The spine is composed of a series of bones called vertebrae. Each bone is composed of a body as well as a structure called the superior articular process on its interior upper side. An inferior articular process is normally located on the bottom side of the bone; the connection between the top process of one vertebra and the articular one of the bone above is called the zygapophyseal joint. Also called the Z-joint, it normally connects one vertebra to another and guides the movement of the spinal bones. The zygapophyseal joint also protects the back bones from motions that could damage them.
Most often visible in a side view of the spinal column, the zygapophyseal joint is also called a facet joint. This term, however, more often applies to where there is cartilage lining various other small joints in the body. Another name given to the structure is the apophyseal joint. In the lumbar, or lower, spine, the zygapophyseal joint can protect the back from rotation, over-flexing, as well as shear forces. It also restricts flexing and enables rotation of the middle, or thoracic spine.
The functions of the Z-joint are sometimes affected by injuries, degeneration, and arthritis. It can also become dislocated or be fractured, while surgery can sometimes reduce the motion allowed by the joint. Degenerative changes to the zygapophyseal joint are most common with age, and typically occur because of normal wear and tear. Conditions such as osteoarthritis can cause pain, which is often felt in other parts of the body because these joints are deep in the spine and covered with spinal muscles. Pain in the thigh and buttocks is sometimes felt as a result of problems with the joint.
Medical equipment such as Magnetic Resonance Imaging (MRI) and Computerized Tomography (CT) machines are often used to diagnose zygapophyseal joint inflammation and other problems. Pain is sometimes managed by steroid injections. Doctors also often advise someone with a Z-joint problem to improve his or her posture or participate in physical therapy.
Pain in the zygapophyseal joint can be misdiagnosed as a condition involving the spinal discs in between the verebrae. Back pain that is caused by arthritis of the Z-joint can occur if nerve roots become entrapped, as a result of structural changes after the condition sets in. Genetics, repeated strain, and muscle weakness can also affect the zygapophyseal joint. The resulting back pain is common in many people over 65 years old, while some individuals as young as 40 may experience the symptoms of joint degradation.
