A Closer Look At Cryosurgery For Neuromas

Marc Katz, DPM

   The future of most medical procedures will be minimally invasive with some type of guidance. Therefore, I believe podiatry needs to continue to develop its own techniques to move into the future. Instead, the profession may be concentrating too heavily on teaching new podiatrists reconstructive surgical procedures while leaving other options behind. The well-rounded practitioner will have many techniques, both invasive and minimally invasive, to offer his or her patients.

Pertinent Insights On The Mechanism Of Action

The cryoprobe is designed to use compressed gas such as CO2 or nitrous oxide. The compressed gas enters the probe and is released through a small opening at the closed distal chamber portion of the probe. When the gas expands in the small chamber at the probe tip, the temperature drops to about -70ºC, leading to a frozen ball of ice that surrounds the involved nerve. This phenomenon is known as the Joule-Thomson effect. The freezing of the area leads to destruction of the endoneurial capillaries, which is followed by Wallerian degeneration and axon destruction. The intensity and duration of analgesia depends on the degree of nerve damage from the ice ball.6 Accordingly, accurate placement of the ice ball is essential to obtaining a long-lasting cryolesion, leading to nerve death and prolonged analgesia.

   Since the perineurium and epineurium are preserved during the freeze, stump neuroma formation is unlikely when the nerve regeneration occurs. This is one of the major advantages of cryosurgery in comparison to traditional nerve excision and alcohol injections. The typical freeze time varies between two and three minutes with one to two defrost cycles occurring between treatments. The time varies depending on the probe and ice ball size. A delicate balance is necessary to allow for adequate freezing without damaging surrounding structures or causing an abscess.

   It is my belief that there is no larger vessel damage because of the heat sink of the blood flowing through the artery and vein. In addition, the shorter freeze times allow for nerve injury to occur rapidly before the temperature damages other tissues.

   I have seen no major vessel damage in my experience with cryosurgery. I would caution, however, that more is not better when it comes to the duration of the freeze. More freeze time will lead to complications including abscess. I would also use caution when applying cryosurgical techniques to mixed motor and sensory nerves. I do not recommend cryosurgery on motor nerves as destruction will lead to loss of function in some cases.

Essential Diagnostic Insights

A diagnosis of neuroma or nerve damage within a specific anatomic area is essential prior to performing cryosurgery. I have found ultrasound to be the best tool in identifying the neuroma in addition to clinical exams and taking a thorough history. The longitudinal view provides the practitioner with an excellent view of the neuroma. I also use this view to ensure accurate placement of the probe on the nerve for ablation.

   To confirm the diagnosis, I will do an ultrasound-guided injection of the nerve with approximately 1 cc of bupivacaine directly surrounding the area just proximal to the neuroma. This will provide significant relief and confirmation that the nerve is truly the pain source. Flooding the area with larger amounts of anesthetic will not provide an adequate confirmation.

   I have found magnetic resonance imaging (MRI) to be unpredictable. This is likely due to foot placement by the technician and a lack of familiarity with neuroma by some radiologists. With that being the case, I also do not rely on the MRI results to diagnose neuromas. I often see patients who have had treatment based on MRI and, in my opinion, have capsulitis, plantarflexed metatarsals and fat pad atrophy as opposed to a neuroma.

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