What is Morton's Neuroma?

Morton's neuroma is defined as an irritative process involving a nerve that supplies adjacent toes in the foot (figure 1 below). The major nervous supply to the bottom of a person's foot comes from the inside of the ankle. As the nerve passes to the toes, it begins to break into smaller branches. The bottom of each toe will receive two small nerve branches, which provide feeling to the skin. The nerves are relatively close to the plantar skin, and are often nestled between the metatarsal heads. The metatarsals are the long bones located just behind each toe. The metatarsal head is the rounded far end of the bone that makes contact with the small bones in the toes. As the nerve passes between adjacent metatarsal heads, it will branch into small nerves that enter the toes. Neuromas typically occur just prior to this branching, between the metatarsal heads.

Another important structure is a ligament that holds the metatarsal heads together (called the deep transverse intermetatarsal ligament). It is located between the metatarsal heads and just above the nerves on the bottom of the foot. Neuromas are the result of an anatomical "mistake" in which a nerve becomes squeezed between two bones (metatarsal heads) on either side. Chronic irritation of the nerve from repetitive trauma or constriction causes nerve thickening and damage resulting in scar tissue around the nerve. The close proximity of adjacent metatarsals and a deep ligament that passes between the two metatarsals results in a confinement of the plantar nerve. This results in trauma to the nerve. Slowly, the nerve becomes thicker and begins to degenerate.

A neuroma occurs most commonly between the third and fourth toes, but can present anywhere along the metatarsal heads. The term "neuroma" is actually a misnomer. This condition does not involve a tumorous growth; rather it is a reaction of normal nerve cells to some sort of traumatic event. This reaction involves enlargement of the nerve and improper function of the nerve itself.