Some anatomy of the foot
There are many bones in the foot.
They can briefly be divided into the tarsal bones, the metatarsal bones
and the phalanges. The tarsal bones are the larger bones that form the
back section of the foot, with the calcaneum being the largest. There
are five metatarsal bones and these are given names from the first to
the fifth. The first metatarsal bone is the largest and is the bone
that joins to the big toe. Each toe has three phalanges, except the big
toe which only has two.
There are many nerves, muscles and ligaments within the foot. Of note,
the common plantar digital nerves run between the metatarsal bones in
the foot. These have branches that supply sensation to the skin of the
toes.
What is Morton's neuroma?
Morton's
neuroma is named after Dr Morton who first described this condition in
1876. It is sometimes called Morton's metatarsalgia or interdigital
neuroma.
It is a condition that affects one of the common
plantar digital nerves that run between the metatarsal bones in the
foot. It most commonly affects the nerve between the third and fourth
metatarsal bones, causing pain and numbness in the third and forth
toes. It can also affect the nerve between the second and third
metatarsal bones, causing symptoms in the second and third toes.
Morton's
neuroma rarely affects the nerve between the first and second, or
between the fourth and fifth, metatarsal bones. It tends to affect only
one foot. It is rare to get two neuromas at the same time in the same
foot.
What causes Morton's neuroma?
Some
say that this condition should not be called Morton's neuroma as, in
fact, it is not actually a neuroma. A neuroma is a benign
(non-cancerous) tumour that grows from the fibrous coverings of a
nerve. There is no tumour formation in Morton's neuroma.
The
exact cause of Morton's neuroma is not known. However, it is thought to
develop as a result of chronic (longstanding) stress and irritation of
a plantar digital nerve. There are a number of things that are thought
to contribute to this. Some thickening (fibrosis) and swelling may then
develop around a part of the nerve. This can look like a neuroma and
can lead to compression of the nerve.
The anatomy of the bones
of the foot is also thought to contribute to the development of
Morton's neuroma. For example, the space between the metatarsals (the
long bones of the foot) is narrower between the second and third, and
between the third and fourth metatarsals. This means that the nerves
that run between these metatarsals are more likely to be compressed and
irritated. Wearing narrow shoes can make this compression worse.
Sometimes,
other problems can contribute to the compression of the nerve. These
include the growth of a fatty lump (called a lipoma) and also the
formation of a bursa (a fluid-filled sac that can form around a joint).
Also, inflammation in the joints in the foot next to one of the digital
nerves can sometimes cause irritation of the nerve and lead to the
symptoms of Morton's neuroma.
Who gets Morton's neuroma?
About
three-quarters of people with Morton's neuroma are women. It commonly
affects people between the ages of 40 and 50 but can affect someone of
any age.
Poorly fitting or constricting shoes can contribute to
Morton's neuroma. It is more likely in women who wear high-heeled shoes
for a number of years or men who are required to wear constrictive shoe
gear. It may also be more common in ballet dancers.
What are the symptoms of Morton's neuroma?
People
with Morton's neuroma usually complain of pain that can start in the
ball of the foot and shoot into the affected toes. However, some people
just have toe pain. There may also be burning and tingling of the toes.
The symptoms are usually felt up the sides of the space between two
toes. For example, if the nerve between the third and fourth metatarsal
bones is affected, the symptoms will usually be felt up the right hand
side of the forth toe and up the left hand side of the third toe. Some
people describe the pain that they feel as being like walking on a
stone or a marble.
Symptoms can be worse if you wear
high-heeled shoes. The pain is relieved by taking your shoe off,
resting your foot and massaging the area. You may also experience some
numbness between the affected toes. Your affected toes may also appear
to be spread apart, which doctors refer to as the 'V sign'.
The
symptoms can vary and may come and go over a number of years. For
example, some people may experience two attacks of pain in a week and
then nothing for a year. Others may have regular and persistent pain.
How is Morton's neuroma diagnosed?
