A thoracic vertebra. The zygapophysial joint is the joint between the superior articular process (labeled at top) and the inferior articular process (labeled at bottom)
A zygapophysial joint (zygapophyseal, apophyseal, Z-joint, or facet joint) is a synovial joint between the superior articular process, in humans (cranial in nonhuman animals) of one vertebra and the inferior (caudal) articular process of the vertebra directly above it. There are two facet joints in each spinal motion segment.
The biomechanical function of each pair of facet joints is to guide and limit movement of the spinal motion segment. In the lumbar spine, for example, the zygapophysial joints function to protect the motion segment from anterior shear forces, excessive rotation and flexion. Zygapophyseal joints appear to have little influence on the range of side bending (lateral flexion). These functions can be disrupted by degeneration, dislocation, fracture, injury, instability from trauma, osteoarthritis, and surgery. In the thoracic spine the zygapophysial joints function to restrain the amount of flexion and anterior translation of the corresponding vertebral segment and function to facilitate rotation.
Facet joint arthritis
In large part due to the mechanical nature of their function, all joints undergo degenerative changes with the wear and tear of age. This is particularly true for joints in the spine, and the zygapophysial joint in particular. This is commonly known as facet joint arthritis or facet arthropathy.
Facet joint arthritis often manifests as a dull ache across the back. However like many deep organs of the body it can be experienced by the patient in a variety of referral pain patterns. The location of facet joints, deep in the back and covered with large tracts of paraspinal muscles, further complicate the diagnostic approach. Typically facet joint arthritis is diagnosed with specialized physical examination by specialist physicians. Advanced imaging such as MRI or CT may be necessary to confirm the diagnosis and to rule out other conditions.
Conservative treatment of facet joint arthritis involves chiropractic, physical therapy, or osteopathic medicine with correction of posture and biomechanics being the key. Acupuncture and Chinese medicine can provide pain relief as well as increasing blood flow to the tissues to promote healing. More advanced cases involving severe inflammatory response in the Z-joint, not unlike a swollen arthritic knee. Steroid injections may provide temporary pain relief. This is typically performed under image guidance to ensure accuracy given the complex shape and deep location of the facet.
Ancient Greek: zygon ("yoke") + apo ("out/from") + phyein ("grow")
- Diagram at spineuniverse.com
- Diagram at necksurgery.com
- Emedicine article on Lumbosacral Facet Syndrome