Morton Neuroma

Morton neuroma is perineural fibrosis and degeneration of a common plantar digital nerve as it passes beneath the deep transverse metatarsal ligament. It is not a true neoplasm. It most commonly affects the third web space (nerve to the third and fourth toes), then the second. Peak age is 40 to 60 years, with a female to male ratio of about 4 to 1.

Mechanisms are repetitive compression and ischemia from tight or high heeled shoes, hallux valgus, flatfoot and a tight gastrocnemius. Ten to 30% of asymptomatic adults show an incidental neuroma on imaging. The course is chronic, and symptoms are usually progressive without treatment.

• Burning pain in the forefoot radiating to the toes, a feeling of walking on a pebble or a bunched sock, relieved by removing the shoe and massage
• Numbness or tingling in adjacent toe surfaces
• Pain on squeezing the forefoot (Gauthier test), tenderness in the web space on dorsal plantar palpation
• A palpable click with lateral compression of the forefoot while palpating the web space (Mulder sign)
• Splaying of toes (Sullivan sign)
• Red flags: bilateral multi site symptoms (suggest neuropathy), night pain, fever, and rapid growth

• Clinical diagnosis by history and web space palpation.
• Ultrasound (sensitivity about 90%): a hypoechoic, oval mass in the intermetatarsal space with a diameter over 5 mm.
• MRI for equivocal cases, showing a low signal mass on T1 and T2 beneath the metatarsal heads, and for exclusion of other pathology.
• Radiographs for stress fracture, arthritis and deformity.
• Nerve conduction studies when neuropathy is considered.

Differentials: metatarsophalangeal synovitis, stress fracture, plantar plate tear, intermetatarsal bursitis, peripheral neuropathy, S1 radiculopathy, tarsal tunnel syndrome, Freiberg infraction.

• Footwear modification: wide toe box, low heel and a rocker sole, with a metatarsal pad placed proximal to the metatarsal heads for 6 to 12 weeks.
• Corticosteroid injection: methylprednisolone acetate 20 to 40 mg with lidocaine 1% 1 mL into the web space using a dorsal approach, under ultrasound guidance. At most 3 injections, 3 months apart. Risks: fat pad atrophy, plantar plate rupture, toe deformity, transient numbness. Relief lasts 3 to 6 months.
• Alcohol sclerosis: dehydrated ethanol 4% 0.5 mL injected into the web space weekly for 3 to 7 weeks.
• Radiofrequency ablation or cryoablation for recurrent pain.
• Neuropathic pain: gabapentin 300 mg orally at night, increased to 900 to 1800 mg/day in 3 divided doses, if needed.
• Surgery after failed 3 to 6 months of conservative treatment: neurectomy through a dorsal incision between the metatarsals, dividing the deep transverse ligament and resecting the nerve proximal to the ligament. Cefazolin 2 g IV before incision. Success about 80 to 85%.
• Complications: stump neuroma (5 to 10%), numbness in the toes, wound complication.

Rehabilitation with a postoperative shoe for 2 weeks. Follow up at 2 weeks and 6 weeks. Counsel on shoe choice and avoidance of prolonged high heels.