Sciatica: Causes, Symptoms and Treatments

Sciatica is pain that follows the path of the sciatic nerve, the longest nerve in the human body. It radiates from the lower back to the buttock, back of the thigh and calf, sometimes reaching the foot. In 85% of cases, it is caused by a lumbar disc herniation compressing an L5 or S1 nerve root.

Sciatica, or lumbosciatic pain, is one of the most debilitating back conditions. In France, approximately 5 to 10% of the population will suffer from sciatica during their lifetime, with peak incidence between 40 and 60 years of age. The good news: in the vast majority of cases, sciatica heals spontaneously within a few weeks without surgery.

Dr Christian Dimitriu, a neurosurgeon specialising exclusively in spine surgery, explains everything you need to know about sciatica: its causes, symptoms, diagnosis and treatments.

What is the sciatic nerve?

The sciatic nerve is the longest and largest nerve in the human body. It originates from the junction of five nerve roots emerging from the lumbar spine and sacrum (L4, L5, S1, S2, S3). It descends through the buttock, passes behind the hip, runs along the back of the thigh and divides at knee level into two branches: the tibial nerve (which innervates the calf and sole of the foot) and the peroneal nerve (which innervates the top of the foot and toes).

The sciatic nerve performs two essential functions:

• Motor function: it enables leg movement, knee bending, foot lifting and toe movement.
• Sensory function: it transmits sensations of touch, pain and temperature from the leg to the brain.

When a nerve root that forms the sciatic nerve is compressed or irritated at the lumbar spine level, pain propagates along the entire nerve pathway: this is sciatica.

Causes of sciatica

Sciatica is not a disease in itself, but a symptom. It indicates compression or irritation of a nerve root in the lumbar region. The main causes are:

1. Lumbar disc herniation (85% of cases)

This is the most common cause of sciatica. The intervertebral disc, a natural shock absorber between two vertebrae, tears and allows part of its gel-like nucleus (nucleus pulposus) to escape. This fragment compresses an adjacent nerve root, most commonly at L4-L5 (L5 root) or L5-S1 (S1 root). Sciatic pain appears suddenly, often after exertion, coughing or a sudden movement. To learn more, visit our dedicated page on lumbar disc herniation.

2. Lumbar spinal stenosis (spinal canal narrowing)

With age, spinal arthritis causes narrowing of the spinal canal through which nerves pass. This progressive narrowing can compress nerve roots and cause sciatica, often bilateral. Symptoms typically appear during walking and improve with rest or when leaning forward. This condition mainly affects people over 60. Discover our complete page on lumbar spinal stenosis.

3. Spondylolisthesis

This is a forward slippage of one vertebra over the one below, which can narrow the channels through which nerves exit (foramina) and cause nerve compression. Spondylolisthesis can be degenerative (related to arthritis) or isthmic (related to a stress fracture of the vertebra). For more information, visit our page on spondylolisthesis.

4. Piriformis syndrome

The piriformis muscle is a small deep muscle in the buttock that passes over the sciatic nerve. When contracted or enlarged, it can compress the nerve and cause pain resembling sciatica, but with no spinal origin. This syndrome is often related to muscle overuse, poor posture or trauma.

5. Sciatica in pregnancy

Approximately 1% of pregnant women suffer from sciatica, especially in the third trimester. Pressure from the uterus on the sciatic nerve, hormonal changes (which loosen ligaments) and postural changes can cause nerve compression. Pregnancy-related sciatica typically resolves within weeks after delivery.

6. Rarer causes

• Spinal tumours (benign or malignant)
• Infections (spondylodiscitis, epidural abscess)
• Epidural haematoma (after injection or in patients on anticoagulants)
• Vertebral fracture (osteoporosis, trauma)

Symptoms: recognising sciatica

Sciatica presents with characteristic symptoms that distinguish it from simple low back pain (lower back pain without leg radiation):

Radicular pain

This is the main symptom. Pain follows a precise path, corresponding to the territory of the compressed nerve root:

• L5 sciatica (L4-L5 herniation): pain descends along the buttock, posterolateral thigh, lateral calf, dorsum of foot and big toe.
• S1 sciatica (L5-S1 herniation): pain descends along the buttock, posterior thigh, calf, heel and sole of foot to the small toes.

Pain is typically described as burning, electric shock, stabbing or intense cramping. It is often pulsating and aggravated by coughing, sneezing, straining (bowel movement) or certain movements (forward bending).

Paraesthesias

Patients experience tingling, pins and needles, numbness or "electric current" sensations along the nerve pathway. These abnormal sensations indicate nerve root irritation.

Sensory deficit

The area innervated by the compressed root may become less sensitive to touch, pinprick or temperature. Patients describe their skin as feeling "cardboard-like" or "anaesthetised".

Motor deficit

In severe cases, nerve compression causes loss of muscle strength:

• L5 sciatica: difficulty lifting the foot (foot drop) and walking on heels, weakness of toe-spreading muscles.
• S1 sciatica: difficulty standing on tiptoes, calf weakness, loss of ankle reflex.

