Morton's neuroma is a condition that affects one of the nerves that run between the long bones (metatarsals) in the foot. The exact cause is not certain. Symptoms include pain, burning, numbness and tingling between two of the toes of the foot. About a third of people just need simple treatments including modification of their footwear. Sometimes surgery is needed for long-standing (chronic) symptoms.
Some anatomy of the foot
There are many bones in the foot. They can briefly be divided into the tarsal bones, the long bones (metatarsals) and the phalanges. The tarsal bones are the larger bones that form the back section of the foot, with the calcaneum being the largest. There are five metatarsal bones and these are given names from the first to the fifth. The first metatarsal bone is the largest and is the bone that joins to the big toe. Each toe has three phalanges, except the big toe which only has two.
There are many nerves, muscles and ligaments within the foot. Of note, the common plantar digital nerves run between the metatarsal bones in the foot. These have branches that supply sensation to the skin of the toes.
What is Morton's neuroma?
Morton's neuroma is named after Dr Morton who first described this condition in 1876. It is sometimes called Morton's metatarsalgia or interdigital neuroma.
It is a condition that affects one of the common plantar digital nerves that run between the long bones (metatarsals) in the foot. It most commonly affects the nerve between the third and fourth metatarsal bones, causing pain and numbness in the third and fourth toes. It can also affect the nerve between the second and third metatarsal bones, causing symptoms in the second and third toes.
Morton's neuroma rarely affects the nerve between the first and second, or between the fourth and fifth, metatarsal bones. It tends to affect only one foot. It is rare to have two neuromas at the same time in the same foot.
What causes Morton's neuroma?
Some say that this condition should not be called Morton's neuroma as, in fact, it is not actually a neuroma. A neuroma is a non-cancerous (benign) tumour that grows from the fibrous coverings of a nerve. There is no tumour formation in Morton's neuroma. Instead, there is a thickening of the nerve.
The exact cause of Morton's neuroma is not known. It is thought to develop as a result of long-standing (chronic) stress and irritation of a plantar digital nerve. This may be due to the nerve being squashed (compressed), rubbed, or stretched. Some thickening (fibrosis) and swelling may then develop around a part of the nerve. This can look like a neuroma and can lead to compression of the nerve.
The anatomy of the bones of the foot is also thought to contribute to the development of Morton's neuroma. For example, the space between the long bones (metatarsals) in the foot is narrower between the second and third and between the third and fourth metatarsals. This means that the nerves that run between these metatarsals are more likely to be compressed and irritated. Wearing narrow shoes can make this compression worse.
Sometimes, other problems can contribute to the compression of the nerve. These include the growth of a fatty lump (called a lipoma) and also the formation of a fluid-filled sac that can form around a joint (a bursa). Also, inflammation in the joints in the foot next to one of the digital nerves can sometimes cause irritation of the nerve and lead to the symptoms of Morton's neuroma.
Who develops Morton's neuroma?
About three people out of four who have Morton's neuroma are women. It commonly affects people between the ages of 40 and 50 but can occur at any age.
Poorly fitting or constricting shoes can contribute to Morton's neuroma. It is more common in women who habitually wear high-heeled shoes or in men who are required to wear tight (constrictive) footwear. It may also be more common in ballet dancers and runners. In some people there is no obvious cause.
What are the symptoms of Morton's neuroma?
People with Morton's neuroma usually complain of pain that can start in the ball of the foot and shoot into the affected toes. Some people just have toe pain. There may also be burning and tingling of the toes. 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.
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.
How is Morton's neuroma diagnosed?
Morton's neuroma is usually diagnosed by your doctor listening to your symptoms and examining your foot. Sometimes your doctor can feel the 'neuroma', or an area of thickening in your foot, which may be tender. Your doctor may press on the area between the long bones in your foot to try to find the tender spot.
Sometimes, your doctor may suggest an ultrasound scan or MRI scan to confirm the diagnosis but this is not always necessary. Occasionally other tests, such as blood tests or an X-ray may be needed to rule out other conditions.
What is the treatment for Morton's neuroma?
Non-surgical treatments may be all that are needed for many people with a Morton's neuroma. From the simple to the more technical, they include the following:
- Choosing the right footwear is very important. If you have a Morton's neuroma you should avoid high-heeled and narrow or pointed-toe shoes. Also avoid shoes with thin soles. Wear comfortable, wide-fitting shoes which don't squash your feet.
- Pads inside the shoes are often helpful. Shoe inserts (also called orthoses) for this condition can be bought in pharmacies over-the-counter. To protect the nerve, obtain a metatarsal pad, that is, a soft pad which sits below the ball of your foot. Follow the instructions to place the pad in the right place. It should fit behind the ball of your foot, rather than directly underneath it. Insoles with metatarsal domes may also be effective. These are cushions for the whole foot, with a raised dome-like area under the ball of your foot. It may be better to have an insole fitted by a trained foot specialist (podiatrist).
- Steroid or local anaesthetic injections (or a combination of both) into the affected area of the foot may be needed if the simple footwear changes do not fully relieve symptoms. This may be done by a specialist in ultrasound scans (radiologist), who injects whilst doing the ultrasound scan. It may also be done by a podiatrist, or an orthopaedic surgeon. However, the footwear modification measures should still be continued.
- Sclerosant injections involve the injection of alcohol and local anaesthetic into the affected nerve under the guidance of an ultrasound scan. Some studies have shown this to be as effective as surgery. However, this may not be widely available in the UK yet.
- Freezing (cryotherapy) is sometimes used but is not widely available in the UK.
- Radiofrequency ablation is another treatment which has been studied. This involves treating the nerve with heat energy waves. It is not yet proven how effective this is.
If these non-surgical measures do not work, an operation is sometimes needed. Surgery normally involves a small cut (incision) being made on either the top or the sole of the foot, between the affected toes. The surgeon will cut out (resect) the affected nerve. Alternatively, the surgeon may create more space around the affected nerve (known as nerve decompression). If the nerve is resected, there will be some permanent numbness of the skin between the affected toes. This does not usually cause any problems.
You will usually have to wear a special shoe for a short time after surgery until the wound has healed and normal footwear can be used again.
Surgery is usually successful. At least three quarters of people have a satisfactory result. As with any surgical operation, there is a small risk of complications. For example, after this operation a small number of people can develop a wound infection. Major problems after the operation are very rare.
What is the outlook (prognosis) for Morton's neuroma?
About one third of people with Morton's neuroma get better just with changing their footwear and using metatarsal pads. Of those who choose to have surgery, about three out of four will have good results with relief of their symptoms.
Recurrent or persisting (chronic) symptoms can occur after surgery. Sometimes, decompression of the nerve may have been incomplete or the nerve may just remain 'irritable'. In those who have had cutting out (resection) of the nerve (neurectomy), a recurrent or 'stump' neuroma may develop in any nerve tissue that was left behind. This can itself be very painful. In one in four people who have got better with an operation, the problem returns at a later date. It is important to keep wearing the right shoes to prevent this from happening.
Can Morton's neuroma be prevented?
Ensuring that shoes are well fitted, low-heeled and with a wide toe area may help to prevent Morton's neuroma.
Dr Michelle Wright
Dr Mary Harding
Dr John Cox