Point-Counterpoint: Intermetatarsal Neuromas: Is Neurectomy The Best Option?

   Yes. By Patrick A. DeHeer, DPM. While this author has had success with conservative treatment, particularly sclerosing therapy, he emphasizes that a plantar approach to the neurectomy can be effective when surgery is indicated.    Morton’s neuroma is a commonly encountered forefoot pathology that has many different treatment options available for the foot and ankle specialist. What are these options, when does one implement each type of treatment and when does surgical intervention become the best option for the patient?    Before looking at any treatment options, it is of vital importance to confirm the diagnosis of Morton’s neuroma as many forefoot pathologies can mimic the symptoms. Accordingly, one must work through the differential diagnosis. It is well documented in the literature that clinicians should include conditions such as lumbar radiculopathy, tarsal tunnel syndrome, stress fracture, calluses, Freiberg’s infarction, peripheral neuropathy, bursitis, rheumatoid arthritis, metatarsophalangeal joint disorders and tumors in the differential diagnosis.

Essential Diagnostic Pointers

   When it comes to diagnosing Morton’s neuroma, clinicians should base the diagnosis on the patient’s history and physical findings, and subsequently confirm it with at least one diagnostic injection. The patient’s history is often enough to direct the experienced foot and ankle surgeon to the correct diagnosis, especially when one utilizes the NLDOCAT (nature, location, duration, onset, course, aggravation and treatment) chief complaints approach during the interview process.    In the physical examination, a positive Mulder’s sign is the traditional indicator of a Morton’s neuroma. Although the literature shows marginal reliability of the Mulder’s sign, I have found it to be very helpful in the clinical diagnosis.    In the literature, Gauthier’s test is reportedly highly sensitive for nerve compression syndrome. This test consists of compression of the metatarsal heads while actively dorsiflexing and plantarflexing the digits for 30 seconds. A positive test results in pain to the patient or a sensory abnormality.    It is very important to examine the adjacent metatarsal joints to rule out any potential joint pathology, especially predislocation syndrome or metatarsalgia. When working through the differential diagnosis of a Morton’s neuroma, radiographic examination is indicated to rule out any potential osseous pathology.

Using Diagnostic Injections To Guide Treatment Decisions

   After making the differential diagnosis of Morton’s neuroma, it is of utmost importance to confirm the diagnosis with a diagnostic nerve injection. I like to inject 0.5 cc of xylocaine and 0.5 cc of dexamethasone phosphate in the involved innerspace just behind the toe sulcus. Then one can ask the patient to ambulate in the office setting and record his or her initial response. The patient will track the injection results over approximately one week. At the end of the week, the patient usually returns for a follow-up visit.    The subsequent treatment is based on the patient’s response to the injection. The patient will usually have one of four findings: no change, better while numb, better for two to three days, better for the entire time. If there is no change, reconsider the diagnosis.    If the patient feels better while numb or better for two or three days, I start the patients on sclerosing therapy as described by Dockery. I have used this treatment for the past five to six years with 80 to 85 percent success rates, similar to those reported by Dockery.1    If the patient responds with sustained pain relief from the initial diagnostic nerve injection, I tend to follow with oral steroids and orthoses. If at any time the patient is not progressing with this treatment, I will initiate sclerosing therapy as above. In regard to orthoses, it has been my experience that unless the neuroma is asymptomatic, the symptoms tend to be aggravated by the device. I have tried several different styles of orthoses with many different modifications and found this to be a consistent finding through the years.

What The Literature Reveals About Neuroma Surgery

   Prior to using sclerosing therapy, neuroma surgery was probably the most common type of surgery I did. Now I perform it much less frequently and this is wholly due to sclerosing therapy. With that being said, when a patient does not respond to conservative care, there are two very well accepted surgical procedures available for treatment.    The more traditional excisional approach has been more documented in the literature and has had overall favorable outcomes. In their critical clinical analysis, Mann and Reynolds had 76 to 100 percent improvement in 71 percent of neuroma patients and 81 percent of stump neuroma patients with an average follow-up of 22 months.2 In a long-term study, Keh, et. al., had a 93 percent success rate with an average follow-up of 58 months.3 Finally, Coughlin and Pinsonneault had 85 percent excellent or good rates with an average follow-up of 5.8 years.4

