This month’s topic is Sciatica.
What is Sciatica? We as physicians generally don’t use this term since it is vague. People generally don’t have complete damage or compression of the entire sciatic nerve. Generally people have compression of one of the many nerves that comprise the sciatica nerve. The sciatic nerve has branches form the lower lumbar and upper sacral levels. Thus damage or compression of any of these nerves (L4 to S3) can lead to what is called sciatica. When one of these nerves is compromised, we refer to this as a radiculopathy. Thus, when people have a herniated disc or spinal stenosis that causes pressure on these nerves, usually only one or two of the nerves that comprise the sciatic nerve are affected, and not the entire sciatic nerve. This is important because when surgery or injections are considered they must be directed at the exact level that has the nerve injury. Thus, we use the word radiculopathy to describe these conditions since it is more specific.
When speaking of nerves, it is important to realize that a nerve such as the sciatic nerve is not only made up of numerous nerve roots from the spinal cord but also that each of these nerve roots has thousands of nerves within it. There might be a million nerves (or neurons) in the sciatic nerve. The best way to think of the sciatic nerve, or any nerve, is like a telephone cable. One cable has numerous wires within it. Generally, the outer telephone wires are used for homes near the source while the deep inner wires are for the more distant homes. The cable thus gets smaller as it reaches the last homes, which use those deep wires in the middle of the cable. Your nerves are the same way. The outer portion of the main nerve has small nerves that innervate the regions near the spine while the deep middle of the nerve innervates the distant areas such as the hands or feet. This is important since when something, such as a herniated disc, pushes on the nerve, the outer little nerves are affect first. This is why people will often get shoulder pain or buttock pain before they get arm pain. Only when the nerve get further compresses does those deep inner nerves get affected and then the pain radiates down the arm or leg. This also explains why some people can have pain that one day goes further down the arm or leg than on other days. It all depends on the extent of compression of the nerve bundle.
When people get numbness or weakness, this simply implies that the transmission of the nerve is gone due to damage. No sensation means “no nerve information” or the telephone wire has been cut. As long as the nerve is working, you’ll have pain and muscular cramps, but when it goes too far, those cramps become weakness and the pain becomes numbness. This nerve damage often can be resolved with surgery but can sometimes become permanent. In a later newsletter we will discuss the treatments of nerve compression but this month I am focusing on helping you to understand the anatomy. It is also to understand that due to our spinal curvature, most problems occur at those curves. These points are Cervical levels C5-6-7, Thoracic levels T6-7-8, and Lumbar levels L4-5-S1. These levels also result in the most pain since C5-6-7 innervates much of the arm while L4-5-S1 innervates much of the leg. Thoracic issues are less common due to the rigidity of the thorax and usually only represent 10% of spinal issues. I hope you now realize that when we speak of spinal problems, we are talking about spinal nerve root issues and peripheral nerve problems such as the sciatic nerve.