Dr. Ebraheim’s educational animated video describes the condition of interdigital neuroma - Morton's Neuroma.

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Interdigital Neuroma Morton’s Neuroma
Morton’s neuroma is a compressive neuropathy of the interdigital nerve. It occurs most commonly in the third interdigital space. Perineural fibrosis and entrapment of the interdigital nerve may be the cause of this problem. The patient usually describes a forefoot pain on the plantar aspect of the foot, especially during standing and walking. This is usually associated with radiation of tingling and burning into the toes that are affected. The pain is usually localized to a specific area, and it does not involve the entire forefoot. It occurs predominantly between the 3rd and 4th web space in 80% of the time and between the 2nd and 3rd web space 20% of the time. The pain is radiating distally in about 60% of the time and numbness occurs about 40% of the time. When you examine the patient, the area of focal and localized tenderness is in the plantar webspace and not over the joints. The interdigital neuroma (Morton’s neuroma) occurs in middle aged females with forefoot pain that is worse with shoe wear. The pain is worse with weight bearing or wearing tight shoes with high heels. The weight transfer to the metatarsal heads will aggravate the condition. Dorsiflexion of the toes will also aggravate the condition. The symptoms are relieved by removing the shoes and massaging the foot. The paresthesia is most commonly on the plantar aspect of the web space. The patient will have chronic pain in the interdigital space between the 3rd and 4th toes that occasionally radiates down distally into the toes, and the foot exam is normal. Compression test of the web space may be positive. Compression of the metatarsals medially and laterally (squeezing the metatarsals) while pushing on the plantar tissue dorsally. The bursal tissue may crease a “click”, and if this happens it is the classic test. Ultrasound and MRI are helpful, but it is usually not as good as the history and physical examination. MRI has a very limited role in the diagnosis of Morton’s Neuroma. EMG and nerve studies are of little benefit. The history and physical exam is the gold standard for the diagnosis of interdigital neuroma. You can add diagnostic injection to see the result. Injection of local anesthesia into the are of the interdigital nerve can be diagnostic for Morton’s neuroma. Differential diagnoses include metatarsalgia, stress fractures, MTP synovitis, complex regional pain syndrome, arthritis, osteonecrosis of the metatarsal head, neoplasm, and lumbar radiculopathy. X-rays are helpful in excluding metatarsal stress fractures. Consider MTP synovitis especially after digital nerve block. Treatment can be conservative or surgical. To treat conservatively, start with shoe wear modification (no high heals or tight shoes). Conservative treatment also includes injection of steroids. This will give relief of symptoms in 1/3 of the patients with multiple injections. Injection is usually done dorsally, and it may be more diagnostic than therapeutic. Surgery an be neurectomy, done after failure of nonoperative treatment (approach the neuroma through dorsal or plantar approach). Dorsal approach is most commonly used. Incise the transverse metatarsal ligament. Resect the nerve 3 cm proximal to the metatarsal heads. Bury the proximal stump within the intrinsic muscles. If the neuroma is recurrent, then there may be a retained neuroma distal to the metatarsal heads. In this case, you may want to do surgery through the plantar approach, and you may want to do the research of the nerve and transpose it to muscle on the plantar foot (there might be about 70% success rate). The most likely cause of recurrent symptoms following excision of a 3rd web space neuroma is a traumatic neuroma tethered by plantar neural branches. When a recurrent neuroma occurs at the end of the resected nerve, it does not retract far enough because the transection may not be far proximal enough or it may be tethered by the plantar neural branches. Stump neuroma can also occur due to inadequate resection. Causes of surgical failure include resection of the common plantar nerve is too distal, there may be a coexisting tarsal tunnel syndrome, wrong diagnosis, or wrong interdigital space.

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