Foot & Ankle

Morton’s Neuroma (described by Thomas Morton 1876) is not a true neuroma as the condition is degenerative rather than neoplastic. It is also referred to as Morton’s metatarsalgia, interdigital neuritis, Morton’s entrapment, interdigital neuralgia, interdigital neuroma, interdigital nerve compression syndrome, and intermetatarsal neuroma.

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Incidence

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Morton neuroma is common in middle-aged women, and the incidence is at up to 15 times higher in females than males. The exact incidence is unknown. It is common in the third interspace because the 3rd interspace is narrower compared to other spaces. Rarely, both feet can be affected and two web spaces can be affected in the same foot.

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Pathogenesis

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It is thought to occur as a result of compression of the interdigital nerve against the distal end of the transverse metatarsal ligament during dorsiflexion of the toes. Compression and repetitive trauma to the nerve results in vascular changes, endoneurial edema, and excessive bursal thickening leading to perineural fibrosis.

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Common associations include narrow toe-box footwear, hyperextension of the toes in high-heeled shoes, deviation of the toes, inflammation of the intermetatarsal bursa, thickening of the transverse metatarsal ligament, forefoot trauma, some high impact sporting activities (running, football, basketball), MTP joint pathology and lipoma.

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Microscopically there is endarterial thickening of the digital artery, usually with thrombosis, fibrosis surrounding and within the nerves, Schwann cell and fibroblast propagation, and damage of myelinated nerve fibres.

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Clinical Presentation

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Patients usually present with plantar pain between metatarsal heads that is aggravated by walking and wearing tight-fitting, high-heeled shoes and relieved by resting and removing shoes.

 

Pain is described as burning, stabbing, or tingling. Some patients describe the sensation as ‘walking on a stone or pebble’. Numbness between the toes is present in less than half of the patients.

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Clinical Assessment

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Diagnosis is based on the history and clinical examination as above. Palpation in the affected space may reproduce the symptoms. Compression of the forefoot while palpating the affected space often results in a significant crunching or clicking feeling (Mudler’s clunk).

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Plain weight-bearing radiographs should be taken to rule out any bony masses, deformities, subluxation, dislocation, or arthritis. Ultrasound scan performed by an experienced radiologist can be a useful diagnostic aid.

 

A steroid injection under ultrasound guidance can be given at the same time. MRI is helpful for definitive diagnosis and to exclude other pathologies of pain in cases of inconclusive US scan.

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Treatment

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Conservative Treatment

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Orthotics

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Wearing a wide, soft-soled, laced shoe with a low heel can be effective in relieving pressure on the nerve. A soft metatarsal support can help to spread the metatarsal heads. In the presence of synovitis, instability or deformity of the toe, a Budin splint or canopy toe strapping can decrease secondary neuralgia.

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Medical Therapy

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Anti-inflammatory medications, neuropathic medications (amitriptyline, gabapentin) have also been tried to lessen the severity of pain. Blind or ultrasound-guided steroid injections can occasionally help, but their effect is usually short-lived. Radiofrequency ablation, cryotherapy, and alcohol nerve injections have been proposed as less invasive and more conservative methods of treating neuromas.

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Injection Therapy

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The effectiveness of the injection appears to be more significant and long-lasting for lesions smaller than 5 mm, greater than 80%, and according to some authors over 90%, but the risk of recurrences is high.

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Greater effectiveness is achieved by alcohol injections or radiofrequency ablation. Dockery reported 89% efficiency after a 4% alcohol injection with a follow-up after 12 months.

 

Musson et al. describe alcohol ablation under ultrasound control with 66% efficiency in the 14th month of the observation period. In another study by Pasquali et al., 74% of 500 patients achieved satisfactory results within a one year follow-up period.

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Another interesting method of treatment was presented by Chuter et al. involving ultrasound-guided radiofrequency ablation with more than 85% effectiveness over a six-month follow-up.

 

Greenfield et al. reported on a study where 95% of the patients treated by local injections relapsed within two years.

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Surgical Treatment

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If non-operative management fails, surgery is indicated. The type and duration of conservative treatment has no influence on the results of surgical treatment, which means that neurectomy is effective at every stage of the disease.

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Neuroma is excised using a dorsal or a plantar approach. Dorsal approach is preferred by many surgeons as it is considered to be tolerated better by patients due to potential concerns with the plantar scar being quite painful.

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The plantar incision is mainly reserved for recurrent neuromas or when the patient has a very proximal focal tender trigger point for the neuralgia. However it decreases the rate of missed neuroma, and it does not require an incision of the transverse metatarsal ligament.

 

Furthermore, plantar approach permits a more direct exposure of the nerve and allows its more proximal resection. The artery and vein can be better visualized and preserved. The main disadvantages are painful plantar scars and plantar keratosis in about 5% cases.

 

Pace et al. presented more than 80% good results, while Keh and Ballew reported 93% long-term subjective relief from neurectomy. The longest follow-up reported – over 10 years – was studied by Lee et al., who showed that the longterm results of neurectomy are slightly worse than those observed in a short period after surgery, but still very good.

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Dorsal vs Plantar Approach

 

There are few reports in the literature that directly compare dorsal and plantar approaches. In a meta-analysis presented by Glasoe and Coughlin, the majority of authors recommended plantar approach rather than dorsal approach.

