Cryosurgery Or Sclerosing Injections: Which Is Better For Neuromas?
Cryogenic neuroablation is a safe, minimally invasive option that is less painful than alcohol injections and may facilitate a reduced risk of stump neuromas, according to this author. By Lawrence Fallat, DPM Morton’s neuroma (perineural fibroma) is a common painful forefoot disorder that can present treatment challenges to all podiatric physicians. The common digital nerves, usually in the second and third intermetatarsal spaces, become enlarged in the area of the deep transverse metatarsal ligament and subsequently cause pain in the ball of the foot with cramping, pain and numbness of the toes. Histological findings of the nerve include endoneural edema with perineural, epineural and endoneural fibrosis. Endarterial thickening occurs along with axonal loss and demyelination. These findings are consistent with a degenerative process and it is generally accepted that this occurs as a result of nerve entrapment. Conservative treatment consists of shoe modification, orthotics, NSAIDs and steroid injections. Neurolytic agents such as phenol and, more commonly, diluted 4% alcohol have been advocated.1 When conservative treatment fails, surgical intervention may be indicated. Excision of the neuroma is the most common surgical procedure performed but significant failure rates have been reported.2,3 Poor results can occur from incomplete excision or the formation of a stump neuroma that can be more troublesome than the original pain. With this in mind, one should consider the possible use of cryogenic neuroablation, which describes the destruction of axons to prevent them from carrying painful impulses. This technique involves applying extremely cold temperatures between –50ºC and –70ºC to the nerve. This results in degeneration of the intracellular elements, axons and myelin sheath with Wallerian degeneration.4 These changes are consistent with a second-degree nerve lesion. The epineurium and perineurium remain intact, and this prevents the formation of stump neuromas as the nerve regenerates. The preservation of these structures differentiates cryosurgery from surgical excision and neurolytic agents. Comparing Alcohol Injections To Cryosurgery I have used 4% alcohol injections for many years but with mixed results. Some patients do respond favorably to this treatment but many continue to have neuroma pain. In my experience, many patients have severe pain associated with the alcohol injections and approximately 50 percent of patients do not complete the series of injections because of pain associated with these injections. We recently had two patients who were treated in the emergency room later in the day because of burning pain at the injection site. I am also concerned about the effect of the alcohol on the peripheral nerves. Presumably the alcohol destroys the axon and its myelin sheath but it cannot be tissue specific and must also destroy the endoneurium, perineurium and epineurium. If the destruction of the nerve is complete, there will be a neurotomesis that will invariably form a stump neuroma as the axons regenerate. In this sense, the nerve destruction may carry the same risks as neuroma excision. It’s also important to keep in mind that the long-term results of alcohol injections have not been reported. With cryosurgery, the destruction of the axons is almost completely painless. I used to perform the procedure using only 1/2 cc of local anesthetic for the skin where I made the incision. I did not use any anesthetic to block the nerve. When I applied the ice ball to the neuroma, the patients experienced only a mild burning sensation that resolved after one to two minutes. There was only minimal postoperative discomfort that was controlled with NSAIDs. More significantly, cryogenic neuroablation does not destroy the epineurium or perineurium, the basic architecture of the nerve. As a result, stump neuromas do not form as the nerve regenerates. Having performed this procedure for approximately 200 patients over the last three years, I have found that very few patients have had a recurrence of their neuroma pain. If the pain returns a year or two later, I simply repeat the procedure. Axons regenerate at the rate of 1 to 3 mm per day. The prevailing thinking is that the ice ball destroys a 1-cm portion of the nerve. Therefore, the axon regeneration should be complete within several weeks.