Morton's neuroma is an enlarged nerve that usually occurs in the third interspace, which is between the third and fourth toes. To understand Morton's neuroma further, it may be helpful to look at the anatomy of the foot. Problems often develop in the third interspace because part of the lateral plantar nerve combines with part of the medial plantar nerve here. When the two nerves combine, they are typically larger in diameter than those going to the other toes. Also, the nerve lies in subcutaneous tissue, just above the fat pad of the foot, close to an artery and vein. Above the nerve is a structure called the deep transverse metatarsal ligament. This ligament is very strong, holds the metatarsal bones together, and creates the ceiling of the nerve compartment. With each step, the ground pushes up on the enlarged nerve and the deep transverse metatarsal ligament pushes down. This causes compression in a confined space.
Morton's neuroma develops for several reasons. The primary reason is wearing narrow toe-box shoes, which compress the metatarsal heads. Certain anatomical factors also make nerve compression more likely with the narrow toe box shoes. In some people fibers, the medial and lateral plantar nerves converge close to the heads of the third and fourth metatarsals. This junction creates a larger nerve structure between the metatarsal heads making it more vulnerable to compression.
People with Morton's neuroma usually complain of pain that can start in the ball of the foot and shoot into the affected toes. However, some people just have toe pain. There may also be burning and tingling of the toes. The symptoms are usually felt up the sides of the space between two toes. For example, if the nerve between the third and fourth long bones (metatarsals) of the right foot is affected, the symptoms will usually be felt up the right-hand side of the fourth toe and up the left-hand side of the third toe. Some people describe the pain that they feel as being like walking on a stone or a marble. Symptoms can be made worse if you wear high-heeled shoes. The pain is relieved by taking your shoe off, resting your foot and massaging the area. You may also experience some numbness between the affected toes. Your affected toes may also appear to be spread apart, which doctors refer to as the 'V sign'. The symptoms can vary and may come and go over a number of years. For example, some people may experience two attacks of pain in a week and then nothing for a year. Others may have regular and persistent (chronic) pain.
During the exam, your doctor will press on your foot to feel for a mass or tender spot. There may also be a feeling of "clicking" between the bones of your foot. Some imaging tests are more useful than others in the diagnosis of Morton's neuroma. Your doctor is likely to order X-rays of your foot, to rule out other causes of your pain such as a stress fracture. Ultrasound. This technology uses sound waves to create real-time images of internal structures. Ultrasound is particularly good at revealing soft tissue abnormalities, such as neuromas. Magnetic resonance imaging (MRI). Using radio waves and a strong magnetic field, an MRI also is good at visualizing soft tissues. But it's an expensive test and often indicates neuromas in people who have no symptoms.
Non Surgical Treatment
If your Morton's neuroma is painful, your doctor usually will begin treatment with conservative therapies, including a switch to shoes with low heels, wide toes and good arch support. Padding techniques, including metatarsal pads or toe crest pads. Shoe inserts (orthotics) to help correct any mechanical imbalance in the foot. Anti-inflammatory medication, such as ibuprofen (Advil, Motrin and other brand names) or naproxen (Aleve, Naprosyn and other brand names) A local injection of anesthetic and corticosteroid medication into the affected area. Inflamed or injured nerves can take months to improve, even after the underlying problem has been corrected.
Patients are commonly offered surgery known as neurectomy, which involves removing the affected piece of nerve tissue. Postoperative scar tissue formation (known as stump neuroma) can occur in approximately 20%-30% of cases, causing a return of neuroma symptoms. Neurectomy can be performed using one of two general methods. Making the incision from the dorsal side (the top of the foot) is the more common method but requires cutting the deep transverse metatarsal ligament that connects the 3rd and 4th metatarsals in order to access the nerve beneath it. This results in exaggerated postoperative splaying of the 3rd and 4th digits (toes) due to the loss of the supporting ligamentous structure. This has aesthetic concerns for some patients and possible though unquantified long-term implications for foot structure and health. Alternatively, making the incision from the ventral side (the sole of the foot) allows more direct access to the affected nerve without cutting other structures. However, this approach requires a greater post-operative recovery time where the patient must avoid weight bearing on the affected foot because the ventral aspect of the foot is more highly enervated and impacted by pressure when standing. It also has an increased risk that scar tissue will form in a location that causes ongoing pain.