Sciatica

Sciatica is pain that travels along the path of the sciatic nerve — the longest and thickest nerve in the body. Despite its name, the sciatic nerve is not a single nerve but a thick bundle formed from several nerve roots (L4 to S3) that exit the lower spine and join together, running from the lower back through the buttock, down the back of the thigh, and branching below the knee to supply the lower leg and foot.

Sciatica itself is not a diagnosis — it is a symptom, describing a specific pattern of pain caused by irritation or compression of one or more of the nerve roots that form the sciatic nerve. Successfully treating sciatica depends on identifying and addressing whatever is causing that irritation in the first place, which is why understanding the underlying cause matters just as much as managing the pain itself.

What Is Actually Happening to the Nerve

Each sciatic nerve is formed from five nerve roots — L4, L5, S1, S2 and S3 — that exit the spine through small bony openings called intervertebral foramina and merge together in the pelvis before travelling down the back of the leg. Sciatica occurs when one or more of these nerve roots is compressed, stretched, or chemically irritated by inflammation before they merge into the main nerve, most commonly where a nerve root exits the lower lumbar spine at the L4-L5 or L5-S1 level.

This irritation disrupts the normal transmission of signals along the nerve, producing the characteristic combination of pain, altered sensation, and sometimes weakness in the areas the nerve supplies. Because the sciatic nerve runs such a long course, symptoms can be felt anywhere along its path — but the specific pattern of where the pain, numbness or weakness is felt often helps a specialist identify which exact nerve root is affected, which in turn guides diagnosis and treatment.

The specific area affected can offer useful clues: irritation of the L4 nerve root typically affects sensation over the outer shin and the muscles that lift the foot; L5 involvement is often felt across the top of the foot and big toe and can affect the ability to walk on the heels; and S1 involvement typically affects the outer heel and sole of the foot and can weaken push-off strength when walking or standing on the toes.

Symptoms of Sciatica

Sciatica can range from mild to severe, and symptoms may affect the lower back, hip, buttock or leg, sometimes extending as far as the foot or toes depending on which nerve root is involved. The following are the symptoms most commonly reported.

Pain: Pain results from pressure or irritation affecting the nerve, and is most often described as burning, electric-shock-like, or a sharp, shooting sensation that radiates down the leg on the affected side, typically worse with sitting, coughing or sneezing.
Tingling or numbness: Tingling or numbness: A pins-and-needles sensation similar to when a limb "falls asleep," or reduced ability to feel sensations on the skin of the affected back, buttock or leg.
Muscle weakness: A more significant symptom that occurs when nerve signals have difficulty reaching the muscles of the leg or foot, sometimes noticed as a foot that catches or drags while walking, or difficulty pushing off when walking on tiptoe.
Loss of bladder or bowel control: A rare but serious symptom that, together with numbness in the groin or inner thighs, can indicate a spinal emergency requiring immediate treatment — described further below.
Urinary or fecal incontinence: Another severe symptom of sciatica.

If pain is severe, lasts more than a few weeks, or is accompanied by sudden numbness, leg weakness, or difficulty controlling the bladder or bowel, prompt medical assessment is important rather than waiting for symptoms to resolve on their own.

Causes of Sciatica

Sciatica arises from an underlying condition affecting the spine or the nerve roots that form the sciatic nerve, rather than being a condition in itself. The most common underlying causes include the following.

Degenerative disc disease: The intervertebral discs — the cushions between the vertebrae — naturally lose hydration and structural integrity with age, which can lead to bulging, herniation or collapse that irritates nearby nerve roots. This is the leading underlying cause of sciatica.
Herniated (slipped) disc: Occurs when the soft inner core of a disc (the nucleus pulposus) pushes through a tear in the tough outer layer (the annulus fibrosus) and presses directly on a nerve root — one of the most common specific causes of sciatica, particularly in younger and middle-aged adults.
Osteoarthritis of the spine: Wear-and-tear arthritis of the small joints of the spine (facet joints) can lead to bone spur formation that narrows the space through which nerve roots exit the spine, irritating the nerve.
Spinal stenosis: Narrowing of the spinal canal or the nerve root exit canals, often related to a combination of disc, joint and ligament changes with age, which reduces the space available for the nerve roots.
Spondylolisthesis: A condition in which one vertebra slips forward over the one beneath it, which can narrow the space available for the nerve root and cause sciatic symptoms.
Pregnancy: The growing uterus and hormonal changes during pregnancy can place added pressure on the sciatic nerve, and pregnancy-related pelvic changes can alter spinal mechanics, both of which can trigger sciatic symptoms.
Tumors, cysts or other growths: Rarely, growths pressing on or near a nerve root — including tumors, cysts or other masses — can cause sciatica, which is one of the reasons persistent or unusual sciatica warrants proper medical assessment rather than assumption.
Piriformis syndrome: The piriformis muscle, located deep in the buttock, sits close to the sciatic nerve, and in some people, spasm or tightness of this muscle can irritate the nerve and mimic sciatica arising from the spine, even though the spine itself is not the source.

