufferers have no choice but to resort to another plastic surgery. In clinical operations, we often use bone flaps deriving from mandible to reshape the mental region. After long term follow-up, we find that bone flaps are easy to form bones of adequate shape, without shifting and jolting. These results indicate that mandible, a kind of cancellous bone, is quite different from long bone in the ability as well as the pattern of bone formation. Though plastic surgeons routinely replant bone flaps in situ to recover outline of the lower face judging by their experience, there are few evidences regarding to development and outcome of these replanted bone flaps. By using the adult goat model with the replanted bone flaps in situ, we evaluated recovery results and outcome of mandibles and masseters, expecting to provide histological and imaging supports for clinical practice.Methods: We selected 13 adult goats (26 sides of the faces in total, without considering sexes) as the objects of our study. Weights range from 25 kg to 30 kg. 12 goats were randomly assigned into 3 different groups (group A, B and C, 4 goats in each group). Each left mandibular angle of every goat underwent excessive osteotomy and the bone flaps were replanted in situ after trimming. The right mandibular angles underwent the same operation coupled with fixation of kirschner wires. By using three-dimensional computer tomography (3D CT) before and after the operation, we measured multiple parameters, including the angle of each goat's mandibular angle, the width between both mandibular angles of every separate goat, and thickness of masseters. We took out specimens of group A, B, C separately at three different times (1, 2 and 3 months after operation). Then we conducted histological observations and certain measurements of these specimens. The goat left underwent a sham operation as the control. Taking clinical datas into consideration, we statistically analyzed these experimental results. Results: 1. Dynamic observations in morphology are as follows:â‘ Morphology of the bone: From group A to group C, post-operational calluses of these specimens got smaller, and the texture got stiffer. Three months after operations, the incision lines were almost invisible. Using light microscope for further observation, we could see that cartilaginous and intra-periosteal ossification co-existed in the replanted bone flaps. A large amount of fibroplasias were also found in it. We could detect obviously the transition of cartilages, from immature bone trabeculas, to mature bone trabeculas. Fibrous tissue in group B (2 months after operation) were much more than group A (1 month after operation), and in group C (3 months after operation), remodeling of the new bones was achieved successfully. Compared with the left mandibular angles, the right counterparts undergoing excessive osteotomy coupled with fixation of kirschner wires demonstrated no significant differences in histology.â‘¡Morphology of the masseters: No significant differences were observed between both masseters of a separate goat in three groups. Post-operational observations in histology indicated the atrophy of the muscle fibers, reduction of cross-section area with changes in polygon, and muscle fibers arranged in disorder. In the earlier period after operation (group A), the sarcomeres became shorter, while the length of them recovered in group B with multiple capillaries visible in it. 2. Dynamic observations by 3D CT and statistical results of the measurements: Observation results through 3D CT were in accordance with gross observations. Compared with group A (1 month after operation), incision lines of group C (3 months after operation) were almost invisible. Significant differences could be revealed in all of the parameters (the angle of each goat's mandibular angles, the width between two mandibular angles of every separate goat, and thickness of masseters).Results: In three months after being replanted in situ of the mandibular angle undergoing excessive osteotomy, bone flaps could fully heal in gross observation, 3D CT, and histology. Length of sarcomeres and thickness of masseters changed adaptively, which demonstrated the remodeling of masseters accomodating to the replanted bone flaps. Significant differences were also revealed between preoperative and postoperative angles of the mandibular angles, changes of the widths between both mandibular angles, and variations of the thickness of masseters.