Diagnosis

History

Sciatic pain is usually sharp, jabbing, aching, throbbing, lancing, or nerve-like in quality. Your physician will want to know where you experience pain, as this can help determine the affected nerve. For example, L2 and L3 pain usually do not extend beyond the knee. An L4 radiculopathy can reach the inside of the leg, below the knee. L5 and S1 radiculopathies often extend down the back and outside of the thigh and leg and may extend into the foot. If the instep of the foot is more involved, L5 may be more likely; if the outside is affected, S1 radiculopathy may be more likely.

Sciatica pain might be worse with sitting, bending forward, coughing, or straining.  

Physical Findings

In the physical examination, the practitioner builds on the details of the history supplied by the patient. She will test your muscle function, sensation, and reflexes to assess how the nerves are functioning grossly. She may observe walking and movement to assess how pain and weakness might affect activities of daily living. Often the muscles on either side of the spine, called paraspinal muscles, might be taut and tender with spasm. The natural curve of the lumbar spine, called lordosis, may be lost. Certain conditions that mimic sciatic pain may be considered so assessment of hip joints, sacro-iliac joints, facet joints, and muscle imbalances is important. Finally, she might perform special tests that are thought to specifically evaluate for neural irritation.

Work Up

Imaging

The first imaging test performed is often a plain radiograph, commonly called an x-ray. This is because radiographs are easily obtained, inexpensive, and informative. Radiographs only show the bones of the spine, but can be helpful in assessment of intervertebral disc height, the size of the foramina, evidence of degenerative disease, and stability of the spine.

Computed Tomography uses x-ray technology to generate cross-sectional images. CT provides better visualization of soft tissues than plain radiographs. CT provides better images of bone than MRI. CT can be enhanced by myelography, in which contrast material is injected into the subarachnoid space, which encloses the spinal cord. Myelography allows better visualization of nerve roots. CT with myelography is sometimes obtained as part of preoperative planning in patients who have elected to proceed with surgical management of their herniated disc.

Magnetic Resonance Imaging (MRI) provides cross-sectional images of a body part and is considered the imaging study of choice for nerve-root impingement. The area of interest, in this case the spine, is placed in a large magnetic field. The resonance of hydrogen in the body is detected and converted into images by a computer. MRI offers views of discs, nerves, the spinal cord, muscle, and other soft tissues not visualized by an x-ray. Nevertheless, an MRI is not necessary in all patients with sciatica without particular risk factors. MRI is obtained only when the patient's response to conservative treatment is not as expected. MRIs cannot be performed on people with implanted magnetic or electronic devices, such as a pacemaker, and metal around the eyes.

The ordering physician must correlate findings on MRI with the patient's presenting symptoms and physical exam. This is because not all findings on MRI are clinically significant. One study showed that lumbar disc herniations were identified in 30-40% of individuals without symptoms of radiculopathy. Similar rates were found for CT with myelography and on autopsy.

Electrodiagnostics

Electromyography and nerve conduction studies are sometimes obtained when careful history and physical examination do not reveal a clear diagnosis. In this study, a physician uses electrical stimulation and needle electrodes to assess the health of nerves and their connectivity to muscles. Most patients who have a clear-cut clinical picture do not require electrodiagnostic testing. Electrodiagnostics may also be helpful in determining whether the location of nerve injury is at the spine or elsewhere in the lower extremity.