I saw an interesting question posted today – something to the effect of, ‘If you have nerve decompression and/or transection, shouldn’t you feel immediate relief?” This question is a very important one, but the answer may not be intuitively obvious. The nervous system is truly complex and often quite difficult even for medical professionals to understand. Therefore, in an effort to explain why it can often take many months before a patient experiences the hoped for improvement, I’ll use an analogy to which many people can hopefully relate.
Most everyone has at some point, had the experience of falling asleep on their arm and waking up with slightly numb fingers. Upon waking, you notice the altered sensation in the fingers, shake them out and within a few seconds, sensation returns to normal. Many people have also had the experience of waking up after having fallen asleep on their arm for a longer time, getting up and realizing that they not only have very numb fingers, but also that they have difficulty moving their elbow, wrist and/or fingers very well. “Oh my gosh, did I just have a stroke?!?”, often comes to mind. In this scenario, you try to shake out the arm as best you can and it often takes a few minutes before things start to move again and sensation returns to the digits. Moreover, once the blood starts flowing again and sensation begins to recover, there is often a period of hypersensitivity before things settle down.
The difference in these two scenarios is the degree of pressure and the duration of pressure on the nerves in the upper extremity, obviously worse in the second scenario. Given the overall greater amount of pressure in this second scenario where you’ve probably slept on your arm for a few hours, it takes longer for the nerves to recover. Now take this second scenario and stretch it out much longer. In other words, let’s assume you’ve had pressure on your upper extremity for several years? Would the nerves be expected to recover in a few hours or days following decompression? Given what we know from the above examples, the answer is, ‘Probably not’. Recovery in these cases can take many months. The situation with neurectomy is a little bit different in mechanism, but the same in practicality. When you transect a nerve proximal (i.e. upstream) from an injured segment, you now have a “live” nerve end that you bury within the local muscle. However, doing so is not the same as turning off a fuse to an outlet with a short where the sparks stop immediately. Remember that this nerve is still attached to the spinal cord and therefore the brain, so impulses will still travel back and forth to that “live” end. However, with time, that sensory nerve end will likely make connections with other motor nerves within the muscle and in effect this “fools” that sensory nerve into thinking that it has found its downstream counterpart. You now have a sensory nerve connected to a motor nerve, a situation in which the impulses travel as they normally would, but have no effect on the muscle since the muscle only responds to motor nerve impulses. It would be like me having written this post in Sanskrit (which hopefully nobody reading this post understands). You might recognize it as writing, but it would make no sense and therefore would elicit no reaction. That being said, this process takes time which is the reason that relief following neurectomy with muscle implantation is often not immediate. The take home message is that recovery from any nerve operation is a process, not a moment in time. Hopefully that helps.