A disc herniation, also known as a spinal disc herniation, is a condition affecting the intervertebral disc between two vertebrae, usually caused by excessive strain or trauma to the spine. It may result in back pain, pain or abnormal sensation in different parts of the body, and physical disability. The most conclusive diagnostic tool for disc herniation is MRI, and treatments may range from painkillers to surgery. The risk of disc herniation may be reduced by maintaining core strength and an awareness of body mechanics including good posture.
When a tear in the outer fibrous ring of an intervertebral disc allows the soft, central portion to bulge out beyond the damaged outer ring, the disc is said to be herniated.
Disc herniation is frequently associated with age-related degeneration of the outer ring, known as the annulus fibrosus, but is normally triggered by trauma or straining from lifting or twisting. Tears are almost always posterolateral (on the back sides) owing to relative narrowness of the posterior longitudinal ligament relative to the anterior longitudinal ligament. A tear in the disc ring may result in the release of chemicals causing inflammation, which can result in severe pain even in the absence of nerve root compression.
Disc herniation may develop from a pre-existing disc protrusion, in which the outermost layers of the annulus fibrosus are still intact, but can bulge when the disc is under pressure. In contrast to a herniation, none of the central portion escapes beyond the outer layers. Most minor herniations heal within several weeks. Anti-inflammatory treatments for pain associated with disc herniation, protrusion, bulge, or disc tear are generally effective. Severe herniations may not heal of their own accord and may require surgery.
The condition may be referred to as a slipped disc, but this term is considered inaccurate as the spinal discs are firmly attached between the vertebrae and cannot "slip" out of place.
Signs and symptoms Symptoms of a herniated disc can vary depending on the location of the herniation. Symptoms may include pain in the lower back or neck.
It is possible to have a herniated disc without pain or noticeable symptoms if the extruded nucleus pulposus material does not press on soft tissues or nerves. A small-sample study examining the cervical spine in symptom-free volunteers found focal disc protrusions in 50% of participants, suggesting that a considerable part of the population might have focal herniated discs in their cervical region that do not cause noticeable symptoms.
A herniated disc in the lumbar spine may cause radicular pain (radiating nerve pain in the lower extremities or groin area) and may sometimes be associated with bowel or bladder incontinence.
Typically, symptoms are experienced only on one side of the body, but if a herniation is very large and presses on the nerves on both sides within the spinal column or the cauda equina, both sides of the body may be affected, often with serious consequences. Compression of the cauda equina can cause permanent nerve damage (or paralysis if left untreated) which can result in loss of bowel and bladder control and sexual dysfunction. This disorder is called cauda equina syndrome. Other complications include chronic pain.
Cause When the spine is straight, such as when standing or lying down, internal pressure is equalized on all parts of the discs. While sitting or bending to lift, internal pressure on a disc can move from (lying down) to over (lifting with a rounded back). Herniation of the contents of the disc into the spinal canal often occurs when the anterior side (stomach side) of the disc is compressed while sitting or bending forward, and the contents (nucleus pulposus) get pressed against the tightly stretched and thinned membrane (annulus fibrosus) on the posterior side (back side) of the disc. The combination of membrane-thinning from stretching and increased internal pressure () can result in the rupture of the confining membrane. The jelly-like contents of the disc then move into the spinal canal, pressing against the spinal nerves, which may produce intense and potentially disabling pain and other symptoms.
Some authors favour degeneration of the intervertebral disc as the major cause of spinal disc herniation and cite trauma as a minor cause. Disc degeneration occurs both in degenerative disc disease and aging. With degeneration, the disc components – the nucleus pulposus and annulus fibrosus – become exposed to altered loads. Specifically, the nucleus becomes fibrous and stiff and less able to bear load. Excess load is transferred to the annulus, which may then develop fissures as a result. If the fissures reach the periphery of the annulus, the nuclear material can pass through as a disc herniation.
Mutations in several genes have been implicated in intervertebral disc degeneration. Probable candidate genes include type I collagen (sp1 site), type IX collagen, vitamin D receptor, aggrecan, asporin, MMP3, interleukin-1, and interleukin-6 polymorphisms. Mutation in genes – such as MMP2 and THBS2 – that encode for proteins and enzymes involved in the regulation of the extracellular matrix has been shown to contribute to lumbar disc herniation.
Disc herniations may result from general wear and tear, such as weightlifting training, constant sitting or squatting, driving, or a sedentary lifestyle. Herniations can also result from the lifting of heavy loads.
Professional athletes, especially those playing contact sports, such as American football, Rugby, ice hockey, and wrestling, are known to be prone to disc herniations as well as some limited contact sports that require repetitive flexion and compression such as soccer, baseball, basketball, and volleyball. Within athletic contexts, herniation is often the result of sudden blunt impacts against, or abrupt bending or torsional movements of, the lower back.