How To Maximize Outcomes With A Plantar Approach To Excision

   Dorsal and plantar approaches for the excision have been well described with many more surgeons opting for the dorsal approach. However, I have been using the plantar approach for the past 12 to 13 years with continued good results. I have not encountered the wound or scar complications that are often cited as reasons for avoiding this approach. In fact, plantar incisions typically heal very nicely. I have on occasion had instances in which small pinpoint callus formation or a diffuse callus formation has occurred. This is usually responsive to debridement and topical acid therapy as needed. I routinely will allow the patient to bear weight in a postoperative shoe with plantar incision and have not found the need to have the patient be non-weightbearing.    There are a couple of reasons why I utilize the plantar approach. First, one can avoid severing the deep transverse metatarsal ligament (DTML). Secondly, the surgeon is able to resect the common digital branch well behind the ball of the foot into a non-weightbearing area. Regeneration of the DTML is well noted in the literature but what is not known is how long this process takes and what kind of destabilization to the forefoot occurs during this healing period. The most common significant complication with excision is stump neuroma formation, which surgeons will often locate at one of the adjacent metatarsal heads in follow-up surgical revision. I have long felt that the dorsal approach limits how far one can resect the proximal nerve and this has been my primary deciding factor to use the plantar approach.    There are also a couple of pointers to consider in regard to the plantar approach. When excising a third innerspace neuroma, if you are having trouble locating the nerve, you may be in too deep and need to hone in on the more superficial, retracted tissues.    Also keep in mind that the third innerspace consists of a branch from both the medial and lateral plantar nerves. The branch of the lateral plantar nerve is the larger and more obvious of the two while one often overlooks the branch of the medial plantar nerve. It travels through a foramen just proximal to the third metatarsal head. Although this branch is not always present, it is present a majority of the time. The surgeon should resect this branch in a way that will allow it to retract more proximally in the foramen, well behind the metatarsal head.    When excising a second innerspace neuroma, if one is unable to locate the nerve, it is probably deeper towards the deep transverse metatarsal ligament. Several articles have shown that second innerspace involvement is probably more common than originally thought. Keh, et. al., had 67.1 percent second innerspace involvement.3 Okafor, et. al., had second innerspace involvement in 16 out of 35 patients.5 Biasca, et. al., showed second innerspace involvement in 32 percent of their patients.6 In my personal experience, second innerspace involvement is far more common in men than women. As far as excision, it is also well documented that the symptoms associated with this condition are not related to the size of the neuroma clinically.    The other option in the surgical approach to Morton’s neuroma is neurolysis with or without relocation. Gauthier originally described neurolysis/decompression of Morton’s neuroma and reported an 83 percent success rate in 206 feet. Others have shown similar or better results. Vito and Talarico used decompression and relocation as surgical treatment and reported that 95 percent had complete relief of symptoms.7 Okafor, et. al., also using decompression and relocation, had a 98 percent overall satisfaction rate.5 I have not used this technique to date but the literature is very encouraging and significant enough to warrant consideration.

