The vertebral column consists of 33 vertebrae joined by ligaments and cartilage. The upper 24 vertebrae are separate and movable, but the lower 9 are fixed: 5 are fused to form the sacrum, and the last 4 are usually fused to form the coccyx. The vertebral column consists of 7 cervical (C1–7), 12 thoracic (T1–12), 5 lumbar (L1–5), 5 sacral (S1–5), and 4 coccygeal (Co1–4) vertebrae. In some individuals, vertebra L5 is partly or completely fused with the sacrum.
Figure 6–1 illustrates the relation of the spinal cord itself to the surrounding vertebrae. Recall that the spinal cord tapers and ends at the L1 or L2 level of the vertebral column. Below that level, the dural sac within the vertebral column contains the cauda equina.
CLINICAL ILLUSTRATION 6–1
A 61-year-old former house painter with a history of alcoholism was admitted to the medical service after being found in a hotel room in a confused state that was attributed to alcohol withdrawal syndrome. The patient did not complain of pain but said he was weak and could not get out of bed. He had a fever. The intern's initial neurologic examination did not reveal any focal neurologic signs. The lumbar puncture yielded CSF containing a moderate number of white blood cells and protein of about 100 mg/dL (elevated) with normal CSF glucose. Despite treatment with antibiotics, the patient did not improve, and neurologic consultation was obtained.
On examination, the patient was confused and uncooperative. He stated he was weak and could not walk. Motor examination revealed flaccid paraparesis. Deep tendon reflexes were absent in the legs, and the plantar responses were extensor. The patient was not cooperative for vibratory or position sense testing. He denied feeling a pin as painful over any part of the body; however, when the examiner watched for a facial wince on pinprick, a sensory level T5–6 could be demonstrated. On gentle percussion of the spinal column, there was tenderness at T9–10.
Imaging of the spinal column revealed an epidural mass. The patient was taken to surgery, and an epidural abscess, extending over five vertebral segments, was found. The spinal cord under the abscess was compressed and pale, probably as a result of ischemia (vasospasm leading to inadequate perfusion with blood).
The motor status of this patient suggested a spinal cord lesion, which was confirmed on sensory examination. Percussion tenderness over the spine, which is often seen with epidural abscesses or tumors, provided additional evidence for disease of the spinal column. Epidural spinal cord compression is especially common in the context of neoplasms (eg, breast, prostate) that metastasize to the spine. The possibility of spinal cord compression should be considered, and the vertebral column gently percussed, in any patient with a known malignancy and recent-onset or worsening back pain. As noted earlier, epidural spinal cord compression can be effectively treated in many patients if recognized early in its course. However, if it is not diagnosed and rapidly treated, it can progress to cause irreversible paraplegia or quadriplegia. Any patient with suspected spinal cord compression must be evaluated on an urgent basis.
The vertebral column is slightly S-shaped when seen from the side (Fig 6–6). The cervical spine is ventrally convex, the thoracic spine ventrally concave, and the lumbar spine ventrally convex, with its curve ending at the lumbosacral angle. Ventral convexity is sometimes referred to as normal lordosis and dorsal convexity as normal kyphosis. The pelvic curve (sacrum plus coccyx) is concave downward and ventrally from the lumbosacral angle to the tip of the coccyx. The spinal column in an adult is often slightly twisted along its long axis; this is called normal scoliosis.
Most vertebrae share a common architectural plan. A typical vertebra (not C1, however) has a body and a vertebral (neural) arch that together surround the vertebral (spinal) canal (Fig 6–7). The neural arch is composed of a pedicle on each side supporting a lamina that extends posteriorly to the spinous process (spine). The pedicle has both superior and inferior notches that form the intervertebral foramen. Each vertebra has lateral transverse processes and superior and inferior articular processes with facets. The ventral portion of the neural arch is formed by the ventral body.
Computed tomography image of a horizontal section at midlevel of vertebra L4.
Articulation of a pair of vertebrae is body to body, with an intervening intervertebral disk and at the superior and inferior articular facets on both sides. The intervertebral disks help absorb stress and strain within the vertebral column.
CLINICAL ILLUSTRATION 6–2
A 74-year-old male, with a history of prostate cancer, complained of 3 weeks of lower back pain. He noted that he felt tingling in his feet and legs, extending all the way up to the waist. He did not complain of weakness, but admitted that he had fallen several times while walking stairs.
Physical examination revealed a sensory level (loss of pinprick and light touch sensation) in both legs, extending to just below the umbilicus. Vibration and position sense were present but impaired in the legs. There was mild (4+/5) weakness of the legs. Deep tendon reflexes (knee jerks, Achilles reflexes) were hyperactive in the legs, and the plantar response we extensor bilaterally.
Imaging revealed a tumor, most likely metastatic from the patient's prostate cancer, that had infiltrated the vertebral body at T1, which was now compressing the spinal cord. The patient was immediately referred for treatment.
This case illustrates several important points: First, back pain and neurological complaints in the legs must always trigger consideration of spinal cord compression. Second, while sensory symptoms (such as numbness or tingling or pain) often occur early, patients may not complain of motor loss early in the course of disease—this patient did not explicitly complain of weakness, although he admitted to falling and was found on examination to have mild weakness of the legs. Third, because the spinal cord is shorter than the vertebral column, there is not perfect alignment between the segment of the bony vertebral column that is involved, and the affected segment of the spinal cord. In this case, a lesion of the T1 vertebra compressed the T4 spinal cord. The anatomic relationship between the segments of the bony vertebral column and the spinal cord within it are shown in Figure 5–3 and Table 5–1.
Each disk (Fig 6–8) contains a core of primitive gelatinous large-celled tissue, the nucleus pulposus, surrounded by a thick annulus fibrosus. The disks are attached to the hyaline cartilage, which covers the superior and inferior surfaces of the vertebral bodies. The water content of the disks decreases with age, resulting in a loss of height in older individuals.
Computed tomography image of a horizontal section through L4 at the level of the L3–4 intervertebral disk. (Reproduced, with permission, from deGroot J: Correlative Neuroanatomy of Computed Tomography and Magnetic Resonance Imaging. 21st ed. Appleton & Lange, 1991.)