Applied anatomy of the temporomandibular joint
The temporomandibular joint (TMJ) is sited at the base of the skull and formed by parts of the mandible and the temporal bone, separated by an intra-articular meniscus. It is a synovial joint capable of both hinge (rotation) and sliding (translatory) movements. Like other synovial joints, it may be affected by internal derangement, inflammatory arthritis, arthrosis, and muscular disorders.
Bones
The mandible has a horizontal part (the body) and a vertical part (the ramus). They meet at the mandibular angle. The cranial end of the ramus has two processes: anteriorly the coronoid process and posteriorly the condylar process, which has a head on top and a distinct neck below. The squamous portion of the temporal bone contains the articular surface with a concave articular fossa posteriorly and a convex articular tubercle anteriorly. The articular surface is about three times as large as that of the mandibular head and is covered with fibrocartilage which continues anteriorly into the articular tubercle, the posterior aspect of which is the most important part of the joint. From the temporal bone develops a zygomatic process which, together with the temporal process of the zygomatic bone, forms the zygomatic arch (Fig. 1).
Fig 1 Osseous structures of the temporomandibular joint: 1, mandibular head (condylar process); 2, neck of mandible; 3, ramus; 4, body; 5, coronoid process; 6, mandibular angle; 7, zygomatic arch.
The midline fusion of the left and right mandibular bodies provides a connection between the two temporomandibular joints, so that movement in one joint always influences the opposite one.
Joint capsule and ligaments
The joint capsule is wide and loose on the upper aspect around the mandibular fossa. Distally, it diminishes in a funnel shaped manner to become attached to the mandibular neck (Fig. 2). Its laxity prevents rupture even after dislocation.
Fig 2 The joint capsule and the intra-articular meniscus: 1, condylar process; 2, mandible; 3 meniscus; 4, joint capsule; 5, articular fossa; 6, articular tubercle.
