Facet syndrome occurs when the joints in the back of the spine degenerate and cause pain.
Found at every level on both sides of the lumbar spine, facet joints provide about 20% of the twisting stability in the lower back. They also prevent each vertebra from slipping over the one below.
A small capsule surrounds each facet, providing a nourishing lubricant. These joints also contain a rich supply of tiny nerve fibers that provide a painful stimulus when injury or irritation occurs. Inflamed facets can cause powerful muscle spasms.
A common cause of low back pain, facet syndrome is attributed to osteoarthritis of the interarticular vertebrae.
Symptoms include low back pain that increases upon extension, radiates to the posterior thigh and ends at the knee. X-ray and CT imaging reveal narrowing of disc space with osteophyte formation.
(Source: McGraw-Hill Concise Dictionary of Modern Medicine)