A spinal disc herniation (prolapsus disci intervertebralis), informally andmisleadingly called a "slipped disc", is a medical conditionaffecting the spine, in which a tear in the outer, fibrous ring(annulus fibrosus) ofan intervertebral disc (discus intervertebralis) allows the soft, centralportion (nucleuspulposus) to bulge out. Tears are almost always posterior-ipsilateralin nature owing to the presence of the posterior longitudinal ligament inthe spinal canal. This tear in the disc ring may result in the release ofinflammatory chemical mediators which may directly cause severe pain, even inthe absence of nerve root compression (see "chemical radiculitis"below). This is the rationale for the use of anti-inflammatory treatments forpain associated with disc herniation, protrusion, bulge, or disc tear.
It is normally a further development of a previously existing discprotrusion, a condition in which the outermost layers of the annulus fibrosus are still intact,but can bulge when the disc is under pressure.
Symptoms of a herniated disc can vary depending on the location of theherniation and the types of soft tissue that become involved. They can rangefrom little or no pain if the disc is the only tissue injured, to severe andunrelenting neck or low back pain that will radiate into the regionsserved by affected nerve roots that are irritated or impinged by the herniatedmaterial. Often, herniated discs are not diagnosed immediately, as the patientscome with undefined pains in the thighs, knees or feet. Other symptoms mayinclude sensory changes such as numbness, tingling, muscular weakness,paralysis, paresthesia, and affection of reflexes. If the herniateddisc is in the lumbar region the patient may also experience sciatica due toirritation of one of the nerve roots of the sciaticnerve. Unlike a pulsating pain or pain that comes and goes, which can becaused by muscle spasm, pain from a herniated disc is usually continuous or atleast is continuous in a specific position of the body.
It is possible to have a herniated disc without any pain or noticeablesymptoms, depending on its location. If the extruded nucleus pulposus materialdoesn't press on soft tissues or nerves, it may not cause any symptoms. Asmall-sample study examining the cervical spine in symptom-free volunteers hasfound focal disc protrusions in 50% of participants, which shows that aconsiderable part of the population can have focal herniated discs in theircervical region that do not cause noticeable symptoms.
Typically, symptoms are experienced only on one side of the body. If theprolapse is very large and presses on the spinal cord or the caudaequina in the lumbar region, affection of both sides of the body may occur,often with serious consequences.
There is now recognition of the importance of “chemical radiculitis” in thegeneration of backpain. A primary focus of surgery is to remove “pressure” or reducemechanical compression on a neural element: either the spinal cord,or a nerveroot. But it is increasingly recognized that back pain, rather than beingsolely due to compression, may also be due to chemical inflammation. There isevidence that points to a specific inflammatory mediator of this pain. Thisinflammatory molecule, called tumor necrosis factor-alpha (TNF), is released notonly by the herniated disc, but also in cases of disc tear (annular tear), byfacet joints, and in spinal stenosis. In addition to causing pain andinflammation, TNF mayalso contribute to disc degeneration.