Sciatica is a general term for pain originating from the sciatic nerve. Sciatica is a symptom of a disorder that causes mild to sharp and sometimes excruciating pain. Patients have described sciatic pain as mildly disturbing to burning, aching, deep, and similar to a sudden bolt of lightning. Sciatic nerve pain travels from the buttock, down the back of the thigh, and into the leg. Leg pain is the classic hallmark of sciatica. Low back pain may accompany sciatica, and some patients experience sciatic pain extending into the foot. Another characteristic of sciatica is it usually affects either the lower left or right side of the body.
Sciatic pain can make life miserable. Walking, standing, bending over, driving a car, working at a computer, catching up on household chores, sneezing or coughing, and many other activities of daily living can cause sudden and intense pain. Patients who suffer sciatica, especially of a more acute nature, find the symptoms disrupt many aspects of their life.
One reason the sciatic nerve causes so much pain is because it is the longest nerve in the body! The nerve starts at the back of the pelvis and runs downward through the hip area and buttocks into each leg. Near the knee, the sciatic nerve divides into two nerves—the tibial and peroneal nerves. The tibial nerve runs behind the knee and the peroneal nerve runs along the side of the calf and ankle. Through the tibial and peroneal nerves, the sciatic nerve innervates (‘stimulates’) the action of many muscles in the lower legs and enables feeling in the thighs, legs, and feet.
Besides pain, other symptoms may accompany sciatica. These symptoms include sensations such as tingling, pins and needles, burning, numbness or muscle weakness. Such symptoms may be felt in the buttock, thigh, behind the knee, calf, ankle, and sometimes the foot.
Causes of Sciatica
It’s important to understand which conditions cause sciatica because sciatica is not a condition, it’s a medical term used to describe symptoms caused by other low back conditions.
Several low back conditions can cause sciatica, including:
- Bulging disc or herniated disc: This is the most common cause of sciatica. When a disc bulges, the gel-like center (nucleus pulposus) pushes against the outer wall of the disc (annulus fibrosus). A herniated disc means that the nucleus pulposus breaks through the annulus fibrosus. With both bulging and herniated discs, the disc material can press on nerve roots, causing sciatica. The consequences of a herniated disc are worse than those of a bulging disc. The disc material that leaks out contains an acidic, chemical irritant (hyaluronic acid) that causes nerve inflammation.
- Degenerative disc disease (DDD): Sciatica is a common result of the aging process that affects discs called degenerative disc disease. DDD is a change in the disc shape and function, and it can result in a bulging disc or a herniated disc and pain.
- Piriformis syndrome: The piriformis muscle, located in the lower part of the spine, connects to the thighbone, and helps you rotate your hip. The sciatic nerve runs under the piriformis muscle, so muscle spasms can compress the sciatic nerve. It may be difficult to diagnose and treat as it is not easily identified by x-ray or MRI.
- Pregnancy: The extra weight and pressure on your spine caused by pregnancy can cause compression of the sciatic nerve. The symptoms will usually go away after childbirth.
- Spinal stenosis: Your nerves travel through passageways in your spine, and when this space narrows (stenosis), it can put pressure on the nerves in your low back.
- Spinal tumors and spinal infections: Although very rare, tumors and infections can compress the sciatic nerve.
- Spondylolisthesis: If a vertebra slips forward over the vertebra below it, it’s called spondylolisthesis. This slip can pinch the nerve root and cause sciatica.
- Trauma: You can develop sciatica because of direct nerve compression from an outside force. For example, you could be injured in a car accident, resulting in a pinched nerve in your low back.
Sciatica is diagnosed by physical examination, neurological testing and patient history. Generally if a patient reports the typical radiating pain in one leg as well as one or more neurological indications of nerve root tension or neurological deficit, sciatica can be diagnosed.
The most applied diagnostic test is the straight leg rising test, which is considered positive if pain in the sciatic nerve is reproduced with between 30 and 70 degrees passive flexion of the straight leg.
Diagnosis of sciatica through imaging can be achieved either with computerized tomography (CT scan) or with magnetic resonance imaging (MRI). MR neurography may help diagnose piriformis syndrome, another cause of sciatica that does not involve disc herniation.