The human spine extends from the skull to the coccyx, or tailbone. It performs several crucial anatomical functions for human movement and function; it is a support structure for the skull, a component for the movement of the head and neck, and a protective mechanism for the vital spinal cord and the internal organs.
The spine is composed of 24 hard, semicircular bones known as vertebrae, organized in a column. The individual vertebrae are connected by durable fibrous tissue known as facet joints; each vertebra is afforded both separation from adjacent bones as well as cushioning from stresses and strains of movement and applied forces by its intravertebrae disks. Each disk is composed of a cartilage-like substance, annulus fibrosis, that contains a gel substance that, when subjected to most physical stresses, is remarkably durable.
When pressure is applied to the center of the disk, the gel content may be forced against cartilage shell, causing it to break down and rupture. This rupture is also known as a herniation of the disk; it may also be known as a "slipped disk," although it is not an accurate description of the mechanism. The condition will often result in pain for the person, as the gel content of the disk may leak onto the nerves of the spinal cord, causing pressure to be applied this structure. When the disk does not break, but when its surface bulges out as a result of the pressure applied to it, the condition is known as a bulging disk. Bulging disks do not necessarily cause pressure and resultant pain on the adjacent nerve structures; a bulging disk is at greater risk to herniate than a normal intra-vertebrae disk. In its most extreme form, a herniated disk will both rupture and portions of the cartilage exterior of the disk will float freely in the area outside of the disk.
The mechanisms of a herniated disk are numerous, given the wide range of both movements and forces to which the vertebrae and the disks are exposed. The primary location of a herniated disk is in the lumbar region of the spine (the low back); the second most likely location is the cervical spine, the seven vertebrae that form the top of the spine below the skull. Any type of direct force that is applied to the disk can potentially cause the gel center of the disk outward into the exterior wall. Herniated disks can result from a sudden or explosive movement, such as the lifting of a heavy object or a sudden twisting of the spine; the most frequent cause of disk herniation is exposure to regular loads or strains on the disk over a period of time. In many circumstances, what is believed to be a sudden herniation of a disk is the result of a culminating incident involving a previous bulging or otherwise damaged disk. If the herniation results in pressure being applied to the spinal cord or the associated nerve endings, pain sensations will tend to radiate along the arms or legs.
Depending on the location of the herniated disk, the consequences may extend beyond the musculoskeletal structure. If a lumbar disk is damaged, the pressure produced may impact on the nerve structures responsible for the regulation of the function of the bladder and bowels.
The herniation of disks occurs most commonly in persons after age 35; it is believed that the regular stresses of daily living often create a favorable basis for disk damage to occur. In addition to the subjective observations of the affected person, diagnostic tools such as x rays, the injection of radioactive dye into the spinal canal for observation of narrowing that would be indicative of a herniated disk, and magnetic resonance imaging (MRI) are indicated. The identification of the precise location of a herniated disk is often difficult.
In addition to the high-technology analytical tools, there are a number of physical tests employed to isolate the location of a herniated disk. Various movements of the body, including the straight leg raise to determine the existence of pressure on the nerve roots that emanate from the spinal cord at the lumbar spine, are used to assist in the process.
Surgery is generally regarded as an absolute last resort in the treatment of a herniated disk. Many such injuries will resolve themselves with therapy over time. Chiropractic manipulation is sometimes employed as a technique to free the limitations of movement caused by the damaged disk. Acupuncture has also been more frequently employed in recent years to alleviate the pain of the contacting disk against the nearby nerve system. Massage therapies, ultrasound, and anti-inflammatory medications are all components to a comprehensive pain management and treatment program.
When surgery is performed to repair the disk, the severity or invasiveness of the procedure will vary depending on the extent of the disk damage. In some circumstances, the disk can be re-inflated with a synthetic gel; in others, the damaged portions of the disk will be removed from contact with the nerve structure.