Dr. Robert F. Kidd    

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Sciatica - Is It a Pinched Nerve?

See also: Backache, Caudal Epidural Block, Prolotherapy

Sciatica is a word used to describe a pain running down the back of the leg. It is usually thought to come from the sciatic nerve, which develops from several little nerve roots branching off the spine. When one of more of these nerve roots are "pinched" by a herniated disc, sciatica develops, or at least so we have been lead to believe.

But is this the whole story? - not always, and perhaps not even as often as we think. Sciatica is not always what it seems to be. In fact, often no nerve is pinched at all, but rather pain is referred down the leg from painful structures in the back.

Referred pain is different from the pain of a pinched nerve. It is harder to understand because it does not follow the pathways of any nerve and is often felt in locations quite far removed from where it is coming. An example that many people know about is referred pain from the heart, which is often felt in the left arm. No nerve runs from the heart to the elbow, but somehow the brain perceives the pain to be coming from the elbow as well as (or instead of) the heart. This is a mistake on the part of the brain, but it probably doesn't matter much, as the purpose of the pain is really to make the patient lie down and rest for a while until the heart heals.

"Sciatica" due to referred pain is similar to that from a pinched nerve, but at the same time is different is some respects. This is important as the treatment of the two conditions may be quite different.

Sciatica from a pinched nerve tends to go down the back of the leg to the foot. It may be felt as a band right down the back of the leg, or it may be felt in only part of the back of the leg, - the calf, for example. Often pain or numbness is felt in part of the foot or the toes as well. Coughing will often provoke a shot of pain into the back of the leg, and sometimes there is weakness in the leg or ankle.

Sciatica from referred pain may go down the back of the leg, or the front, or the side. When it goes down the back, it will skip the back of the knee. This is one of the most important ways of telling the difference from sciatica caused by a pinched nerve. Sometimes there is pain or numbness in the foot, but it tends to be vaguer than that from a pinched nerve.

Xrays are not much help in separating these two types of sciatica. CT scans and MRI's may be useful, but are far from fool-proof as they sometimes show us more than we really want to know. In fact, 30% of pain free people will have bulging or herniated discs if we look for them, yet are experiencing no problems whatsoever. So for someone with sciatica, a bulging disc on the CT scan is no guarantee that it is the cause of the pain. What it boils down to is that there is no replacement for a careful examination to separate these two types of sciatica.