Sciatica simply means an irritation of the sciatic nerve. Sciatica symptoms normally include leg pain, weakness, numbness or tingling. Confusingly, it is often used as a layman’s terms to describe any lower back pain.
The spine is made up of large bones called vertebra and these are separated from one another by spinal discs. In the lower back these discs are large and they act as shock absorbers between the vertebrae.
Your spinal cord runs in a bony channel from your brain to your tailbone. The channel is formed by the vertebrae which encircle it and protect it from injury.
The spinal cord encircled by the bony channel of the vertebrae
As it passes down the bony channel the spinal cord branches out to form nerve roots. These nerve roots are in pairs and they leave the spinal canal, on on each side, in a small bony gap between each of the vertebrae called the foramen.
Nerve roots leaving the spinal cord through the gap called the foramen
These nerve roots bundle together to make up the nerves in our arms and legs. They are called peripheral nerves.
The femoral and sciatic nerves are formed by
nerve roots bundling together. This shows which roots make
up the bigger nerves.
In the legs there are two main bundles of nerves.
The sciatic nerve starts off at the spinal cord
and runs down the back of the thigh
into the calf and foot (image adapted from Grays Anatomy)
Sciatica is caused by an irritation of a nerve root as it leaves the spine.
The medical name for it is lumbar radiculitis or radiculopathy - often people refer to it simply as a pinched nerve in the back.
There are several different things that can irritate this nerve:
In practice the findings in a clinical examination are taken together with your history, symptoms and how the symptoms behave to help your doctor make a diagnosis.
Van, R.M. et al., 2012. Computed tomography for the diagnosis of lumbar spinal pathology in adult patients with low back pain or sciatica: A diagnostic systematic review. European Spine Journal, 21(2), pp.228–239.
Wassenaar, M. et al., 2012. Magnetic resonance imaging for diagnosing lumbar spinal pathology in adult patients with low back pain or sciatica: A diagnostic systematic review. European Spine Journal, 21(2), pp.220–227.