A common vertebral problem is changes in the intervertebral disks. Each disk is composed of a tough, outer layer of fibrocartilage (annulus fibrosus) and an elastic central mass (nucleus pulposus). As a person ages, these disks degenerate, the central masses losing firmness and the outer layers thinning and weakening, and developing cracks. Extra pressure, as when a person falls or lifts a heavy object, can break the outer layers of the disks, squeezing out the central masses. Such a rupture may press on the spinal cord or on spinal nerves that branch from it. This condition, called a ruptured, or herniated, disk, may cause back pain and numbness or loss of muscular function in the parts innervated by affected spinal nerves.

A surgical procedure called a laminectomy may relieve the pain of a herniated disk. In this procedure, a portion of the posterior arch of a vertebra is removed to reduce the pressure on the affected nerve tissues. In other instances, a protein-digesting enzyme (chymopapain) may be injected into the injured disk to shrink it.

Sometimes problems develop in the curvatures of the vertebral column because of poor posture, injury, or disease. For example, if an exaggerated thoracic curvature appears, the person develops rounded shoulders and a hunchback. This condition, called kyphosis, occasionally develops in adolescents who undertake strenuous athletic activities. Unless the problem is corrected before bone growth completes, the vertebral column may be permanently deformed.

Sometimes the vertebral column develops an abnormal lateral curvature, so that one hip or shoulder is lower than the other. At the same time, the thoracic and abdominal organs may be displaced or compressed. This condition is called scoliosis. Although it more commonly develops without known cause in adolescent females, it also may accompany such diseases as poliomyelitis, rickets, or tuberculosis. An accentuated lumbar curvature is called lordosis, or swayback.

As a person ages, the intervertebral disks tend to become smaller and more rigid, and compression is more likely to fracture the vertebral bodies. Consequently, height may decrease, and the thoracic curvature of the vertebral column may be accentuated, bowing the back.