At the back of each spinal segment, a pair of small facet joints connect the spine’s vertebral bones. The facet joints of the lumbar (lower back) spine bear a large amount of stress and weight, making them vulnerable to degeneration and injury. These joints are richly innervated with many spinal nerves, which makes them susceptible to developing pain1 that is often felt in the lower back and/or leg (sciatica).
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Pain originating from a facet in the lower back may initially be acute (short term) and become chronic over time. The pain may be localized to the lower back or involve one or both legs if a spinal nerve(s) gets impinged near the facet, resulting in sciatica. Research indicates that 15% to 45% of lower back pain originates from the lumbar facets.1
There are many terms and diagnoses related to facet joint disorders. When degeneration breaks down the joint surfaces of the facets, it is called spinal osteoarthritis.2 Other diagnoses related to facet joint disorders include facet joint arthritis, facet joint disease, and facet syndrome. These disorders may also be included in the general descriptive term for spinal degeneration—spondylosis.
This article provides complete information on the causes of lumbar facet joint disorders, along with prominent signs and symptoms, and the available treatment options.
Facet Joint Anatomy in the Lower Back
All along the back of the spine, at each level, a pair of small facet joints connect the vertebrae—the bony building blocks of the spine, holding the spine together, and providing support. These joints, otherwise known as the zygapophyseal joints, are synovial, which means they allow the spine to bend and twist in different directions.
- Formation of the joint. A facet joint is formed by the articulation between paired bony projections called articular processes. These processes are located at the back of each vertebra and connect adjacent vertebrae. For each disc space, there are two facet joints and a disc, which together form a tripod that creates the motion segment. The spinal nerves exit just above the upper facet at each level.
- Movement within the joint. The joint surfaces of the articular processes are coated with cartilage and encapsulated by a thin, fluid-filled synovial membrane to facilitate smooth movements and prevent friction.
- Protective covering of the joint. The joint is surrounded by an outer capsule, which is tough, resilient, and slightly flexible, and holds about 2 ml of joint fluid for lubrication. A small amount of fat enters and leaves the capsule during spinal movements for additional lubrication.3
Pain can originate from the joint surfaces of a facet or the outer capsule surrounding the facet joint.2
Support, Motion, and Protection from Lumbar Facet Joints
The facets of the lumbar spine support most of the spine’s weight and aid in upper and lower back movements. These joints also do their part in protecting the spinal cord and cauda equina, which runs behind the discs and in front of the facets.
The primary functions of the lumbar facet joints are to:
- Allow a considerable range of motion. The lumbar facets allow spinal movements in various directions4:
- The shape of the facet joint allows a large amount of flexion (forward bending), up to almost 60°.
- The shape and size of these joints significantly limit twisting movements, protecting the intervertebral discs from rotational injury.
- The joints allow limited extension (backward bending).
- Absorb loads. The lumbar facets absorb compressive and shear forces placed on the spine, both while standing erect and during spinal movements.4
- Provide support. The facet joints support the spine by preventing the vertebrae from engaging in movements that can overload and damage the surrounding spinal structures, such as the discs, spinal nerve roots, and spinal cord.5
- Contribute to lumbar proprioception. The nerves that supply the facet joint capsule help contribute to lumbar proprioception (the body's ability to perceive its own position in space).4,6
The lower part of the lumbar spine provides the majority of mobility and supports the largest portion of the upper body, making the lower lumbar facet joints at L4-L5 and L5-S1 more susceptible to injury and degeneration.7
How a Facet Joint Disorder Can Cause Back Pain
The facet joints in the lower back are frequently subject to large amounts of compressive, shear, and axial loading from regular activities of daily living, exercise, work, and other actions and movements.4,8 These joints can become painful from:
- Regularly engaging in poor posture and unsupported body mechanics
- Age-related degeneration of the intervertebral disc and other supporting tissues of the spine
- Sudden, acute trauma, such as from an accident, fall, or sports-related injury
- Chronic lower back injury due to repetitive overuse or microtrauma to the facets
The symptoms of a lumbar facet joint disorder may stem from one or more parts of the joint. These symptoms may be localized to the lower back or radiate into the leg.
Pain that originates within the facet joint
Degenerative or traumatic conditions affecting the facet joint’s surface and/or the nearby discs may cause4:
- Spinal osteoarthritis: Natural wear-and-tear of the facet’s cartilage due to aging may result in inflammation and stiffness due to bone-on-bone grinding within the joint during movement.
- Disc degeneration: Degeneration of the intervertebral disc followed by a reduction in disc height brings the joint surfaces closer together. This movement alters the normal mechanics of the joint and can increase stresses on the facets.
- Overexertion of the facets. Movement of the spine beyond its normal limit can cause the facet joint’s surfaces to be forced out of place.
Pain may also result from the entrapment of soft tissue between the facets.
Pain that originates from the facet’s outer capsule
The outer capsule surrounding the facet is made of connective tissue and ligaments. This capsule may become painful in the following conditions:
- Strain. The ligamentous tissue of the outer capsule may get overstretched during spinal movements.4
- Inflammation. Damage to the outer capsule can lead to an inflammatory reaction. This reaction includes the release of chemicals that send pain signals through the nerves that supply the capsule.9
Degeneration and trauma to the facet joints may lead to instability of the entire motion segment. This segmental instability can affect nearby structures, such as the spinal nerves, muscles, and connective tissues.
When the pain from a facet is localized to the lower back, it is called referred pain. When the pain travels through a nearby nerve root and affects the leg, it is called radicular pain, commonly known as sciatica.
When Facet Joint Pain Is Serious
While rare, a lumbar facet joint problem may indicate a serious underlying condition if one or more of the following signs and symptoms are present:
- Pain that suddenly becomes severe and intolerable
- Numbness in the groin and/or genital area
- Severe weakness in both legs
- Retention of urine
- Reduction or complete loss of bowel and/or bladder control
The facet joints connect the spine’s vertebral bones, allow motion in the spine, and protect spinal structures, such as the discs and spinal cord. These joints undergo various degrees of stress and strain on a daily basis, which are more concentrated on the lumbar facets, making them susceptible to injury and degeneration. Pain from a lumbar facet joint disorder may be localized to the lower back or travel down into the buttock, thigh, and/or leg.