Sciatica is a medical term describing nerve pain that radiates from the lower back down the leg, following the path of the sciatic nerve. This condition is common, with estimates suggesting that between 10% and 40% of people will experience it at some point. The pain is typically felt in the buttock and posterior thigh, often extending below the knee, and can range from a dull ache to a sharp, shooting, or electric-shock sensation. Sciatica is a symptom of an underlying issue, not a diagnosis itself, and it most frequently affects individuals between the ages of 30 and 50 years old.
Understanding Sciatica: Definition and Common Triggers
The sciatic nerve is the longest and thickest nerve in the human body, formed by the joining of nerve roots from the lower spine (L4 through S3). This substantial nerve travels through the pelvis and the buttock before branching down the back of each leg. Sciatica occurs when this nerve, or one of the nerve roots that form it, becomes compressed, irritated, or inflamed in the lower back region.
The vast majority of sciatica cases (approximately 90%) are caused by a herniated or bulging intervertebral disc in the lumbar spine. A disc herniation happens when the soft, jelly-like inner material pushes through a tear in the tougher outer layer, directly pressing on a nearby sciatic nerve root. Other common underlying triggers include lumbar spinal stenosis (the narrowing of the spinal canal) and spondylolisthesis (where one vertebra slips forward over the one below it). Piriformis syndrome, where the piriformis muscle spasms and compresses the nerve, is a less frequent cause.
Addressing the Misconception of “Four Stages”
Many people search for the “four stages of sciatica,” but there is no formal, universally accepted medical classification system that uses numbered stages to describe the progression of the symptom complex itself. Sciatica is a descriptive term for radiating leg pain, and its course is usually characterized by duration and severity, not a distinct stage progression. This misconception often arises because the most common cause of sciatica, a herniated disc, does have a recognized, four-part pathological progression.
This four-stage system describes the increasing damage to the spinal disc, beginning with disc protrusion, where the disc bulges but the inner material remains contained. This progresses to prolapse, where the inner material pushes deeper, followed by extrusion, where the inner material breaks through the outer layer but remains connected. The final and most severe stage is sequestration, where a fragment of the disc breaks off completely. While this progression of disc pathology often leads to increasingly severe sciatica, the sciatica symptom itself is not classified by these structural changes.
Clinical Classification by Duration and Severity
Clinicians primarily categorize sciatica based on how long the symptoms last, which helps guide treatment decisions and prognosis. The most common classification by duration divides the condition into acute, subacute, and chronic phases.
Classification by Duration
Acute sciatica is defined as pain that has been present for less than six weeks, and this initial phase often involves the most intense and sudden discomfort. Most cases of sciatica fall into this category and resolve with conservative treatment within two months.
If the pain persists beyond six weeks but for less than twelve weeks, it is termed subacute sciatica. This represents a transitional period where the severity of pain may lessen but discomfort continues, and treatment typically shifts from pain management to active physical therapy.
Sciatica is considered chronic when the pain lasts for more than twelve weeks, indicating a persistent issue that may require a comprehensive and long-term management plan.
Classification by Severity
Severity is the second way clinicians grade the condition, assessing the pain’s impact on daily life and the presence of neurological deficit. Mild sciatica causes discomfort that is manageable and does not significantly interfere with regular activities. Moderate pain requires medication and limits certain movements, while severe sciatica can be debilitating, making it difficult to sit, stand, or walk comfortably.
Neurological deficits, such as muscle weakness, numbness, or foot drop, are signs of more severe nerve compression. The presence of such deficits, especially in conjunction with severe pain, often dictates the need for more aggressive interventions like injections or surgery.