Morton’s Neuroma

Introduction

Morton’s neuroma is a compressive neuropathy of the interdigital nerve, most often found in the 3/4 webspace. Whilst the name implies a benign neoplasm, this is a misnomer as the “neuroma” actually represents a swelling of the common digital nerve near the bifurcation with infiltration of degenerate fibrotic tissue. Various theories have been proposed for the formation of neuromas, such as compression under the intermetatarsal ligament, however none of these have been proven.

Presentation

  • Often non-specific symptoms
  • Often females in their 40s or 50s
  • Neuralgic-type pain in the forefoot, usually on the plantar surface or into toes
  • Usually worse with tight-fitting and / or high-heeled shoes and relieved by removal
  • True numbness is present in <50% of patients

History and Examination

Thorough history and examination are required to differentiate from:

  • other causes of “metatarsalgia”
  • proximal / central nerve lesion (spine / tarsal tunnel syndrome / peripheral neuropathy)
  • plantar plate rupture

Clinical tests that include:

  • webspace tenderness
  • foot squeeze
  • plantar percussion
  • toe tip sensation deficit

Mulder’s clunk is more commonly absent than positive. Tests are sensitive but not specific, explaining why clinical experience is required for diagnosis.

Imaging

  • Ultrasound and / or MRI is often utilised; both have ~90% sensitivity
  • USS is cheaper but MRI is said to be more specific, up to 100%
  • Morton’s neuromas are identified in up to 33% of asymptomatic feet on MRI, emphasising the importance of thorough clinical assessment
  • MRI is useful if clinical findings are atypical and another cause of metatarsalgia is suspected
  • USS can be used to guide injections

Conservative treatments

  • Activity and shoe wear modification (wide, high toe-box shoes without a heel)
  • Orthotics (metatarsal bar / dome) may be helpful but not always well tolerated
  • No evidence for heel wedges, even in patients with malalignment

In the largest meta-analysis to date, the only conservative treatments with sufficient evidence to recommend are:

  • manipulation / physiotherapy
  • steroid injection

No consensus exists on whether injections should be blind or US-guided

Other non-operative treatments have been trialled:

  • sclerosing alcohol injections: beneficial in small studies in the short-term, poor long-term
  • radiofrequency ablation: reasonable results in several studies but lacking long-term data
  • cryoablation therapy: numbers too low to provide meaningful conclusions
  • shockwave therapy: RCT shows no significant reduction in neuroma pain: not recommended

Operative treatments

The mainstay of surgical treatment remains neurotomy:

  • dorsal or plantar approach
  • intermetatarsal ligament is incised
  • nerve is excised 2-3cm proximal to the bifurcation

No difference demonstrated in long-term outcomes between the two approaches

Perceived benefits:

  • Dorsal approach:
    • immediate ability to weight-bear
    • absence of a painful plantar scar
  • Plantar approach
    • better access and exposure of the neuroma

Good long-term symptom relief in up to 85% of patients. Recently, PROMs data has also supported operative management.

Recurrence or stump pain can occur with inadequate resection. Some advocate burying the stump in either the intrinsic muscles or the metatarsal.

Other surgical treatments have been trialled:

  • neurolysis
  • nerve decompression by division of intermetatarsal ligament
    • reasonable reported results but lacking long-term data
    • increased resurgence, particularly in Europe
  • minimally invasive techniques / ultrasound guidance

MCQs

Toe tip numbness as a presentation of Morton’s neuroma is present in what percentage of patients?

  1. <50%
  2. 51-60%
  3. 61-70%
  4. 71-80%
  5. 81-100%

Asymptomatic Morton’s neuroma may be identified by MRI in what percentage of feet?

  1. 0-20%
  2. 21-40%
  3. 41-60%
  4. 61-80%
  5. 81-100%

Which conservative treatment for Morton’s neuroma has been proven to provide good reduction of pain?

  1. Shoe wear modification
  2. Metatarsal bar orthosis
  3. Heel wedge orthosis
  4. Manipulation / physiotherapy
  5. Shockwave therapy

References

Bhatia M, Thomson L. Morton's neuroma - Current concepts review. J Clin Orthop Trauma. 2020;11(3):406-409. doi:10.1016/j.jcot.2020.03.024

Gougoulias N, Lampridis V, Sakellariou A. Morton's interdigital neuroma: instructional review. EFORT Open Rev. 2019;4(1):14-24. Published 2019 Jan 23. doi:10.1302/2058-5241.4.180025

Owens R, Gougoulias N, Guthrie H, Sakellariou A. Morton's neuroma: clinical testing and imaging in 76 feet, compared to a control group. Foot Ankle Surg. 2011 Sep;17(3):197-200. doi: 10.1016/j.fas.2010.07.002. Epub 2010 Sep 17. PMID: 21783084.

Matthews BG, Hurn SE, Harding MP, Henry RA, Ware RS. The effectiveness of non-surgical interventions for common plantar digital compressive neuropathy (Morton's neuroma): a systematic review and meta-analysis. J Foot Ankle Res. 2019;12:12. Published 2019 Feb 13. doi:10.1186/s13047- 019-0320-7

Thomson CE, Gibson JN, Martin D. Interventions for the treatment of Morton's neuroma. Cochrane Database Syst Rev. 2004;(3):CD003118. doi: 10.1002/14651858.CD003118.pub2. PMID: 15266472.