> Table of Contents > Morton Neuroma (Interdigital Neuroma)
Morton Neuroma (Interdigital Neuroma)
Catherine Mygatt, MD
J. Herbert Stevenson, MD
image BASICS
DESCRIPTION
  • Perineural fibrosis of the common digital nerve as it passes between metatarsals
    • The interspace between the 3rd and 4th metatarsals is most commonly affected.
    • Between the 2nd and 3rd metatarsals is the next most common site.
  • System(s) affected: musculoskeletal, nervous
  • Synonym(s): plantar digital neuritis; Morton metatarsalgia; intermetatarsal neuroma
EPIDEMIOLOGY
Prevalence
  • Unknown
  • Mean age: 45 to 50 years
  • Predominant sex: female > male (8:1)
ETIOLOGY AND PATHOPHYSIOLOGY
  • Lateral plantar nerve joins a portion of medial plantar nerve, creating a nerve with a larger diameter than those going to other digits.
  • Nerve lies in SC tissue, deep to the fat pad of foot, just superficial to the digital artery and vein.
  • Overlying, the nerve is the strong, deep transverse metatarsal ligament that holds the metatarsal bones together.
  • With each step the patient takes, the inflamed nerve becomes compressed between the ground and the deep transverse metatarsal ligament. This can generate perineural fibrotic reaction with subsequent neuroma formation.
RISK FACTORS
  • High-heeled shoes
    • Transfer more weight to the forefoot.
  • Shoes with tight toe boxes
    • Cause lateral compression
  • Pes planus (flat feet)
    • Pulls nerve medially, increasing irritation
  • Obesity
  • Female gender
  • Ballet dancing, basketball, aerobics, tennis, running, and similar activities
GENERAL PREVENTION
  • Wear properly fitting shoes.
  • Avoid high heels and shoes with narrow toe boxes.
image DIAGNOSIS
PHYSICAL EXAM
  • Intense pain when pressure applied between metatarsal heads, sometimes with a palpable nodule
  • Assess midfoot motion and digital motion to determine if arthritis or synovitis.
  • Palpate along metatarsal shafts to assess for metatarsalgia or stress fractures.
DIFFERENTIAL DIAGNOSIS
  • Stress fracture
  • Hammer toe
  • Metatarsophalangeal synovitis
  • Metatarsalgia
  • Arthritis
  • Bursitis
  • Foreign body
DIAGNOSTIC TESTS & INTERPRETATION
Initial Tests (lab, imaging)
  • Predominantly a clinical diagnosis; imaging should be reserved for when the diagnosis is unclear or more than one web space is involved (1)[A],(2)[B].
  • Radiographs may help to rule out osseous pathology if diagnosis is in question, but films usually are normal in patients with a Morton neuroma (1)[A].
  • US has 79% specificity and 99% sensitivity for Morton neuromas but is poor at assessing the size of the lesion. Specificity declines to 50% for lesions <6 mm (1)[A].
  • MRI can rule out an osseous tumor and help determine how much of the nerve to resect surgically; it has a sensitivity of 83% and a specificity of 99% (1)[A].
Diagnostic Procedures/Other
  • Five special tests have been described: thumb index finger squeeze test, Mulder sign, foot squeeze test, plantar percussion test, and toe tip sensation deficit.
    • Thumb index finger squeeze test is the most sensitive and specific (96% and 96%, respectively). Positive when pain elicited by squeezing the symptomatic intermetatarsal space between the index finger and thumb (3)[B].
    • Mulder sign is a painful “click” produced by squeezing the metatarsal heads together while compressing the neuroma between the thumb and index finger of the other hand; sensitivity 40-84% (1)[A].
    • Foot squeeze test is positive when pain is induced in the symptomatic web space when the metatarsal heads are compressed by grasping the foot; sensitivity 40% (3)[B].
    • Plantar and dorsal percussion tests are positive when percussion of the affected webspace is painful.
    • Toe tip sensation deficit exists when the sensation of the toe distal to the affected web space is decreased relative to the other toes.
  • More than one of the above tests being positive increases the diagnostic accuracy (4)[B].
Test Interpretation
Chronic fibrosis and thickening of the digital nerve
image TREATMENT
GENERAL MEASURES
  • Wear flat shoes with a roomy toe box.
  • Plantar pads may help with alignment of metatarsal heads and provide relief.
  • NSAIDs for temporary symptom relief
MEDICATION
First Line
Injectable steroids (e.g., betamethasone phosphate/acetate or methylprednisolone): use if general measures fail; number needed to treat (NNT) for significant benefit over conservative measures = 2.3 (5,6)[A].
P.685

Second Line
  • US-guided alcohol ablation therapy to sclerose the nerve is safe, reduces pain, and may offer an alternative to surgery (7,8)[B].