In Conclusion

   Morton’s neuroma is often treatable with conservative care, particularly sclerosing injections. When adequate conservative care fails, surgical treatment is clearly supported and well documented in the literature with either the more traditional excision method or the newer emerging neurolysis with relocation. Dr. DeHeer is a Fellow of the American College of Foot and Ankle Surgeons, and is a Diplomate of the American Board of Podiatric Surgery. He is also a team podiatrist for the Indiana Pacers and the Indiana Fever. Dr. DeHeer is in private practice with various offices in Indianapolis. References 1. Dockery GL. The treatment of intermetatarsal neuromas with 4% alcohol sclerosing injections. J Foot Ankle Surg. 1999 Nov-Dec;38(6):403-8. 2. Mann RA, Reynolds JC. Interdigital neuroma--a critical clinical analysis. Foot Ankle. 1983 Jan-Feb;3(4):238-43. 3. Keh RA, Ballew KK, Higgins KR, Odom R, Harkless LB. Long-term follow-up of Morton's neuroma. J Foot Surg. 1992 Jan-Feb;31(1):93-5. 4. Coughlin MJ, Pinsonneault T. Operative treatment of interdigital neuroma. A long-term follow-up study. J Bone Joint Surg Am. 2001 Sep;83-A(9):1321-8. 5. Okafor B, Shergill G, Angel J. Treatment of Morton’s neuroma by neurolysis. Foot Ankle Int. 1997 May;18(5):284-7. 6. Biasca N, Zanetti M, Zollinger H. Outcomes after partial neurectomy of Morton’s neuroma related to preoperative case histories, clinical findings, and findings on magnetic resonance imaging scans. Foot Ankle Int. 1999 Sep;20(9):568-75. 7. 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. Additional References 8. Alexander IJ, Johnson KA, Parr JW. Morton’s neuroma: a review of recent concepts. Orthopedics. 1987 Jan;10(1):103-6. 9. Bourke G, Owen J, Machet D. Histological comparison of the third interdigital nerve in patients with Morton’s metatarsalgia and control patients. Aust N Z J Surg. 1994 Jun;64(6):421-4. 10. Dellon AL. Treatment of Morton’s neuroma as a nerve compression. The role for neurolysis. J Am Podiatr Med Assoc. 1992 Aug;82(8):399-402. 11. Diebold PF, Daum B, Dang-Vu V, Litchinko M. True epineural neurolysis in Morton’s neuroma: a 5-year follow up. Orthopedics. 1996 May;19(5):397-400. 12. Friscia DA, Strom DE, Parr JW, Saltzman CL, Johnson KA. Surgical treatment for primary interdigital neuroma. Orthopedics. 1991 Jun;14(6):669-72. 13. Greenfield J, Rea J Jr, Ilfeld FW. Morton’s interdigital neuroma. Indications for treatment by local injections versus surgery. Clin Orthop Relat Res. 1984 May;(185):142-4. 14. Hort KR, DeOrio JK. Morton’s interdigital neuroma. Indications for treatment by local injections versus surgery. Clin Orthop Relat Res. 1984 May;(185):142-4. 15. Johnson JE, Johnson KA, Unni KK. Persistent pain after excision of an interdigital neuroma. Results of reoperation. J Bone Joint Surg Am. 1988 Jun;70(5):651-7 16. Nashi M, Venkatachalam AK, Muddu BN. Surgery of Morton’s neuroma: dorsal or plantar approach? J R Coll Surg Edinb. 1997 Feb;42(1):36-7. 17. Wu KK. Morton’s interdigital neuroma: a clinical review of its etiology, treatment, and results. J Foot Ankle Surg. 1996 Mar-Apr;35(2):112-9; discussion 187-8.    No. By Bruce Werber, DPM. Emphasizing that Morton’s neuroma is an entrapment neuropathy, this author says decompression is the best surgical option.    Is excision the best course of option when treating an intermetatarsal neuroma? I say one should decompress and not excise. It is only tradition that has taught us to cut the nerve out yet the literature and clinical experience show us there is a better way to alleviate our patients’ pain.    Why do we excise an interdigital neuroma when Morton’s neuroma is not really a true neuroma but an entrapment neuropathy? For example, think about the type of patients who have presented with symptoms of a Morton’s neuroma. Typically those patients have either a hypermobile, fully compensated foot, typically with contracted digits and hallux abducto valgus, or a fairly rigid cavus foot with severe contracture of the digits. This puts the intermetatarsal ligament under tension and brings the nerve into direct, constant contact with the ligament.    The entrapment neuropathy results from compressive forces against the transverse intermetatarsal ligament. In an article in 1940, Betts noted “the naturally thicker nerve in the third web space is more likely to be compressed against the transverse intermetatarsal ligament. The thickness develops between the fascicles in a Morton’s neuroma. This is in comparison to a true neuroma where there is axonal proliferation.”1 In a 2004 study by Giannini and Bacchini, the authors cite 63 cases in which they found intraneural fibrosis and sclerohyalinosis, with an increase of the stroma and an increase in the number of elastic fibers.2    In 1984, Graham and Graham noted a relationship between the level of the distal edge of the intermetatarsal ligament. A cross-section the authors took at that area showed changes distally in nerve diameter, fascicle number and size, blood vessel number and size, and perineural width. They concluded these changes are consistent with the interdigital neuroma being an entrapment condition.3    The bottom line of these findings indicates that the process is degenerative due to repetitive trauma and entrapment. In 1991, Shereff and Grande utilized electron microscopy of interdigital neuromas specimens and found edema of the endoneureum, fibrosis beneath the perineurium, axonal degeneration and necrosis. They concluded that this finding suggests nerve damage occurs secondary to mechanical impingement.4    A 1994 Australian histological study by Bourke and Machet offers further confirmation of these findings. They compared the third interdigital nerve in patients with Morton’s metatarsalgia and control patients. The histological findings in control patients were identical to that of the Morton’s patients with the exception of demyelination, which was more common in the Morton’s group.5    In reviewing neurosurgical papers on neuromas, typically acoustical neuromas, the classic findings reported are of axonal proliferation. However, in the last 10 years, there have been no reports of axonal proliferation with interdigital neuromas of the foot.

