La sindrome di Morton

Abstract

Morton’s syndrome (MS) is a typical metatarsalgia, due to an intermetatarsal neuroma. Patients complain of burning pain in the lateral metatarsal region, extending into the third, fourth or both toes. Patients typically experience pain relief by sitting down, removing the shoe, and massaging the foot.

The diagnosis is primarily clinical, producing pain by compression with the fingers in the second or third web-space and moving the neuroma up and down between metatarsal bones according to the Mulder’s manouvre.

Other sources of forefoot pain can be misdiagnosed as an interdigital neuroma, like metatarsal stress fractures, early rheumatoid arthritis, Freiberg’s infraction, biomechanical disorders of the Mp joint. Therefore, diagnosis needs a confirmation with advanced imaging. Ultrasound (US) intermetatarsal exploration of forefoot, reproducing local pain and Mulder’s click with dynamic manoeuvres, is today, if performed by a well-experienced examinator, an easy and economical test to confirm clinical suspect, with an accuracy of about 90% for intermetatarsal masses greater than 4 mm. There are differing reports about the accuracy of diagnosis with magnetic resonance imaging (MRI), more indicated as a second level examination fot doubtful cases.

As for treatment of MS, alcohol injection under sonographic guidance is today a preferred method for intermetatarsal masses greater than 4 mm. Two or three injections of 1 cc of medical alcohol 30% diluted with 70% of xylocaine 2%, injected directly in the mass, are required. In our experience of 150 published cases, success rate is about 80%, without any hindrance to surgery in case of persistent pain.

Surgery is indicated in refractory cases and can be done in a formal operative suite in outpatient surgery. The dorsal intermetatarsal approach is preferred, isolating the neuroma from distal to proximal, after transverse intermetatarsal ligament transection. After careful isolation of the third common digital nerve from the thin plantarly directed branches and, if present, the accessory branch of the lateral plantar nerve, the nerve is resected with a new fifteen blade and passed through the fibers of the transverse adductor muscle (neurectomy/relocation technique) to prevent mechanical irritation in case of a stump neuroma.

According to literature, results of surgery have been favorable, with 90% of success, when MS was localized in a third web space, but with a worse outcome in cases with second web space (60%) or multiple web space intervention.