Morton's Neuroma is a common foot condition caused by the irritation of the common intermetatarsal nerve as it passes through the forefoot to the toes. This condition was first described by Dr. Morton, a Viennese physician, in 1876.

To help understand this condition, let's break the word down into its' root terms. Neuro, of course, relates to the nervous system. Oma is the Latin term that defines a tumor or swelling that is of primary origin. Put the terms together and what is described is a tumor or swelling of a peripheral nerve. For most of us, the term tumor sends up a red flag and really gets our attention. Not all tumors are the bad or so called malignant types we tend to hear so much about. The term tumor simply defines a swelling that develops with no other recognizable cause.

One of the tests your doctor may use to diagnose Morton's Neuroma is called a Muldier's Sign (1). To perform this test, your doctor will gently squeeze the foot from side to side and use their thumb to push up between the 3rd and 4th toes. In advanced cases of Morton's Neuroma, there will be a palpable snap as the intermetatarsal nerve moves between the adjacent bones. Performing a Muldier's Sign mimics what takes place in the shoe with every step. Squeezing the foot simulates the shoe and pushing up on the bottom of the foot simulates the reactive forces of the ground as it pushes against the foot with each step.

Tight shoes will contribute to the symptoms of Morton's Neuroma by binding the forefoot and compressing the nerve. Higher heels will also act to increase the ground reactive forces. Certain activities, such as squatting, will also increase the force applied to the plantar foot and aggregate the symptoms of Morton's Neuroma.

We've learned a lot about Morton's neuroma over the past ten years. A podiatrist in the Houston Texas area, Dr. Steve Barrett, was the one individual who really changed the way that we treat Morton's Neuroma. It's interesting to note that we've treated Morton's Neuroma the same for the past 100 years ever since it was first described by Dr. Morton. Dr. Barrett was the first to take a critical look at Morton's Neuroma and recognize how this problem develops and perhaps, how could we treat it more effectively.

What Dr. Barrett recognized was that the common intermetatarsal nerve, the peripheral nerve where we find Morton's Neuroma, became entrapped as it passed beneath the intermetatarsal ligament. This was a new concept for us in light of the fact that we had considered Morton's Neuroma something that was the effect of the adjacent bone irritating the nerve. In fact, Dr. Barrett's findings made Morton's Neuroma similar to other nerve entrapments such as carpal tunnel. Subsequently, the treatment of Morton's Neuroma has been slowly changing over the last ten years as the result of a new endoscopic surgical procedure first described by Dr. Barrett.

Not all Morton's Neuroma require surgical correction. 50% or more of new Morton's Neuroma patients respond to simple changes in shoes such as a wider toe box. Shoe padding can also help treat Morton's Neuroma. Metatarsal pads are an important tool for patients with Morton's neuroma symptoms. A metatarsal pad is a small lift that is positioned in the shoe just proximal (behind) the weight bearing surface of the metatarsal bones. A metatarsal pad lifts and separates the metatarsal bones thereby decreasing the wear on the intermetatarsal nerve. Metatarsal pads come in varying sizes and densities, therefore it's important to have your pedorthist or shoe repair shop position and glue the pad. Higher quality prefabricated arch supports come with a metatarsal pad already seated in the correct position. Using inserts with a metatarsal pad is sometimes the easier way to go because they can be moved from shoe to shoe.

If padding and shoe changes don't work, we fall back on some of the original suggestions of Dr. Morton, first and foremost, injections of cortisone. Bear in mind, we've discussed the fact that Morton's Neuroma is a nerve entrapment. Cortisone does not change the fact that the common intermetatarsal nerve is prone to become entrapped, but it can reduce the painful inflammation in the nerve. If we can use cortisone effectively and avoid surgery, all the better. It's interesting that cortisone, unlike other medications, comes with no directions for treating Morton's Neuroma. Much of the use of cortisone depends upon the previous experiences of your doctor and the successes or failures that he or she has seen with cortisone. Can you overuse cortisone? Yes you can. But it's actually the safest and most effective medication for Morton's Neuroma and therefore should be used when needed. Over use of injectable cortisone in treating Morton's Neuroma can contribute to atrophy or thinning of the fat pad of the bottom of the foot.

That brings up another interesting point. Dr. Morton's original treatment plan as described in 1895 included changes in shoes, multiple injections of cortisone and if necessary, complete excision of the common intermetatarsal nerve. We've mentioned before that Morton's Neuroma is a nerve entrapment much like carpal tunnel. Now let's see if we can apply Dr. Morton's treatment plan to a carpal tunnel case. Perhaps we'd splint the wrist, try some injectable cortisone, but completely excise the nerve? No way. But that's what's been done for the past 100 years for Morton's Neuroma. Post-op complications were common and included thinning of the plantar fat pad and loss of sensation in the 3rd and 4th toes.

The introduction of Dr. Barrett's EDIN procedure has revolutionized the treatment of Morton's Neuroma and really represents the first unique contribution to treating this condition in over 100 years. The EDIN procedure stands for endoscopic decompression of the common intermetatarsal nerve. Interestingly enough, Steve describes first thinking about this procedure as he watched another surgeon perform an endoscopic carpal tunnel surgery. Steve recognized the problem to be the ligament and not the nerve. The EDIN procedure selectively releases the ligament and leaves the nerve intact.

