Plantar callus: Throw the kitchen sink at it

A plantar callus is that thick hard skin that builds up under the ball of the foot. The skin progressively gets thicker with time and more painful when it becomes too thick. Plantar calluses, technically known as a hyperkeratosis, are a common problem that can cause pain under the ball of the foot.

Symptoms of a Plantar Callus

A plantar callus feels harder than the surrounding skin. It tends to have a more yellowish or whiter appearance than the surrounding skin. The callus may be under a discrete metatarsal head or more diffuse and over several metatarsal heads. The skin lines that pass through a callus tend to be more widely separated than those on the normal skin. They will become painful when the calluses are thick enough to cause the pain.

Just because a plantar callus is present does not mean that it is the cause of the symptoms. If the callus is under the first metatarsal head, then there could also be a sesamoiditis present as well, so treatment of the callus may not relieve symptoms. There are other causes of metatarsalgia that could also be coincidentally present with a plantar callus. It is important to check for these as the callus which is usually the most obvious may not necessary be the reason for the pain or discomfort.

Cause of a Plantar Callus

The cause of a plantar callus or a callus anywhere is too much pressure. For some reason, if there is too much pressure on an area, the skin thickens up to protect itself. This is quite a normal process (for example, the calluses you get on your hands if you use an axe to chop of lot of wood). The problem comes about if the higher pressure continues and the skin keeps on getting thicker. It will eventually get so thick that it becomes painful.

There are many reasons for that increased pressure on any specific area under the ball of the foot leading to the plantar callus. For example:

there may be a plantarflexed first ray that leads to increased pressure under the head of the first metatarsal bone causing the callus, or even a sesamoiditis.
as well as the first ray being in a plantarflexed position, this could affect any of the metatarsal bones leading to higher pressure under them.
things like a hammer toe or claw toe, put a retrograde pressure on the metatarsal causing more pressure under the metatarsal head on the ball of the foot (and there may also be a callus on the top of the hammer toe).
the first and fifth metatarsals may be elevated somewhat, resulting on the middle three metatarsals taking all the weight and pressure leading to a more diffuse callus across the middle of the ball of the foot
there may be some plantar fat pad atrophy under the ball of the foot, meaning that the metatarsal heads loose some of their protection and cushioning.
there may be an old fracture that has healed with poor alignment causing problems with increased pressure in some locations.
problems like bunions and a tailors bunion mean the affected metatarsophalangeal joint does not bear weight properly leading to an increase in pressure on the other metatarsal heads.
hallux rigidus typically can cause a plantar callus under the outer metatarsal heads as the big toe does not bear weight adequately due to the rigid joint.
high heel shoes will increase the pressures under the ball of the foot
tight fitting shoes will also increase pressure under different parts of the ball of the foot.
foot biomechanics or the way the foot moves may also increase pressure under different metatarsal heads under the ball of the foot. For example a higher arched foot (‘pes cavus’) leads to more pressure on the ball of the foot.
there could be any number of other reasons for altered weightbearing under the ball of the foot that can lead to a plantar callus from the higher pressures.

Identifying the cause of the higher pressures that are leading to the plantar callus are an important first step in the treatment.

Treatment of a Plantar Callus

The treatment approach to a plantar callus is based on: understanding; pain relief; pressure reduction

Understanding. It is important to understand the nature of a plantar callus. They are caused by too much pressure. Something is causing that pressure and that should be identified to remove the cause. Calluses, like corns, do not have roots or anything like that which they grow back from. They come back after being removed becasue the pressure that caused them is still there.
Pain relief. Pain relief from a callus is relatively straight forward. The callus needs to be removed. This can be done skillfully with a painless scalpel debridement by a Podiatrist or if you are careful and don’t have diabetes, you could use a electric callus remover. Do not use a medicated corn or callus pad. They contain an acid that is supposed to eat the callus or corn, however, the acid does not know what is normal skin and what is callused skin, so its to easy to have a problem, especially if you have diabetes or fragile skin. This part to get rid of the plantar callus is relatively easy. The only issue is, that this will not stop it happening again as the cause of the higher pressure is still there. It may need to be removed again anywhere from 4-6 weeks to a year or so, depending on the nature of the higher pressure and the resilience of the skin.
Pressure reduction. Once the cause of that higher pressure is identified, then steps can be taken to reduce it. This could be as simple as changing to a wider fitting and lower heel shoe or it could be as complicated as surgery to elevate the metatarsal bone so that there is no pressure coming from under the metatarsal head. Foot orthotics or supports are often used which might use a thicker material where the callus isn’t and thinner over the callus – this has the effect of spreading out the weight over the whole foot and not just on the higher pressure area. If a hammer toe or bunion is the reason for the increased pressure, then they are going to need to be dealt with over the long term. The key to the pressure reduction is the identification of the cause.

Personal Opinion on Plantar Calluses

These are going to be an ongoing problem. Either see a podiatrist to come up with a plan for regular pain relief, or even better to work out why you have it and come up with a plan to reduce the pressure that is causing the problem. If you do not want to see a podiatrist, you can use things like the electric callus removers, but this is going to be an ongoing problem until you address the cause.