Morton neuroma, or interdigital neuritis, is a compression neuropathy with associated perineural fibrosis that is caused by entrapment of the interdigital nerve near the distal edge of the transverse intermetatarsal ligament. The second and third interdigital nerves in the forefoot are most commonly involved. In one series, Morton neuroma was found to occur at an average age of 55 years (range, 29 to 81 years), predominantly in women.1 Most patients can be treated nonsurgically with shoe wear modification, plantar pad placement, nonsteroidal antiinflammatory drugs, Achilles stretching, and, on a limited basis, cortisone injection. Surgical treatment should be reserved for select patients with a clear diagnosis. Surgery is done to decompress the entrapped interdigital nerve by transecting the intermetatarsal ligament, releasing or resecting the interdigital nerve itself, and/or releasing any nerve branches causing tethering, thereby allowing the nerve to move more proximally away from the weight-bearing portion of the forefoot.
Patient history and physical examination are required to confirm the exact location of the neuroma (Figure 1). Careful palpation along the interdigital nerves is helpful in determining the location of compression and whether additional nerves are symptomatic. Confirmatory, but not necessarily pathognomonic, signs include reproducible pain and paresthesias with plantar pressure directed between the metatarsal heads (Figure 2), reproducible painful click upon simultaneously squeezing the forefoot while pushing upward with the thumb in the involved interspace (ie, Mulder sign), and symptomatic relief following a selective lidocaine injection beneath the intermetatarsal ligament approximately 2 cm proximal to the metatarsal head. Magnetic resonance imaging or ultrasound can be used to support the diagnosis and may have prognostic value, but clinical evaluation is critical for diagnosis.