Morton's neuroma
Morton's neuroma, initially described by Morton in 1876, is a reactive fibrosis of a communicating branch of the third nerve and, histopathologically, is not a true neuroma.1 The neuroma is believed to be mechanically induced and most commonly affects the third common digital nerve located in the region of the third webspace of the foot (figure 2). Anatomic factors along with injury, irritation, or pressure from wearing pointed and/or high-heeled shoes result in compression and irritation of the third common digital nerve and lead to nerve fiber degeneration, intraneural and juxtaneural fibrosis, and hypertrophy of the nerve. Anatomical factors that may contribute to this condition include excessive motion of the third and fourth metatarsals, juxtaposition of the third and fourth metatarsal heads and the branches of medial and lateral plantar nerves between the third nerve, and the third transverse intermetatarsal ligament overlying the third common digital nerve and its communicating branches.
Interdigital plantar (Morton's) neuroma. Reproduced with permission. Copyright 2005 American College of Foot and Ankle Surgeons. All rights reserved.
Pathologic findings alone are insufficient to explain the symptoms of Morton's neuroma, since these same findings may occur in asymptomatic individuals. The diagnosis of Morton's neuroma is suspected clinically when patients complain of pain located in the webspace of their toes. Early in the course, patients may describe burning or tingling in this region. These symptoms may progress to the more typical paroxysmal, severe, sharp, lancinating pain that occurs with weightbearing and walking and is relieved by sitting, removing the shoes, and massaging and manipulating the affected region of the forefoot. The pain, as previously noted, typically involves the third and occasionally the fourth webspace and may radiate to the third and fourth toe.
The webspace compression test is used clinically for the diagnosis of Morton's neuroma and takes advantage of the pathophysiologic process responsible for this condition. With the patient in a sitting or prone position, the examiner squeezes the third and fourth metatarsal heads together with one hand and, using the other hand, compresses the soft tissue in the involved webspace. A positive test results in pain. Ultrasonography may be used in cases of diagnostic uncertainty, however, Morton's neuroma remains a clinical diagnosis.
Treatment options for Morton's neuroma include avoiding pointed and/or high-heeled shoes, using metatarsal pads, and administering local corticosteroid injections, the latter of which must be approached with caution. Inadvertent extravasations into the toe adjacent to the MTP joint may result in significant MTP joint instability. In refractory cases, neurolysis, transposition, or surgical excision of the nerve is performed. Recurrence of symptoms must provoke a search for a "stump neuroma" or pathology of adjacent structures, such as the MTP joints. Recurrence after surgical excision is most commonly associated with incomplete nerve release or excision.