The development of traumatic temporomandibular joint bony ankylosis: a course similar to the hypertrophic nonunion?

The traumatic temporomandibular joint (TMJ) bony ankylosis has generated great interest in the cranio-maxillofacial surgeons yet remains an enigma, due to its unknown pathogenesis. Organization and ossification of hematoma is the classical hypothesis concerning the underlying pathophysiology, but it could not explain all the unique characters of TMJ bony ankylosis. The previous imaging descriptions about bony ankylosis tend to over-emphasize the obliteration of joint space and the overgrowth of new bone around the joint. Our recent study has found that the radiolucent zone in the bony fusion area indicating impaired bone healing is one of the most important imaging features of bony ankylosis, and this imaging feature is similar to that of hypertrophic nonunion of long bone. We also observe that there is close relationship between the mouth opening and the degree of calcification of radiolucent zone. Therefore, we hypothesize that the development of traumatic TMJ bony ankylosis may be the course of bone healing of two injured articular surfaces under the interference of opening movement, which is similar to the hypertrophic nonunion. Our hypothesis could help to explain some unintelligible characters of bony ankylosis, and deserves further studies.