Patients with Morton’s neuroma present with pain in the forefoot, particularly in the “ball” of the foot. However, not all pain in the forefoot is a Morton’s neuroma. In fact, most chronic pain in the forefoot is NOT the result of a Morton’s neuroma, but rather is from metatarsalgia – inflammation (synovitis) of the “toe/foot” joints. The symptoms from Morton’s neuroma are due to irritation to the small digital nerves, as they pass across the sole of the foot and into the toes (Figure 1). Therefore, with a true Morton’s neuroma, it is not uncommon to have nerve-type symptoms, which can include numbness or a burning sensation extending into the toes. There are several interdigital nerves in the forefoot. The most common nerve to develop into a neuroma is between the 3rd and 4th toes. With a true neuroma, the pain should be isolated to just one or two toes.
In many cases, a neuroma may develop as a result of excessive loading on the front of the foot. Sometimes, a patient’s anatomic alignment in the forefoot contributes to the overload. There may be some cases where the neuroma develops spontaneously, for no obvious reason. However, once the nerve is irritated, pressure from walking, and from the adjacent bony prominences (metatarsal heads), as well as from the intermetatarsal ligament that binds the heads together, all may contribute to persistent pain. (Figure 2). Repetitive pressure on the nerve causes localized injury with resulting scarring and fibrosis of the nerve. This leads to symptoms in the distribution of the nerve.
Patients will feel pain that worsens with walking, particularly when walking in shoes with thin soles or high heels. Also, anything that squeezes the metatarsal heads together may aggravate symptoms, such as narrow shoes. A patient may feel the need to remove the shoe and rub the foot to soothe the pain.
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) (Figure 3). 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 (Figure 4).
Plain x-rays of the foot may demonstrate that one or more of the metatarsals are long (Figure #5). Not uncommonly, the second and/or third metatarsal may be long relative to the third or fourth. This can create a situation where excessive load is occurring in and around the vicinity of the interdigital nerve.
Most non-operative treatment is usually successful, although it can take a while to figure out what combination of non-operative treatment works best for each individual patient. Non-operative treatment may include:
It has been proposed that an alcohol injection in and around the nerve will cause a controlled death to the nerve and subsequently eliminate symptoms. In theory, this may be helpful. In practice, adequate prospective studies have not demonstrated the benefit of this procedure above and beyond the other standard, non-operative treatments available. In addition there is the concern that the alcohol will cause excessive scarring and damage to other important structures in the area.
Potential operative complications include:
Operative treatment of Morton’s neuroma should be entertained only after failure of non-operative management. Standard operative treatment involves identifying the nerve and cutting (resecting) it proximal to the point where it is irritated/injured. This is usually done through an incision on the top (dorsal) aspect of the foot, although an incision on the sole (plantar) aspect of the foot can be used.
Some physicians will attempt to treat Morton’s neuroma by releasing the intermetatarsal ligament, and freeing the nerve of local scar tissue. This may also be beneficial.
The ultimate success of a Morton’s neuroma treated surgically can be variable. In cases where the underlying problem is only an irritated nerve (a true Morton’s neuroma), then surgery will probably be curative (although it may take a few months for the foot to fully heal). But in many cases, forefoot pain is more complex. There may be an irritated nerve or two causing pain, but the real problem is often excessive loading of the lesser metatarsals. The generic term for this condition is metatarsalgia. When considering surgery, identifying and addressing these problems may lead to a better end result.