Morton's
neuroma is usually diagnosed by your doctor listening to your symptoms
and examining your foot. Sometimes your doctor can feel the 'neuroma',
or an area of thickening in your foot, which may be tender.
Sometimes,
your doctor may suggest an ultrasound or MRI scan to confirm the
diagnosis but this is not always necessary. Some doctors inject a local
anaesthetic into the area where you are experiencing pain. If this
causes temporary relief of pain, burning and tingling, it can sometimes
help to confirm the diagnosis and show the doctor where the problem is.
What is the treatment for Morton's neuroma?
Non-surgical treatments
Simple treatments may be all that are needed for some people with a Morton's neuroma. They include the following:
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Footwear adjustments including avoidance of high-heeled and narrow shoes and having special orthotic pads and devices fitted into your shoes.
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Calf-stretching exercises may also be taught to help relieve the pressure on your foot.
-
Steroid or local anaesthetic injections (or a combination of
both) into the affected area of the foot may be needed if the simple
footwear changes do not fully relieve symptoms. However, the footwear
modification measures should still be continued.
-
Sclerosant injections involve the injection of alcohol and
local anaesthetic into the affected nerve under the guidance of an
ultrasound scan. Some studies have shown this to be as effective as
surgery. However, this may not be widely available in the UK yet.
Surgical treatments
If these non-surgical
measures do not work, surgery is sometimes needed. Surgery normally
involves a small incision (cut) being made on either the top, or the
sole, of the foot between the affected toes. Usually, the surgeon will
then either create more space around the affected nerve (known as nerve
decompression) or will resect (cut out) the affected nerve. If the
nerve is resected (cut out), there will be some permanent numbness of
the skin between the affected toes. This does not usually cause any
problems.
You will usually have to wear a special shoe for a
short time after surgery until the wound has healed and normal footwear
can be used again.
Surgery is usually successful. However, as
with any surgical operation, there is a risk of complications. For
example, after this operation a small number of people can develop a
wound infection. Another complication may be long-term thickening, or
callus formation, of the skin on the sole of the foot (known as plantar
keratosis). This may require chiropody.
What is the outlook (prognosis) for Morton's neuroma?
About
a quarter of people do not require any surgery for Morton's neuroma and
their symptoms can be controlled with footwear modification and
steroid/local anaesthetic injections. Of those who choose to have
surgery, about three quarters have good results with relief of their
symptoms.
Recurrent or persisting symptoms can occur after
surgery. Sometimes, decompression of the nerve may have been incomplete
or the nerve may just remain 'irritable'. In those who have had
resection of the nerve (neurectomy), a recurrent or 'stump' neuroma may
develop in any nerve tissue that was left behind. This can sometimes be
more painful than the original condition.
Can Morton's neuroma be prevented?
Ensuring that shoes are well fitted, low-heeled and with a wide toe area may help to prevent Morton's neuroma.
References
-
Schaller TM; Morton Neuroma. eMedicine. Last Updated May 2008.
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Gonzalez P, Bowman II RG; Morton Neuroma. eMedicine. Last Updated June 2006.
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Prior T; Common Foot Disorders. Arthritis Research Campaign. Reports on the Rheumatic Diseases Series 5: Hands On. October 2006: No 10
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Hughes RJ, Ali K, Jones H, et al;
Treatment of Morton's neuroma with alcohol injection under sonographic
guidance: follow-up of 101 cases. AJR Am J Roentgenol. 2007
Jun;188(6):1535-9. [abstract]
-
Wheeless' Textbook of Orthopaedics; Morton's Neuroma: Interdigital Perineural Fibrosis
Disclaimer: This article is for information only and should not
be used for the diagnosis or treatment of medical conditions. EMIS and
PiP have used all reasonable care in compiling the information but make
no warranty as to its accuracy. Consult a doctor or other health care
professional for diagnosis and treatment of medical conditions.
© EMIS and PiP 2008 Updated: 19 Jun 2008 DocID: 8742 Version: 1
