Sciatic is a common problem we see but can be easily misdiagnosed. This article will identify the key symptoms of sciatica and why they occur.

Firstly, why the term sciatica? The answer is simple. Sciatica defines an irritation of the sciatic nerve. The nerve comes from the lower back and runs deep to the buttock muscles, before sheltering under the hamstring muscle as it passes down the back of the thigh. At the back of the knee, it branches into two and runs down the outside and back of the lower leg respectively and ends in the foot (see illustration). It is the largest nerve in the lower extremity and supplies the majority of the structures. To give you a sense of its size, if you imagine the main nerves in the body having a diameter of tree branches then the equivalent diameter of the sciatic nerve would be that of the tree trunk.

So how does the sciatic nerve become irritated? The two most common ways are compression and / or chemical irritation. Compression is simply extra mechanical pressure placed on the nerve by the surrounding structures. Usually surrounding tissues will simply slide past each other during movement. However if a surrounding tissue is tight or damaged it may take up more space (as a result of swelling for example) and thus squeeze the sciatic nerve. Chemical irritation results from the chemicals released during inflammation. One of the roles of these chemicals is to sensitize the local nerves to induce pain. Therefore, if the surrounding tissue is damaged [or indeed the sciatic nerve itself] then the resulting inflammation will chemically irritate the sciatic nerve.

Both of these processes will alter the conduction of the sciatic nerve. When there is a low intensity compression or chemical irritation the sciatic nerve will produce pain along part or the whole of its pathway. As the compression or irritation increases in intensity the functionality of the sciatic nerve will be compromised. This results in pins/needles, numbness or weakness in the muscles along the sciatic nerve pathway.

So therein lies the symptoms of sciatica, back pain with a altered sensation into the buttock, posterior thigh or leg and foot. When the sciatic nerve is weakly compromised it will produce pain in the named distribution, but as the severity increases it will also produce pins/needles, numbness or weakness.