Corpus: Intervertebral joint

The intervertebral joints, or facet joints, are small, paired joints that exist between the articular processes of neighboring vertebrae and are responsible for the mobility of the spine. Together with the intervertebral discs and surrounding ligaments, they form a functional unit.

The intervertebral joints are classified as flat joints with relatively wide joint capsules, making them part of the diarthroses group. The joints are formed between the cartilage-covered surfaces of the superior articular process of one vertebra and the inferior articular process of the vertebra directly above it. These joints allow movement in three planes, giving the spine three degrees of movement:

• Flexion and extension in the sagittal plane (forward and backward bending)
• Lateral flexion in the frontal plane (side bending)
• Rotation

The orientation of the joint surfaces differs in various sections of the spine, which influences the range of motion:

• In the cervical spine, the joint surfaces are almost horizontal, with the superior articular processes facing dorsally and slightly upwards. This allows significant rotational movement and makes the cervical spine the most mobile part of the spine.
• In the thoracic spine, the joint surfaces also face dorsally and upwards but are slightly inclined laterally
• In the lumbar spine, the joint surfaces are nearly in the sagittal plane, limiting rotation. The primary movements in this region are forward flexion and backward extension.

Almost all intervertebral joints contain small meniscoid synovial folds, which protrude into the joint space in a crescent shape. These folds consist of vascularized loose or dense connective tissue from the joint capsule and are lined with an intima coat. Their role is to help compensate for any incongruence between the joint surfaces.

Degenerative changes in the facet joints are known as spondyloarthrosis.