The term sciatica refers to sciatic nerve symptoms that originate in the lower spine, radiate deep into the buttock, and travel down into the leg and foot. Sciatica is so common that many use the term in an overly broad manner, incorrectly applying it to other types of lower back and leg problems.
This article synthesizes the essential medical facts about the causes and treatments to provide a correct understanding of sciatica.
Sciatica Is the Symptom of an Underlying Condition
The term sciatica refers to a set of symptoms caused by an underlying medical condition and it’s not an actual medical diagnosis.1 The symptoms occur when a nerve root in the lower spine is irritated or compressed by a chemical or mechanical source.
The sciatic nerve is formed by the union of 5 nerve roots (L4 to S3) in the lumbar and sacral spine.2 Irritation or compression of any of these nerve roots (also called radiculopathy) can cause pain, numbness, and/or weakness along the entire distribution of the nerve. Nerve root irritation is most common at the L4, L5, and/or S1 level of the spine.3
Common causes of sciatica include4:
- Lumbar disc herniation. The bulging and/or extrusion of the inner core of a spinal disc in the lower back may cause nerve root irritation or compression due to:
- The leaking of certain chemicals from the disc, or
- Direct mechanical pressure
- Lumbar degenerative disc disease. Weakened discs in the lower back allow excess motion in the spine and may cause irritation of the nerve roots.
- Isthmic spondylolisthesis. A condition where one vertebra slips over another and pinches a nerve root.
- Lumbar spinal stenosis. Narrowing of bony openings in the spine, which may cause compression of nerve roots as they exit the spinal canal.
Rarely, spinal tumors and infections may cause sciatica and require immediate medical attention.
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Sciatica Symptoms Vary
Sciatica pain travels down from the lower back, into the leg, and may sometimes affect the feet and toes. Other sensations associated with sciatica may include tingling, numbness, burning, and/or a prickly feeling.
Depending on the location of nerve compression, different sciatica symptoms may be experienced. For example, the L5 and S1 nerve roots are commonly affected and may cause the following symptoms:
- Sciatica from the L5 nerve root may cause pain along the outer part of the thigh and leg, and weakness while lifting the foot.
- Sciatica from the S1 nerve root may cause pain in the calf and foot, and numbness along the outer side of the foot and in the third, fourth, and fifth toes.
Typically sciatica symptoms affect one leg at a time. Rarely, both legs may be affected if the underlying cause compresses the left and right nerve roots together.5 The severity and duration of pain from sciatica can also vary. Most commonly, a sharp, burning, or searing pain may be felt. Sometimes, the pain may be a dull ache or a mild discomfort that comes and goes.
It is important to understand that sciatica is radiculopathy and originates from the sciatic nerve roots (L4 to S3) in the lower spine.2 Sciatica-type symptoms may occur in other conditions, such as hip arthritis, piriformis syndrome, or sacroiliac joint dysfunction, but are not medically considered to be sciatica.