Temporomandibular joint ankylosis (TMJA) can cause severe functional impairment and facial deformity. Condylar fractures, the main cause of TMJA, account for about 69% to 74% in mainland China[ 1, 2 ] , and about 80% to 98% in other high-prevalence regions of the world[ 3, 4 ] .The postoperative recurrence rate of TMJA is about 6% to 8%[ 325 ] . The conditions of formation, mechanisms of occurrence and developmental course of traumatic TMJA have not really been revealed; the principles and methods of treatment are also not uniform. Zhang Yi, Department of Maxillofacial Surgery, Peking University Oral Hospital, Beijing, China Condylar fractures are more common in clinical practice, while only about 014% of condylar fractures occur tonic. There are many different types of condylar fractures, and the results of the study show that sagittal fractures and comminuted fractures are the most likely types of fractures with secondary articular ankylosis. In the past, the diagnosis of ankylosis was based on the clinical manifestation of severe restriction of opening [opening < (10-15) mm] and the formation of ankylosed bone in the joint on radiographs. At this point, the ankylosis has entered the type II and III stage, and joint resection is inevitable. Type I ankylosis is histologically fibrous ankylosis; the clinical diagnosis is mainly based on the history of joint injury and persistent and unimproved restriction of opening. However, the need for surgical intervention is an undetermined issue. In our opinion, in sagittal and comminuted condylar fractures, surgical intervention should be performed at the earliest possible time when the displaced disc is confirmed by MRI and the opening is limited after conservative treatment and the opening is < 20 mm for 4 to 5 months without improvement. Unlike the treatment of old fractures of the condyle, the surgical objective of early ankylosis is to release the adherent joint and reset the articular disc. The latter is particularly important. The formation of traumatic TMJA is the result of a "dysregulated over-repair" of the injury by the body. In type II ankylosis surgery, it has been observed that early ankylotic bridges appear in areas without articular discs, and that disc displacement plays an important role in the formation of ankylosis. It has been confirmed that once the ossification mechanism of the joint is activated, the opening training can only slow down the ankylosis process, but not stop it. In the present study, the long-term restriction of opening caused by unilateral joint type IV ankylosis did not lead to joint ankylosis on the healthy side. This suggests that joint braking is not a single condition for the development of joint ankylosis. The treatment outcome of traumatic TMJA is closely related to the degree of destruction and recovery of joint structures. In early-stage ankylosis (types I and II), the joint disc is structurally intact and can be repositioned, and it is not necessary to remove the whole joint in the process of joint release. In the past, the diagnosis of ankylosis was often delayed based on the formation of ankylosed bones on X-ray, and there are no reports that the development of ankylosis can be terminated automatically. When ankylosis progresses to type III or IV, it not only causes more serious functional impairment and facial deformity, but also complicates the treatment and has a higher recurrence rate after surgery. Therefore, early diagnosis of traumatic TMJA for early implementation of interventional treatment is of great clinical importance to improve the outcome.