The lumbar facets in the lower back bear a significant amount of stress and load from the upper motion segments. Over a period of time, these facets may degenerate, become weak, or be subject to repetitive trauma, causing them to become a significant source of lower back pain. The facets may also undergo fracture, mild dislocation, or complete displacement from acute trauma.
Pain from the facet joint(s) may be localized to the lower back, referred to the buttocks and different parts of the thigh, and/or radiate into the leg if a nearby spinal nerve is affected.
Degenerative Conditions Affecting the Lumbar Facets
Degeneration due to aging and tissue wear-and-tear is the most common cause of facet joint disorders in the lower back.1 Degeneration of the facets is closely related to degenerative changes in other spinal structures, such as the intervertebral discs,1 and may result in both conditions occurring consecutively. While not a clinical diagnosis, a general term to describe spinal degeneration involving one or more structures, including the facets, is spondylosis.
Due to their significant load-bearing function and a greater range of motion, degeneration is more common in the lumbar facets at the very bottom of the spine, L4-L5 and L5-S1, than in those higher up in the spine.
Facet joint osteoarthritis
The wear-and-tear of the facets due to aging (osteoarthritis or spinal arthritis) typically causes1:
- Damage to the protective cartilage that covers the joint surfaces
- A reduction of the lubricating fluid inside the synovial membrane (inner membrane of the joint)
- Excess bone growth at the joint surface of a facet (due to repetitive friction between these surfaces) called bone spurs or osteophytes
These changes cause inflammation within the joint, which may progress over time and lead to lower back pain and stiffness. A degenerated facet may impinge a nearby nerve root and cause sciatica, similar to a lumbar herniated disc.
Read more about Osteoarthritis of the Spine
The displacement of a vertebra over the one below it (spondylolisthesis) may occur due to arthritic facet joints that become weak and fail to provide enough support for the spinal motion segment. The slippage usually results from1:
- Progressive loss of cartilage
- Segmental instability between the vertebrae
- Dislocation of the facets
Read more about Degenerative Spondylolisthesis
Synovial facet joint cyst
Arthritis may lead to the development of a cyst (fluid-filled sac) within the facet joint’s synovial membrane. Synovial facet joint cysts can cause pressure to develop within the joint and compress nearby structures, such as spinal nerve roots and/or the spinal cord, causing additional pain and/or dysfunction.1
Traumatic Injuries of the Lumbar Facets
Acute or repetitive trauma can cause breakage or displacement of the facets, resulting in an instability of the motion segment.
- Acute facet injury typically results from direct trauma, such as motor vehicle accidents, falls, or sports injuries.
- Repetitive minor traumas to the facets may result from work-related tasks, for example, manual labor that requires bending, twisting, and lifting, or sports injuries, such as gymnastics moves that require backward bending and twisting.
These injuries cause inflammation of the facet and its surrounding tissues, which is perceived as back pain and/or leg pain (sciatica). Specific traumatic injuries of the facets are described below.
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An external force on the spine may cause the facets to drift away from their normal position (facet dislocation). Two types of facet dislocation are possible in the lumbar spine:
- Subluxation. The facets of a vertebra are mildly displaced in a forward position, over the facet surface of the vertebra below. This condition results in a mild anterior (forward) displacement of one vertebral body over the other.
- Locked facet. The displacement of a facet joint that causes the articulating portion of the facet(s) to ride over the entire joint surface and become locked in this position.
Dislocation can occur unilaterally (involving one facet) or bilaterally (involving both facets on each side of the spine).
Traumatic spondylolisthesis, where the entire vertebral body slips over the one below it may result from acute facet dislocation.
Articular process fracture
Injuries involving combined flexion (forward bending) and rotation of the spine may cause movement of the facets beyond their physiologic limit. This force can cause the articular process (part of the vertebra that forms the facet joint) to fracture. The fracture may include one or both articular processes of a vertebra.
Articular process fractures typically occur in conjunction with other injuries of the motion segment, including those affecting the disc, ligaments, and other parts of the vertebral body.
Facet capsule strain
The outer covering of a facet consists of a tough and resilient capsule, made of connective tissue and spinal ligaments. This capsule is flexible and slightly loose to accommodate the joint’s movements. Exertion beyond physiologic limits can cause the capsule to overstretch, causing pain.1
Posture-induced facet injury
Facet joints can become painful due to the repetitive and continuous use of ergonomically unsupported postures. When incorrect posture is used, the spinal alignment is not supported and balanced, creating an abnormal concentration of stresses in the facets. While the pain may be relieved when the posture is corrected, repeated use of poor posture may cause chronic pain and inflammation in the facets.
Disorders of the lumbar facets typically occur due to degenerative changes within the joint or as a progression of disc degeneration, and less commonly due to direct trauma to the joint. Conditions affecting the facets can cause instability in the spinal motion segment, resulting in pain and stiffness in the lower back.
Facet joint disorders typically occur along with disc and spinal nerve problems within the affected motion segment, causing overlapping signs and symptoms.