The spinal column is a complex structure of bones, ligaments, and cushioning discs that provides support and allows movement. Stacked vertebrae protect the central nervous system components. The spinal cord is housed in the central spinal canal, the main pathway for nerve signals. Nerves branch off and exit the spine through protected openings to reach the limbs and organs. When degenerative changes occur, these spaces can narrow, potentially compressing nervous system components.
Understanding Spinal Stenosis vs. Foraminal Narrowing
The term “spinal stenosis” describes an abnormal reduction in the size of any of the bony openings within the spine. This general term indicates less room for the spinal cord or nerve roots, which can lead to irritation or compression. Spinal stenosis is broadly categorized by the location of the narrowing within the spinal column.
Foraminal narrowing (also known as foraminal or lateral stenosis) refers to a specific type of narrowing. It occurs in the neural foramen, which are the small, paired openings on the sides of the vertebral column where individual nerve roots exit the spine. Foraminal narrowing is a localized form of spinal stenosis, not an entirely separate condition.
Stenosis can also occur in the central spinal canal, the main passageway that runs through the middle of the vertebrae and contains the spinal cord. This is known as central canal stenosis. The central canal can be viewed as the main highway and the neural foramina as the exit ramps; stenosis can affect either or both simultaneously. The location dictates which nerves are compressed and the resulting symptoms.
Underlying Causes of Spinal Narrowing
Most spinal narrowing is caused by age-related wear and tear (degenerative change or osteoarthritis). Over decades, intervertebral discs lose water content, causing them to flatten and bulge outward. This disc degeneration is a primary mechanism that reduces the height of the foramen, leading to narrowing.
Joint instability often leads to the formation of bone spurs (osteophytes), which are bony growths that develop on the edges of the vertebrae and facet joints. These spurs can project into the central canal or directly into the neural foramen, constricting the space available for the nerves. The facet joints, located at the back of the vertebrae, can also enlarge due to arthritis, further encroaching on the nerve root openings.
Another factor is the thickening of spinal ligaments, particularly the ligamentum flavum, which runs along the inside of the central canal. Over time, this ligament can hypertrophy, pushing into the spinal canal and causing central stenosis. A herniated disc can also directly protrude into the foramen or the central canal, compressing the nerve structures.
Symptoms Resulting from Nerve Compression
When narrowed spaces compress a spinal nerve root, the resulting condition is known as radiculopathy. This compression manifests as pain, numbness, tingling, or muscle weakness that follows the path of the affected nerve. If the compression is in the lower back (lumbar spine), the result is often sciatica, characterized by pain radiating down the buttocks and into the leg.
Symptoms often begin gradually and may worsen over time. A characteristic symptom of lumbar spinal stenosis is neurogenic claudication, a condition where pain, tingling, or weakness in the legs occurs with walking or prolonged standing. The pain improves when a person bends forward or sits down, positions that temporarily increase the space in the spinal canal.
Compression in the neck (cervical spine) causes similar symptoms, but they are felt in the shoulders, arms, and hands. If central canal narrowing is severe enough to compress the spinal cord, a more serious condition called myelopathy can occur. Myelopathy can lead to issues with balance, coordination, weakness, and problems with bladder or bowel control.
Common Approaches to Management
Initial management focuses on conservative, non-surgical methods aimed at reducing pain and improving function. Physical therapy is recommended to strengthen core muscles and improve flexibility, which helps alleviate pressure on the compressed nerves.
Medications include nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, to reduce inflammation around the irritated nerve roots. For more persistent pain, physicians may recommend epidural steroid injections, which deliver powerful anti-inflammatory medication directly into the space near the compressed nerves. These injections offer temporary relief, allowing patients to participate more effectively in physical therapy.
Surgery is considered only when conservative treatments fail or when neurological deficits, such as muscle weakness, are worsening. Surgical procedures decompress the nerves by removing the material causing the narrowing. A foraminotomy specifically enlarges the neural foramen, while a laminectomy removes a portion of the vertebral bone to open the central spinal canal.