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Nashi et al. prospectively compared 52 patients alternatively assigned to either a dorsal or plantar approach and found that patients in the dorsal group had a faster return to work, shorter hospital stay, better subjective satisfaction and fewer complications. However, this study made no statistical comparison between the groups and did not employ any validated outcome assessments.

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Wilson and Kuwada retrospectively compared the results and complications of both the approaches in 44 patients. In the dorsal approach group, 68% patients achieved complete resolution of symptoms. Complications in this group included 6 cases of amputation neuromas. In the plantar approach group, 100% patients achieved relief of preoperative symptoms. Complications in this group included 2 painful scars and no amputation neuromas. Although operative time was not one of the outcome criteria for this study, the authors noted that the operative time was approximately 15 minutes for the plantar group compared to 30-45 minutes for the dorsal group.

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Habashi et al, in a retrospective study on 37 patients, reported the use of either approach for the resection of Morton neuroma and suggested that a plantar approach for primary resection can produce satisfactory results. Plantar approach is technically easier than dorsal approach because the nerve is more accessible with this approach and it reduces the chances of recurrent neuroma with similar complication rate as compared to the dorsal approach.

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Recurrent Neuroma

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If there has been inadequate proximal resection or failure of the nerve to retract, the neural stump can become enlarged and bulbous. The clinical examination, investigations and non-operative management are same as for a primary neuroma.

 

For surgery, both dorsal and plantar incisions are recommended. The dorsal incision has to be extended proximally to visualise the stump, but sometimes, exposure can be difficult. The plantar approach is considered to provide a better exposure so that the nerve is identified and resected easily.

 

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References

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• Munir U, Morgan S. Morton Neuroma. [Updated 2017 Nov 13]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2017 Jun-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK470249.

• Morgan P, Monaghan W, Richards S. A systematic review of ultrasound-guided and non-ultrasound-guided therapeutic injections to treat Morton's neuroma. J Am Podiatr Med Assoc. 2014 Jul;104(4):337-48

• Bucknall V, Rutherford D, MacDonald D, Shalaby H, McKinley J, Breusch SJ. Outcomes following excision of Morton's interdigital neuroma: a prospective study. Bone Joint J. 2016 Oct;98-B(10):1376-1381.

• Seok H, Kim SH, Lee SY, Park SW. Extracorporeal Shockwave Therapy in Patients with Morton's Neuroma A Randomized, Placebo-Controlled Trial. J Am Podiatr Med Assoc. 2016 Mar;106(2):93-9.

• Pace A, Scammell B, Dhar S: The outcome of Morton’s neurectomy in the treatment of metatarsalgia. Int Orthop 2010, 34, 511–515.

• Keh R, Ballew K: Long term follow-up of Morton’s neuroma. J Foot Surg 1992, 31, 93–95.

• Fanucci E, Masala S, Fabiano S, Perugia D, Squillaci E, Varrucciu V, Simonetti G: Treatment of intermetatarsal Morton’s neuroma with alcohol injection under US guide: 10-month follow-up. Europ Rad 2004, 14, 514–518.

• Pasquali C, Vulcano E, Novario R, Varotto D, Montoli C, Volpe A: Ultrasound-guided alcohol injection for Morton’s neuroma. Foot Ankle Int 2015, 36, 55–59.

• Chuter GS, Chua YP, Connell DA, Blackney MC: Ultrasound-guided radiofrequency ablation in the management of interdigital (Morton’s) neuroma. Skeletal Radiol 2013, 42, 107–111.

• Greenfield J, Rea J Jr, Ilfeld FW: Morton’s interdigital neuroma. Indications for treatment by local injections versus surgery. Clin Orthop Relat Res 1984, 185, 142–144.

• Dockery GL: The treatment of intermetatarsal neuromas with 4% alcohol sclerosing injections J Foot Ankle Surg 1999, 38, 403–408.

• Lee MJ, Kim S, Huh YM, Song HT, Lee SA, Lee JW, Suh JS: Morton neuroma: Evaluated with ultrasonography and MR imaging. Korean J Radiol 2007, 8, 148–155.

• Habashy A, Sumarriva G, Treuting RJ. Neurectomy Outcomes in Patients With Morton Neuroma: Comparison of Plantar vs Dorsal Approaches. Ochsner J. 2016 Winter;16(4):471-474.

• Habashy A, Sumarriva G, Treuting RJ. Neurectomy Outcomes in Patients With Morton Neuroma: Comparison of Plantar vs Dorsal Approaches. The Ochsner Journal. 2016;16(4):471-474.

• Nashi M, Venkatachalam AK, Muddu BN. Surgery of Morton's neuroma: dorsal or plantar approach? J R Coll Surg Edinb. 1997. February; 42 1: 36- 37.

• Wilson S, Kuwada GT. Retrospective study of the use of a plantar transverse incision versus a dorsal incision for excision of neuroma. J Foot Ankle Surg. 1995. Nov-Dec; 34 6: 537- 540.

• Soe WM, Coughlin MJ: A critical analysis of Dudley Morton’s concept of disordered foot function. J Foot Ankle Surg 2006, 45, 147–155.