What is a neuroma?
A neuroma is generally used to describe a chronic pinched nerve that develops a mass of scar tissue around it as a result of that chronic irritation.
Is a Morton's neuroma the same thing as a neuroma?
Not exactly. The term "Morton's neuroma" is only properly used to describe the condition when the affected nerve is the one that supplies the adjacent sides of the third and fourth toes. (See diagram to the right.) The word "neuroma" could be used to describe a chronically pinched or irritated condition of any nerve--say, the nerve providing nervous sensation to the second and third toes, for example. That's how the words "neuroma" and "Morton's Neuroma" are used today, but in truth, neither phrase is really proper. How so? |
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First, it's not really a neuroma. Adding the Greek suffix "-oma" to a word literally means "tumour". That's why we attach it to words referring to cancerous conditions like lymphomas and benign tumours like fibromas.
But a neuroma is not really a tumour at all. It's actually a growth of scar tissue around a nerve, due to chronic irritation. Instead of our using the word "neuroma", the more proper name for the condition would be "perineural fibrosis", which literally translates to "scar tissue around the nerve".
The second reason the condition is misnamed is that the Morton's neuroma wasn't really first described by Morton. The first to accurately describe the condition was a chiropodist to the Queen of England, Louis Durlacher. In 1845 he accurately discerned that the condition was a nerve problem.
Thirty-one years later, in 1876, Thomas G. Morton, a physician in Philadelphia, described a type of discomfort in the region as being an inflammation of the fourth toe joint (the fourth metatarsophalangeal joint). Today we'd describe this condition joint problem as "capsulitis". (You can read more about capsulitis in the section below entitled "What Other Conditions Mimic a Neuroma?".)
In any event, what we know today as a Morton's Neuroma should probably be called Durlacher's Perineural Fibrosis. It goes to show you that getting it right and getting it first is sometimes worse than getting it wrong and getting it decades late.
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What nerves are affected? The most common location for a neuroma to develop is the classic "Morton's Neuroma" location--involving the nerve that supplies sensation to the third and fourth toes. This is the location in over 80% of cases, with the nerve between the second and third toes involved in 15% of cases. This nerve lies deep in the foot, and represents joined branches from the medial and lateral plantar nerves. For more information about nerves in the feet, visit our page on neurology. |
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Why does the condition develop?
Several theories have been put forth as to how the nerve is exactly irritated. The irritation to the nerve may come from chronic friction caused by the adjacent metatarsal bones, the adjacent toe bones, or Deep Transverse Metatarsal Ligament between the metatarsals under which the afflicted nerve passes en route to the toes.
But because the Morton's Neuroma involves the joined branches of two nerves coming together, it is likely that the enlargement where those nerve join together predisposes that nerve to irritation.
Who gets neuromas?
Anyone can get a neuroma, but it is more commonly seen with women, particularly those who have had children and those in middle age. The most common precipitating factors are having a foot that flattens too much (a pronated foot), having hammertoes or some other similar pathology, and making poor shoe choices. (Tight toe box shoes and high heels are the worst choices.)
What does it feel like?
Symptoms vary. Sometimes the patient simply experiences numbness, or diminished sensation. It may also feel simply like sensation inappropriate to the degree of stimulus, for example, pain with light touch of the skin, or feeling as though there's something inside the shoe when there is nothing present.
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But the most common feeling is one of a sharp, stabbing pain..................... |
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...............or like a severe sudden jolt of electricity shoot up the leg or down to the end of the toes, particularly if the foot is squeezed. |
What other conditions mimic a neuroma?
There are quite a few potential differential diagnoses (possible alternative diagnoses):
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Capsulitis Joint capsule is the covering that extends around a joint, so capsulitis is an inflammation of that joint covering. There are two major joints immediately adjacent to the location where neuromas develop--one on each side of the nerve. Capsulitis is more likely in conditions where there is an abnormality associated with those joints, such as a hammertoe, or if there is abnormal or excessive flattening of the feet, or pronation.
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Synovitis (inflammation of the joint fluid known as synovium) is closely-related to capsulitis. In fact, the synovial fluid is actually manufactured by the capsule. Some believe that if you have capsulitis, you also have synovitis.