Rapidly progressing motor deficit is a neurosurgical emergency.

Warning signs (red flags)

Certain symptoms require urgent consultation:

• Cauda equina syndrome: urinary problems (difficulty urinating, incontinence), loss of perineal sensation (saddle anaesthesia), weakness in both legs, erectile dysfunction.
• Fever associated with intense lower back pain (possible infection).
• Severe night pain not relieved by painkillers (possible tumour).
• Unexplained weight loss (possible tumour).
• History of cancer.

Diagnosis of sciatica

Sciatica diagnosis is primarily clinical, based on history and physical examination. Complementary tests confirm the cause and guide treatment.

Clinical examination

The neurosurgeon assesses:

• Pain pathway to identify the affected nerve root (L5 or S1).
• Lasègue's sign: reproduction of sciatic pain when raising the straight leg beyond 30-45 degrees confirms radicular origin.
• Tendon reflexes: absent ankle reflex (S1) or diminished patellar reflex (L5).
• Muscle strength: testing foot extensors (L5) and plantar flexors (S1).
• Sensation: checking for reduced sensation in the radicular territory.

Lumbar MRI

This is the gold standard examination. It precisely visualises discs, nerves, vertebrae and soft tissues. MRI confirms the presence of a disc herniation, its level, size, type (extruded, sequestrated, protruded) and degree of nerve root compression. It is essential before any surgical decision.

Lumbar CT scan

Less effective than MRI for visualising discs and nerves, but useful when MRI is contraindicated (pacemaker, severe claustrophobia, incompatible metal prosthesis). CT scan visualises bony structures very well and can be combined with contrast injection (CT myelogram) to better visualise nerve compressions.

Electromyography (EMG)

This test measures the electrical activity of muscles and nerve conduction. It is useful in cases of diagnostic doubt, to precisely locate the affected root, to assess the chronicity of nerve damage or to rule out other causes (polyneuropathy, carpal tunnel syndrome in the upper limb).

Treatment of sciatica

Sciatica treatment depends on its cause, intensity, duration and impact on daily life. In 80% of cases, sciatica heals spontaneously within 4 to 6 weeks with conservative treatment.

Conservative treatment (first-line)

Dr Dimitriu systematically favours a non-surgical approach initially:

• Relative rest: avoid prolonged bed rest which delays recovery. Stay active within pain limits.
• Painkillers: paracetamol, tramadol, morphine for severe pain.
• Non-steroidal anti-inflammatory drugs (NSAIDs): ibuprofen, ketoprofen, unless contraindicated.
• Oral corticosteroids: short course (5-7 days) to reduce inflammation around the nerve root.
• Muscle relaxants: to relax contracted muscles.
• Gabapentinoids (pregabalin, gabapentin): for resistant neuropathic pain.

Physiotherapy and rehabilitation

Physiotherapy should only begin after the acute phase, when pain starts to decrease. It aims to:

• Strengthen deep back and abdominal muscles.
• Improve flexibility and posture.
• Learn proper movements to protect the back.
• Gradually resume daily activities.

Epidural injections

When medical treatment is insufficient, the neurosurgeon may propose corticosteroid injection at the compressed nerve root. This injection, performed under radiological guidance (fluoroscopy), delivers powerful anti-inflammatory medication directly to the inflamed area. One to three injections spaced 2 to 3 weeks apart may be necessary. Success rate is 50 to 70% for pain relief lasting several weeks or months, allowing the herniation to resolve naturally.

Surgery (specific indications)

Surgery is only considered after failure of well-conducted conservative treatment for 6 to 8 weeks, or in case of neurological emergency. Surgical indications are:

• Cauda equina syndrome (absolute emergency).
• Progressive motor deficit (foot drop).
• Hyperalgesic pain resistant to all treatments.
• Disabling sciatica despite optimal medical treatment for 6-8 weeks.

The reference procedure is microdiscectomy: the surgeon removes the disc fragment compressing the nerve root, through a 3 to 4 cm incision, under microscope. The operation lasts 30 to 45 minutes and the patient goes home within 24 to 48 hours. Minimally invasive techniques (endoscopy, percutaneous) allow even faster recovery. Surgical success rate is 85 to 95% for relieving sciatic pain.

When to seek emergency care?

Certain situations require urgent consultation in A&E or with a neurosurgeon:

• Rapid loss of strength in foot, ankle or knee.
• Urinary problems: difficulty urinating, incontinence, frequent urination.
• Perineal anaesthesia: loss of sensation between legs, around anus or genitals.
• Bilateral sciatica with weakness in both legs.
• High fever associated with intense lower back pain.

These signs may indicate cauda equina syndrome, a neurosurgical emergency requiring surgery within 24 to 48 hours to avoid permanent sequelae (paralysis, incontinence).

Frequently asked questions about sciatica

Sources: HAS (Haute Autorité de Santé, 2025), SFCR (French Spine Surgery Society), EANS (European Association of Neurosurgical Societies), Ropper AH, Zafonte RD. Sciatica. N Engl J Med. 2015;372(13):1240-1248.