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.
Unfortunately, the cause of Morton?s Neuroma remains unknown to researchers. It is likely that a variety of factors may play a role in the development of this condition, including the presence of chronic pain conditions like fibromyalgia. Factors that may contribute to the development of Morton?s Neuroma include Wearing improperly fitting shoes can cause pressure on your foot, leading to swelling around the toe nerves. High heels are of particular concern as they cause a large amount of weight to be shifted to the ball of the foot. Repetitive activities like jogging, walking, and aerobics can also place a lot of pressure on the feet. This could lead to Morton?s Neuroma. Having a previous foot or muscle injury may cause you to hold your foot in a poor position when walking, contributing to nerve inflammation. Some people are just born with poorly shaped feet. People with extremely low arches or "flat feet" may suffer from Morton?s Neuroma more than others.
Pain is usually increased by forefoot weight bearing activities (such as running), with narrow-fitting footwear, or with high heeled shoes. It is usually painful to firmly touch the affected region and, in chronic cases, pain and sometimes an audible click, may be heard when squeezing the foot and toes together with the hand. Often a localized area of swelling may be evident at the site of injury.
Patients with classic Morton?s neuroma symptoms will have pain with pressure at the base of the involved toes (either between the 2nd and 3rd toes, or between the 3rd and 4th toes). In addition, squeezing the front of the foot together can exacerbate symptoms. As well, they may have numbness on the sides of one toe and the adjacent toe as this corresponds with the distribution of the involved nerve.
Non Surgical Treatment
The first line of treatment is to try modifying footwear. Often simply wearing broader fitting shoes can reduce pressure on the neuroma and so reduce pain. Orthotic inserts can also help as they can again help reduce pressure on certain parts of the foot. Padding and taping the toe area is another option. In some cases a steroid injection into the foot may be suggested. This can be done as a day case without the need for anaesthesia and helps reduce inflation of the nerve. It can halt the pain in round 70 % of cases. Sometimes a combination of alcohol and local anaesthesia may be injected as this helps reduce pain.
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.