Musculoskeletal Imaging

Subluxation

a partial loss of contact between two bones surfaces in a joint that normally articulate. This abnormality is less severe than a dislocation, in which loss of contact is complete. Whether or not dislocations and subluxations form a continuum of injury or are discrete entities remains unclear. A diastasis is present when the separation involves a joint that is normally only slightly movable.

Subluxations may be closed or open; in a closed subluxation the skin and soft tissues remain intact, whereas in an open subluxation the joint is exposed to the outside environment. In many cases a subluxation is related to a fracture of a neighboring bone.

Causes include trauma, congenital or acquired muscular imbalances (neurologic disorders), seizures and diseases producing instability due to incongruities in the joint surface (as in rheumatoid arthritis).

Although numerous joints may undergo subluxation, certain sites merit specific mention, especially the atlanto axial joints (Fig.1), acromioclavicular joint, glenohumeral joint, interphalangeal joint, elbow, hip (developmental dysplasia of the hip DDH ), knee (including congenital subluxation and hyperextension of the knee), odontoid process, patella and subaxial joints.

Subluxation of the tendon of the long head of the biceps brachii muscle may also occur, sometimes as an isolated lesion but usually with massive tears of the rotator cuff (Fig.2). Other tendons, such as the peroneal tendons, may also subluxate, and similar abnormalities may even affect nerves (e.g. the ulnar nerve at the elbow).

DR/RB

To view high resolution images,
please register first.

Click  here to register.

Already registered? Enter your e-mail in the window below.
Re-register

Fig.1

Lateral extension (a) and flexion (b) radiographs of the cervical spine in a patient with rheumatoid arthritis demonstrate anterior subluxation of the atlas relative to the axis during flexion.
Subluxation, Fig.1 (a)
Subluxation, Fig.1 (b)
Subluxation, Fig.2 (a)
Subluxation, Fig.2 (b)