An intervertebral disc is a fibrocartilaginous structure found between the bodies of vertebra. These discs are located between each pair of vertebra in the spine. Think of this disc as being a jelly doughnut: there is a series of fibrous rings on the outside and a soft inside. The outer annular rings are thinnest posterior and lateral; most disc herniations occur at this location due to the weakness of the disc wall. The disc functions as a cushion, allows for movement, and serves as a cartilaginous joint between adjacent vertebrae. Inflammation, damage or degeneration of a disc can cause a range of symptoms, which vary based on the severity of the problem. Disc pathology may produce a loss of back motion, back pain, pain that radiates into the leg and foot, numbness, tingling, lower leg weakness and associated muscle spasms or some combination of these symptoms. The lumbar levels with the highest rate of disc degeneration and herniation are the fourth and fifth (L4-L5), and lumbar fifth and sacrum (L5-S1) levels.
A disc herniation occurs when the outer walls of the intervertebral disc are torn. Other terms for this condition are ruptured disc, prolapsed disc, or slipped disc. When outer annular rings are torn, the center gel-like nucleus can push out and place pressure on the other structures in the area. The herniation usually occurs at the posterior lateral wall where the annulus fibrosis is thinnest. Unfortunately this is where the nerves of the spine exit and track distally into the body. The larger the tear, and the further the nucleus pushes out into the surrounding area, the more severe the symptoms.