Intermetatarsal (Morton's) Neuroma
Forefoot and Toe Pain
This is one of the most common problems affecting the foot of an adult. It tends to affect women much more often than men probably owing to the use of high-heeled shoes. The nerves are tensed stretching them over and between the metatarsal heads (balls of the forefoot); over the long term this causes swelling and scarring of the nerve. The nerve irritated in this way will cause a sensation of either pain and/or numbness. The pain can be localized or can be throughout the toes.
This problem has to be distinguished from metatarsalgia. Metatarsalgia is a term that means “pain in the forefoot related to poor weight distribution across the ball of the feet.” Metatarsalgia is usually solved with shoe inserts and improved footwear, i.e. better padding of the foot and better weight distribution. It is usually a little bit difficult to be certain whether a person has Morton’s neuroma or metatarsalgia, however, Morton’s neuroma tends to be localized more to one location, i.e. either one or two web spaces, as opposed to metatarsalgia which one would anticipate more soreness directly under the ball of the foot (metatarsal heads) as opposed to into the web spaces. Metatarsalgia does not include numbness since in that case a nerve is not specifically injured.
In order to avoid unnecessary surgery and the minor risks of a necessary surgery, in the case of metatarsalgia and Morton’s neuroma “cortisone” injection (dexamethasone, betamethasone, etc.), a nonsteroidal anti-inflammatory medication such as meloxicam, naproxen, or Celebrex (NSAIDs), plus shoe inserts are typically the first line of care. Avoidance of pointy-toed and high-heeled shoes and shoes with extremely thin soles is also necessary. If this means of treatment fails to provide relief, surgery may be beneficial. Tibial nerve entrapment in the tarsal tunnel may be the problem, i.e. entrapment of the main nerve from which the digital nerves arise. This is sometimes difficult to determine and involves tapping on the nerve at the ankle and may require nerve conduction testing as well. It is not unusual for the nerves to be entrapped both at the tarsal tunnel (ankle) and at the intermetatarsal area which is analogous to a person having entrapment of the ulnar nerve at the elbow and at the wrist as well, dual-level entrapment. Of note is that the person who develops tarsal tunnel syndrome frequently is the same person who has or has already been treated for carpal and/or cubital tunnel syndrome, i.e. entrapment of nerves in the upper extremities. This suggests some sort of predisposition to nerve irritation from local pressure.
The mainstay of surgical treatment for resistant Morton’s neuroma for years has been removal of the damaged portion of the nerve. This is known as a “Morton’s neurectomy”. Though this usually works to get rid of the pain, it also renders the involved toes permanently numb. Sometimes the person gets neuromatous pain, i.e. pain at the end of the cut off nerves, requiring further treatment. Though this treatment has fallen out of favor, many surgeons who have used it for years have continued to offer only this. Much better treatment has evolved. The best surgical treatment is endoscopic. Release of the intermetatarsal ligament, i.e. the tight band holding adjacent metatarsals close together, thus takes the pressure and strain off of the common digital nerve. This treatment does not hurt much, the patient can immediately walk on their foot, and it does not render the toes numb. If this were to fail, Morton’s neurectomy would always be a back-up but is rarely indicated.
Over 10 years ago an endoscopic technique was developed for release of the intermetatarsal ligament and minimized discomfort through a tiny incision in two places on the foot. This is a minor outpatient surgery that can be done exclusively under local, however, local plus IV sedation to relieve anxiety is the preferred anesthesia. Endoscopic technique means that an arthroscope is utilized to provide visualization through a tiny wound while using instruments via other tiny wounds monitoring the whole procedure on a flat screen.
Endoscopic intermetatarsal neuroma decompression requires inserting a thin, slotted, stainless steel tube from one puncture wound to the other beneath the intermetatarsal ligament visualizing with a scope from one end of the tube, inserting a hooked knife through the other end of the tube, and releasing the intermetatarsal ligament under direct vision while the metal sides of the tube protect the digital nerves and arteries.
It is essential to keep the foot clean for about five days to prevent infection. It may require longer in some patients. The foot can be a dirty area and a person must wear clean socks and it would probably be a good idea to cleanse the inside of the shoe with iodine or alcohol unless a simple postoperative shoe (open-toed postop slipper) is worn.
History of Care
Decompression of the intermetatarsal neuroma rather than removal was first reported in 1979. At the time of introduction, the surgeon, Guathier, reported his results in 304 patients. Since that time the treatment has been championed by Dellon at Johns Hopkins and the endoscopic technique to provide this treatment was developed and promoted by Barrett in Houston.
Risks of Surgery
The risks of surgery are very small but the predominant risk is that of infection. There is a small possibility of nerve injury, i.e. temporary or permanent numbness in the nerve. Some patients will fail any treatment and thus a rare person will fail to get relief from decompressing the intermetatarsal neuroma. Fortunately, this is not common.