The EDIN procedure provides us with a new alternative. In the past we knew that the traditional surgery used to treat Morton's Neuroma, called a neurectomy, was destructive and carried a fair amount of post-op complications. Therefore, we would tend to use excessive amounts of cortisone as our only method of treatment. The EDIN procedure provides a new alternative using non-invasive endoscopic techniques that usually return patients to activities much sooner than the traditional surgery. And, what I find most helpful is the fact that it enables us to use less cortisone, thereby avoiding fat pad atrophy. Was fat pad atrophy due to the neurectomy or from the overuse of cortisone? The EDIN procedure shows none of the traditional post-op complications as seen in the neurectomy, therefore we can assume that fat pad atrophy was in part due to overuse of cortisone. Thanks Steve; I like a guy who can think outside of the box.

Surgeons are slow to change, and rightly so. They prefer to use what they were taught and not test new procedures on their patients. The EDIN procedure has been used for at least ten years and has shown promising results. It can be technically challenging for some who are not familiar with endoscopic techniques. As with other surgical procedures there are pros, cons and possible complication that need to be discussed thoroughly with your physician prior to surgery.

There are other non-surgical methods of treating Morton's neuroma. Sclerosis of the nerve with diluted alcohol (4%) injections is starting to gain popularity (2). Multiple injections are used to scar the wall of the nerve and inhibit inflammation. Recent literature suggests injections weekly for three to seven weeks. The success rates of injectable sclerosing solutions have been reported to be as high as 60-90%.

Another new technique is called cryogenic neuroablation. Cryo surgery is surgery that uses extremely cold instrumentation to selectively destroy tissue. Cryosurgery has been used commonly to destroy superficial skin lesions such as warts and moles. In the case of Morton's neuroma, work has recently been done by several Michigan podiatrists that suggests cryogenic neuroablation may have a future in treating Morton's neuroma. The technique uses what is referred to as the Joule-Thompson effect. The Joule-Thompson effect occurs when a gas is passed through an area where it may expand. As the gas expands, it cools to approximately -70 degrees centigrade . In the case of neuroablation, the expansion of the gas is controlled in a 5.5 mm probe that freezes and subsequently destroys the nerve tissue.

In the cryogenic ablation study carried out by Drs. Caporusso, Fallet and Savoy-Moore, thirty one neuromas were treated in 20 patients. All procedures were performed in an office setting. The proecdure used a small amount of local anesthetic to numb the skin to allow the passage of a 12-gauge cannula through the skin. A nerve stimulator was passed through the cannula to locate the nerve. Once the position of the nerve was established, two three minute freeze sessions were utilized to destroy the nerve tissue. A sterile dressing was applied to the site and the patient was dismissed without the need for pain medication. The study cites a 65% success rate.

Anatomy:

As the posterior tibial nerve descends the leg, it biforcates (splints into two parts) at the level of the medial ankle. The two branches, the medial and lateral plantar nerves, continue forward into the foot to supply motor function to the muscles of the foot and sensory innervation to the bottom of the foot. The medial and lateral plantar nerves converge at the 3rd interspace (the space between the 3rd and 4th toes) to form the 3rd common intermetatarsal nerve. As a result of this unique anatomical configuration, the nerve between the 3rd and 4th toes is bound and unable to move out of the way when the adjacent bones move in the forefoot. As a result, the 3rd common intermetatarsal nerve is much more prone to the formation of Morton's Neuroma.

As the 3rd common intermetatarsal nerve passes distally to the toes it is forced to pass beneath the intermetatarsal ligament. At this point the nerve takes a slight turn in direction as it passes into the 3rd and 4th toes. This is the primary location where a Morton's Neuroma is found.

Biomechanics:

Biomechanics do contribute to the formation of Morton's Neuroma. Morton's Neuroma is more commonly seen in flat feet and flexible feet. It is not uncommon to find Morton's Neuroma in conjunction with other foot problems such as bunions and hammer toes.

Symptoms:

A dull achy sensation in the forefoot, usually between the 3rd and 4th toes Pain that increased with the time a person spent on their feet, particularly in high heels Pain that decreased once a person got off their feet Numbness of the 3rd and 4th toes A sensation of walking on something, such as a bunched up sock Occasionally, a snapping sensation or electrical shock sensation

Differential Diagnosis:

Bursitis/capsulitis

Metatarsalgia

Metatarsal stress fracture

Additional references include;

Dockery GL: The Treatment of Intermetatarsal Neuromas With 4% Sclerosing Injections. JFAS, 38(6):403-408, 1999

Miller SJ: Morton's Neuroma: A Syndrome. In McGlamry ED, Banks AS, Downey MS (ed): Comprehensive Textbook Of Foot Surgery, 2nd ed. Ch.11, Williams and Wilkens, Baltimore, 1992;304-320

Mendicino, SS, Rockett MA:Morton's Neuroma: Update On Diagnosis And Imaging. Clin Pod Med. Surg. 14:303-311, 1997

Caporusso, EF, Fallet, L, Savoy_Moore, R: Cryogenic Neuroablation for the Treatment of Lower Extremity Neuromas. JFAS, 41(5):286-290, 2002