Describe and discuss the etiology and implication of ruptured and herniated intervertebral discs
- Herniation of Nucleus Pulposus
- Herniation or protrusion of the gelatinous nucleus pulposus into or through the anulus fibrosus is a well-recognized cause of lower back pain (LBP) and lower limb pain. However, there are many other causes of LBP; further, herniations are often coincidental findings in asymptomatic individuals.
- The IV discs in young persons are strong—usually so strong that the vertebrae often fracture during a fall before the discs rupture. Furthermore, the water content of their nuclei pulposi is high (approaching 90%), giving them great turgor (fullness). However, violent hyperflexion of the vertebral column may rupture an IV disc and fracture the adjacent vertebral bodies.
- Flexion of the vertebral column produces compression anteriorly and stretching or tension posteriorly, squeezing the nucleus pulposus further posteriorly toward the thinnest part of the anulus fibrosus. If the anulus fibrosus has degenerated, the nucleus pulposus may herniate into the vertebral canal and compress the spinal cord or the nerve roots of the cauda equina. A herniated disc is inappropriately called a “slipped disc” by some people.
- Herniations of the nucleus pulposus usually extend posterolaterally, where the anulus fibrosus is relatively thin and does not receive support from either the posterior or the anterior longitudinal ligaments. A posterolateral herniated IV disc is more likely to be symptomatic because of the proximity of the spinal nerve roots. The localized back pain of a herniated disc, which is usually acute pain, results from pressure on the longitudinal ligaments and periphery of the anulus fibrosus and from local inflammation caused by chemical irritation by substances from the ruptured nucleus pulposus. Chronic pain resulting from compression of the spinal nerve roots by the herniated disc is usually referred pain, perceived as coming from the area (dermatome) supplied by that nerve. Because the IV discs are largest in the lumbar and lumbosacral regions, where movements are consequently greater, posterolateral herniations of the nucleus pulposus are most common here (Fig. B4.11B).
- Approximately 95% of lumbar disc protrusions occur at the L4-L5 or L5-S1 levels. The marked decrease in the radiographic intervertebral space (i.e., in disc height) that may occur as a result of acute herniation of a nucleus may also result in narrowing of the IV foramina, perhaps exacerbating the compression of the spinal nerve roots, especially if hypertrophy of the surrounding bone has also occurred.Because the nucleus becomes increasingly dehydrated and fibrous or even granular or solid with aging, a diagnosis of acute herniation in advanced years is regarded with suspicion. It is more likely that the nerve roots are being compressed by increased ossification of the IV foramen as they exit.
- FIGURE B4.11. Herniation of nucleus pulposus. A. Right half of hemisected lumbosacral joint and median MRI of lumbosacral region. B. Inferior views, transverse section and transverse MRI of herniated IV disc C. Posterior view, cauda equina.
- Acute middle and low back pain, may be caused by a mild posterolateral protrusion of a lumbar IV disc at the L5-S1 level that affects nociceptive (pain) endings in the region, such as those associated with the posterior longitudinal ligament. The clinical picture varies considerably, but pain of acute onset in the lower back is a common presenting symptom. Because muscle spasm is associated with low back pain, the lumbar region of the vertebral column becomes tense and increasingly cramped as relative ischemia occurs, causing painful movement.
- Sciatica, pain in the lower back and hip radiating down the back of the thigh into the leg, is often caused by a herniated lumbar IV disc that compresses and compromises the L5 or S1 component of the sciatic nerve. The IV foramina in the lumbar region decrease in size and the lumbar nerves increase in size, which may explain why sciatica is so common. Bone spurs (osteophytes) developing around the zygapophysial joints or the posterolateral margins during aging may narrow the foramina even more, causing shooting pains down the lower limbs. Any maneuver that stretches the sciatic nerve, such as flexing the thigh with the knee extended (straight legraising test), may produce or exacerbate (but in some individuals relieves) sciatic pain.
- IV discs may also be damaged by violent rotation (e.g., during a golf swing) or flexing of the vertebral column. The general rule is that when an IV disc protrudes, it usually compresses the nerve root numbered one inferior to the herniated disc; for example, the L5 nerve is compressed by an L4-L5 IV disc herniation. Recall that in the thoracic and lumbar regions the IV disc forms the inferior half of the anterior border of the IV foramen and that the superior half is formed by the bone of the body of the superior vertebra (Fig. 4.14).
- The spinal nerve roots descend to the IV foramen from which the spinal nerve formed by their merging will exit. The nerve that exits a given IV foramen passes through the superior bony half of the foramen and thus lies above and is not affected by a herniating disc at that level. However, the nerve roots passing to the IV foramen immediately and farther below pass directly across the area of herniation. Symptomproducing IV disc protrusions occur in the cervical region almost as often as in the lumbar region.
- Chronic or sudden forcible hyperflexion of the cervical region, as might occur during a head-on collision or during illegal head blocking in football (Fig. B4.12), for example,
P.476may rupture the IV disc posteriorly without fracturing the vertebral body. In this region, the IV discs are centrally placed in the anterior border of the IV foramen, and a herniated disc compresses the nerve actually exiting at that level (rather than the level below as in the lumbar region).
However, recall that cervical spinal nerves exit superior to the vertebra of the same number, so the numerical relationship of herniating disc to nerve affected is the same (e.g., the cervical IV discs most commonly ruptured are those between C5-C6 and C6-C7, compressing spinal nerve roots C6 and C7, respectively). Cervical IV disc protrusions result in pain in the neck, shoulder, arm, and hand. Any sport or activity in which movement causes downward or twisting pressure on the neck or lower back may produce herniation of a nucleus pulposus