Temporomandibular joint (TMJ) ankylosis is a disease that severely affects the human health. Although it is well known that trauma is the most common cause of TMJ ankylosis, the mechanisms by which the traumatic TMJ ankylosis develops are unclear. The existing hypothesis is not convincing in explaining the genesis of traumatic TMJ ankylosis. We make a hypothesis that the distraction osteogenesis (DO) of the lateral pterygoid muscle combining with the dislocated and damaged disc is an important factor in genesis of traumatic TMJ ankylosis. If this hypothesis is verified, it will be helpful for the prevention of traumatic TMJ ankylosis and change the principle of management of sagittal fracture of mandibular condyle (SFMC).