Lumbar Disc Herniation

Excerpt

Lower back pain (LBP) is one of the most common presenting complaints globally, as approximately 80% of the population sustains an episode once in their lifetime. This highly prevalent and disabling ailment costs more than $100 billion annually in the United States. Among the many differential diagnoses of LBP, degenerative disc disease and lumbar disc herniation (LDH) are the most common. Approximately 95% of disc herniations in the lumbar area occur at L4-L5 or L5-S1.

The lumbar spine contains five vertebrae and intervertebral discs, producing a lordotic curve. The intervertebral discs with the laminae, pedicles, and articular processes of adjacent vertebrae create the space in which the spinal nerves exit. The intervertebral discs consist of an inner nucleus pulposus (NP), outer annulus fibrosus (AF), and the cartilaginous endplates that anchor the disc to its vertebras.

The nucleus pulposus is a gel-like structure that is composed of approximately 80% water, with the rest made by type 2 collagen and proteoglycans. The proteoglycans include the larger aggrecan, which is responsible for retaining water within the nucleus pulposus. Also, it provides versican that binds to hyaluronic acid. This hydrophilic matrix is responsible for maintaining the height of the intervertebral disc.

The annulus fibrosus is a ring-shaped structure that surrounds the nucleus pulposus. It is made of highly organized fibrous connective tissue, consisting of 15 to 25 stacked sheets of predominantly collagen lamellae with interspersed proteoglycans, glycoproteins, elastic fiber, and the connective tissue cells that secreted these extracellular matrix products. The inner part of the annulus fibrosus is predominantly made of type 2 collagen, while the outer part is mostly of type 1 collagen.