First of all, what is a neuroma? A neuroma can be defined in one of two ways. One, as a tumor composed of nerve tissue such as an acoustic neuroma. Almost overwhelmingly, these tumors are benign. The more common usage of the term neuroma means a mass of nerve tissue consisting of regenerating nerve fibers that have been previously severed or injured somehow. When a nerve is injured, it tries to re-grow - that’s what nerves do. If that nerve re-grows into the scar at the skin, it can cause exquisite pain even with light touch in the area. This situation would be akin to having a cavity (which hurts because the nerve at the root of the tooth is exposed) and eating ice cream - ouch! So if a nerve is severed or injured in some other way, how do you prevent a neuroma from occurring?
Well, as with anything in medicine there is no sure-fire way to prevent a neuroma. The only guarantees in life are, sadly, death and taxes. However, conventional wisdom states that by burying a severed nerve end into muscle, a neuroma will not form. This dictum is based upon a paper written by one of the fathers of peripheral nerve surgery, Dr. A. Lee Dellon. Dr. Dellon was able to demonstrate that when a nerve is buried into muscle, the structure of the regenerating nerve fibers is different than if a severed nerve was left in the subcutaneous tissues. It is thought that this structural difference accounts for the relative paucity of symptoms when a nerve is buried into muscle. However, as suggested by some on this forum, muscle burial isn’t always effective. Why is that? One possibility is that the original theory is incorrect. Another is that the buried nerve has come out of the muscle which is why it is important to bury a solid length of nerve into the muscle. Another is that the amount of muscle covering the nerve is small and there is therefore still pain as a result of cutaneous pressure in the area. Luckily, there is hope.
A suspected neuroma can be re-explored, re-excised and buried deeper within the local muscle. More muscle can be brought into the area such as with free-tissue transfers wherein a muscle is dissected out of a distant location with its own artery and vein and then re-implanted into a recipient artery and vein at the site of a neuroma to cover it. Yet another more elegant solution exists. It has recently been proposed that if you connect the injured nerve with another nerve, a neuroma will not form. The basic idea is that the regenerating nerve fibers will ultimately hook up to this other nerve’s fibers and the abnormal nerve structure will never form. In layman’s terms, you are giving the injured nerve fibers something to do and a target to re-innervate. This concept has been very successfully applied to neuroma stump pain in amputees. In these patients, we excise the neuroma, thus leaving a fresh nerve end. We then find another target nerve and co-apt our cut nerve end to that second nerve. My personal experience with these cases is wonderful. After the surgical pain goes away, much of the neuroma pain also disappears.
I have attached a picture of a woman with an above-knee amputation who had a neuroma of the sciatic nerve and significant stump pain such that she couldn’t wear a prosthesis. This neuroma was excised and the nerve separated into its two main components. We then found two redundant motor nerves in her hamstrings (which flex the knee and are therefore now superfluous since she has no knee) and connected the sciatic nerve ends to these nerves. As the sensory (and motor) nerve fibers from the upstream sciatic nerve grow into the motor nerves, there will be some mismatch, but that doesn’t matter since a neuroma (free regenerating nerve fibers at a cut nerve end) will presumably not form. I say presumably because we don’t re-operate on her just to check. At her last visit, 4.5 months post-op, she had no more neuroma pain. When the cut nerve end is not near another target nerve, we even have the ability to take cadaveric nerve to use as a “splice”, to bridge the distance gap. Take-home message: a neuroma is never fun, but can be addressed by someone knowledgeable in dealing with nerve problems. For more information on neuroma or other nerve pain issues, please visit www.peledmigrainesurgery.com and www.pelednervesurgery.com today, and call us at 415-751-0583 to make an appointment.