Metatarsalgia/Morton’s neuroma/Intermetatarsal Neuropathy

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Morton’s Neuroma – Intermetatarsal Neuropathy

There is a painful condition of the forefoot that feels like an electrical shock.

This feeling of walking with a stone under the ball of your foot will quickly limit your activity level. There could be many reasons that pain to the ball of the foot could happen. Your doctor will need to perform a thorough examination and only your doctor can diagnose your condition. This section explains the mechanical reason for nerve disease between the metatarsal heads. Let’s explore why this is such a painful issue and why historic treatments don’t make a lot of sense.

Foot with painful condition - Morton’s Neuroma

What is a Morton’s Neuroma?

There is a nerve located between the heads of the 3rd and 4th metatarsal bones that develops a nerve callus. There is a swelling of the nerve that gets bigger and bigger. This condition is referred to as a Morton’s neuroma after Dr. Thomas George Morton who published an article in 1876 describing this condition. It was previously published by Filippo Civinini in 1835 but news back in those days did not spread as far and wide as it does now.

foot with visible nerve-callus and swelling metatarsal bones

This is a specific condition that is found between the heads of the metatarsal bones of the foot.

The most common location is the 4th interspace between the 3rd and 4th toes but they are commonly found in other intermetatarsal spaces as well. The nerve within this space develops swelling of specialized nerve tissue. Neuroma means “nerve tumor” but that is somewhat of a mischaracterization of what is actually happening. It is more of a nerve callus, a thickening of tissue as a result of mechanical trauma. Just like when you get a callus on your toe. It occurs due to excessive, repeated micro-trauma. After decades of millions and millions of steps, this nerve callus forms as a protective mechanism. Just like that callus on the toe, this nerve callus will eventually reach a point when it gets very painful. The big difference between a callus on your skin and one on the nerve inside your foot is that the callus on your toe can get reduced with a pumice stone. The poor nerve within your foot does not have that luxury. Meanwhile, every step is a reminder that the nerve callus is there.

Feet with normal nerve, mild nerve callus, moderate nerve callus, severe nerve callus

When a nerve is subjected to repeated microtrauma, it will eventually react as a form of self-protection like that callus on the bottom of a foot is trying to protect the skin.

This is only a temporary solution because, just like that callus, it will continue to grow since the underlying cause is still there causing more micro-trauma. Eventually, the callus gets so big that it is no longer part of the solution, it becomes part of the problem. Just like a callus, it can get thick enough that it causes a blister or even worse an ulcer.

The micro-trauma on the nerve happens during the walking cycle. There is a specific point when the heel lifts off the ground which causes compression of the nerve. Damage occurs when walking; no walking – no damage. Nerves can heal from a reasonable amount of strain/compression. Eventually, that micro-trauma takes its toll and a point is reached when the nerve is no longer able to repair during the night when you are sleeping and off of your feet.

Once the nerve reaches a certain point in the disease process it will give you a signal – PAIN! That is a warning signal that something is wrong. Both pain and numbness can be experienced. Nerve disease is called neuropathy. Once this has occurred attention needs to be directed immediately because failure to eliminate the trauma will result in permanent nerve damage.

How do we know this is the case? When surgeons remove the nerve callus from someone’s foot, they send it for analysis. The typical findings are:

  1. Fibrosis around and within the nerve
  2. Schwann cell and fibroblast proliferation
  3. Loss of myelinated nerve fibers

What that means is there is scar tissue surrounding and inside the nerve.

Scar tissue develops after trauma. The Schwann cell and fibroblast proliferation are signs that the nerve is trying to repair itself from the trauma but at the same time there is also more scar tissue thickening. Finally, the loss of myelin means that the important nerve fibers are no longer connected. It’s like the wiring to the light switch has worn away – that means loss of nerve function.

Why do people get nerve-calluses?

An online search for the cause of nerve callus formation is pretty generic. They claim it’s from wearing tight shoes, running, high arched feet, and low arched feet. There is an underlying condition that is seen in the majority of people with nerve calluses which has to do with ankle bone instability. A stable ankle bone on the heel bone means a stable foot structure. A partially dislocating ankle bone on the heel bone leads to excessive forefoot motion. Let’s take a closer look. The bones of the foot are divided into 2 columns, the inner/medial and outer/lateral. The inner column of bones is allowed to have a slight amount of motion. The outer column of bones should have little to no motion. That slight amount of motion between the inner and outer columns allows the foot to handle an uneven ground surface. Ankle bone instability, the partial dislocation of the ankle bone in the heel bones leads to excessive inner column motion. So, what does all of this have to do with forming a nerve callus? Everything. Where do we see the most common location of the nerve callus? Between the 3rd and 4th metatarsal bone. This is between the inner and outer columns of foot bones.
Ankle bone instability pushes the inner column of foot bones away from the outer column of bones. The excessive motion, even a slight amount, is going to put a strain on the ligaments between the heads/necks of the 3rd and 4th metatarsal bone. That strain is the micro-trauma that is inflicted on the nerve. That strain happens with every step taken and constantly when standing. That’s thousands of times per day.

When do people start developing pain from the nerve callus?

It is usually when they are over 40 years old. At that point in life, they have taken over 72 million steps. That’s 72 million times the nerve had micro-trauma. Imagine tapping your finger on the table 72 million times. Eventually, you will develop a callus and then an ulcer due to the repeated trauma.

Why is intermetatarsal neuropathy a bad thing?

Nerve pain can be extremely painful. That’s why it’s a warning signal that something is wrong. More foot pain leads to decreased activity level meaning you are not burning off the calories from the food you eat. Eventually, weight gain will occur which leads to other metabolic issues such as diabetes, hypertension, and heart disease. The nerve damage will continue to get worse with every step taken. It is very rare for this condition to just go away on its own when the underlying cause is still present.

What is the best form of treatment?

There are many different treatments for damaged intermetatarsal nerves. Injections will provide temporary relief. Some physicians recommend injections to “kill” the nerve. The only problem is that nerves will regenerate. How do we know? Many people have their nerves cut out only to have the nerve pain reoccur. The surgeons go back in a second time to cut off the nerve and it was back. The best way to treat a nerve that is being compressed and strangulated is to cut the noose that causing the damage. It is better to cut that tissue than to cut out the nerve. The only issue with cutting the noose is that it can grow back, and the ankle bone instability is still present. So, it would make sense to have a combination of procedures. First, stabilize the ankle bone with HyProCure to prevent the excessive metatarsal motion, then cut the noose.

What happens if you don’t treat intermetatarsal neuropathy?

The nerve will continue to form a callus and create more and more pain. It is possible that eventually, the nerve will become so damaged that it will stop transmitting nerve impulses. In other words, you could end up with numb toes. Also, you could develop cold toes because the blood flow to the toe could also be affected.

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