Common Conditions Causing Low Back Pain

The age of the patient makes certain diagnostic possibilities more or less likely. Sprains, postural abnormalities (scoliosis, kyphosis), congenital malformations (e.g., spondylolisthesis and spondylolysis), and osteochondritis (Scheuermann disease) are the most frequent causes of chronic back pain in childhood and adolescence. Lumbosacral sprains, discogenic disease, rheumatoid spondylitis, ankylosing spondylitis, and trauma are the predominant sources of back pain in early and middle adult years. Degenerative arthropathy ("arthritis"), stenosing spondylo-sis, osteoporosis with vertebral collapse, and metastatic tumor tend to occur in older people.

Lumbosacral strain or sprain At any age, but mostly in physically vigorous individuals, this disorder may cause intense low-back pain and muscle spasm. Plain films of the lumbosacral region are usually unre-vealing. Unless there are paresthesias, weakness unrelated to pain, or reflex changes, there is no way of deciding whether this condition is due to a prolapsed disc or to a ligamentous or muscular lesion (low-back strain). Bed rest, the application of cold and heat, and sufficient analgesic medication relieve the pain in a few days. Hospitalization is only a matter of convenience. A history of one or several such episodes is often elicited in patients who are later found to have disc disease.

Spondylolisthesis This disorder is one in which a vertebral body, along with its pedicles and articulatory processes, slips forward on the vertebra below (usually L5 on S1, less often L4 on L5). It reveals itself in late childhood and adolescence and at first may cause little difficulty. Later, low-back pain, limitation of motion, a palpable "step" of the spinous process forward from the one below, and an exaggerated lumbar lordosis are the usual manifestations. In severe cases, the lower lumbar roots may be compressed, with slight weakness or sensory changes in the legs, diminished ankle reflexes, and disturbances of bladder function. The symptoms are increased by standing and walking, like those of lumbar stenosis (see below). Treatment is surgical.

Spondylolysis is the name given to a common genetic defect of the pars interarticularis (the segment at the junction of pedicle and lamina) of the lower lumbar vertebrae. The defect predisposes to fracture at this location. The defect is occasionally unilateral but far more often bilateral. In the latter form, the vertebral body, pedicles, and superior artic ular facets move anteriorly, in which case the disorder results in spondylolisthesis.

Herniated intervertebral discs Trauma (usually a flexion injury) or fraying of the annulus fibrosus and posterior longitudinal ligaments allows the soft nucleus pulposus to extrude posterolaterally into the spinal canal and compress a spinal root. The injury need not be severe because of underlying degenerative changes; a sudden twist or lifting from a flexed position of the trunk may be sufficient. The sites of rupture are usually at L5-S1 and L4-L5 and are progressively less frequent at the upper lumbar and lower thoracic levels. The other common sites are C6-C7, C5-C6 and C4-C5. Of importance is the fact that bulging of the disc in itself is not a cause of any significant pain or radicular symptoms.

Usually pain and paresthesias are more conspicuous than weakness, although weakness can be severe with anterior root compression. Despite overlapping effects, one finds S1 lesions to weaken plantar (dorsi) flexors; L5, extensors of ankle and big toe; L4, ankle evertors; L3, knee extensors; L2, thigh adductors; and L1, hip flexors.

Protrusion of the L4-L5 disc, by compressing the L5 root, causes sciatica with pain extending along the lateral surface of the thigh and calf and dorsal surface of the foot and first three toes. With an L5-S1 disc (compression of S1), the pain is in the posterior thigh and calf, lateral border of the foot, and fourth and fifth toes; the ankle jerk is reduced or absent. Straight-leg raising stretches L5 and S1 roots, hence the presence of a Lasegue sign. With an L3-L4 disc, the pain extends to the anterior thigh and anteromedial leg into the knee, and the knee jerk is diminished. Large central disc protrusion may cause bilateral symptoms, with severe weakness of the legs and paralysis of bladder and bowel (cauda equina syndrome). The configurations of root compressions by protruded discs are illustrated in Fig. 11-2.

Bed rest usually relieves the pain of root compression. If there is a large free fragment the patient may be most comfortable in the seated or standing position and bed rest may fail. If bed rest fails, MRI or CT scan with or without myelography confirms the diagnosis and serves as a guide to hemilaminectomy and excision of disc tissue. If diagnostic procedures disclose a protruded disc, a protracted period of conservative therapy (rest for 2 weeks and analgesics) should be tried before resorting to laminectomy. Epidural injection of corticosteroids may give temporary relief. Unremitting sciatica with evidence of L5 or S1 root involvement responds to appropriate surgery 9 times out of 10. A large central protrusion with signs of cauda equina compression demands immediate MRI or myelography and surgical removal.

Only about 1 percent of patients with low-back pain have unmistakable signs of root compression that cannot be relieved by conservative measures and requires surgical decompression. Of those operated upon,

FIG. 11-2 Mechanisms of compression of the fifth lumbar and first sacral roots. A lateral disc protrusion at the L4-L5 level usually involves the fifth lumbar root and spares the fourth; a protrusion at L5-S1 involves the first sacral root and spares the fifth lumbar root. Note that a more medially placed disc protrusion at the L4-L5 level may involve the fifth lumbar root as well as the first (or second and third) sacral root.

FIG. 11-2 Mechanisms of compression of the fifth lumbar and first sacral roots. A lateral disc protrusion at the L4-L5 level usually involves the fifth lumbar root and spares the fourth; a protrusion at L5-S1 involves the first sacral root and spares the fifth lumbar root. Note that a more medially placed disc protrusion at the L4-L5 level may involve the fifth lumbar root as well as the first (or second and third) sacral root.

as many as 10 percent in some series need further surgery, and as many as 25 percent are left with troublesome back pain ("failed back syndrome"; see the Principles for details).

Degenerative arthropathy of lumbar spine Wear and tear and repeated subclinical trauma are blamed for degenerative changes in the most mobile parts of the spine (low cervical and lumbar). This leads to osteophyte formation, both anteriorly and posteriorly into the spinal canal, infolding and thickening of the posterior longitudinal ligament, bulging of discs, and thickening of the ligamentum flavum—all leading to segmental pain, stiffness, and limitation of motion and, at times, to stenosis of the lumbar spinal canal (lumbar spondylosis, or lumbar stenosis). Pain in the affected region is associated with stiffness and limitation of motion. Treatment follows conservative lines if no stenotic compression of roots is present. Superimposition of the osteoarthritic changes on a congenitally narrower-than-normal canal may cause compression of lumbosacral roots.

Patients may have pain in the low back with radiation into thighs and legs. Typically, the pain increases on standing and walking and may resemble the intermittent claudication associated with vascular disease. Weakness and numbness of the feet are added in some cases. Sitting and flexing the trunk reduce or abolish the symptoms. Weakness and reflex loss in the legs may be brought out by having the patient walk one or two blocks or sit in a chair and attempt to touch his toes with legs extended. The neurologic signs may be localized to the roots by EMG of paraspinal muscles and conduction studies of proximal nerves.

Other conditions that narrow the lumbar spinal canal will produce the same syndrome. The most frequent causes, after lumbar spondylosis, are central disc protrusion and spondylolisthesis. Surgical decompression gives satisfactory relief. For discussion of visceral pain referred to the spine, see the Principles.

Spinal cord and column, and other intraspinal tumors These important causes of back pain are considered in Chap. 43.

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