The vertebral column, commonly known as the spine, forms the central support structure of the human body and houses the delicate spinal cord. Each individual bone in this column is a vertebra. The lamina is a specific, shelf-like component of a vertebra, serving as a significant structural element in the bony ring that surrounds the spinal cord.
Location and Structure of the Lamina
The lamina is a flattened, plate-like segment of bone found on the posterior side of a typical vertebra. There are two laminae on every vertebra, one extending from the left side and one from the right, which meet in the center of the back. These two bony plates are a major part of the structure known as the vertebral arch, which forms the protective enclosure around the spinal canal.
Each lamina extends inward from the transverse process, which projects sideways. It meets the lamina from the opposite side to form the base of the spinous process, the prominent point that juts out backward. This arrangement effectively creates a roof over the spinal cord.
The lamina’s connection to the main body of the vertebra is achieved through a short, thick pillar of bone on each side called the pedicle. The pedicle acts as a bridge, connecting the lamina and the rest of the posterior arch to the vertebral body, the large, cylindrical, weight-bearing front section of the vertebra. This entire complex structure, consisting of the body, the pedicles, the laminae, and the processes, encircles a large opening called the vertebral foramen. When all the vertebrae are stacked together, these foramina align to create the continuous bony tunnel of the spinal canal.
Role in Protecting the Spinal Cord
The primary function of the lamina is to act as the posterior bony shield for the spinal cord and the nerves that branch off it. As a segment of the vertebral arch, it forms a strong, continuous layer of bone that protects the neural tissue from impact or trauma originating from the back.
Beyond its protective role, the lamina also serves as an attachment site for various muscles and ligaments that stabilize the spine. One notable connection is to the ligamentum flavum, a series of short, thick, paired ligaments that join the laminae of adjacent vertebrae. This ligament has a high concentration of elastic fibers, allowing it to stretch during forward bending motions.
The elastic recoil of the ligamentum flavum helps the spine return to an upright position without requiring significant muscle effort. By anchoring these supportive structures, the lamina helps maintain the mechanical integrity and stability of the vertebral column.
The Lamina in Surgical Procedures
The specific anatomy of the lamina makes it a frequent target in spinal surgery, particularly in a decompression procedure known as a laminectomy. A laminectomy involves the surgical removal of all or part of the lamina to create more space within the spinal canal. This procedure is performed when conditions cause a narrowing of the spinal canal, which puts painful pressure on the spinal cord or nerve roots.
One of the most common reasons for this surgery is spinal stenosis, a condition where the spinal canal narrows due to the overgrowth of bone or the thickening of ligaments, including the ligamentum flavum. When this narrowing occurs, the compressed nerves can cause symptoms such as pain, numbness, or weakness that radiates down the arms or legs.
During the procedure, the surgeon may remove the entire lamina or only a section, depending on the extent of the compression. In some cases, a partial removal, called a laminotomy, is performed to create a small opening just large enough to address a specific issue, such as a herniated disc. Removing a portion of the lamina grants access to the underlying disc material that is pressing on a nerve.
Another related procedure, laminoplasty, is sometimes used in the neck region. It involves creating a hinge on the lamina to open up the canal space without completely removing the bone.