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Joint subluxation In cases where the joint is misaligned enough, the base of the toe bone may actually tear through the capsule, causing a dislocation of the joint. Once considered rare, this diagnosis seems to be much more commonly picked up than in years past.
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Degenerative arthritis Arthritis may develop in the joints in the area, mimicking the symptoms of a neuroma. This sort of arthritis comes from repetitive trauma to the joint.
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Other rheumatolgical conditions (other types of arthritis) may affect the joints adjacent to the classic location of a neuroma. This is particularly true of Rheumatoid Arthritis and Psoriatic Arthritis.
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Metatarsalgia This literally means pain in the bones in the ball of the foot (the metatarsals). It would be best described as a bruise to the metatarsal bones adjacent to the nerve.
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Stress fractures One step beyond metatarsalgia, stress fractures are small cracks in the metatarsals or toe bones that develop over time as a result of excessive strain or stress.
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Avascular necrosis This is a degenerative condition where the constant stress to the metatarsal bones gets severe enough that a portion of the bone actually begins to die.
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Tendinitis There are a lot more tendons in the area of the classic neuroma location than you might think, any one of which may develop tendinitis. Tendons to the Flexor Digitorum Longus, Flexor Digitorum Brevis, Extensor Digitorum Longus, Extensor Digitorum Brevis, the 3rd Dorsal Interosseus, the 2nd Plantar Interosseus and the 3rd Lumbrical muscles all attach in the area immediately adjacent to the classic neuroma location.
If the sensation varies so much, and if other conditions cause symptoms similar to those of a neuroma, how do I know what I have?
Diagnosis is not easy sometimes. The classic test for a neuroma is the "Mulder's Sign". The foot is grasped and squeezed from the sides with one hand, with the other hand pushing the nerve up in between the third and fourth metatarsal bones. When this test is positive, the nerve gets squeezed and creates a clicking sound, and often severe pain in the foot.
While this test often works well for well-established neuromas, it doesn't work in every case. As the sensation caused from a neuroma may vary a great deal, and as there are several structures in the immediate area that can create similar sensations as a neuroma, definitive diagnosis of this condition can be elusive. For this reason, neuromas are frequently diagnosed as something else, and it is particularly common that other conditions of the foot are mislabeled as being a neuroma. For this reason, it is important to have a foot specialist examine you for this condition.
How do you treat a neuroma?
Many treatments have been developed for short-term relief of the symptoms of a neuroma. Rest, ice, elevation, anti-inflammatory medications, steroid injections, physiotherapy, taping, padding, immobilization are all common early treatments. These conservative treatments work best if the patient is seen early.
Long-term, making different choices in shoes may be required. And changes in the types of activities chosen may be helpful. (For example, using a stair-climbing machine at the gym may not be advised.) Orthoses are very helpful with controlling any abnormal mechanical motions and with diminishing pressure to the affected nerve. There are special additions to the orthotic appliance that may be made when a neuroma is diagnosed.
When more conservative means fail, more invasive techniques may be required. One possibility is to cauterize the nerve with a specialized alcohol injection. Often effective, this treatment may require a series of several injections to resolve a neuroma.
When nothing else is helpful, surgical intervention to remove the nerve may be necessary.
What's the surgery like?
The surgery consists of making a small incision on the foot, either from the top or bottom, then carefully dissecting the afflicted nerve out from the surrounding tissue and removing the diseased portion. Sometimes the ligament that lies on top of the nerve is cut to allow the remaining nerve more room. The procedure may be done under local anaesthesia, and the patient is typically allowed a limited amount of walking immediately after the procedure.
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Left: A typical two-pronged pitchfork appearance of an excised neuroma. The two branches on the left are the branches that would supply innervation to the third and fourth toes. The long branch on the right is the branch coming into the toes from the foot. |
Some authors report only an 80% success rate with this surgery (meaning about 20% have little or no improvement after the surgery), but we find the success rate to be higher when patients are properly chosen. (We believe that other similar conditions are frequently misdiagnosed as being a neuroma, that appropriate conservative treatments are under-utilized, and inappropriate surgical intervention is too quickly suggested.)
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