The lateral recess is a small, specialized anatomical space within the bony channel of the spine, most frequently discussed in the context of the lower back (lumbar spine). This area functions as a critical passageway for the nerves traveling down the spinal column before exiting the body. Understanding this tight space is important because it is a common site where age-related changes can lead to irritation of the delicate nerve roots. When this space narrows, it can cause significant back and leg pain due to nerve compression.
Anatomical Definition and Location
The lateral recess is a segment of the central spinal canal located immediately before the nerve roots leave the spine through the neural foramen. It is sometimes referred to as the subarticular zone because of its close relationship to the facet joints. This space is defined by a distinct set of boundaries created by the surrounding bony and soft tissues of the vertebra.
The anterior boundary of the recess is formed by the back surface of the vertebral body and the adjacent intervertebral disc margin. Posteriorly, the superior articular facet of the facet joint and the ligamentum flavum create the wall of this canal. The lateral boundary is marked by the medial side of the pedicle, which is the stout bony projection extending from the vertebral body.
This region is shaped somewhat like a funnel, gradually becoming narrower as it descends toward the neural foramen. Because of its constrained, three-dimensional boundaries, the lateral recess is extremely sensitive to any overgrowth or structural change in the surrounding tissues.
Key Structures Occupying the Recess
The functional significance of the lateral recess lies in its role as a conduit for the traversing nerve root. This specific nerve root has descended from the dural sac and is traveling down to exit the spine at the level below. For example, at the L4-L5 vertebral level, the L5 nerve root passes through the lateral recess before exiting the foramen below the L5 pedicle.
This pathway distinguishes the lateral recess from other nearby spinal structures. The central spinal canal contains the entire dural sac, while the neural foramen is the final exit opening through which the nerve root passes before becoming a peripheral nerve.
The traversing nerve root is housed within the lateral recess for a short distance as it angles downward and outward. This nerve root is covered by a protective layer and bathed in cerebrospinal fluid, but its close proximity to the bony and ligamentous walls makes it vulnerable.
Understanding Lateral Recess Stenosis
Lateral recess stenosis is the medical term for the pathological narrowing of this specific subarticular region of the spinal canal. This narrowing physically reduces the space available for the traversing nerve root, causing it to become compressed or pinched. This condition is a localized form of spinal stenosis, specifically affecting the side channel rather than the main central canal.
Compression of the nerve root in this area leads to symptoms known as radiculopathy, commonly referred to as sciatica if it occurs in the lower back. The mechanical pressure on the nerve disrupts its normal function and can impede the blood flow that supplies its tissues.
The primary symptom is often sharp, shooting pain that radiates from the buttocks down the leg, sometimes into the foot. In addition to pain, a person may experience neurological symptoms such as tingling, numbness, or a pins-and-needles sensation. If the compression is severe or prolonged, it can lead to muscle weakness in the leg.
Common Mechanisms Leading to Narrowing
The narrowing of the lateral recess is predominantly an acquired condition resulting from degenerative changes associated with aging.
Hypertrophy of the Facet Joints
One of the most common mechanisms is the overgrowth, or hypertrophy, of the superior articular facet. As the facet joints develop arthritis, they can form bone spurs, or osteophytes, which project into the already small lateral recess space.
Thickening of the Ligamentum Flavum
Another significant contributor is the thickening of the ligamentum flavum, a strong ligament that runs down the back of the spinal canal. With chronic stress and degeneration, this ligament can become thickened and buckle inward, further reducing the space between the posterior wall and the traversing nerve root.
Intervertebral Disc Pathology
Intervertebral disc pathology can also play a role in reducing the size of the lateral recess. While disc herniations often affect the central canal, a posterolateral disc bulge or herniation can protrude directly into the lateral recess. This disc material then physically pushes against the nerve root, compounding the existing narrowing caused by arthritic changes.