What Causes Sciatica?

What Is Sciatica?

Sciatica describes symptoms caused by irritation or compression of one or more nerve roots that contribute to the sciatic nerve.

These nerve roots originate in the lower spine and ultimately contribute to nerves supplying different areas of the legs.

When a nerve root is affected, symptoms can travel away from the spine and into the buttock, thigh, lower leg or foot.

Sciatica is therefore not a disease in itself. It describes a pattern of nerve-related symptoms for which there can be several underlying causes.

What Does Sciatica Feel Like?

Sciatica can feel different from ordinary lower back pain because symptoms often travel along the course of an affected nerve.

Possible symptoms include:

• pain extending from the buttock into the leg
• sharp or shooting pain
• burning pain
• tingling or pins and needles
• numbness or altered sensation
• weakness affecting part of the leg or foot

Symptoms often affect one leg, although the exact pattern depends upon the cause and which nerves are involved.

Some people have back pain as well as leg pain, while others find that the leg symptoms are much more significant than the pain in their lower back.

What Is the Most Common Cause of Sciatica?

A lumbar disc prolapse, commonly called a slipped disc, is an important cause of sciatica.

Intervertebral discs sit between the vertebrae of the spine. If part of a disc protrudes or herniates, the disc material can irritate or compress a nearby spinal nerve root.

This can produce pain and neurological symptoms along the distribution of the affected nerve.

Not every disc prolapse causes sciatica. Disc abnormalities can be present without symptoms, so the findings on an MRI need to be considered alongside the patient's clinical presentation.

Read more: Slipped Disc: Symptoms, Diagnosis and Treatment.

Can Spinal Stenosis Cause Sciatica?

Yes. Lumbar spinal stenosis is another cause of nerve compression in the lower spine.

Spinal stenosis occurs when the spaces available for the spinal nerves become narrowed. This can develop as a result of several age-related or degenerative changes, including changes affecting the discs, facet joints and ligaments.

If narrowing affects an individual nerve root, symptoms can resemble sciatica, with pain, tingling, numbness or weakness extending into a leg.

More central spinal stenosis can produce a somewhat different pattern called neurogenic claudication, in which pain, heaviness, numbness or weakness develops in the legs during standing or walking and improves with sitting or bending forwards.

Read more: Lumbar Spinal Stenosis: Symptoms and Treatment.

Can Age-Related Changes in the Spine Cause Sciatica?

Yes. The structures of the spine change naturally with age. Intervertebral discs, joints and ligaments can all alter over time.

In some people, a combination of these changes reduces the space available around a spinal nerve and contributes to sciatica.

However, degenerative changes are also frequently found on scans in people without symptoms.

The presence of age-related changes on an MRI therefore does not automatically establish that they are responsible for a person's leg pain.

Can Spondylolisthesis Cause Sciatica?

It can.

Spondylolisthesis describes a condition in which one vertebra has moved relative to the vertebra next to it. There are different types and causes of spondylolisthesis.

In some patients, the altered relationship between the vertebrae contributes to narrowing around one or more spinal nerves. If a nerve root is compressed, symptoms can include pain, numbness, tingling or weakness in the leg.

The presence of spondylolisthesis on imaging does not necessarily mean that it is symptomatic or that surgery is required. Its significance depends upon the patient's symptoms, clinical findings and imaging.

Can Sciatica Start After Lifting or Bending?

Sciatic symptoms can sometimes begin during or after lifting, bending, twisting or another physical activity, particularly when a disc prolapse is involved.

However, many people develop sciatica without being able to identify a specific event that caused it.

This means that the absence of an injury does not rule out a disc or nerve problem, and experiencing symptoms after a particular movement does not necessarily prove that the movement damaged the spine.

Can Sciatica Occur Without Back Pain?

Yes.

Although sciatica originates from irritation or compression of a nerve associated with the lower spine, lower back pain does not have to be the main symptom.

Some patients experience severe pain in the buttock, thigh, calf or foot with relatively little discomfort in the lower back.

