Sciatica is pain that originates in the buttocks or lower back and spreads—down one thigh to below the knee, usually into the foot. This is the pathway of the sciatic nerve and its branches—actually a group of nerves bound together in one sheath. The discomfort tends to persist and is worse than a typical backache. Sufferers may also experience numbness, tingling and/or muscle weakness.
It’s hard to know how common sciatica is, partly because there is still debate over how to define it, and because a variety of disorders can cause sciatica. One estimate is that four in 10 people will experience it at some time in their lives. As with other types of back pain, your doctor won’t always be able to pinpoint the reason for the discomfort. However, one common cause is a bulging or herniated intervertebral disc that irritates or compresses a spinal nerve root.
Spinal stenosis can also irritate the sciatic nerve, causing sciatica as a complication. This is a more common cause of sciatica in people over 50 than disc herniation. Piriformis syndrome, which occurs when the piriformis muscle deep in the buttock and pelvis (which helps move the thigh away from the body and enables the leg to pivot outward) goes into spasm or becomes inflamed and presses on the sciatic nerve. Here, pain is likely to be deep in the buttocks, especially if you sit for an extended period. You may also feel pain when you cross your legs or walk.