Morton’s Neuroma- Causes, Symptoms, Diagnosis, Treatment and Ongoing care

Basics

Description

Perineal fibrosis of the common digital nerve as it passes between metatarsals; the most common site is the interspace between the 3rd and 4th metatarsals, with the interspace between the 3rd and 2nd metatarsals being the 2nd most common site.System(s) affected: Musculoskeletal; NervousSynonym(s): Plantar digital neuritis

Epidemiology

Incidence

UnknownMean age: 45–50 yearsPredominant sex: Female > Male (8:1)

Prevalence

Unknown

Risk Factors

High-heeled shoes: Cause more weight to be transferred to the front of the footTight-toed shoes (tight toe boxes): Cause lateral compressionPes planus (flat feet): Causes nerve to be pulled more medially, which increases irritationObesityBallet dancing, basketball, aerobics, tennis, running, and similar activities

General Prevention

Wear properly fitting shoes.Avoid high heels and narrow toe boxes.

Pathophysiology

Lateral plantar nerve combines with part of medial plantar nerve. The 2 nerves combine, creating a nerve with larger diameter than nerves going to other digits.Nerve lies in subcutaneous 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.

Etiology

Excessive stress of the forefootRepetitive traumaCongenitally enlarged plantar digital nerve

Diagnosis

History

Most common complaint is pain localized to interspace between 3rd and 4th toes.Pain is less severe when non-weight bearing.Pain, cramping, or numbness of the forefoot with weight bearing or immediately after strenuous foot exertionRadiation of pain to the toesPain is relieved by removing the shoe and massaging the foot.Patients often state: “Feels like I am walking on a marble.”A burning pain in the ball of the foot that may radiate into the toesTingling or numbness in the toesAggravated by wearing tight or narrow shoes

Physical Exam

A palpable nodule in the metatarsal interspace is an occasional finding.Positive Mulder sign: See Diagnostic Procedures.Intense pain on pressure between metatarsal headsAssess midfoot motion and digital motion to determine if arthritis or synovitis.Palpate along metatarsal shafts to assess for metatarsalgia or stress fractures.

Diagnostic Tests & Interpretation

Imaging

Initial approach

Radiographs may help to rule out osseous pathology if diagnosis is in question, but films usually are normal in patients with a Morton neuroma.Ultrasound shows a hypoechoic nodule between the metatarsal interspace. Ultrasound had a 65% specificity and a 98% sensitivity for Morton neuromas. Ultrasound is not good at assessing the size of the lesion (1)[C].MRI is used to ensure that compression is not caused by a malignant tumor in the foot. MRI is helpful in determining how much of the nerve to resect surgically. MRI has a sensitivity of 83% and a specificity of 99% (1)[C].

Diagnostic Procedures/Surgery

Mulder sign: A “click” and pain produced by squeezing the metatarsal heads together and simultaneously compressing the neuroma between the thumb and index finger of the other handCorticosteroid injection can significantly reduce symptoms. Inject 1–2 mL lidocaine and 0.5–1 mL dexamethasone just proximal to the metatarsal heads. More than 1 injection is often needed, usually once a week × 3 weeks (2).

Pathological Findings

Chronic fibrosis and thickening of the digital nerve

Differential Diagnosis

Stress fractureHammer toeMetatarsophalangeal synovitisMetatarsalgiaArthritisBursitisForeign body

Treatment

Medication

First Line

Injectable steroids (e.g., betamethasone phosphate/acetate or methylprednisolone): Use if general measures fail (2,3)[C].

Second Line

Nonsteroidal anti-inflammatory drugs (NSAIDs) for temporary symptom relief (1,2)[C]

Additional Treatment

General Measures

Flat shoes with a roomy toe box (4)[C]Metatarsal pads placed immediately proximal to the 2 involved metatarsal heads (4)[C]Corticosteroid injection into the dorsal part of the foot with medium- or long-acting steroid (e.g., betamethasone, methylprednisolone) mixed with local anesthetic (e.g., lidocaine) (4)[C]If patient has pes planus, an arch support is used (4)[C].Literature suggests wide variability in success rate (50–98%) (4).

Issues for Referral

Continued pain despite conservative treatments and injections

Additional Therapies

Serial alcohol injection therapy into the neuroma to sclerose the nerve has been successful (5)[C].

Surgery/Other Procedures

Surgical removal of the neuroma, release of the transverse metatarsal ligament, or both in refractory cases

Ongoing Care

Follow-Up Recommendations

If no improvement after 3 months of conservative treatment, consider corticosteroid injection. Repeat injection if no improvement after 2–4 weeks.

Patient Education

Wearing of properly fitted, comfortable shoes

Prognosis

40–50% improve after 3 months of conservative treatment.45–50% improve after steroid injection.96% improve after surgery.

Complications

Hip and knee pain related to gait changes

References

1. Sharp RJ, et al. The role of MRI and ultrasound imaging in Morton’s neuroma and the effect of size of lesion on symptoms. Br J Bone Joint Surg. 2003;85:999–1005.

2. Tallia AF, Cardone DA. Diagnostic and therapeutic injection of the ankle and foot. Am Fam Physician. 2003;68:1356–62.

3. Wu KK. Morton’s interdigital neuroma: a clinical review of its etiology, treatment, and results. J Foot Ankle Surg. 1996;35:112–9; discussion 187–8.

4. Thompson CE, Gibson JNA, Martin D. Interventions for the treatment of Morton’s neuroma. Cochrane Database Sys Rev. 2005.

5. Hughes RJ, Ali K, Jones H, et al. Treatment of Morton’s neuroma with alcohol injection under sonographic guidance: follow-up of 101 cases. Am J Roentgenol. 2007;188:1535–9.

Codes

ICD9

355.6 Lesion of plantar nerve

Snomed

30085007 Morton’s metatarsalgia (disorder).

Clinical Pearls

Diagnosis of Morton neuroma is usually made clinically.Footwear modification, metatarsal pads, and shoe inserts are mainstays of treatment.Corticosteroid injection into the neuroma may be helpful.