The spine is a column of stacked bones, called vertebrae, that provides structure and flexibility. Each vertebra is composed of several distinct parts that support weight and facilitate movement. The lamina is a thin, plate-like section of bone that forms part of the protective ring around the spinal cord.
Defining the Lamina and Its Location
The lamina is a flat, bony plate located on the posterior side of each vertebra. It consists of two symmetrical plates of bone that extend backward from the main vertebral body. These left and right laminae converge and fuse at the midline of the spine.
The lamina connects laterally to the pedicles, which are short, thick projections of bone linking the lamina to the vertebral body. The vertebral body is the large, cylindrical front section that bears the majority of the body’s weight. Where the two laminae meet, they project outward to form the spinous process, the bony protrusion felt beneath the skin of the back. Together, the pedicles and the laminae create the vertebral arch, also known as the neural arch. This arch structure encloses the vertebral foramen, the hollow space through which the spinal cord passes.
The Lamina’s Role in Spinal Protection
The primary function of the lamina is to act as a shield for the delicate nervous tissue within the spinal column. This bony enclosure provides substantial defense for the spinal cord and the exiting spinal nerve roots.
The laminae also serve as attachment sites for the ligamentum flavum, a strong, yellowish ligament that connects adjacent laminae. The ligamentum flavum helps stabilize the spine and maintain upright posture. This ligament works with the laminae to prevent excessive forward bending of the spine, contributing to necessary spinal stability.
Surgical Importance: Understanding the Laminectomy
The lamina is often the target of a common surgical procedure called a laminectomy. This decompression surgery involves removing all or part of the lamina to relieve pressure on the spinal cord or nerve roots. The procedure is typically performed when non-surgical treatments have failed.
The most common reason for this surgery is spinal stenosis, an abnormal narrowing of the spinal canal. This narrowing is caused by degenerative changes, such as thickening of the ligamentum flavum, bony spurs, or disc herniations. Compression of neural tissues leads to symptoms like pain, numbness, or weakness in the legs, known as neurogenic claudication.
By surgically removing the lamina, the surgeon expands the space within the spinal canal, reducing pressure on the entrapped nerve roots. A laminectomy may use a traditional open approach or a minimally invasive laminotomy, which removes only a small portion of the lamina on one side. In some cases, a spinal fusion may also be performed to stabilize the segment of the spine.