Lumbosacral Spinal Stenosis

Spondylolisthesis, in which one vertebral body translates anteriorly or posteriorly with respect to an adjacent vertebral body, can also occur, exacerbating the spinal canal narrowing. The L4-5 level is most commonly involved, followed by L5-S1 and L3-4.

The majority of patients with spinal stenosis are men, and most are in at least their sixth decade of life. However, spinal stenosis may occur early in life in patients with certain developmental bony abnormalities, such as achondroplasia, osteochondrodystrophy, and mucopolysaccharidosis.

Clinical Manifestations. The classic clinical presentation of lumbar spinal stenosis is neurogenic (or pseudo) claudication, characterized by symptoms of pain or aching in the legs to be exacerbated with walking, standing, and/or maintaining certain postures (especially extension of the spine), and relieved with sitting or lying. Many patients with lumbar spinal stenosis (LSS) are symptomatic only when active. The symptoms are similar to vascular claudication of the leg(s) due to arterial insufficiency exacerbated by walking. Symptoms of neurogenic claudication are reported in the majority of patients with lumbar spinal stenosis. Other common symptoms include paresthesia, low back pain, and weakness. Symptoms are bilateral in over half of patients, but are often asymmetric. Often, the whole leg is symptomatic, including the hip, buttock, thigh, and leg.

Patients with spinal stenosis can pedal long distances on a bicycle or push a grocery cart throughout a store as long as they maintain a fully flexed position, in contrast to patients with arterial insufficiency. Walking uphill or upstairs involves hyperextension of the spine and so is more likely to cause exacerbation of symptoms in patients with lumbar spinal stenosis, in contrast to walking downhill or downstairs when the spine is in a flexed position. As the degree of canal stenosis increases, spinal nerve roots are continuously compressed, and symptoms and weakness become constant, even at rest.

Diagnosis. Results of examination of the patient with spinal stenosis may be relatively benign, especially in comparison with results in patients in whom a herniated nucleus pulposus produces nerve root disease. At rest, these patients are usually comfortable and have no back pain, muscle spasm or loss of lumbar lordosis. Straight leg raising does not aggravate symptoms, as it does in disk disease. In contrast, in spinal stenosis, hyperextension of the spine precipitates symptoms, which may be relieved by forward flexion. At times, the physician does not consider the patient’s symptoms to be serious because testing of strength, reflexes, and sensation often fails to reveal any deficit. When exercise fails to elicit changes in pulses, the unwary physician may cease the evaluation. The precise mechanism that produces spinal stenosis is not clear. It has been postulated that interaction occurs between mechanical compression and exercise-precipitated nerve root ischemia.

Plain radiographs of the spine demonstrate spondylosis. MRI usually shows high-grade stenosis of the central canal, while CT myelography may demonstrate severe obstruction or complete block. Frequently, multiple levels are involved, usually L2 or L3-5. In contrast to acute disk rupture, L5-S1 is rarely involved.

Treatment. Wide laminectomy of the affected levels, with unroofing of the most symptomatic nerve roots, is the treatment of choice. The surgeon must search for extruded disk fragments. Postoperatively, neurogenic claudication is fully relieved in most patients, allowing them to lead much fuller lives. It should be stressed that in contrast to midline disk herniation, which can also produce bilateral paresthesias, surgery is not urgent. Rather, the patient and surgeon may wish to follow a conservative course of observation until the symptoms produce significant discomfort and interfere with normal leg patterns.

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