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Morton’s neuroma -Quick revision card

compression neuropathy of the interdigital nerve also known by several other names as intermetatarsal neuroma , intermetatarsal neuritis , plantar interdigital neuroma , interdigital neuritis , plantar interdigital neuroma how it happens / pathomechanisms are controversial but the histologic end point is perineural fibrosis not true neuromas ( no histological evidence of neuroma with axonal degeneration and collagen proliferation ) but masses composed of perineural fibrosis & nerve degeneration ( they become symptomatic once they reach 5 mm size ) it is not sure what happens and several theories have been proposed
○ the interdigital nerve is compressed against the deep transverse intermetatarsal ligament 
○ an enlarged intermetatarsal bursa may cause ischaemia or compression of the nerve 
○ repeated trauma to the interdigital nerve at the edge of the intermetatarsal ligament
○ vascular injury the common digital nerve to the 3rd space receives branches from medial & lateral plantar nerve -ie it has increased thickness and is prone to compression & trauma typically this happens between the 3rd and 4th metatarsal space ( about 80 % occur in the 3rd webspace )

 

Presentation -pain in forefoot , worse on weight bearing 2nd or 3rd web space or metatarsal interspace location of pain is most commonly in the plantar aspect of the forefoot , followed by toe(s) and then the dorsal webspace patients may describe walking on a marble sensation burning or tingling sensation pain may radiate distally to the toes with associated numbness made worse by walking in high heel shoes with narrow toe box and relieved by rest and removing the shoes ( the patient often wants to remove the shoes and massage the area )

 

How common -one of the most common presenting symptoms in primary care affects women more than men during middle ages most common compression neuropathy after carpal tunnel syndrome in the UK it is thought that in UK about 50.2 men & 87.5 women per 100,000 new presentations in primary care suffer with this condition and about 3 % of them would need operative care

 

Examination/ Diagnosis -palpation may elicit symptoms maximum tenderness localised to the involved interspace at the level of metatarsal heads Lateral squeeze test ( Mulder’s click bursal click on squeezing the
metatarsal together ) often positive Compression tests -squeezing all the metatarsal heads between index and thumb while 
holding position in which pain is elicited over the involved interdigital space direct plantar pressure between the metatarsal heads reproduces pain and paraesthesia no single clinical feature is enough in confirming the diagnosis Ultrasound in good hands has accuracy approaching that of MRI thickened nerve with a tranverse diameter of > 5 mm reliably confirms the diagnosis.

 

The differentials of forefoot pain is wide , in primary care plain XR ( weight bearing AP/lateral / Oblique ) should be considered to conditions as bony masses , deformities , subluxation , dislocation , arthritis , stress fracture , Frieberg’s infarction etc when evaluating a patient with possible neuroma

 

Differentials –metatarsalgia stress fracture hammertoe synovitis / capsulitis rheumatoid arthritis ganglion cyst malignancy

 

Conservative management -wider , low heeled footwear metatarsal padding foot orthoses activity modification NSAID’s corticosteroid injections sclerosing injections extracorporal shockwave therapy

 

Surgery -surgical excision of neuroma- neurectomy complication of surgery include
○ development of a symptomatic stump or bulb neuroma
○ permanent numbness in the affected webspace
○ painful platar scar.

PATIENT INFORMATION

Printable 8 page information leaflet from Sheffield Teaching Hospital https://publicdocuments.sth.nhs.uk/pil3300.pdf

REFERENCES

  1. Matthews, Barry G et al. “The effectiveness of non-surgical interventions for common plantar digital compressive neuropathy (Morton’s neuroma): a systematic review and meta-analysis.” Journal of foot and ankle research vol. 12 12. 13 Feb. 2019, doi:10.1186/s13047-019-0320-7
  2. Munir U, Tafti D, Morgan S. Morton Neuroma. [Updated 2021 Aug 3]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK470249/
  3. Morton neuroma | Radiology Reference Article | Radiopaedia.org
  4. Interdigital (Morton’s) Neuroma – Foot & Ankle – Orthobullets
  5. Lee, Mi-Jung et al. “Morton neuroma: evaluated with ultrasonography and MR imaging.” Korean journal of radiology vol. 8,2 (2007): 148-55. doi:10.3348/kjr.2007.8.2.148
  6. Morton’s neuroma : a clinical versus radiological diagnosis Philip Pastides et al Foot and Ankle Surgery Volume 1, Issue 1 , March 2012 , Pages 22-44
  7. Prevalence of Interdigital Nerve Enlargements in an Asymptomatic Population Panagiotics D Symeonidis et al  Foot and Ankle International 2012

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