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Dr. Thomas F. Bembynista
Morton's Neuroma
Morton's neuroma is an enlarged nerve that usually occurs in the third interspace, between the third and fourth toes.
Problems often develop in this area because part of the lateral plantar nerve combines with part of the medial plantar nerve here. When the two nerves combine, they are typically larger in diameter than those going to the other toes. Also, the nerve lies in subcutaneous tissue, just above the fat pad of the foot, close to an artery and vein. Above the nerve is a structure called the deep transverse metatarsal ligament. This ligament is very strong, holds the metatarsal bones together, and creates the ceiling of the nerve compartment. The ground pushes up on the enlarged nerve with each step and the deep transverse metatarsal ligament pushes down. This causes compression in a confined space. The reason the nerve enlarges has not been determined. Flat feet can cause the nerve to be pulled more medially than normal, which can cause irritation and possibly enlargement of the nerve. The syndrome is more common in women than men, possibly because women wear confining shoes more often. High heels cause more weight to be transferred to the front of the foot and tight toe boxes create lateral compression. As a result, there is more force being applied in the area and the nerve compartment is squeezed on all sides. Under such conditions, even a minimal enlargement in the nerve can elicit pain. The most common symptom of Morton's neuroma is localized pain in the third interspace between the third and fourth toes. It can be sharp or dull, and is worsened by wearing shoes and by walking. Pain usually is less severe when the foot is not bearing weight. Morton's neuroma is the most common cause of localized pain in the third interspace and these diagnostic tests produce good indications of the condition. It is also important to rule out other, potentially serious, problems. The podiatrist commonly palpates the area to elicit pain, squeezing the toes from the side. Next he or she may try to feel the neuroma by pressing a thumb into the third interspace. The podiatrist then tries to elicit Muldor's sign, holding the patient's first, second, and third metatarsal heads with one hand and the fourth and fifth metatarsal heads in the other and pushing half the foot up and half the foot down slightly. In many cases of Morton's neuroma, this causes an audible click, known as Muldor's sign. In most cases an injection of local anesthetic to relieve pain and a corticosteroid to reduce inflammation may be administered. The patient is advised to return in a week or 2 to monitor progress. If the pain has been relieved, the neuroma is probably small and caused by the type of shoes the patient wears. A custom orthotic that shifts weight from the third interspace, where the neuroma lies, and better fitting shoes usually are sufficient to allow the patient to walk without pain. If pain persists, chemical neurolysis, the administration of a nerve-destroying agent, may be considered. Dehydrated alcohol is injected into the neuroma and destroys nerve fibers, which reduces the pain but also may result in numbness. If conservative treatment does not work, minor surgery is an option. The surgeon makes an incision on the top of the foot (called the dorsal approach). This approach permits the patient to walk soon after surgery because the stitches are not on the weight-bearing side of the foot. Because the surgical area contains very small blood vessels, nerves, and muscles, complications can occur. Surgery can lead to instability in the forefoot that may require future attention and cause long-term numbness. Also, once the neuroma is removed, the empty space may fill with blood, resulting in a painful hematoma. The stump of nerve remaining after the neuroma has been removed may begin to grow. The nerve grows in width and length, creating another neuroma that causes burning pain that requires injection therapy or another surgery. All surgeries carry the risk for infection. If the incision site becomes warm or red within a day or 2 after surgery, of fever develops, the surgeon must be contacted immediately.
Overview This is a condensed version of an original article on Morton's neuroma from podiatrychannel.
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Dr. Thomas F. Bembynista
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