This retrospective study evaluated the potential influence of the sagittal fracture pattern and articular disc displacement on the development of temporomandibular joint (TMJ) ankylosis. 33 sagittal fractures of mandibular condyles (SFMCs) in 19 patients were treated conservatively and were divided into non-ankylosis and ankylosis groups based on their prognosis. Using computed tomography (CT) images, the SFMCs were classified into types I, II and III, and the displacement of the articular disc was investigated using magnetic resonance imaging (MRI). There were 19 (58%) SFMCs in the non-ankylosis group: 5 were type I SFMCs, which did not show any disc displacement; the other 14 were type II SFMCs, which included 5 cases without disc displacement and 9 cases with disc displacement. In the non-ankylosis group, the lateral poles were completely or incompletely covered by the discs. There were 14 (42%) SFMCs in the ankylosis group, all of which were type III SFMCs showing disc displacement, and the lateral poles in these cases were not covered by the discs. This investigation confirmed that the disc position was highly associated with the position of the fractured fragment and that some SFMC patterns, especially type III SFMCs, indicated a high risk of TMJ ankylosis.
Condylar fracture accounts for 80–98% of cases of temporomandibular joint (TMJ) ankylosis . Post-traumatic TMJ ankylosis is rare with an incidence of approximately 0.4% . The incidence of TMJ ankylosis is considered to be highly related to the severity and patterns of joint injuries, and sagittal fracture of the mandibular condyle (SFMC) is noted for its susceptibility to TMJ ankylosis . Displacement of the articular disc results in the loss of the physical impediment to transarticular bony fusion, thereby playing a key role in inducing TMJ ankylosis . Several investigations using magnetic resonance imaging (MRI) and arthroscopy have revealed the positions of the articular discs in the cases of condylar fractures . The variation in the disc position according to the sagittal fracture patterns and its relation to TMJ ankylosis has not been elucidated. In this retrospective study, the authors aimed to evaluate the potential influence of the sagittal fracture pattern and joint disc displacement on the development of TMJ ankylosis.
Materials and methods
19 patients with 33 SFMCs confirmed by computed tomography (CT) were included in this study, which was conducted from January 2004 to April 2007. 13 patients underwent the complete treatment procedure at the authors’ hospital, and 6 patients were treated conservatively for 2–12 months at other hospitals and were transferred to the authors’ hospital with a complaint of persistent limited mouth opening.
The SFMCs were initially treated using conservative procedures, including intermaxillary elastic traction for 1–2 weeks, followed by mouth-opening exercises for at least 2 months. The patients who initially visited the authors’ clinic received a duck rostra shaped, jaw dilation prop ( Fig. 1 ) and underwent physical therapy using ultrasonic waves or infrared rays with calcium or iodide infiltration to facilitate rehabilitation. The concomitant body or symphysis fractures were treated by open reduction and plate fixation.
Although all the patients cooperated with the conservative treatment, seven patients showed a serious deterioration in maximal mouth opening (range, 12–25 mm); this group included six patients who were initially treated in local hospitals and one patient who underwent initial treatment at the authors’ hospital. Surgical intervention was performed to release the supposed ‘ankylosed’ joint, and the intervention was followed by mouth-opening exercises and physical therapy. The supposed ‘ankylosed’ joints were validated by intraoperative visualization of fibrous adhesions or partial bony fusion between the lateral pole of the condyle and the lateral rim of the joint fossa. During the follow-up period (6–24 months; average, 8.7 months), all but one of the patients showed considerable improvement in mandible movement (maximal mouth opening, 30–50 mm); in the patient who did not show considerable improvement, the maximal mouth opening was 2 mm, and a second operation had to be performed to dissect the right condyle and release the left joint. The surgically repositioned disc on the right side was found to be displaced again.
On the basis of the prognosis of the conservative treatment, the patients were divided into two groups. The non-ankylosis group contained 12 patients (6 women and 6 men) with 19 SFMCs. The ages of the patients in this group ranged from 6 years to 21 years, except for one patient who was 45 years old (mean age, 15 years). 11 patients had suffered injuries due to falls, and 1 patient had suffered an injury in a traffic accident. Six patients had concomitant body or symphysis fractures. The ankylosis group contained seven patients (one woman and six men) with 14 SFMCs. In this group, three patients had suffered injuries in traffic accidents, and the rest had suffered injuries due to falls. The mean age of the patients in this group was 20 years (range 6–33 years), and all patients had sustained concomitant symphysis fractures.
In order to interpret the displacement of the fractured fragment on the coronal sections of the CT images, the SFMCs were classified into three types ( Fig. 2 ). In type I (fissure type), the medial part of the condyle split and formed a V-shaped gap between the fragment and the lateral pole of the condyle. In type II (displacement type), the fractured fragment was anteromedially displaced, and the lateral pole of the condyle was located within the fossa. In type III (dislocation type), the fractured fragment was anteromedially displaced, and the lateral pole of the condyle was laterally or superolaterally dislocated out of the fossa. In the MRI images, the disc position relative to the joint fossa in the sagittal section was visualized, and the SFMCs were classified into displacement and non-displacement groups. The cases were also classified into covered, incompletely covered, and uncovered groups on the basis of the relative position of the disc to both the fractured fragment and the lateral condyle pole.
19 (58%) SFMCs were classified into the non-ankylosis group, of which 5 (15%) were type I ( Fig. 2 A) SFMCs showing no signs of articular disc displacement ( Fig. 3 A and B ). The remaining 14 (42%) SFMCs were type II ( Fig. 2 B) SFMCs, including 5 cases with no displacement of the articular disc ( Fig. 3 C and D) and 9 cases with disc displacement ( Fig. 3 E and F). In this group, all the fractured fragments (19 cases) were superiorly covered by the articular discs. The lateral poles were completely or incompletely covered by discs on the sagittal (18 cases) and coronal planes (14 cases) ( Tables 1 and 2 ).