Morton neuroma, which was first described by Thomas Morton in 1876, refers to a constellation of symptoms including tenderness and burning pain in the plantar surface of the forefoot, with associated painful dysesthesias into the affected two toes. This pain syndrome is thought to be caused by perineural fibrosis of the interdigital nerves (Fig. 177.1). There is often coexistent intermetatarsal bursitis as the pathogenesis of both pathologic conditions is similar. Although the nerves between the third and fourth toes most often are affected, the second and third toes and, rarely, the fourth and fifth toes can be affected.

The majority of patients who present with Morton neuroma present with the complaint of pain in the plantar surface with associated dysesthesias radiating into the adjacent toes. Patients commonly complain that it feels like they are walking with a stone caught in their shoe. Walking, standing, or wearing tight shoes makes the pain worse, with rest and heat providing some relief. The pain is constant and is characterized as aching and may interfere with sleep.

On physical examination, the pain associated with Morton neuroma can be reproduced by performing the Mulder maneuver. This is accomplished by firmly squeezing the two metatarsal heads together with one hand while placing firm pressure on the interdigital space with the other hand (Fig. 177.2). A palpable click may also be appreciated as the neuroma is forced from between the metatarsals. The patient with Morton neuroma often exhibits an antalgic gait in an effort to reduce weight bearing during walking.

Plain radiographs are indicated in all patients who present with Morton neuroma. Based on the patient’s clinical presentation, additional testing may be indicated, including complete blood cell count, sedimentation rate, and antinuclear antibody testing. Magnetic resonance imaging (MRI) or ultrasound of the Morton neuroma is indicated to help confirm the diagnosis and if fracture, effusion, tendinopathy, crystal arthropathy, joint mice, synovitis, foreign body, bursitis, or ligamentous injury is suspected (Figs. 177.3 and 177.4).

In a manner analogous to that of the digital nerves of the hand, the digital nerves of the foot travel through the intrametatarsal space to innervate each toe. The plantar digital nerves, which are derived from the posterior tibial nerve, provide sensory innervation to the major portion of the plantar surface (Fig. 177.5). These nerves are subject to entrapment and resultant development of perineural fibrosis and degeneration resulting in the clinical syndrome known as Morton neuroma (see Fig. 177.1). The dorsal aspect of the foot is innervated by terminal branches of the deep and superficial peroneal nerves. The overlap of the innervation of these nerves may be considerable.