Morton Neuroma (Interdigital Neuroma)
BASICS
Description
- Painful condition of the webbed spaces of the toes
- Perineural fibrosis of the common digital nerve (most commonly between 3rd and 4th metatarsals)
- Also called: plantar digital neuritis, Morton metatarsalgia, intermetatarsal neuroma
EPIDEMIOLOGY
- Prevalence unknown
- Mean age: 45–50 years
- Female:Male ratio ~8:1
ETIOLOGY & PATHOPHYSIOLOGY
- Lateral plantar nerve joins medial plantar nerve between 3rd/4th toes (large nerve diameter)
- Four main theories:
- Chronic traction damage
- Inflammatory environment (intermetatarsal bursitis)
- Compression by deep transverse intermetatarsal ligament
- Ischemia of vasa nervorum
- Repetitive compression → perineural fibrosis, neuroma formation
RISK FACTORS
- High-heeled/tight shoes
- Pes planus (flat feet)
- Obesity
- Female gender
- Activities: ballet, running, basketball, aerobics, tennis
- Hyperpronation
PREVENTION
- Proper footwear (avoid high heels/narrow toe boxes)
DIAGNOSIS
History
- Pain between 3rd and 4th toes (sometimes 2nd/3rd)
- Less pain when not weight-bearing
- Burning pain, cramping, numbness in forefoot/toes
- Feels like “walking on a marble”
- Worse with tight shoes; relieved by shoe removal/massage
Physical Exam
- Intense pain on pressure between metatarsal heads; may feel nodule
- Check for midfoot/digital motion, metatarsalgia, stress fractures
- Special tests (see below)
Differential Diagnosis
- Stress fracture, hammer toe, synovitis, arthritis
- Metatarsalgia, traumatic neuroma, osteomyelitis, bursitis, foreign body
- Freiberg infraction, neoplasm, gout
DIAGNOSTIC TESTS
- Primarily clinical diagnosis
- Imaging for unclear diagnosis or >1 web space involved
- X-ray: rule out bone pathology (usually normal)
- US: 79% specificity, 99% sensitivity (less for <6mm lesions)
- MRI: sensitivity 83%, specificity 99% (surgical planning)
- Special tests:
- Thumb-index squeeze: pain with compression (96% sensitive/specific)
- Mulder sign: “click” with squeezing metatarsal heads and neuroma
- Foot squeeze test, percussion tests, toe tip sensation deficit
- Pathology: perineural fibrosis, sometimes arterial thickening/thrombosis
TREATMENT
General Measures
- Stepwise: conservative → infiltrative → surgical
- Success rates (≥6mo): operative (89%) > infiltrative (84%) > conservative (48%)
- Conservative: flat/wide shoes, plantar pads/bar, NSAIDs for temporary relief
- No benefit from varus/valgus padding or ESWT
Medications
- First Line: Injectable steroids (e.g., betamethasone, methylprednisolone)
- NNT = 2.3 vs conservative
- US guidance improves results
- Second Line: US-guided alcohol ablation (nerve sclerosis, fewer complications than surgery)
REFERRAL
- Persistent pain after conservative/injection therapy
- Large neuroma (>5mm) or younger patients (may need earlier surgery)
SURGERY/PROCEDURES
- Surgical removal (neurectomy, metatarsal shortening, ligament release): 89% success at 6 mo
- Other: botulinum toxin, cryoablation, radiofrequency, PRP (limited evidence)
ONGOING CARE
Follow-Up
- If no improvement after 3 months: consider steroid injection
- May repeat injection in 2–4 weeks or refer for surgery
- 21–51% of injection patients need surgery within 2–4 years
- Lesions >5mm and younger patients: higher likelihood of surgery
Patient Education
- Proper, comfortable footwear essential
PROGNOSIS
- Conservative: 48% satisfaction
- Infiltrative: 85% satisfaction
- Operative: 89% satisfaction
COMPLICATIONS
- Hip/knee pain (gait changes)
- Failure rates: 47% (conservative), 9–23% (invasive/nonsurgical), 4% (surgery)
- Surgical: keloid, CRPS, stiffness (21% global complication rate)
ICD-10
- G57.60: Lesion of plantar nerve, unspecified
- G57.61: Lesion of plantar nerve, right
- G57.62: Lesion of plantar nerve, left
Clinical Pearls
- Clinical diagnosis; US/MRI to confirm
- Stepwise treatment: conservative → infiltrative → operative
- >5mm neuromas and younger age more likely need surgery
- Neurectomy is definitive
- Educate about surgical risks/complications