Sciatica: Causes and Evidence-Based Treatment

The most common cause of sciatica is herniation of the nucleus pulposus of a lumbar intervertebral disc, most often at the L4-L5 or L5-S1 level. An intervertebral disc acts as a shock absorber between vertebrae — a gel-like nucleus surrounded by a fibrous ring. When that ring tears or weakens enough for the nucleus to bulge out of its normal position, it can press directly on a nerve root exiting the spinal canal, triggering both mechanical compression and an inflammatory reaction around the irritated nerve. It's this inflammatory component, not just the raw mechanical pressure, that explains why symptoms can be disproportionately severe relative to how large a herniation looks on imaging.

Beyond disc herniation, nerve root compression can also result from spinal stenosis (narrowing of the spinal canal, usually tied to degenerative changes in older adults), spondylolisthesis (one vertebra slipping forward relative to another), and, much more rarely, tumors or infections affecting the spine. It's worth stressing that a disc herniation visible on an MRI doesn't automatically mean it's the cause of someone's sciatica — degenerative disc changes are also very common in people with no symptoms at all, so imaging always has to be interpreted alongside the clinical picture, not in isolation from it.

Near the buttock, the sciatic nerve runs directly alongside the piriformis muscle, and in some people even passes through its fibers. When that muscle is overly tight, overloaded, or in spasm, it can compress the sciatic nerve independently of the condition of the intervertebral discs — a phenomenon known as piriformis syndrome. A key distinguishing feature is that, unlike nerve root compression from a herniated disc, classic piriformis syndrome usually doesn't come with objective neurological deficits such as weakness in specific muscle groups or diminished reflexes.

For decades, the intuitive advice for sciatica was bed rest — the logic seemed straightforward: if movement makes the pain worse, avoiding movement should help. That assumption was tested in a Dutch randomized clinical trial, one of the most frequently cited studies in this area.

Nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen or naproxen are among the most commonly reached-for treatments for sciatic pain — the rationale being the inflammatory component that accompanies nerve root compression. The largest available systematic review on the topic, though, paints a more complicated picture than everyday practice would suggest.

The large majority of sciatica cases resolve with conservative treatment. Surgery (usually a discectomy — removing the portion of the herniation compressing the nerve) is typically considered when at least 6-8 weeks of properly conducted conservative treatment hasn't produced improvement, the pain is severe enough to significantly limit daily function, or progressive neurological deficits appear. The largest trial evaluating this decision is the American SPORT trial.

Beyond cauda equina symptoms, urgent medical evaluation is also warranted for sciatica accompanied by fever, unexplained weight loss, a history of spinal trauma, a history of cancer or osteoporosis, or pain that doesn't ease or changes character when lying down — these signals can point to rarer but more serious causes than a typical disc herniation, such as a spinal infection or tumor.

Sciatica is one of those areas of medicine where the clinical evidence has clearly diverged from long-held, deeply ingrained intuition. Bed rest, treated for decades as the obvious first response, turned out to be ineffective in a well-designed trial, and anti-inflammatory drugs — despite widespread use — have surprisingly weak evidence support for pain reduction specifically. What's best documented to actually work is staying active within the limits of tolerable pain and gradual, targeted rehabilitation, with surgery reserved for cases where conservative treatment has genuinely failed.

The most important practical takeaway, though, is recognizing when sciatica stops being an ordinary, if uncomfortable, problem and becomes a medical emergency. Cauda equina syndrome is rare, but the consequences of missing it can be irreversible — so new problems with urination, bowel control, or sensation around the groin should never wait for the next available primary-care slot.