When a disc pushes out of the sac that holds it in place, it can press on the nerve root at that level as it leaves the spinal cord. Enough pressure can cause back pain that goes down the leg.

During the SLR test the patient is lying down on a table and one leg is lifted off the table. This movement stretches the nerve and reproduces the painful symptoms when there's a disc problem.

The MRI helps show the exact spot and how big the bulge is. If the SLR is negative, further tests are done by the doctor in the office. The cost of the MRI is saved when no other tests point to a disc or spine problem. The MRI helps the doctor see how much pressure is on the spinal cord or nerve root. Too much pressure may require surgery to keep the patient from having permanent nerve damage.