Unfortunately, there is still a widespread reluctance to accept the undeniable truth that a “Morton’s neuroma” is nothing more than a peripheral nerve entrapment. However, I think there is more of a universal acceptance that when you cut out a Morton’s entrapment, the patient will end up with a recurrent Morton’s neuroma.1,2
These neuromas can be very problematic. I had the great fortune to work at a tertiary nerve clinic where the average new patient had four prior surgeries and had seen numerous surgeons, neurologists and other specialists to solve the problem. This is not to mention the really “lucky” patients who had radiographic adornment about their spinal columns with lead wires and a battery pack. After this experience, I have the greatest respect for the intact but entrapped nerve.
The sad fact was we averaged seven to eight patients per month whose lives had been absolutely destroyed by a simple Morton’s neurectomy. This valuable experience gave me a perspective that many of my colleagues cannot appreciate.
If you refer to much of the past literature, there is significant repetition from article to journal article of an 85 percent success rate for the treatment of Morton’s entrapment with resection of the nerve.3,4 From my clinical experience, I have never believed those figures and Womack and Richardson recently supported my assertion.5 In 2008, they reported on a series of 120 patients who had undergone surgical resection for the treatment of “Morton’s neuroma.” Interestingly, only 50 percent of their 120 patients reported a good or excellent result.
A 2009 Podiatry Today poll demonstrated that there was still a wide spread and significant misunderstanding about the true pathology of a Morton’s entrapment. (I cannot make myself write or say “Morton’s” and “neuroma” in the same sentence.) Of the 165 people who voted in the poll, 59 percent classified a Morton’s neuroma as a peripheral nerve entrapment syndrome, 12 percent classified it as a true neuroma and 28 percent classified it as a painful mass of mixed tissue etiology. (To access the poll, visit http://www.podiatrytoday.com/in-your-clinical-perspective-how-would-you-... .)
There is simply no way to effectively communicate to some practitioners regardless of the facts. Dogma is like an invisible intellectual force field that even Dr. Evil’s “tractor beam laser” cannot penetrate. Many surgeons are simply byproducts of their training and have never continued to grow after they have completed their formalized training. When you ask them why they do what they do, they invariably say “because that was the way I was trained.”
Can you not overcome that three-year period of indoctrination called residency and look outside our profession’s literature, read and think? (Truth be told, almost all three-year residency trained podiatric surgeons get it. The one who does not get it is the dinosaur out there who has been “grandfathered” and has never taken the time to step out of the 1970s and learn. That is another subject entirely.)
Why Attempting To ‘Kill The Nerve’ Can Lead To Serious Complications
If the peripheral nerve is simply entrapped, it does not make physiological sense to primarily orient one’s treatment toward some type of peripheral nerve injury. You and the patient can pay a very serious price, and you simply do not know when that can happen. I have heard many practitioners describe that they are going to “kill the nerve” with a sclerosing injection, cryoablation or thermal ablation.
Statements like this simply scream out that there is no understanding of peripheral neurophysiology because you cannot simply “kill“ the nerve. You can injure the damn thing but you cannot kill it. Okay?
These treatments may, in a best case scenario, result in a type IV Sunderland classification of nerve injury. This is a complete conduction block without destruction of the perineurium. You also could get a type III injury, which is not all bad. Occasionally, as Schneider and Mayhew delineated in their veterinary article, a type VI nerve injury, which is a “neuroma in continuity,” may occur with percutaneous cryoablation.6 This type VI nerve injury can be as problematic as an amputation neuroma.
Authors have demonstrated that a true neuroma is a spontaneous pain generator that develops ectopic receptor sites.7-10 This ultimately leads to ephaptic cross-talk with other sensory neurons, which then communicates with the cortical level of the brain and is ultimately perceived as pain. Bottom line: If the peripheral nerve is pinched, un-pinch it.
What You Should Know About Denervation Procedures
It is okay sometimes to hurt an already hurt peripheral nerve. There are many of these situations are out there, primarily due to the aforementioned “force field” because so many practitioners continue to sclerose or simply cut out the entrapped nerve.
The question then becomes what to do with this true neuroma, which is a spontaneous peripheral pain generator. There are numerous treatments recommended and one of the most common surgical procedures is to denervate the nerve and subsequently transpose the fresh nerve endings into innervated skeletal muscle. This technique has been well documented, works generally well and is well established in the literature.7
However, as someone who has focused on peripheral nerves over the last decade, I can assure you that this is not always a “home run.” From what I have seen clinically, there are huge differences in the nerves that we denervate. This could correlate to the amount of skin surface area innervated by the nerve but that is conjecture.
