Dalley, 10th Edition

Chapter 2 ■ Back

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with suspicion. It is more likely that the nerve roots are be ing compressed by increased ossi cation of the IV foramen as they exit. 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 liga ment. The clinical picture varies considerably, but pain of acute onset in the lower back is a common presenting symp tom. Because muscle spasm is associated with low back pain, the lumbar region of the vertebral column becomes tense and increasingly cramped as relative ischemia (local loss of blood supply) occurs, causing painful movement. Sciatica , pain radiating from the lower back into the but tock and down the posterior or lateral aspect 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 (Fig. B2.11C). The IV foramina in the lumbar region decrease in size, and the lumbar nerves in crease in size, as the vertebral column descends. This may explain why sciatica is so common. Bone spurs (osteophytes) developing around the zygapophysial joints, or the postero lateral margins during aging, may narrow the foramina even more, causing shooting pains down the lower limbs. The straight leg test, also called Lasègue sign, is performed to determine if a patient with LBP has a herniated IV disc. The patient’s hip is passively exed by the examiner with the knee in full extension (Fig. B2.12). This maneuver will cause traction on the nerve roots forming the sciatic nerve and in the case of a herniated disc in the lumbar region will reproduce the pain. IV discs may also be damaged by violent rotation (e.g., during an erratic golf swing) or exing of the vertebral col umn. 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 (Fig. B2.11C). In the tho racic and lumbar regions, the IV disc forms the inferior half of the anterior border of the IV foramen and that the supe rior half is formed by the bone of the body of the superior vertebra (see Figs. 2.2 and 2.16). 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. Symptom-producing IV disc protrusions occur in the cervi cal region, almost as often as in the lumbar region. Chronic or sudden forcible hyper exion of the cervical region, as might occur during a head-on collision or during illegal head blocking in football (Fig. B2.13), for example, may 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 relation ship 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.

FIGURE B2.12. Straight leg test.

Spinal Fusion and Intervertebral Disc Replacement

Degenerative disc disease that results in a markedly diminished IV disc space (Fig. B2.14A) often pro duces spinal stenosis (narrowing of the vertebral canal or an intervertebral foramen producing neuropathy) that may be treated surgically by laminectomy with or without spinal fusion. The laminectomy decompresses involved nerves (see the Clinical Box “Laminectomy” earlier in this chapter), while spinal fusion ( arthrodesis ) eliminates move ment between two or more motion segments (IV joints) of the back that may produce additional compression. Using bone obtained from the pelvic bone or a bone bank, a bridge (graft) is constructed between adjacent vertebrae (Fig. B2.14B).

Torn supraspinous and interspinous ligaments

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Lateral view

Rupture of intervertebral disc C5/C6 with nucleus pulposus compressing C6 spinal nerve roots

FIGURE B2.13. Flexion injury of cervical vertebrae.