Morton neuroma refers to symptoms caused by painful branches of the common digital nerves most often in the second or third web spaces of the foot. The term IDN has replaced Morton neuroma because the condition likely results more from inflammatory changes rather than true neuroma tumor formation. The pathogenesis results from a traction phenomenon where the edge of the intermetatarsal ligament compresses the nerve during the normal gait cycle, leaving it susceptible to irritation or direct trauma (Fig. 29-1). Most patients with symptoms are middle-aged women who have a history of wearing shoes with a narrow toe box or high heels, which can increase the plantar pressure in the forefoot. IDN most commonly develops at the second or third web space causing a primary complaint of pinpoint burning or tingling pain worsened by shoe wear. The symptoms are often alleviated by removing the shoes and massaging the toes. A patient may report decreased sensation, but it is uncommon to see diffuse pain, pain on the plantar surface, or the patient to walk with a limp.¹

A full examination of the foot should be undertaken in both the standing and seated positions in order to distinguish separate IDN from other forefoot pathology. Pain with palpation on the plantar surface of the lesser metatarsal heads and hypercallosity of skin may be indicative of metatarsalgia or fat pad atrophy. Tenderness and/or fullness of the MTP joints indicate degenerative arthritis, synovitis, or Freiberg infarction (avascular necrosis of the second metatarsal head). Fullness of the distal interspace may indicate bursitis, or rarely, a soft tissue mass.

The most characteristic exam finding is reproducible pain with palpation of the second or third interspaces. With the foot stabilized with one hand, the index finger and thumb squeeze between the respective metatarsal heads, and the typical pain will radiate toward the affected digits. Simultaneous medialtolateral compression of the metatarsal heads while palpating the interspaces may create a clicking sensation, referred to as the classic Mulder sign (see Fig. 29-2) of Morton neuroma; however, this is not often reproduced.²