For example, we do extremely well with a plantar mini-neurectomy for a recurrent Morton’s neuroma with transposition of the common plantar digital nerve into the intrinsic musculature in the non-weight bearing arch of the foot. We also do very well with the medial calcaneal nerve. We do not do that well with the superficial peroneal nerve or sural nerve. Denervation of a small nerve like the medial calcaneal requires a “big” surgery to explore all the possible neural variants and that means some postoperative morbidity for your patient.
Can Radiofrequency Ablation Have An Impact With Amputation Neuromas?
Recently, we have also approached the treatment of amputation neuromas with radiofrequency ablation. We have had an incredible amount of success with virtually no post-treatment pain and immediate full activity for the patient. The complications from this type of procedure are minimal, including either failure to respond or a slight skin burn. If you think about it, this is an excellent modality as an intermediary step prior to a denervation procedure.
However, I must emphasize that I have huge disagreement with using this technology for a primary musculoskeletal disorder such as plantar fasciopathy. It is my opinion that using any type of modality to injure a peripheral nerve to primarily treat a musculoskeletal condition is not warranted and I would still say this is misguided.
Entrapment or injury to the medial calcaneal nerve is frequently the etiology of a complex pain syndrome of the heel and in order to denervate this nerve, an open tarsal tunnel surgery is required. If I am able to apply a percutaneous radiofrequency treatment on an area that will ultimately be subject to open surgery and if the procedure fails, then I am really not losing in the treatment of these types of patients. Potentially, we can save them an invasive surgical experience.
Radiofrequency ablation is not a new technology and surgeons have used it to treat peripheral nerve problems with success in treating trigeminal neuralgia.11 The technology that we are using is called the NeuroTherm NT250 (NeuroTherm). Protocols are now under development for treatment of amputation neuromas of peripheral nerves in both the lower and upper extremity lesions in our centers.
Our experience with this technology is very limited (including five very complex pain patients who had exhausted virtually every treatment). Based on the incredible response these patients have had, with virtually no postoperative discomfort and an immediate return to full activity, this technology merits further investigation.
Editor’s note: Dr. Barrett has no financial interest in NeuroTherm, the company that manufactures the NeuroTherm NT250.
1. Dellon AL. Treatment of recurrent metatarsalgia by neuroma resection and muscle implantation: case report and proposed algorithm of management for Morton's "neuroma." Microsurgery 1989;10(3):256-9.
2. Gauthier G. Thomas Morton's disease: a nerve entrapment syndrome. A new surgical technique. Clin Orthop. 1979 Jul-Aug(142):90-2.
3. Okafor B, Shergill G, Angel J. Treatment of Morton’s neuroma by neurolysis. Foot Ankle Int. 1997 May;18(5):284-7.
4. Vito GR, Talarico LM. A modified technique for Morton’s neuroma. Decompression with relocation. J Am Podiatr Med Assoc. 2003 May-Jun;93(3):190-4.
5. Womack JW, Richardson DR, Murphy GA, Richardson EG, Ishikawa SN. Long-term evaluation of interdigital neuroma treated by surgical excision. Foot Ankle Int. 2008 Jun;29(6):574-7.
6. Schneider RK, Mayhew IG, Clark GL. Effects of cryotherapy on the palmer and plantar digital nerves in the horse. Am J Vet Research 1985; 46:7-12.
7. Dellon AL, Mackinnon SE, Pestronk A. Implantation of sensory nerve into muscle: preliminary clinical and experimental observations on neuroma formation. Ann Plast Surg. 1984 Jan;12(1):30-40.
8. Mackinnon SE, Dellon AL, Hudson AR, Hunter DA. Alteration of neuroma formation by manipulation of its microenvironment. Plast Reconstr Surg. 1985 Sep;76(3):345-53.
9. Meyer RA, Raja SN, Campbell JN, Mackinnon SE, Dellon AL. Neural activity originating from a neuroma in the baboon. Brain Res. 1985 Jan 28;325(1-2):255-60.
10. Nath RK, Mackinnon SE. Management of neuromas in the hand. Hand Clin. 1996 Nov;12(4):745-56.
11. Huibin Q, Jianxing L, Guangyu H, Dianen F. The treatment of first division idiopathic trigeminal neuralgia with radiofrequency thermocoagulation of the peripheral branches compared to conventional radiofrequency. J Clin Neurosci. 2009 Nov;16(11):1425-9.