Facet syndrome is a syndrome in which the zygapophysial joints (synovial diarthroses, from C2 to S1) cause back pain. 55% of facet syndrome cases occur in cervical vertebrae, and 31% in lumbar. Facet syndrome can progress to spinal osteoarthritis, which is known as spondylosis.[Needs reference, none found] Pathology of the C1-C2 (atlantoaxial) joint, the most mobile of all vertebral segments, accounts for 4% of all spondylosis.

The facet joints are formed by the superior and inferior processes of each vertebra. The first cervical vertebra has an inferior articulating surface but, as it does not restrict lateral or posterior translation, is not always considered a proper zygoma (zygoma is Greek for “yoke,” i.e. something that restrains movement). In the lumbar spine, facets provide about 20 percent of the twisting stability in the low back. Each facet joint is positioned at each level of the spine to provide the needed support especially with rotation. Facet joints also prevent each vertebra from slipping over the one below. A small capsule surrounds each facet joint providing a nourishing lubricant for the joint. Also, each joint has a rich supply of tiny nerve fibers that provide a painful stimulus when the joint is injured or irritated. Inflamed facets can cause a powerful muscle spasm.