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
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 ageing 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 herniate 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
Other causes of sciatica
Root compression by other degenerative disease (bone spurs, canal stenoss, spondylolisthesis, facet arthropathy)
Root compression of sinister causes (tumour, fractures, TB)