For this reason, the pattern and distribution of the leg symptoms can be particularly important during assessment.

Why Does Sciatica Usually Affect One Leg?

A disc prolapse or other area of narrowing may predominantly affect a nerve root on one side of the spine. This can result in symptoms affecting the corresponding leg.

The location of pain and altered sensation can vary according to which nerve root is involved.

Symptoms affecting both legs can occur, particularly where there is more central narrowing or compression involving multiple nerves. Bilateral symptoms associated with certain bladder, bowel or saddle-area sensory changes require urgent medical assessment.

Which Nerves Cause Sciatica?

The sciatic nerve is formed from nerve roots arising from the lower lumbar and sacral spine.

Different nerve roots supply different areas of sensation and control different muscle groups. As a result, the location of pain, numbness or weakness can provide clues about which nerve may be affected.

For example, symptoms may extend into different areas of the:

• buttock
• thigh
• calf
• shin
• ankle
• foot
• toes

Clinical patterns are useful, but symptoms are not always identical between patients. Examination and imaging may be required when a more precise diagnosis is necessary.

Is Every Pain Down the Leg Sciatica?

No.

Leg pain can arise from several different structures and medical conditions. Pain in the buttock, hip, thigh or lower leg does not automatically mean that a spinal nerve is compressed.

Other possible causes of leg symptoms can include problems affecting:

• muscles and tendons
• the hip or other joints
• peripheral nerves
• blood vessels and circulation
• other musculoskeletal or medical conditions

This is one reason why assessment focuses on the complete symptom pattern rather than the presence of leg pain alone.

How Is the Cause of Sciatica Diagnosed?

Assessment begins with understanding the symptoms and performing an appropriate clinical examination.

A clinician may ask about:

• where the pain starts and where it travels
• whether symptoms affect one or both legs
• numbness, tingling or altered sensation
• weakness
• lower back pain
• activities or positions that aggravate or relieve symptoms
• walking and standing tolerance
• how and when the symptoms began
• previous episodes or treatment

A neurological examination may assess muscle strength, sensation and reflexes. Other clinical tests may be used to determine whether symptoms are consistent with nerve root irritation.

The findings can then help determine whether imaging or another investigation is necessary.

Do I Need an MRI to Find the Cause of Sciatica?

Not everybody with sciatica requires an immediate MRI scan.

Many episodes improve over time without surgery. If symptoms are improving and there are no concerning neurological features, imaging may not alter the initial management.

MRI becomes particularly useful when the result is likely to influence treatment. For example, imaging may be considered when:

• significant symptoms persist
• there is neurological weakness or other concerning clinical findings
• the diagnosis remains uncertain
• a spinal injection is being considered
• surgery is being considered

The objective is not simply to find an abnormality. It is to determine whether imaging demonstrates a cause that corresponds with the patient's symptoms.

Read more: MRI Scans for Sciatica: When Are They Needed?.

Can Sciatica Get Better Without Surgery?

Yes. Many people with sciatica improve without an operation.

Where a disc prolapse is responsible, the symptoms can settle over time as inflammation and nerve irritation reduce and the disc prolapse changes naturally.

Initial management may therefore be non-surgical when there is no indication for urgent intervention.

The appropriate approach depends upon the severity of symptoms, neurological findings, general health and how the condition progresses.

How Is Sciatica Treated?

Treatment is individualised according to the cause, severity and duration of symptoms.

Depending upon the circumstances, management may include:

• remaining appropriately active
• exercise and rehabilitation
• physiotherapy where appropriate
• appropriate pain management
• selected spinal injections
• surgery for appropriately selected patients

Most patients do not begin with surgery. The objective is to manage symptoms appropriately while identifying patients whose nerve compression may require more specific treatment.

When Might Sciatica Need Surgery?

Spinal decompression may be considered when significant sciatic symptoms have not improved sufficiently with appropriate non-surgical treatment and imaging demonstrates nerve compression that corresponds with the clinical symptoms.

