Sciatic Nerve and Sciatica

See related articles:

Assessment and Management of Low Back Pain
Sinister Causes of Back Pain
Back Examination

• Sciatica refers to symptoms arising from entrapment of lumbar spinal nerve roots. The symptoms are pain, tingling and numbness in the distribution of lumbar nerve roots - the buttocks, thigh, outer calf, foot and toes. Symptoms in sciatica typically extend to below the knee.
• The terms 'nerve root pain' or 'radicular pain' are also used for sciatica.
• Sciatica may occur together with non-specific low back pain. In this situation, the sciatica symptoms are usually the main problem.

Sciatica is a common problem. The lifetime prevalence of low back pain is 50-70%, and 5-10% of patients with low back pain have sciatica.

For illustration of spinal anatomy and pain mechanisms, see reference.³

Spinal nerve roots are identified by the number of the lower of the two vertebra between which they pass. For example, the L5 nerve root passes between the 4th and 5th lumbar vertebrae.¹

Sciatica occurs when there is compression of lumbosacral nerve root(s), which may have various causes:

• Herniation of a lumbar intervertebral disc.
  • Most commonly occurs at the L5 or S1 levels
• Annular fissure of intervertebral disc with chemical irritation of nerve root.
• Osteophytic nerve root compression.
• Spinal stenosis - narrowing of the spinal canal.
  • Causes of spinal stenosis include:
    • Facet joint osteoarthrosis
    • Congenital stenosis
    • Spondylolisthesis - a vertebra slips forward relative to the lower vertebrae
  • Note: lateral recess stenosis and foraminal stenosis tend to cause sciatica. In contrast, central spinal stenosis tends to cause spinal claudication i.e. symptoms of bilateral calf pain, paraesthesia, or numbness on walking (see differential diagnosis)
• Injury.
  • Fracture or displacement impinging on the spinal nerves
  • Remember that in osteoporotic patients fractures can occur with minor trauma
• Bone or joint disease, e.g. Paget's disease, ankylosing spondylitis.
• Infection:
  • Osteomyelitis - bacterial or tuberculous
  • Discitis
• Spinal tumours, e.g. bony secondaries from breast or prostate cancer and myeloma.
• Failed back surgery syndrome, e.g. recurrent herniation, epidural adhesions or arachnoiditis.
• Epidural varicose veins (rare) due to inferior vena cava obstruction from pregnancy or abdominal mass.⁵

Typical features are:

• Unilateral leg pain radiating to below the knee.
• Back pain (if present) is less severe than leg pain.
• Symptoms/signs of nerve root compression: numbness, tingling (paraesthesia), weakness, or loss of tendon reflexes.
• Straight leg raising test increases the leg pain and/or the nerve compression symptoms.

1. Assess for 'red flags'

• Do a history and examination for 'red flag' features, which may indicate cauda equina syndrome, fracture, spinal infection or cancer (see box below).
• Those with cauda equina syndrome need immediate referral to prevent permanent neurological damage. Other red flag features may need same day or urgent (within a few days) referral, depending on the clinical situation.

2. Confirm diagnosis of sciatica

Typical history is:

• Unilateral leg pain radiating below the knee to the foot or toes.
• Any low back pain is less severe than the leg pain.
• Symptoms of nerve root compression: numbness, tingling (paraesthesia), weakness, or loss of tendon reflexes.

Examination:

• Sensory loss, weakness, or loss of tendon reflexes in a nerve root distribution.
• Straight leg raising test increases leg pain and/or nerve compression symptoms.
• Look for other causes of pain:
  • Check hips, knees and trochanteric bursae.
  • Further examination (e.g. abdomen, pelvis, aorta) if appropriate.

• Sacroiliitis (ankylosing spondylitis and other spondyloarthropathies). With arthropathies the pain may alternate between buttocks.
• Spinal claudication i.e. bilateral calf pain, paraesthesia, or numbness on walking, relieved by sitting, worse on spine extension, usually negative straight leg raising test and few neurological signs.
• Other neurological problems or thoracic spine lesions (usually have more widespread neurological features).
• Shingles (before the rash appears).
• Causes outside the spine:
  • Lower limb: pain from hip, knee or trochanteric bursa, peroneal nerve palsy (nerve entrapment at the fibular head).
  • Thoracic or abdominal pathology, e.g. aortic aneurysm, abdominal tumours.
  • Pelvic lesions, e.g. psoas muscle abscess, pelvic tumours or inflammation; pelvic fractures (may irritate pelvic nerves).
  • Piriformis syndrome (entrapment of the sciatic nerve in the piriformis muscle) and other pelvic nerve entrapments.^7,8
  • Trauma around the sciatic nerve, e.g. misplaced gluteal muscle injection or gluteal muscle compartment syndrome.⁹

Investigations are needed if there are 'red flag' features, or if surgery is considered.¹ Possible investigations include:

• Blood tests: full blood count, ESR/CRP, renal and liver function, bone profile, PSA, serum protein electrophoresis
• Urine tests if suspected infection or cancer: urine dipstick, microscopy and culture; urine Bence Jones protein
• Radiology: possible tests are:
  • Plain X-ray of lumbosacral spine (and thoracic spine, if thoracic pain also present)
  • CT or MRI scan
  • Bone scan

Patient information

Provide information and advice to promote understanding, a positive attitude and realistic expectations. Suggested points to discuss are:

• Explain diagnosis and any concerns. Sciatica often settles by 6–12 weeks.
• Temporary pain relief can be used.
• Recovery is helped by getting moving again and getting back to work as soon as possible.
• Advise when to seek help (progressive symptoms or red flag symptoms).
• Care when lifting and twisting.
• Cold or heat packs can relieve back pain.
• When lying down, it may help to use a small pillow between the knees (if sleeping on the side), or several pillows propping up the knees (when lying on the back).

