Study Of Open Reduction Of Sagittal Fracture Of The Mandibular Condyle With The Technique Of Reduction Screw And Lateral Screws

The incidence of sagittal fracture of the mandibular condyle (SFMC) has increased in recent years, accounting for 18–31% of all adult mandibular condylar fractures. It has been controversial what modality of treatment would get maximum benefit with good results to adult SFMC patients. The damaged structures of temporomandibular joint (TMJ) caused by trauma are difficult to be restored by closed treatment. The complications of poor functional and radiological results of TMJ and even ankylosis of the joint can often be observed in SFMC patients after closed treatment. Many complications can also occur from open reduction of SFMC. These can occur intraoperatively, for instance, hemorrhage, or postoperatively, with examples including facial nerve palsy, auriculotemporal nerve dysfunction, Frey syndrome, infection, and an unsightly scar. In addition, due to the difficulty of anatomical reduction of the fragment, the inadequate stability of internal fixation, or the technical complexity involved, the current surgical procedures treating SFMC are difficult to be widely accepted in clinic. The first stage of this study was to evaluate and compare the treatment results by clinical and radiological examinations and anatomical observation, after open reduction and internal fixation (ORIF) using the technique of a reduction screw assisting anatomical reduction of the fragment and a lateral lag screw in combine with a lateral position screw fixing the fracture, shortening as the technique of reduction screw and lateral screws, and closed treatment in SFMC sheep models. The second stage of this study were to treat SFMC patients using the technique of reduction screw and lateral screws and to evaluate treatment results by clinical and radiological examinations, on condition that the technique was practical and open treatment results using this technique were better than that of closed treatment in animal experiment.Experiment one was the creation of SFMC animal models. Eight adult sheep were cut from the lateral 1/3 of the condylar articular surface to the medial side of the condylar neck by osteotomy and were scanned by helical computed tomography (CT) preoperatively and 1 week after osteotomy. Multiplanar reconstruction (MPR) and three-dimensional reconstruction CT images were obtained to observe the position of the fracture line and the displacement of the fragment. It demonstrated that the fracture line was from the lateral 1/3 of the condylar articular surface to the medial side of the condylar neck, and the fragment displaced anteriorly, medially and inferiorly, which according with the radiological characteristics of SFMC in clinic. This animal model can be used to design and evaluate various treatment methods of SFMC.Experiment two was evaluation and comparision of treatment results after open and closed treatment of SFMC in sheep. Eight SFMC sheep models created through osteotomy were randomly divided into 2 groups. Group 1 (4 sheep) was treated by closed treatment and Group 2 (4 sheep) was treated with ORIF using the technique of reduction screw and lateral screws. Clinical and radiological examinations and anatomical observation were used to evaluate treatment results. Compared to preosteotomy, it demonstrated that there were significant decreases in maximum opening, protrusion and contralateral movement in Group 1, but there was no significant difference in range of jaw movements in Group 2, 12 weeks after treatment. The mean radiological and anatomical scores for TMJ morphological changes in Group 2 were significant less than that in Group 1 at the end of the experiment. In case of SFMC, ORIF is better than closed treatment in restoring function and morphology of TMJ and the technique of reduction screw and lateral screws is a practical treatment with ORIF in animal experiment.Experiment three was design and measurement of trajectories of lateral screws using helical CT before ORIF of SFMC. The TMJ CT data of Group 2 animals scanned at 1 week after osteotomy were imported into the software of Mimics8.1. The lengths of trajectories of lateral screws in the condylar stump and fragment respectively were measured on helical CT images. The total length of trajectory of every lateral screw was then obtained preoperatively. The total length was compared to that measured intraoperatively. Although the fragment was displaced, it demonstrated that the length of trajectories of lateral screws measured using helical CT was accuracy. There was no significant difference between the length of trajectories of lateral screws measured using helical CT preoperatively and that measured intraoperatively (P>0.05). It is helpful to choose the length of lateral screws preoperatively and drill appropriate trajectories of lateral screws accurately and prevent unnecessary injuries intraoperatively.Experiment four was simulated operation in isolated adult mandible using the technique of reduction screw and lateral screws. Eight SFMC models were created on 4 isolated adult mandibles by osteotomy. The fracture line was from the lateral 1/3 of the condylar articular surface to the medial side of the condylar neck. These SFMC models were then treated with ORIF using the technique of reduction screw and lateral screws. It demonstrated that the reduction of the fragment was good and the fixation was stable. The top of lateral screws were close to the medial side of the condylar neck, but did not go beyond the medial bone cortex. Secondary fractures did not occur intraoperatively. The position where adapted to insert a reduction screw lies in the upper 1/3 of articular surface of the condylar fragment. The position where adapted to drill the trajectory of lateral lag screw lies in the condylar neck, and the trajectory should be vertical to the fracture line. The position where adapted to drill the trajectory of lateral position screw lies in the middle of the condylar process, and the trajectory should be parallel to the lateral-medial axis of the condylar process. The technique of reduction screw screw and lateral screws is practical for simulation treatment of SFMC in isolated adult mandible.Experiment five was measurement of the length of trajectories of lateral screws in the mandibular condyle of normal people using helical CT. Sixty temporomandibular joints of 30 volunteers were scanned by helical CT and the data were imported into the software Mimics 8.1. The length of trajectories of lateral screws that adapted to be drilled in condyles of these volunteers was measured on helical CT images, according to the methods described in experiment three and four. Normal reference values of the length of trajectories of lateral screws that adapted to be drilled in case of SFMC of given people were obtained by statistic analysis. These values would be helpful for the production and selection of lateral screws for the treatment of SFMC patients.Experiment six was clinical application of the technique of reduction screw and lateral screws. The position of trajectories of lateral screws was designed and the length of the trajectories was measured on helical CT images, according to the method described in experiment three. Six unilateral SFMC patients were treated with ORIF using the technique of reduction screw and lateral screws. Radiological examination demonstrated that the reposition of the condylar fragment was good and the condylar height was restored and the position of lateral screws was satisfying in all six patients, immediately after operation. Radiological examination also showed that the condylar shape was almost normal and there was no further displacement of the fragment and screws three months after operation. Clinical examinations demonstrated that there were neither occlusal disturbances nor complications related to the surgery in all patients. The maximum mouth opening, protrusion and lateral movement of mandible were restored. Patients were satisfied with the results. The technique of reduction screw and lateral screws is an effective, relatively simple, economical, and minimally invasive ORIF for treating adult SFMC.In conclusion, animal experiment demonstrates that ORIF is more efficient than closed functional treatment in restoring the function and morphology of TMJ for SFMC. Animal experiment and clinical study demonstrate that external pterygoid muscle-condyle anatomical reduction becomes easy and practical with the help of the reduction screw inserted in the fragment and the function of external pterygoid muscle is preserved as far as possible. The combination of the lag and position screw techniques can take advantages of both techniques, simply the operation, and improve the stability of fixation of the fracture. The technique of reduction screw and lateral screws is an effective, relatively simple, economical, and minimally invasive ORIF for treating adult SFMC.