Morton's neuroma is a benign neuroma of an intermetatarsal plantar nerve, most commonly
of the second and third intermetatarsal spaces. This problem is characterised by pain and/or
numbness, sometimes relieved by removing footwear. Despite the name, the condition was first
correctly described by a chiropodist named Durlacher, and although it is labeled a "neuroma",
many sources do not consider it a true tumor, but rather a perineural fibroma.
Symptoms and signs Symptoms include: pain on weight bearing,
frequently after only a short time. The nature of the pain varies widely among individuals.
Some people experience shooting pain affecting the contiguous halves of two toes. Others
describe a feeling like having a pebble in their shoe or walking on razor blades. Burning,
numbness, and paresthesia may also be experienced. Morton's neuroma lesions have been found using
MRI in patients without symptoms. Diagnosis/differential diagnosis
Negative signs include no obvious deformities, erythema, signs of inflammation, or limitation
of movement. Direct pressure between the metatarsal heads will replicate the symptoms, as will
compression of the forefoot between the finger and thumb so as to compress the transverse
arch of the foot. This is referred to as Mulder’s Sign.
There are other causes of pain in the forefoot. Too often all forefoot pain is categorized
as neuroma. Other conditions to consider are capsulitis, which is an inflammation of ligaments
that surrounds two bones, at the level of the joint. In this case, it would be the ligaments
that attach the phalanx to the metatarsal bone. Inflammation from this condition will
put pressure on an otherwise healthy nerve and give neuroma-type symptoms. Additionally,
an intermetatarsal bursitis between the third and fourth metatarsal bones will also give
neuroma-type symptoms because it too puts pressure on the nerve. Freiberg's disease,
which is an osteochondritis of the metatarsal head, causes pain on weight bearing or compression.
Histopathology Microscopically, the affected nerve is markedly
distorted, with extensive concentric perineural fibrosis. The arterioles are thickened and
occlusion by thrombi are occasionally present. Imaging
Though a neuroma is a soft tissue abnormality and will not be visualized on standard radiographs,
the first step in the assessment of forefoot pain is an X-ray in order to evaluate for
the presence of arthritis and exclude stress fractures/reactions and focal bone lesions,
which may mimic the symptoms of a neuroma. Ultrasound accurately demonstrates thickening
of the interdigital nerve within the web space of greater than 3mm, diagnostic of a Morton’s
neuroma. This typically occurs at the level of the intermetatarsal ligament. Frequently,
intermetatarsal bursitis coexists with the diagnosis. Other conditions that may also
be visualized with ultrasound and can be clinically confused with a neuroma include synovitis/capsulitis
from the adjacent metatarsophalangeal joint, stress fractures/reaction, and plantar plate
disruption. MRI can similarly demonstrate the above conditions; however, in the setting
where more than one abnormality coexists, ultrasound has the added advantage of determining
which may be the source of the patient’s pain by applying direct pressure with the
probe. Further to this, ultrasound can be used to guide treatment such as cortisone
injections into the webspace, as well as alcohol ablation of the nerve.
Treatment Orthotics and corticosteroid injections are
widely used conservative treatments for Morton’s neuroma. In addition to traditional orthotic
arch supports, a small foam or fabric pad may be positioned under the space between
the two affected metatarsals, immediately behind the bone ends. This pad helps to splay
the metatarsal bones and create more space for the nerve so as to relieve pressure and
irritation. It may however also elicit mild uncomfortable sensations of its own, such
as the feeling of having an awkward object under one's foot. Corticosteroid injections
can relieve inflammation in some patients and help to end the symptoms. For some patients,
however, the inflammation and pain recur after some weeks or months, and corticosteroids
can only be used a limited number of times because they cause progressive degeneration
of ligamentous and tendinous tissues. Sclerosing alcohol injections are an increasingly
available treatment alternative if the above management approaches fail. Dilute alcohol
is injected directly into the area of the neuroma, causing toxicity to the fibrous nerve
tissue. Frequently, treatment must be performed 2–4 times, with 1–3 weeks between interventions.
An 82–90% success rate has been achieved in clinical studies, equal to or exceeding
the success rate for surgical neurectomy with fewer risks and less significant recovery,
especially if done under ultrasound guidance. Radio Frequency Ablation is also used in the
treatment of Morton's Neuroma The outcomes appear to be equally or more reliable than
alcohol injections especially if the procedure is done under ultrasound guidance.
If such interventions fail, patients are commonly offered surgery known as neurectomy, which
involves removing the affected piece of nerve tissue. Postoperative scar tissue formation
can occur in approximately 20% of cases, causing a return of neuroma symptoms. Neurectomy can
be performed using one of two general methods. Making the incision from the dorsal side is
the more common method but requires cutting the deep transverse metatarsal ligament that
connects the 3rd and 4th metatarsals in order to access the nerve beneath it. This results
in exaggerated postoperative splaying of the 3rd and 4th digits due to the loss of the
supporting ligamentous structure. This has aesthetic concerns for some patients and possible
though unquantified long-term implications for foot structure and health. Alternatively,
making the incision from the ventral side allows more direct access to the affected
nerve without cutting other structures. However, this approach requires a greater post-operative
recovery time where the patient must avoid weight bearing on the affected foot because
the ventral aspect of the foot is more highly enervated and impacted by pressure when standing.
It also has an increased risk that scar tissue will form in a location that causes ongoing
pain. Cryogenic neuroablation is a lesser known
alternative to neurectomy surgery. Cryogenic neuroablation is a term that is used to describe
the destruction of axons to prevent them from carrying painful impulses. This is accomplished
by making a small incision and inserting a cryoneedle that applies extremely low temperatures
of between −50 °C to −70 °C to the nerve/neuroma. This results in degeneration
of the intracellular elements, axons, and myelin sheath with wallerian degeneration.
The epineurium and perineurium remain intact, thus preventing the formation of stump neuroma.
The preservation of these structures differentiates cryogenic neuroablation from surgical excision
and neurolytic agents such as alcohol. An initial study showed that cryo neuroablation
is initially equal in effectiveness to surgery but does not have the risk of stump neuroma
formation. However, the results from this procedure may not be permanent.
Recently, an increasing number of procedures are being performed at specialist centers
under radiological or ultrasound guidance. Recent studies have shown excellent results
for the treatment of Morton's neuroma with ultrasound guided steroid injections, ultrasound
guided sclerosing alcohol injections, ultrasound guided radiofrequency ablation, and ultrasound
guided cryo-ablation. Morton's neuroma in popular culture
Dorothy Zbornak, a character in the NBC television show The Golden Girls, was diagnosed with
a Morton's Neuroma in the episode titled "The Operation".
Singer/songwriter and member of Aerosmith, Steven Tyler, was affected by Morton's neuroma
and underwent surgery for it. Patrick Duffy recently said in an Extra interview
with Billy Bush that he had Morton's neuroma and had surgery to have the nerves removed
in both feet years ago. Bob Harper, trainer of NBC's The Biggest Loser,
currently has Morton's neuroma. See also
Mulder's sign The Center for Morton's Neuroma - A Scientific
Discussion of Morton’s Neuroma References
External links The Center for Morton's Neuroma - useful resource
for anyone with Morton's neuroma Active blog on personal experience having
surgery for Morton's neuroma & recovery. Overview at Mayo Clinic
-664076278 at GPnotebook Who was Thomas George Morton
Image gallery of MRI & Ultrasound evaluation of forefoot pain