Drug treatment

1. First-line: simple analgesics - paracetamol or ibuprofen.
2. For additional analgesia:
   • Combine paracetamol and an NSAID, or
   • Add a weak opioid (e.g. codeine or tramadol).
3. For persistent sciatica not responding to first-line analgesics:
   • Consider a trial of tricyclic antidepressant or gabapentin.
   • If a strong opioid is needed, refer to a specialist or pain clinic.

When to refer

• Red flags: cauda equina syndrome needs immediate referral, other red flags need urgent referral (see Assessment above).
• If neurological deficit is progressive, persistent, or severe, refer for neurosurgical or orthopaedic assessment (preferably to be seen within 1 week).
• If pain or disability remain problematic for >1-2 weeks, consider early referral for physiotherapy or other physical therapy.
• If sciatica is disabling and distressing for >6 weeks, refer for neurosurgical or orthopaedic assessment - preferably to be seen within 3 weeks.
• If pain or disability are problematic despite appropriate pharmacotherapy and physical therapy, consider referral to a multidisciplinary back pain service or a chronic pain clinic.

Follow-up

• This depends on the clinical situation.
• Consider 'yellow flags' for chronicity, which are:
  • Belief that pain and activity are harmful; sickness behaviours, such as extended rest.
  • Social withdrawal, lack of support or overprotective family
  • Emotional problems, e.g. negative mood, depression, anxiety.
  • Problems at work; long time off work (>6 weeks).
  • Problems with compensation claims or benefits.
  • Inappropriate expectations of treatment, e.g. not expecting active participation in treatment.

Surgery and other treatments

Decisions about invasive management should be balanced against the natural history and relatively good prognosis of sciatica (see prognosis). Multidisciplinary care, such as back clinics or pain clinics, may be useful.

Possible procedures include:

• Epidural steroid injection:⁴
  • This can provide short-term pain relief; the longer-term benefits are uncertain.
  • It should be performed under fluoroscopy with contrast for best results.
• Surgery:
  • May be required for major pathology, e.g. fractures, neurological deficit, tumours or infections.
  • May be beneficial for spinal stenosis and spondylolisthesis, compared to non-surgical treatment.
  • For disc herniation, without severe neurological deficit, surgery may promote more rapid return to function compared to the natural course of sciatica.
  • The benefits of surgery vs. conservative treatment are still debated.¹⁰ Some studies suggest good results from surgery.¹⁰ However, 'failed back surgery syndrome' is a recognised complication, where there may be recurrent herniation, epidural adhesions or arachnoiditis.⁴
  • The standard surgical procedures are discectomy or microdiscectomy - the latter uses magnification to view the disc and nerves during surgery. A recent Cochrane review¹¹ of these procedures found that results are comparable between discectomy and microdiscectomy; the choice mainly depends on local expertise.

New treatments and research

• Various minimally invasive surgical techniques have been developed as alternatives to open discectomy. Currently these are regarded as research techniques, until more data is available on their safety and effectiveness:¹¹
  • Percutaneous intradiscal electrothermal therapy.¹²
  • Automated percutaneous mechanical lumbar discectomy.¹³
  • Endoscopic laser foraminoplasty.¹⁴
  • Laser lumbar discectomy.¹⁵
• Injection of oxygen-ozone mixture gas into the disc and foramen is a new technique which shows promise. The mixture is thought to dry out the disc, reduce inflammation and improve local microcirculation.^16,17
• Antibodies against tumour necrosis factor-alpha have been researched, because of the possible causative role of this factor in sciatic pain. Some small trials have used infliximab¹⁸ or etanercept,¹⁶ but with no clear benefit so far.

Possible complications include:

• Permanent nerve damage with sensory deficits and, more importantly, motor weakness.
• Chronic pain and psychosocial problems.
• Loss of employment.

The prognosis for acute sciatica is generally favourable:

• In placebo groups of people with acute sciatica (included in randomised trials of non-surgical interventions), about 50% reported improvement within 10 days, and about 75% reported improvement after 4 weeks.¹
• The herniated portion of an intervertebral disc causing sciatica tends to regress over time, with about two thirds having at least partial resolution after 6 months.
• Up to 30% of people continued to have pain for 1 year or longer. Improvement in symptoms may continue beyond one year.

• Improved general fitness and posture.
• 'Back school' – advice on lifting techniques, advice on coping with pain.
• Occupational therapy and job retraining if these activities precipitate attacks.