A herniated disc AKA a slipped disc is a rupture or bulge in the annulus fibrosus which allows the gelatine like nucleus pulposus to move outwards. There are varying degrees of herniation.
Herniated discs are most common in men under 40 years old.
The herniation irritates the spinal nerve root. Which can cause muscle spasm and referred pain. Exercise therapy is crucial for recovery. The body can reduce the herniation but it will not heal back to its former state.
Disc herniation is usually due to age-related degeneration of the outer ring, known as the anulus fibrosus, although trauma, lifting or straining have been implicated as well.
Most herniations are posterior lateral due to lack of posterior longitudinal ligament in the spinal canal (1).
The herniation can release chemicals which ultimately cause pain (1).
Normally the degree of herniation progresses from a bulge. A minor herniation can heal in a number of weeks (1).
Symptoms can vary according to the location of the herniation. Normally the symptoms are as follows;
Pain radiating into set pattern - dermotome.
Pain into thighs, knees or feet.
Sensory changes – numbness, tingling or paresthesia.
Weakness in a set pattern of muscles – myotome
It is possible to have a herniated disc without pain, depending on the structures that are affected by the herniation, it is suggested that as much as 50% of people may have herniated discs and not know it (2, 3).
Normally the pain caused by a herniated disc travels down one side of body, however if it is a large central herniation pain can be in both legs and can result in cauda equina syndrome and reduced bowel and bladder function.
The majority of authorities believe that disc herniation is caused due to degeneration of disc due to age (4). As the annulus fibrosus degenerates a fissure occurs and the nucleus pulposus leaks or bulges out. It is also common that lifting heavy loads with poor biomechanics and sporting accidents can cause herniated discs.
Different movements can affect the pressure placed upon the discs for example; while sitting or bending to lift, internal pressure on a disc can move from 17 psi (lying down) to over 300 psi (lifting with a rounded back) (1).
Modern science has discovered a number of genes that are associated with intervertebral disc degeneration. For example (5);
Type I collagen
Type IX collagen
Vitamin D receptor
Interleukin – 1
Interleukin – 6
A mutation in genes that are involved in regulation of extracellular matrix for example MMP2 and THBS2, has been demonstrated to contribute to lumbar disc herniation. (6)
This inflammatory molecule, called tumor necrosis factor – alpha (TNF), is released not only by the herniated disc, but also in cases of disc tear (annular tear), by facet joints, and in spinal stenosis [7, 8, 9 ,10, 11).
The majority of spinal disc herniation cases occur in the lumbar region (95% in L4-L5 or L5-S1) [12). The second most common site is the cervical region (C5-C6, C6-C7). The thoracic region accounts for only 0.15% to 4.0% of cases.
The straight leg raise may be positive, as this finding has low specificity; however, it has high sensitivity. Thus, the finding of a negative SLR sign is important in helping to "rule out" the possibility of a lower lumbar disc herniation.