Dentistry and Medicine: The Tempromandibular Joint (TMJ) normal anatomy and Pathology with Radiographic features

The temporomandibular joint (TMJ) is a diarthrodial joint, formed by the squamous portion of the temporal bone and the condyle of the mandible. These two osseous elements are enclosed into a fibrous capsule and articulate with each other by an interposed disc of connective tissue. The disc is fixed to the articular capsule and the lateral margins of the condyle. The joint cavity is therefore divided into an upper and a lower compartment. A synovial membrane lines the inner side of the capsule and disc, except for the articulating surfaces. Synovial fluid produced by this lining membrane fills the joint compartments.

The TMJ is responsible for all movements of the jaw, which take place in different orthogonal planes and around multiple axes of rotation. In these movements, the articular disc plays a major role in compensating the incongruities of the articular surfaces. In the mandibular opening-closing movement, for instance, the condylar head rotates and translates relative to the temporal bone with a simultaneous gliding of the disc. Several theories have been proposed to explain the mechanism that coordinates the disc-condyle complex during jaw movements.The biomechanical properties of the disc are largely involved in this coordination.

Normal Radiographic anatomy of TMJ


Normal Radiographic anatomy of TMJ

Normal Radiographic anatomy of TMJ

Internal Derangements

General orthopedic term implying a mechanical fault that interferes with the smooth action of a joint
The most common internal derangement is disc displacement

Clinical Features

Clicking sounds from joint(s)
Restricted or normal mouth opening capacity
Deviation on opening
Pain

Imaging Features

Anterior disc displacement: posterior band of the disc located anterior to the superior portion of the condyle at closed mouth on oblique sagittal images
Disc may have normal (biconcave) or deformed morphology
In opened mouth position disc may be in a normal position (“with reduction”) or continue to be displaced (“without reduction”)

Partial anterior disk displacement at baseline

Complete anterior disc displacement

Lateral disk displacement and normal bone

Medial disk displacement

Posterior disk displacement

Osteoarthritis

Definition

Non-inflammatory focal degenerative disorder of synovial joints, primarily affecting articular cartilage and sub-condylar bone; initiated by deterioration of articular soft-tissue cover and exposure of bone.

Clinical Features

Crepitation sounds from joint(s)
Restricted or normal mouth opening capacity
Pain or no pain from joint areas and/or of mastication muscles
Occasionally, joints may show inflammatory signs
Women more frequent than men

anteriorly displaced and deformed, degenerated disc and irregular cortical outline with osteophytosis and sclerosis of condyle .

Advanced osteoarthritis and anterior disc displacement, with joint effusion

Bone Marrow Abnormalities

Definition

Bone marrow edema: serum proteins within marrow interstitium surrounded by normal hematopoietic marrow.
Osteonecrosis: complete loss of hematopoietic marrow.

Imaging Features

• Abnormal signal on T2-weighted image from condyle marrow: increased signal indicates marrow edema; reduced signal indicates marrow sclerosis or fibrosis

• Combination of marrow edema signal and marrow sclerosis signal in condyle most reliable sign for histologic diagnosis of osteonecrosis

• Marrow sclerosis signal may indicate advanced osteoarthritis without osteonecrosis, or osteonecrosi