Pathophysiology The majority of disc herniations occur in the lumbar spine (95% at L4–L5 or L5–S1). The second most common site is the cervical region (C5–C6, C6–C7). The thoracic region accounts for only 1–2% of cases. Herniations usually occur postero-laterally, at the points where the annulus fibrosus is relatively thin and is not reinforced by the posterior or anterior longitudinal ligament. In the cervical spine, a symptomatic posterolateral herniation between two vertebrae will impinge on the nerve that exits the spinal canal between those two vertebrae on that side. So, for example, a right posterolateral herniation of the disc between vertebrae C5 and C6 will impinge on the right C6 spinal nerve. The rest of the spinal cord, however, is oriented differently, so a symptomatic posterolateral herniation between two vertebrae will impinge on the nerve exiting at the next intervertebral level down.
Lumbar disc herniation
Lumbar disc herniations occur in the back, most often between the fourth and fifth lumbar vertebral bodies or between the fifth and the sacrum. Here, symptoms can be felt in the lower back, buttocks, thigh, anal/genital region (via the perineal nerve), and may radiate into the foot and/or toe. The sciatic nerve is the most commonly affected nerve, causing symptoms of sciatica. The femoral nerve can also be affected and cause the patient to experience a numb, tingling feeling throughout one or both legs and even feet or a burning feeling in the hips and legs. A herniation in the lumbar region often compresses the nerve root exiting at the level below the disc. Thus, a herniation of the L4–5 disc compresses the L5 nerve root, only if the herniation is posterolateral.
Cervical disc herniation
Cervical disc herniations occur in the neck, most often between the fifth and sixth (C5–6) and the sixth and seventh (C6–7) cervical vertebral bodies. There is an increased susceptibility amongst older (60+) patients to herniations higher in the neck, especially at C3–4. Symptoms of cervical herniations may be felt in the back of the skull, the neck, shoulder girdle, scapula, arm, and hand. The nerves of the cervical plexus and brachial plexus can be affected.
Common causes of disc herniation at C5–6 or C7–T1 (often mistakenly called C7–8) levels can be grouped into mechanical, degenerative, or traumatic causes.
Degenerative changes relate to age-related changes, degenerative disc disease, or bone spurs that naturally degenerate the disc.
Poor posture, heavy lifting, or repetitive neck movements (common in athletes or drivers) can cause strain on the disc.
Finally, genetic factors like inherited predisposition can cause faster disintegration.
Intradural disc herniation Intradural disc herniation occurs when the disc material crosses the dura mater and enters the thecal sac. It is a rare form of disc herniation with an incidence of 0.2–2.2%. Pre-operative imaging can be helpful for diagnosis, but intra-operative findings are required for confirmation.
Inflammation
It is increasingly recognized that back pain resulting from disc herniation is not always due solely to nerve compression of the spinal cord or nerve roots, but may also be caused by chemical inflammation. There is evidence that points to a specific inflammatory mediator in back pain: an inflammatory molecule, called tumor necrosis factor alpha (TNF), is released not only by a herniated disc, but also in cases of disc tear (annulus tear) by facet joints, and in spinal stenosis. In addition to causing pain and inflammation, TNF may contribute to disc degeneration.
Diagnosis Terminology Terms commonly used to describe the condition include herniated disc, prolapsed disc, ruptured disc, and slipped disc. Other conditions that are closely related include disc protrusion, radiculopathy (pinched nerve), sciatica, disc disease, disc degeneration, degenerative disc disease, and black disc (a totally degenerated spinal disc).
The popular term slipped disc is a misnomer, as the intervertebral discs are tightly sandwiched between two vertebrae to which they are attached, and cannot actually "slip", or even get out of place. The disc is actually grown together with the adjacent vertebrae and can be squeezed, stretched, and twisted, all in small degrees. It can also be torn, ripped, herniated, and degenerated, but it cannot "slip". Some authors consider that the term slipped disc is harmful, as it leads to an incorrect idea of what has occurred and thus of the likely outcome.Ehealthmd.com FAQ: "...the entire disc does not 'slip' out of place." However, during growth, one vertebral body can slip relative to an adjacent vertebral body, a deformity called spondylolisthesis.
Spinal disc herniation is known in Latin as prolapsus disci intervertebralis.
Click images to see larger versions
Physical examination Diagnosis of spinal disc herniation is made by a practitioner based on a patient's history and symptoms, and by physical examination. During an evaluation, tests may be performed to confirm or rule out other possible causes with similar symptoms – spondylolisthesis, degeneration, tumors, metastases and space-occupying lesions, for instance – as well as to evaluate the efficacy of potential treatment options.
Straight leg raise The straight leg raise is often used as a preliminary test for possible lumbar disc herniation. A variation is to lift the leg while the patient is sitting. However, this reduces the sensitivity of the test. A Cochrane review published in 2010 found that individual diagnostic tests, including the straight leg raising test, absence of tendon reflexes, or muscle weakness, were not very accurate when conducted in isolation.
Spinal imaging