  • A pilot study has demonstrated that injection with onabotulinumtoxina is of possible usefulness to relieve the pain and improve function in Morton neuroma (9)[B].
  • There is no evidence for the use of supinatory insoles (10)[A].
ISSUES FOR REFERRAL
Continued pain despite conservative treatments and injections.
SURGERY/OTHER PROCEDURES
Surgical removal of the neuroma or shortening of the metatarsals, with or without release of the transverse metatarsal ligament, have a 61-100% success rate defined by satisfaction scores (11)[A].
image ONGOING CARE
FOLLOW-UP RECOMMENDATIONS
At diagnosis, or if no improvement after 3 months of conservative treatment, consider corticosteroid injection.
  • May repeat injection if no improvement after 2 to 4 weeks, or consider referring for surgical management.
  • 21-51% of patients receiving a single corticosteroid injection require surgical intervention within 2 to 4 years (12)[B].
  • Size >5 mm and younger patients are more likely to undergo invasive treatment (12)[B].
PATIENT EDUCATION
Wear properly fitting comfortable shoes.
PROGNOSIS
  • 40-50% improve with 3 months of conservative treatment.
  • 45-60% improve with steroid injection (6)[A].
  • 96% improve with surgery.
REFERENCES
1. Sharp RJ, Wade CM, Hennessy MS, et al. The role of MRI and ultrasound imaging in Morton's neuroma and the effect of size of lesion on symptoms. J Bone Joint Surg Br. 2003;85(7):999-1005.
2. Pastides P, El-Sallakh S, Charalambides C. Morton's neuroma: a clinical versus radiological diagnosis. Foot Ankle Surg. 2012;18(1):22-24.
3. Mahadevan D, Venkatesan M, Bhatt R, et al. Diagnostic accuracy of clinical tests for Morton's neuroma compared with ultrasonography. J Foot Ankle Surg. 2015;54(4):549-553.
4. Owens R, Gougoulias N, Guthrie H, et al. Morton's neuroma: clinical testing and imaging in 76 feet, compared to a control group. Foot Ankle Surg. 2011;17(3):197-200.
5. Saygi B, Yildirim Y, Saygi EK, et al. Morton's neuroma: comparative results of two conservative methods. Foot Ankle Int. 2005;26(7):556-559.
6. Thomson CE, Beggs I, Martin DJ, et al. Methylprednisolone injections for the treatment of Morton neuroma: a patient-blinded randomized trial. J Bone Joint Surg Am. 2013;95(9):790-798.
7. Musson RE, Sawhney JS, Lamb L, et al. Ultrasound guided alcohol ablation of Morton's neuroma. Foot Ankle Int. 2012;33(3):196-201.
8. Hughes RJ, Ali K, Jones H, et al. Treatment of Morton's neuroma with alcohol injection under sonographic guidance: follow-up of 101 cases. AJR Am J Roentgenol. 2007;188(6):1535-1539.
9. Climent JM, Mondéjar-Gómez F, Rodríguez-Ruiz C, et al. Treatment of Morton neuroma with botulinum toxin A: a pilot study. Clin Drug Investig. 2013;33(7):497-503.
10. Thomson CE, Gibson JN, Martin D. Interventions for the treatment of Morton's neuroma. Cochrane Database Syst Rev. 2004;(3):CD003118.
11. Akermark C, Crone H, Skoog A, et al. A prospective randomized controlled trial of plantar versus dorsal incisions for operative treatment of primary Morton's neuroma. Foot Ankle Int. 2013;34(9):1198-1204.
12. Mahadevan D, Salmasi M, Whybra N, et al. What factors predict the need for further intervention following corticosteroid injection of Morton's neuroma? Foot Ankle Surg. In press.
Additional Reading
&NA;
  • Jain S, Mannan K. The diagnosis and management of Morton's neuroma: a literature review. Foot Ankle Spec. 2013;6(4):307-317.
  • Schreiber K, Khodaee M, Poddar S, et al. Clinical inquiry. What is the best way to treat Morton's neuroma? J Fam Pract. 2011;60(3):157-158, 168.
Codes
&NA;
ICD10
  • G57.60 Lesion of plantar nerve, unspecified lower limb
  • G57.61 Lesion of plantar nerve, right lower limb
  • G57.62 Lesion of plantar nerve, left lower limb
Clinical Pearls
&NA;
  • Morton neuroma is usually a clinical diagnosis.
  • Footwear modification is the mainstay of treatment.
  • Corticosteroid injection into, or US-guided alcohol ablation of the neuroma may be helpful.
  • Neurectomy is the definitive treatment. Patients should be aware of the likelihood of postoperative dysesthesias.