Ligamentum flavum infolding (LFI) is the abnormal buckling of a specific ligament into the spinal canal, where the spinal cord and nerves reside. This inward folding is often associated with degenerative changes within the spine during movement. The resulting impingement on neural structures can lead to various neurological symptoms.
Anatomy and Function of the Ligamentum Flavum
The ligamentum flavum (LF) is a paired structure composed of high concentrations of elastic fibers. These ligaments connect the laminae, or bony arches, of adjacent vertebrae throughout the spinal column, extending from the second cervical vertebra down to the sacrum. They are thin in the neck but become progressively thicker in the thoracic and lumbar regions.
The primary function of the LF is to maintain spinal stability and support upright posture. Its unique elasticity allows for smooth and controlled spinal flexion (bending forward) and ensures the spine returns to its neutral position. This elastic recoil helps prevent excessive forward bending and keeps the ligament taut, preventing buckling into the spinal canal during spinal extension.
The Mechanical Process of Ligamentum Flavum Infolding
Infolding describes the mechanical action where the ligamentum flavum folds or protrudes inward, directly encroaching upon the spinal canal. This buckling typically occurs during spinal extension, such as standing or arching the back, when the distance between the two connected vertebrae shortens. In a healthy spine, the ligament’s elasticity prevents this inward buckling, maintaining a clear pathway for the neural tissue.
With age or degenerative changes, the elastic fibers within the LF degrade and are replaced by less flexible, fibrotic tissue. This loss of elasticity, combined with the decreased height of the intervertebral discs often seen in degeneration, causes the ligament to become relatively redundant or slack. When the spine extends, this redundant tissue buckles into the spinal canal, placing pressure on the nerves or spinal cord.
The mechanical compression from this inward fold is distinct from the general thickening (hypertrophy) of the ligament, though both often occur together and contribute to the same problem. The infolding is a dynamic, motion-dependent event, caused by the ligament’s inability to contract fully upon itself. This dynamic compression is why some patients experience an increase in symptoms when they stand or walk, as these movements promote spinal extension and infolding.
Clinical Manifestations of Nerve Compression
Infolding of the ligamentum flavum reduces the space within the vertebral canal, a condition known as spinal stenosis. This narrowing directly compresses the neural structures, including the nerve roots or the spinal cord itself. The location of the compression dictates the specific symptoms a person will experience.
Compression in the lower (lumbar) spine often results in radiculopathy, commonly known as sciatica, characterized by radiating pain, numbness, or tingling that travels down the buttocks and legs. A hallmark symptom is neurogenic claudication, where leg pain or weakness is brought on by walking or standing and is relieved by sitting or leaning forward, a posture that flexes the spine and temporarily unbuckles the ligament.
If the infolding occurs higher up in the neck (cervical spine), it can lead to myelopathy, which affects the spinal cord. Symptoms can include motor function deficits, such as difficulty with fine motor skills in the hands, balance issues, and general weakness in the limbs.
Underlying Causes and Management Strategies
The primary underlying cause of ligamentum flavum infolding is age-related degeneration and spinal instability. The spine undergoes changes, including the loss of disc height and the development of osteoarthritis in the facet joints, which collectively increase mechanical stress on the LF. This chronic stress triggers degenerative changes within the ligament, leading to the loss of elasticity and the eventual mechanical failure known as infolding.
Diagnosis of infolding and the resulting spinal stenosis is achieved through imaging studies, with magnetic resonance imaging (MRI) being the preferred method for visualizing the soft tissues of the spine, including the ligament and its effect on the nerves. Conservative management is the initial approach for most patients. This includes physical therapy focused on core strengthening and flexibility to stabilize the spine, as well as nonsteroidal anti-inflammatory drugs (NSAIDs) to manage pain and inflammation. Epidural steroid injections may also be used to deliver anti-inflammatory medication directly to the area around the compressed nerves.
When conservative treatments fail to provide adequate symptom relief, surgical intervention may become necessary to decompress the neural structures. The most common procedure is a laminectomy or laminotomy, which involves removing a portion of the vertebral bone (lamina) and the thickened or infolded section of the ligamentum flavum. This surgical removal physically expands the spinal canal, relieving the pressure on the compressed nerve roots or spinal cord.