Factors that may influence the decision include:

• the severity of leg pain
• how long symptoms have persisted
• the effect on walking, sleep, work and normal activities
• numbness or weakness
• response to previous treatment
• clinical examination findings
• MRI findings
• the potential benefits and risks of surgery

Significant or progressive neurological weakness may require earlier specialist assessment.

Read more: When Does Sciatica Need Surgery?.

When Should Sciatica Be Assessed by a Specialist?

Specialist assessment may be appropriate when sciatica remains severe or persistent, significantly affects normal activities, is associated with neurological symptoms, or when further investigation or treatment is being considered.

A specialist assessment can help determine:

• whether the symptoms are consistent with spinal nerve compression
• which nerve may be affected
• whether an MRI scan is appropriate
• whether imaging findings correspond with the symptoms
• whether continued non-surgical management, an intervention or surgery should be considered

Read more about Leg Pain / Sciatica.

When Does Sciatica Require Urgent Medical Attention?

Most sciatica does not require emergency treatment. However, certain neurological symptoms need urgent assessment.

Seek urgent or emergency medical help if sciatic or back pain is accompanied by new difficulty controlling or passing urine or stools, loss of sensation around the genitals or anus, or significant or worsening weakness or numbness affecting both legs.

These symptoms can have different causes but may indicate significant compression of the nerves at the bottom of the spinal canal, including cauda equina syndrome.

Significant or rapidly progressive muscle weakness also requires prompt medical assessment.

These symptoms should not be monitored at home or assessed solely using online information.

Frequently Asked Questions About the Causes of Sciatica

What is the main cause of sciatica?

A prolapsed or herniated lumbar disc is a common cause of sciatica. Disc material can irritate or compress a spinal nerve root, causing pain and sometimes numbness, tingling or weakness in the leg. Lumbar spinal stenosis and other causes of nerve narrowing can also produce sciatica.

Can you have sciatica without back pain?

Yes. Some people have significant pain extending through the buttock and leg with little or no lower back pain. The distribution of leg symptoms can be particularly useful when assessing which nerve may be affected.

Does sciatica mean I have a slipped disc?

No. A slipped disc is one common cause, but sciatica can also result from spinal stenosis and other causes of nerve compression. Assessment is needed if establishing the precise cause is clinically important.

Can spinal stenosis cause sciatica?

Yes. Narrowing around an individual lumbar nerve root can cause sciatic-type pain, numbness or weakness. More central stenosis may instead cause symptoms in one or both legs during standing and walking.

Can sciatica affect both legs?

It can, although typical sciatica often predominantly affects one leg. Symptoms involving both legs, particularly when accompanied by bladder or bowel dysfunction or altered sensation around the saddle area, require urgent medical assessment.

Can sciatica get better on its own?

Yes. Many episodes improve with time and appropriate non-surgical management. The course varies between individuals and persistent, severe or worsening neurological symptoms may require further assessment.

Do I need surgery for sciatica?

Most people with sciatica do not require surgery. Decompression may be considered for selected patients when significant symptoms persist despite appropriate non-surgical treatment and imaging demonstrates nerve compression corresponding with the symptoms.

About This Article

This article provides general information about the possible causes of sciatica and leg pain. It is not intended to diagnose an individual's symptoms or replace personalised medical advice.

Medically reviewed by Professor Nasir A. Quraishi
Consultant Spinal Surgeon & Honorary Professor

Clinical sources: NICE guidance on low back pain and sciatica in people aged 16 and over, and NHS guidance on sciatica and slipped discs.

Further Information About Sciatica

If leg pain, numbness, tingling or weakness may be caused by irritation or compression of a spinal nerve, specialist assessment can help establish the likely cause and whether further investigation or treatment may be appropriate.

Learn more about Leg Pain / Sciatica

Sciatica Symptoms: What Does Sciatic Nerve Pain Feel Like?
MRI Scans for Sciatica: When Are They Needed?
Sciatica from a Slipped Disc
Spinal Stenosis and Leg Pain
When Does Sciatica Need Surgery?