Apophyseal joint

the articulations between the articular facets of adjacent vertebrae, also known as facet joints. The apophyseal joints have thin and loose articular capsules as well as a synovial membrane and menisci. Also, see facet joint.

2. Pathology

These joints are a frequent site of degenerative (osteoarthritis), spondylitic and traumatic diseases. In osteoarthritis, fibrillation and erosion of articular cartilage lead to partial or complete denudation of the cartilaginous surface, bone eburnation, formation of osteophytes, and radiographically detectable joint space narrowing. As a result of capsular laxity, the vertebrae may become malaligned and subluxed (termed degenerative spondylolisthesis or pseudospondylolisthesis). CT and MR imaging are the methods of choice in evaluating degenerative disease of the apophyseal joints.

Lumbar facet joint degeneration can be divided into five stages and is a significant cause of local or radiating pain (facet syndrome). Stage 1, synovitis, is marked by hyperaemia and an inflammatory cell infiltrate within the synovium and apophyseal joint capsule. CT scanning and MR imaging cannot reliably detect inflammation confined to the narrow capsule. Stage 2, laxity of the capsule, may lead to the formation of a vacuum phenomenon. In stage 3, the articular cartilage that lines the superior and inferior articular processes becomes thinned, with cartilage erosion leading to a decreased distance between the superior and inferior articular processes on CT scans. Stage 4, subarticular bone erosion, is characterized by loss of bone by resorption, either in the articular processes or in the adjacent laminae. Irregularities of the cortical surfaces of the joint, cysts and sclerosis within the adjacent bone, and sometimes filling of the erosions with gas from the joint space are observed on CT scans. Stage 5 consists of hyperostosis with further bone sclerosis and osteophytosis. Osteophytes may develop on the medial surface of the articular processes and cause narrowing of the spinal canal or the neural foramina, leading to sciatic pain. Synovial cysts may also accompany osteoarthritis of the apophyseal joints.

The destruction of the facet joints (and other structures) in ankylosing spondylitis may result in a conus medullaris syndrome. This syndrome develops as a consequence of a meningeal inflammatory process causing dense adhesive arachnoiditis. In consequence, diverticula developing from the dural sac erode the neural arch and vertebral bodies. The findings in the cervical spine can be striking and simulate those of juvenile chronic arthritis. Diagnosis can usually be made by CT and myelography.

Apophyseal joint abnormalities in rheumatoid arthritis may occur in the subaxial region. Generally the patient develops a fibrous ankylosis rather than bony ankylosis.

Trauma can produce unstable fractures of the apophyseal joints. A "perched" cervical facet joint is demonstrated on CT scans as an abnormally slender lateral mass without a joint space. "Locking" of the cervical facet joints occurs when the superior articular process can be identified posterior to the inferior articular process.

DR