The human spine is a complex, weight-bearing structure made up of 33 bones, called vertebrae, that are stacked one upon the other. These bones are separated by intervertebral discs that act as shock absorbers, cushioning the spine and allowing for flexible movement. This intricate column relies on precise alignment to protect the spinal cord and the nerves that branch out to the rest of the body. When a vertebra shifts out of its normal position, it is known generally as a vertebral displacement.
Defining Backward Spinal Slippage
Degenerative retrolisthesis describes a specific type of vertebral displacement where a bone in the spine shifts in a posterior, or backward, direction relative to the vertebra directly beneath it. This backward movement creates an abnormal step-off or misalignment in the spinal column’s contour, most commonly occurring in the lower back (lumbar spine) or the neck (cervical spine).
This condition differs from its more common counterpart, anterolisthesis, which involves a forward slippage of a vertebra. While both conditions represent a loss of alignment, the directional difference affects how the surrounding soft tissues and nerves are impacted. Clinicians grade retrolisthesis to quantify the severity of the displacement, typically measured on a lateral X-ray image.
A four-grade scale is commonly used, based on the percentage of the vertebral body that has slipped backward. Grade 1 indicates a slippage of up to 25%. Grade 2 represents 25% to 50% slippage, while Grade 3 encompasses a 50% to 75% backward shift. Grade 4 signifies a displacement greater than 75%, which is a rare and unstable condition.
Why Degeneration Causes Retrolisthesis
The “degenerative” component refers to age-related wear and tear that leads to spinal instability. Over time, the materials designed to stabilize the spine begin to lose their integrity, permitting the vertebral body to slide backward. The primary mechanism involves the deterioration of the intervertebral discs, which lose water content and height as part of the natural aging process.
This loss of disc height decreases the space between adjacent vertebrae, causing surrounding ligaments to become lax. The reduced tension and structural support from the flattened disc allow for excessive movement between the bones. This instability is compounded by arthritis in the facet joints, which are the small, paired joints that guide and limit spinal motion.
As the cartilage in the facet joints wears down, these stabilizing joints become compromised and can no longer restrict the backward motion of the vertebrae. The combination of a collapsed disc space and dysfunctional facet joints allows the superior vertebral body to settle in a posterior position.
Recognizing the Physical Symptoms
The physical symptoms of degenerative retrolisthesis can vary significantly among individuals, ranging from no discomfort to severe, debilitating pain. When symptoms occur, they are often a direct result of the mechanical instability or the pressure the misaligned bone places on nearby neural structures. Many people experience localized, dull aching pain in the area of the slippage, typically in the lower back, which often worsens with movement or prolonged standing.
The backward shift of the vertebra can narrow the space available for spinal nerves as they exit the spinal canal, a condition known as spinal stenosis. When nerve roots are compressed, they produce neurological symptoms that radiate away from the spine (radiculopathy).
In the lumbar region, radiculopathy (sciatica) causes pain, tingling, numbness, or muscle weakness that travels down into the buttocks and legs. Similarly, retrolisthesis in the cervical spine can lead to radiculopathy that manifests as pain, numbness, or weakness radiating into the shoulders, arms, and hands. The degree of vertebral slippage observed on an X-ray does not always correlate directly with the severity of a person’s pain.
Options for Managing the Condition
Initial management focuses on non-surgical, conservative treatments aimed at relieving pain and improving spinal stability. This often involves physical therapy designed to strengthen the core musculature, including the abdominal and lower back muscles. A strong core acts as a natural corset, providing external support and reducing mechanical stress on the compromised segment.
Medications are commonly used to manage acute discomfort, including non-steroidal anti-inflammatory drugs (NSAIDs) to reduce inflammation and pain, and muscle relaxants for associated spasms. Epidural steroid injections may also be administered to deliver potent anti-inflammatory medication directly to the irritated nerve roots, providing temporary relief from radicular symptoms. Temporary bracing can offer support during painful flare-ups, but prolonged use is discouraged to prevent muscle deconditioning.
Surgical intervention is reserved for cases where conservative treatments fail to control persistent, severe pain or when there is evidence of progressive neurological deficits, such as worsening weakness or loss of bladder function. The goal of surgery is twofold: to decompress the nerves and stabilize the unstable spinal segment. This is often achieved through a spinal fusion procedure, where the slipped vertebra is realigned and permanently fused to the adjacent bone, eliminating motion at that segment.