A Morton's neuroma, or interdigital neuroma, is a painful condition which involves a nerve on the plantar aspect (bottom) of the foot. Occasionally a neuroma develops following a bruising injury to the sole of the foot, such as might be caused by jumping onto a rock or other objects, but in general, the origin of the condition is unknown.
What is a Morton's neuroma?
The nerves located on the bottom of the foot between the metatarsal heads (the bone of the toe closest to the foot) supply feeling, or sensation, to the toes. One of these nerves may become irritated by the ligament located above it, causing it to become thickened and painful. Generally this problem occurs most often between the third and fourth toes, but it can occur between the second and third toes as well. It is uncommon for a neuroma to be located between the first and second or fourth and fifth metatarsals. Rarely is there more than one neuroma in a foot.
Overview
What are the signs and symptoms of a Morton's neuroma?
The symptoms of a Morton's neuroma are classic in nature. The patient complains of a burning , tingling, slightly numb feeling (dysesthesias) which radiates out to the toes on either side of the interspace that is involved. For instance, a Morton's neuroma of the third interspace will result in pain between the third and fourth toes, and a neuroma in the second interspace will cause pain between the second and third toes. The symptoms are usually aggravated by wearing shoes, particularly those with high heels. Symptoms are relieved by walking in flat, wide shoes or going barefoot. Rarely will the patient experience pain when sitting or laying down.
How is a Morton's neuroma diagnosed?
The physician will make the diagnosis of Morton's neuroma based upon the patient's symptoms as described above in an interview, or history, and a physical examination.
The physical examination will reveal exceptional tenderness in the involved interspace when the nerve area is pressed on the bottom of the foot. As the interspace is palpated, and pressure is applied from the top to the bottom of the foot, a click can sometimes be felt which reproduces the patient's pain. This is known as a Mulder's sign.
Because of inconsistent results, imaging studies such as MRI or ultrasound scanning are not useful diagnostic tools for Morton's neuroma. Thus the physician must rely exclusively on the patient's history and physical examination in order to make a diagnosis.
What is the treatment for Morton's neuroma?
Non-operative Treatment
Most patients' symptoms subside when they change footwear to a wide soft shoe with a metatarsal support inside to relieve the pressure on the involved area. If this treatment fails, a cortisone injection into the nerve is occasionally helpful.
Operative Treatment
When conservative measures are unsuccessful, surgery can be a good choice in the treatment of Morton's neuroma.
The operation for Morton's neuroma does not require an overnight hospital stay. The anesthetic used is an ankle block, which completely numbs the foot during the surgery.
- The physician removes the neuroma from an incision made on the top of the foot between the involved metatarsal heads.
- The nerve to the interspace is exposed and cut next to the metatarsal heads.
What types of complications may occur?
The main complication resulting from a neuroma excision (removal) is a recurrence of the neuroma. The nerve itself doesn't return, but whenever a portion of a nerve is removed, the stump will form a little bulb known as a traumatic or stump neuroma. If this traumatic neuroma is located beneath a metatarsal head or becomes quite large, it may become painful several years after the initial surgery. Most studies have shown that although 80% of patients do well after the removal of a neuroma, 20% will have some degree of nerve pain following the surgery.
Occasionally after surgery, the patient will have an area of numbness on the bottom of the foot which is described as feeling like a wrinkle in the sock. This discomfort usually disappears in time.
The patient's foot remains in a surgical dressing for three weeks to allow the tissues to heal. During this time the patient walks in a stiff post-operative shoe. It usually takes about two months for the patient to comfortably resume usual activities.
Is it possible to have more than one neuroma in a foot at the same time?
Although it is possible to have two neuromas in the same foot simultaneously, it is quite uncommon. Results of the removal of two neuromas are far less successful than when only one neuroma is removed.
Is it common to have a neuroma in both feet at the same time?
This is possible, but it does not usually occur. A neuroma is usually an isolated entity occurring in only one foot at a time.
If a neuroma is removed, can it reoccur?
Once a neuroma is removed, it cannot return. Whenever the nerve is cut, however, a small growth occurs at the end of the nerve called a "stump neuroma". This small ball of tissue at the end of the nerve can be sensitive if it is under a weight-bearing area of the foot.
Botte, M. J., Tran, H.N., et al.: Traumatic neuromas of the foot and ankle. Foot and Ankle Clinics, 3(1): 71- 113, 1998.
Diebold, P. F., Daum, B., Dang-Vu,V, and Litchinko,M.: True Epineural Neurolysis in Morton's Neuroma: A five- year follow-up. Orthopedics, 19(5): 397-399, 1998.
Friscia, D.A., Strom, D.E., Parr,J.W., : Saltzman, C.L., Johnson, K.A.,: Surgical Treatment for primary interdigital neuroma. Orthopedics, 14: 669-672, 1991.
Mann, R. A., and Reynolds, J.: Interdigital neuroma: a critical and clinical analysis. Foot Ankle, 3(4): 238-243, 1983.
Mann, R.A., Coughlin, M. J. Surgery of the Foot and Ankle, 6th edition (Ch. 11) Mosby 1993, pp. 552-553
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