Sciatica

Anatomy

In the lower back, the lumbar spine is composed of five vertebral bodies. The sacrum, a large triangular bone consisting of five fused vertebrae, connects the lumbar spine and the tailbone or coccyx. The spinal cord traverses through the spinal canal of the vertebrae, and nerves coming off the spinal cord travel through the spinal canal and exit through small openings on the sides of the vertebrae called foramina (singular foramen). The sciatic nerve is the largest and longest nerve in the body and originates from a group of nerves in the lower back. It then runs through the buttock and down the lower leg, supplying motor and sensory functions to the thigh, knee, calf, ankle, foot, and toes. Between each of the vertebrae is a vertebral or spinal disk that serves as a shock absorber. Each disk is composed of two parts: (1) an outer tough exterior (annulus fibrosis) that surrounds and contains (2) an inner jelly-like material (nucleus pulposus).

Causes

The leading etiology of sciatica (approximately 90% of cases) is a herniated disk causing nerve root compression. Other etiologies include lumbar stenosis (narrowing of the lumbar spinal canal), facet joint osteoarthritis, spinal cord tumors, and infection. Disk prolapse is more commonly identified as a cause of nerve root compression among younger athletes (20- to 50-year-olds), while osteophytes and degenerative disease are often the culprits in older athletes. The red flags for life-threatening etiologies have been widely recognized, and more aggressive and urgent workup is needed if these are identified (Table 1). Several factors have been shown to increase one's risk for sciatica: age (peak between 45 and 64 years of age), increasing height, mental stress, cigarette smoking, strenuous physical activity, and exposure to vibrations from vehicles.

Clinical Evaluation