What is a Morton’s Neuroma?
We have reviewed Achilles tendonitis before the Mountain Goat, and
three issues ago, plantar fasciitis, two of the most common foot-related causes
of running ailments. Another troublesome condition is Morton’s neuroma.
This problem is due to irritation of one of the nerves that retrieves sensory information from the toes. These nerves begin as a trunk called the posterior tibial nerve, which begins in the lower leg , courses down the calf, curving around the inner bony prominence of the ankle, called the medial malleolus. Below the medial malleolus, the nerve gives off some branches to the heel, and then traverses a tunnel called the tarsal tunnel, analogous to the carpal tunnel in the wrist. The nerve subdivides within the sole of the foot, with branches that connect the intrinsic foot muscles to the central nervous system. Between the slender metatarsal bones, the nerves subdivide for the last time, and at this great distance from the brain, carry only sensory fibers from the toes. It is in this remote location that a Morton’s neuroma may form.
This condition arises when there is pressure on the nerve, usually secondary to pressure between the metatarsals. At this site, the nerves are a “Y” shape, with the stem formed by the last main trunk, and each arm of the “Y” a branch to the side of each toe. It is important to appreciate the fact that the stem portion is in the base of the web space between each toe, such that the arms go to the sides of adjacent toes. Thus with pressure to each stem segment near the web space between the toes, the more distal sides of two adjacent toes will be affected. Since these are sensory nerves, pain and numbness are characteristic.
The most common location is the third web space, i.e.- between the 3rd and 4th toes, where toe #1 is the big toe, or hallux. Usually the process begins as inflammation of the nerve, and as such there may be swelling or fullness within the web space. As the process continues, one can often feel the swollen nerve segment, referred to as a “cocktail onion” sensation. With chronicity, the nerve begins to form scar tissue, and a mass. But early on there may be no palpable lump.
There is usually pain under the ball of the foot, which may radiate to the involved toes. There may be a sensation of something “rolling or sliding around” under the foot, or of a catching sensation. Pain is typically worse with weight-bearing activity, and running may be progressively difficult. The most common causes of this problem stem from inadequate footwear, and chiefly from inadequate room for the toes, or a tight toe box. Thus this problem is most often seen in women runners who wear tight, high-heeled shoes by day. Runners do not have an increased incidence of this condition relative to sedentary individuals, but there may be more disability in a runner with a neuroma.
Treatment is logically aimed at reducing pressure on the nerve, by changing to footwear that has a roomy toe box with a low heal. A soft metatarsal pad placed just behind the the ball of the foot can help a great deal; its purpose being to relieve direct pressure on the nerve, and to help the metatarsals spread out. Some running shoes have forefoot pads to cushion this portion of the foot. In my experience, they are a mixed blessing. I have seen both initiation of this problem, as well as relief from it, after switching to this design. Anti-inflammatory medications may help in the acute stage, as well as the application of ice. If chronic however, these symptoms are not likely to recede so easily, and rest, injections and surgery may be necessary.