The medical definition of sciatica is an injury to or problem involving the sciatic nerve, a large nerve that starts in your lower back and travels down the back of your leg. More informally, any pain, discomfort or tingling that radiates down the leg may be referred to as sciatica, even though it may not in fact originate from the sciatic nerve.
Sciatica symptoms can start from one or more sources. They often arise from pinched nerves in the lower lumbar or sacral parts of the spine as a result of arthritis or a herniated disk that pushes against the nerve. Arthritis produces bony spurs that crowd the openings where the nerves exit from the spine (called foramen). In either case, the pressure on the nerve may irritate it, causing pain or tingling.
Sciatica may also result indirectly from a spasm of the piriformis muscle which intersects with the sciatic nerve deep in the mid-buttock. If your pain seems to originate in your butt, you may have piriformis syndrome. This syndrome is generally caused by a muscle imbalance that leads to overuse of your piriformis muscle. In particular, the piriformis muscle often compensates for a weak gluteus medius muscle, an upper, outer buttock muscle that helps keep your hips stabilised when you are upright. The extra stress placed on the piriformis muscle can lead to spasms, which may then put pressure on the sciatic nerve, causing pain that radiates down that leg.
If your lower back or sciatic pain is interfering with your daily functioning, or if you have noticeable weakness in one leg, you should see your health care provider. Because sciatica has multiple possible causes, each requiring different treatment, fixing it properly depends on a thorough evaluation to get the most specific underlying diagnosis.
Sciatica can often be resolved with conservative treatments such as physical therapy, stretches and oral medications for the symptoms. Any type of invasive procedure, including epidural or trigger point injections, should be considered only after you have consulted a specialist to determine the true source of the pain or weakness.