The experience of pain radiating from the lower back into the leg is commonly called “sciatica,” though the term is often used incorrectly as a diagnosis. Sciatica is not a condition itself but a symptom—the pain, numbness, or weakness that travels along the path of the sciatic nerve. This nerve originates from nerve roots in the lower spine, runs through the buttocks, and extends down the back of each leg. Since many different issues can irritate this nerve or mimic its pain pattern, pinpointing the true source of discomfort is necessary for effective treatment.
The Defining Traits of Sciatic Nerve Pain
True sciatic nerve pain, also known as lumbar radiculopathy, originates when the nerve roots that form the sciatic nerve (L4 through S3) are compressed or inflamed at the spinal column. This irritation typically occurs upstream in the lower back before the nerve fully forms. The most common cause of this compression is a herniated or bulging intervertebral disc pressing against the nerve root as it exits the spine. The pain is characteristically unilateral, affecting only one leg at a time, and is often described as a sharp, shooting, or electric shock-like sensation.
This nerve pain usually begins in the low back or buttock and radiates down the back of the thigh, often extending below the knee and sometimes reaching the calf or foot. Accompanying the pain are neurological symptoms like tingling, numbness in the affected limb, or muscle weakness. Activities that increase pressure on the spine, such as prolonged sitting, coughing, or sneezing, can often aggravate the pain.
Non-Spinal Conditions That Feel Like Sciatica
Not all pain that travels down the leg is caused by a problem in the spine; sometimes, the irritation occurs further down the nerve’s path. One common culprit is Piriformis Syndrome, a neuromuscular condition where the piriformis muscle, located deep in the buttock, spasms or tightens and compresses the sciatic nerve. This causes pain predominantly concentrated in the buttock region, which may radiate down the back of the leg but typically does not extend past the knee. The discomfort is often worsened by activities that engage the muscle, like sitting for long periods, running, or climbing stairs.
Sacroiliac (SI) Joint Dysfunction, where the SI joints connect the base of the spine to the pelvis, is another non-spinal cause that can mimic sciatica. Inflammation or improper movement within this joint can cause referred pain that travels into the buttock and down the leg. This pain is usually localized to the side of the lower back and the buttock, and it can be aggravated by putting weight on the affected side, such as when sitting or going up stairs. High hamstring tendinopathy, inflammation or strain of the hamstring tendons near the sit bone, can also cause pain in the upper back of the thigh that is sometimes mistaken for nerve irritation.
Spinal Structural Issues With Similar Pain
Beyond a simple herniated disc, other structural changes within the spine can compress the nerve roots and cause sciatic-like symptoms. Lumbar Spinal Stenosis involves the narrowing of the spinal canal or the openings where the nerves exit, often due to age-related changes, bone spurs, or thickened ligaments. The resulting nerve compression causes neurogenic claudication, characterized by pain, cramping, or weakness in the legs that is brought on by standing or walking. A distinguishing feature is that the pain is often relieved by sitting or bending forward, a posture sometimes called the “shopping cart sign.”
Another spinal issue is Spondylolisthesis, a condition where one vertebra slips forward over the one below it, most commonly in the lower lumbar spine. This slippage can mechanically narrow the space for the nerve roots, leading to nerve compression and leg pain, numbness, or weakness. The symptoms can be similar to other causes of sciatica, but the back pain is typically worse with activities that involve extension or bending backward, and it often eases when lying down.
Pinpointing the Differences in Symptoms
Identifying the precise location of the pain’s origin is the most practical way to distinguish between these conditions. True sciatica caused by a herniated disc often presents with severe pain that is worse than any associated back pain, and it frequently shoots down past the knee. Conversely, Piriformis Syndrome is usually characterized by more intense, localized pain and tenderness deep within the buttock that rarely travels below the knee. The pain from Piriformis Syndrome is often triggered by directly sitting on the affected side, while disc herniation pain is often provoked by raising the straight leg while lying down.
The timing and aggravating factors provide important clues for differentiation. Lumbar Spinal Stenosis symptoms are uniquely positional, consistently worsening during prolonged standing or walking and finding relief only by sitting or leaning forward. Spondylolisthesis often causes pain during activities that involve hyperextension or bending motions. SI Joint Dysfunction pain is typically felt in the low back and buttock region, but it is often made worse by single-leg loading activities, such as climbing stairs or stepping up.
The quality of the sensation also helps to separate true nerve compression from muscular or joint issues. Sciatica is characterized by a sharp, burning, or electric shock sensation, which is indicative of nerve irritation. In contrast, pain from Piriformis Syndrome or SI Joint Dysfunction might be described as a deep, aching muscular pain or a dull, localized joint ache, even if it refers down the leg.
Urgent Signals Requiring Medical Attention
While most cases of leg pain resolve with conservative care, certain symptoms represent a medical emergency that requires immediate professional evaluation. The sudden onset of bilateral sciatica, meaning pain and weakness in both legs, is a serious warning sign. This bilateral presentation suggests the possibility of severe central spinal cord or nerve root compression.
The most concerning symptoms involve the loss of function in the nerves that control the bowel and bladder, which can signal Cauda Equina Syndrome. This includes difficulty controlling urination, an inability to hold urine, or a loss of bowel control, all of which must be addressed immediately. Another sign of severe nerve compression is “saddle anesthesia,” which is new or worsening numbness in the groin, inner thigh, and genital area. Severe pain following a traumatic injury, or pain accompanied by a fever, should also prompt an urgent medical consultation to rule out fracture or infection.