Risk Factors for Sciatica

Sciatica can affect anyone, but certain factors make it more likely to develop, and understanding them can help guide both prevention and treatment planning.

Previous injuries: A past or current injury to the spine or lower back increases the likelihood of developing sciatica, as previous injury can alter spinal structure and mechanics.
Normal wear-and-tear (age): As the spine ages, normal wear-and-tear can lead to pinched nerves, herniated discs, and other structural changes that commonly cause sciatica — making age one of the most significant risk factors.
Excess weight or obesity: Carrying excess weight increases the load the back muscles and spine must bear to keep the body upright, which can contribute to back strain, disc stress and sciatic symptoms.
Insufficient core strength: The core refers to the group of muscles in the back and abdomen that support the spine; weaker core muscles mean the spine has less support when handling everyday loads, increasing vulnerability to injury and nerve irritation.
Occupational hazards: Jobs involving heavy lifting, frequent bending, or working in awkward positions increase the risk of low back problems, as do jobs requiring prolonged sitting, particularly without proper lumbar support.
Diabetes: Type 2 diabetes is associated with an increased risk of nerve-related problems, including sciatica, related to its broader effects on nerve health.

How Sciatica Is Diagnosed

Diagnosing sciatica involves confirming the pattern of nerve-related symptoms and, importantly, identifying the underlying cause, since treatment is guided by what is compressing or irritating the nerve rather than the sciatica symptom alone.

Clinical History & Neurological Examination: A detailed history of the pain's character, location, radiation and triggers, together with a neurological examination assessing reflexes, muscle strength and sensation in the leg to help identify which specific nerve root is affected. The straight leg raise test — in which the leg is gently lifted while lying down to see if it reproduces the radiating pain — is a specific manoeuvre commonly used to help confirm nerve root irritation.
MRI Scan: The gold-standard imaging test for sciatica, providing detailed visualisation of the discs, nerve roots and spinal canal to identify disc herniation, spinal stenosis or other structural causes of nerve compression, without the use of radiation.
X-Ray: Does not show the discs or nerves directly but is useful for assessing bone alignment, disc height loss, bone spurs, and conditions such as spondylolisthesis, and is often used as an initial or complementary investigation.
CT Scan: Provides detailed bony imaging and may be used when MRI is unsuitable, or to further evaluate bone spurs and the degree of narrowing of the nerve root exit canals.
Electromyography (EMG) and Nerve Conduction Studies: EMG measures the electrical activity in muscles to detect evidence of nerve root involvement, while nerve conduction studies measure the speed and strength of nerve signals. Together, these tests can help confirm which nerve root is affected and distinguish sciatica from other nerve conditions with a similar presentation.

Reducing Your Risk and Managing Sciatica Day to Day

It is not always possible to prevent sciatica, and it can recur even after successful treatment — but several everyday measures can meaningfully reduce your risk and support recovery.

Exercise regularly: Regular exercise helps keep the back strong and builds the core muscles needed for good posture and spinal support, both of which reduce vulnerability to nerve irritation.
Practise good posture: Choosing a seat with proper lumbar support — or placing a pillow or rolled towel in the small of the back when one isn't available — helps maintain the spine's natural curve and reduces disc stress during prolonged sitting.
Use your body correctly: When standing for long periods, resting one foot on a stool or small box occasionally can ease lower back strain; when lifting something heavy, bending the knees and letting the leg muscles do the work — rather than the back — reduces the risk of disc injury.
Maintain a healthy weight: Extra body weight increases the load the spine and back muscles must bear, so maintaining a healthy weight through diet and activity reduces ongoing mechanical stress on the discs and nerves.
Take movement breaks: Taking regular breaks to stand, stretch and move — particularly during desk work or long periods of sitting — helps reduce the sustained pressure on the lower spine that can contribute to sciatica.