Morton's neuroma is one cause of metatarsalgia, which is pain in the ball of the foot. In 1876, Thomas Morton described it. It is due to inflammation of a nerve in the foot. The inflammation is caused by entrap¬ment of the nerve under the metatarsal heads. "Neuroma" means nerve tumor. Tumor in this case means simply enlargement of the nerve, not malignancy.
The cause of nerve enlargement is repeated injury. The nerve becomes trapped under the metatarsal heads when standing and walking. This most often occurs in shoes with high heels or thin hard soles, but can occur in any walking or standing situation. It usually occurs between the third and fourth toes.
The symptoms of Morton's neuroma are pain and numbness in a specific spot in the ball of the foot, sometimes radiating into the toes. At times, the pain may be absent and, at other times, severe enough to cause the individual to stop and take off the shoe. It may feel like a marble or a stone under-the foot, moving around and sometimes causing a sharp "snap" to be felt. The examining physician can sometimes feel this by pressing on the foot. Testing with a pin may reveal numbness in the toes.
Diagnosis may be difficult, especially at first. Several examinations may be necessary. The condition tends to get worse with time. With repeated injury, the nerve becomes largefsr; as it becomes larger, it is more easily injured.
Treatment is first to modify the shoes. A pad in the shoe, and an extra wide, soft shoe will help. A cortisone injection around the nerve may help reduce swelling and inflammation. This will also help localize the problem.
Surgery to remove the neuroma can be done when necessary. It is successful around 80 percent of the time. Since a nerve is removed, there is numbness in the toes and in the ball of the foot afterward. This is not usually a problem and it becomes less with time.
Persisting pain may be due to irritation at the cut end of the nerve, a stump neuroma. This can require additional surgery for those who do not get relief.