Sciatica

Characteristic pain felt in the lower back, buttocks and the posterior and lower leg that results from compression of any of the 5 nerve roots that contribute to the sciatic nerves

Aetiology

  • Compression of a nerve root, most commonly L5/S1
  • Compression is most commonly caused by intervertebral disc prolapse
  • Other causes:
    • Root compression by other degenerative disease (bone spurs, canal stenoss, spondylolisthesis, facet arthropathy)
    • Root compression of sinister causes (tumour, fractures, TB)
    • Root compression outside the spine (piriformis syndrome, endometroisis, pelvic disease, peroneal compression)
    • No root compression (arachnioditis, peripheral neuropathies)

Pathophysiology

Intervertebral disc prolapse

  • Intervertebral discs consist of concentric collagenous fibres (the annulus fibrosus) surrounding a central nucleus (the nucleus fibrosus) of degenerated collagen
  • Healthy discs contain a great deal of water
  • As a result of aging the discs become dehydrated and weaken - more prone to prolapse
  • Prolapse of a disc occurs when there is a defect in the annulus fibrosus that allows the nucleus to herneate out
  • Herniation often occurs as the result of strenuous physical activity involving the lumbar spine
  • The prolapsed disc material can press (impinge) on an exiting nerve root resulting in pain and altered sensation in a dermatomal distribution as well as reduced power in a myotomal distribution
  • The commonest site for this to occur in the spine is the lower lumbar spine with the L4, L5 and S1 nerve roots contributing to the sciatic nerve and pain radiating to the part of the sensory distribution of the sciatic nerve

Clinical presentation

Symptoms

  • Frequently described as unilateral leg pain that is greater than the back pain
    • Some patients may not have any back pain
  • Sharp, shooting, electric pain
  • Pain radiates to foot
  • Numbness and parasthesia in same distribution

Signs

  • Nerve irritation signs
  • Motor, sensory, or reflex changes in one nerve root

Investigations

  • Clinical diagnosis

Management

  • Prognosis reasonable - 50% recover from acute attack in 6 weeks, 90% within 3 months
  • NSAIDs and analgesia
  • Consider surgery if unremitting/recurrent symptoms