Sciatica 

The sciatic nerve is one of the main nerves in the leg and it exits the lower spine at the levels of L4-S3. It travels down through the pelvis and underneath the piriformis muscle and can occasionally be irritated by this muscle if it becomes tight leading to a condition called piriformis syndrome. The nerve continues its path down the back of the leg and splits into the tibial nerve and the common peroneal nerve at a point just above the back of the knee.

As with all nerves the sciatic nerve is very easily irritated by pressure or inflammatory chemicals. There are numerous sites along the nerve where it can be prone to irritation and which can lead to sciatica symptoms. Common symptoms are pain along the distribution of the nerve, altered sensation such as pins and needles and numbness and sometimes weakness in the legs.

The most common cause of sciatica symptoms is a prolapsed intervertebral disc (slipped disc) in the lower lumbar spine. The disc material gets pushed out of place and encroaches on the spinal nerve roots as they exit the lumbar spine on their journey down the leg.

Another common condition, which results in sciatic nerve irritation, is a narrowing of the bony apertures through which the spinal nerve roots exit from the spinal cord (within the backbone) foraminal stenosis. The closing down of these holes can result in a pinching of the nerve roots and lead to sciatic symptoms as described above. Degeneration of the lumbar spine over time causes the spaces between the vertebral bodies (back bones) to narrow. This is called lumbar spondylosis. The height of the discs between these bones reduces and the resultant lack of space can cause pressure on the nerve roots.