The lumbar spine supports much of the body’s weight, with its two lowest vertebrae being the L4 and L5. At the back of the spinal column are small, stabilizing joints known as facet joints. The L4-L5 segment endures substantial stress, making it a common site for structural issues involving the vertebrae, the intervertebral disc, and surrounding nerves.
Anatomy and Function of the L4-L5 Facet Joint
The L4-L5 facet joints are synovial joints, enclosed in a capsule that produces lubricating fluid to minimize friction. Each joint is formed by the connection of the inferior articular process of the L4 vertebra above and the superior articular process of the L5 vertebra below. The surfaces of these processes are coated with smooth articular cartilage, allowing the bones to glide against each other. The primary function of these joints is to provide stability to the lower back. They work with the intervertebral disc to control extension (bending backward) and twisting movements, preventing excessive motion.
Sources of L4-L5 Facet Joint Pain
The most common source of pain is degenerative arthropathy, a form of osteoarthritis in the spine. This condition involves the progressive breakdown of the articular cartilage cushioning the joint. As cartilage wears away, the bones can rub against each other, leading to inflammation and the formation of bone spurs. These changes restrict movement and can irritate surrounding nerve endings.
Direct trauma is another cause of facet joint pain. A sudden impact from a fall, car accident, or sports injury can damage the joint capsule or cartilage, causing inflammation. Repetitive stress from frequent bending or twisting can also accelerate wear and tear on these joints, contributing to their degeneration.
Joint inflammation can also lead to a synovial cyst, which is a fluid-filled sac extending from the joint lining. These cysts often form due to underlying joint degeneration. If a cyst grows large enough, it can compress nearby spinal nerves, causing pain in the back and potentially radiating into the lower extremities.
Associated Symptoms
The primary symptom of L4-L5 facet joint issues is a persistent, dull ache in the lower back, on one or both sides of the spine. The pain often intensifies with movements that extend or twist the spine. Discomfort may also worsen after periods of inactivity, such as in the morning, or after prolonged standing.
Pain from the L4-L5 facet joint often radiates to other areas, a phenomenon known as referred pain. The ache can extend into the buttocks and the back or sides of the thighs. A distinguishing characteristic is that this pain does not travel below the knee, which separates it from classic sciatica. If a nerve is compressed, however, sharp pain radiating down the leg can occur.
Individuals also experience stiffness in the lower back, which can make movements like standing up from a seated position difficult. This combination of pain and stiffness leads to a decreased range of motion, affecting daily activities.
Diagnostic Process
Diagnosing L4-L5 facet joint pain begins with a physical examination. A physician will review the patient’s medical history and symptoms before assessing the spine. This includes palpating the lower back to find tender areas over the facet joints and evaluating range of motion. The doctor will ask the patient to perform movements like bending and twisting to see which actions reproduce the pain.
Imaging tests are ordered to get a clearer picture of the joint’s condition. X-rays can visualize vertebral alignment and reveal signs of arthritis, like joint space narrowing or bone spurs. For a more detailed view of soft tissues such as cartilage and nerves, a magnetic resonance imaging (MRI) or computed tomography (CT) scan is used. These scans can identify cartilage degeneration, joint hypertrophy, or synovial cysts.
The most definitive diagnostic method is a medial branch block. In this procedure, a local anesthetic is injected into the medial branch nerves that supply sensation to the L4-L5 facet joint, using X-ray guidance for accuracy. If the patient experiences a significant, temporary reduction in pain, it confirms the facet joint as the source. This confirmation helps guide further treatment decisions.
Medical Interventions and Management
Initial management focuses on conservative, non-invasive approaches. Physical therapy programs are designed to improve flexibility, strengthen core and back muscles, and correct posture. Over-the-counter nonsteroidal anti-inflammatory drugs (NSAIDs) can reduce pain and inflammation. Activity modification, such as avoiding movements that strain the lower back, can also provide relief.
If conservative treatments fail to provide relief, interventional procedures are considered. Therapeutic corticosteroid injections are a common option, where a powerful anti-inflammatory is injected into the facet joint capsule. This reduces swelling and alleviates pain for a longer duration than a diagnostic block. The relief can last from several weeks to months and the injections can be repeated.
For those who get short-lived relief from diagnostic blocks, radiofrequency ablation (RFA) offers a more durable solution. RFA uses heat from radiofrequency waves to create a lesion on the medial branch nerves. This interrupts their ability to send pain signals from the facet joint to the brain. The procedure can provide pain relief for nine months or longer, though the nerves may eventually regrow.