Morton’s neuroma, also referred to as an interdigital
neuroma, is one of the most common painful disorders of the forefoot.
It was first described in 1845 by Dulacher and is named after Thomas Morton,
who presented, in 1876, a case series of patients afflicted with
this disorder. Patients with an established Morton’s neuroma
are usually cared for by a Podiatrist or an Orthopedist. They may
present to the Emergency Department with a previously undiagnosed
neuroma or with a painful exacerbation of known neuroma.
The term neuroma is actually a misnomer. Histologic investigation
does not reveal the proliferation of axons found in true neuromas.
Instead, in Morton’s neuroma, there is a progressive fibrosis and
thickening of the perineural tissue with degeneration of the underlying
nerve. This most commonly affects the third plantar common digital
nerve located between the third and fourth metatarsal heads. It
may occur between the second and third metatarsals. A neuroma is
rarely seen between the first and second or the fourth and fifth
Morton’s neuroma is most commonly found in women
in their fourth to sixth decades.1 It is especially common
in those who wear high-heeled shoes or shoes that are narrow at
the forefoot. It is more commonly seen in persons with pronated
or pes cavus feet.2 Neuromas do not become symptomatic
until their transverse diameter reaches more than 5 mm.3
Neuromas form just proximal to the bifurcation of the plantar
common digital nerves (Figure 166-1) and below the deep transverse
intermetatarsal ligament (Figure 166-2). The deep transverse intermetatarsal
ligament connects the plantar aspects of the metatarsal heads (Figure
166-2). The neuroma is made up of branches from both the medial
and lateral plantar nerves (Figure 166-1). Most commonly affected
is the third interdigital nerve. It is the largest of the interdigital
nerves and may explain the increased frequency of neuroma formation
in this location.
Morton’s neuroma most commonly occurs in the
third intermetatarsal space beneath the transverse metacarpal ligament.
Anatomy of the forefoot. Cross-section through the distal
Morton and others postulated that the increased mobility of the
fourth and fifth metatarsal heads relative to the others results
in disproportionate trauma to the third interdigital nerve. These mechanical
factors, combined with the impingement and stretching from a tight
transverse intermetatarsal ligament, result in repetitive microtrauma.
Histologic evaluation reveals perineural fibroma formation consistent
with compression-induced trauma.1 There is a progression
from edema of the endoneurium, fibrosis beneath the perineurium,
axonal degeneration, and neuronal necrosis.
Some authors believe that a more significant contributor to neuroma
formation is enlargement of the interphalangeal component of the
intermetatarsophalangeal bursa, leading to microvascular trauma....