Why One Should Rethink Traditional Neuroma Excision

   If Morton’s neuroma is not a proliferative nerve disease and we have significant evidence that it is due to repetitive compression, why do we need to excise it? Why not remove the irritant or reduce the swelling of the intraneural components?    The studies comparing excision with decompression reveal an excellent pattern of consistent positive outcomes. In a study that evaluated 304 decompressions, Gauthier reported 83 percent good results, 14.5 percent improved results and a 2.5 percent failure rate.6 This is in contrast to a 1983 study by Mann and Reynolds that reported on neurectomy. The authors reported 80 percent good outcomes and 6 percent improved outcomes but a 14 percent failure rate.7    In another study reviewing interdigital decompression, Vito and Talarico reported on 82 feet in 78 patients. They found that 95 percent of patients reported a complete resolution of symptoms.8

A Guide To The Benefits Of Decompression

   The techniques for decompressing the interdigital space are relatively easy to master. One can perform these procedures with small incisions. Such a procedure provides minimal risk to the surrounding tissue, most notably the intrinsic musculature and metatarsophalangeal joints.    Various authors have presented three techniques in recent years. The techniques include an endoscopic double portal approach known as the EDIN procedure, a single portal non-visualized procedure known as the Koby (Osteomed) and an open dissection approach.    As noted in several studies by Barrett and Colgrove, the outcomes of these procedures on a statistical basis are excellent with extremely low morbidity rates.9-11 In contrast, the failure rates are higher with neurectomy, especially if one includes secondary development of stump neuromas.    Aside from surgical methods of decompression, we should not leave out the alcohol sclerosing techniques that have been presented by Dockery and various other authors.12 In this technique, one would decompress the interdigital space by sclerosing the interdigital nerve without incision or disruption of the forefoot anatomy.

Final Words

   In summary, it is my opinion that decompression of the interdigital space is an appropriate and recommended method of treating patients with Morton’s neuroma. I believe the evidence is clear that Morton’s neuroma is not a true proliferative neuroma but is due to repetitive trauma with swelling, demyelination and fibrosis of the nerve versus axonal proliferation. It is also clear that decompressing the interspace has significantly less morbidity compared to traditional interdigital neurectomy. Dr. Werber is a Fellow and Past President of the American College of Foot and Ankle Surgeons. He is board-certified in reconstructive foot and ankle surgery by the American Board of Podiatric Surgery. Dr. Werber is also board-certified by the American Board of Podiatric Orthopedics and Primary Care. He is also a Fellow of the American Academy of Podiatric Sports Medicine and is in private practice at various locations in Rhode Island. References 1. Betts LO. Morton’s metatarsalgia neuritis of the fourth digital nerve. Med J Aust 1940;1:514-515. 2. Giannini S, Bacchini P, Ceccarelli F, Vannini F. Interdigital neuroma: clinical examination and histopathologic results in 63 cases treated with excision. Foot Ankle Int. 2004 Feb;25(2):79-84. 3. Graham CE, Graham DM. Morton’s neuroma: a microscopic evaluation. Foot Ankle. 1984 Nov-Dec;5(3):150-3. 4. Shereff MJ, Grande DA. Electron microscopic analysis of the interdigital neuroma. Clin Orthop Relat Res. 1991 Oct;(271):296-9. 5. Bourke G, Owen J, Machet D. Histological comparison of the third interdigital nerve in patients with Morton's metatarsalgia and control patients. Aust N Z J Surg. 1994 Jun;64(6):421-4. 6. Gauthier G. Clin Orthop Relat Res. Thomas Morton's disease: a nerve entrapment syndrome. A new surgical technique. Clin Orthop Relat Res. 1979 Jul-Aug;(142):90-2) 7. Mann RA, Reynolds JC. Interdigital neuroma--a critical clinical analysis. Foot Ankle. 1983 Jan-Feb;3(4):238-43. 8. 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. 9. Barrett, SL, Day SV. Endoscopic plantar fasciotomy: preliminary studies with cadaveric specimens. J Foot Surg. 30:170-172, 1991. 10. Barrett SL, et al. Endoscopic heel anatomy: analysis of 200 fresh frozen specimens. J Foot Ankle Surg. 34:51-56, 1995. 11. Colgrove RC, Huang EY, Barth AH, Greene MA. Interdigital neuroma: intermuscular neuroma transposition compared with resection. Foot Ankle Int, 2000.21: 206-11. 12. Dockery GL. The treatment of intermetatarsal neuromas with 4% alcohol sclerosing injections. J Foot Ankle Surg. 1999 Nov-Dec;38(6):403-8. For further reading, see “Cryosurgery Or Sclerosing Injections: Which Is Better For Neuromas?” in the June 2004 issue of Podiatry Today. Also check out the archives at www.podiatrytoday.com.