Get access to everything we publish when you sign up for Outside+.
The bottom of our feet really take a pounding. There’s no way to get around that, especially for runners. And while it might feel like they were built to do so, there are some considerations to keep in mind as far as keeping them healthy.
If you have something like a knot forming on the bottom of your foot, it may be time to pump the breaks on that daily pounding. A knot on the bottom of your foot could be a sign of plantar fibroma, an “uncommon and challenging disorder,” as it was described in a recent study published in Orthopedic Research and Reviews.
The cause of plantar fibroma is widely debated. A 2018 genetic study conducted at Stanford University Medical Center showed an association with DNA variants that could explain why some people are more likely to have plantar fascial problems (including both plantar fasciitis and plantar fibroma). But overall, “there are differing opinions in the literature about trauma being a causative force,” says Dr. Priya Parthasarathy, a board-certified podiatrist. “Some patients on Dilantin [an anti-convulsive medicine] can develop nodules. Also some comorbidities such as epilepsy, alcoholism, liver cirrhosis, hypothyroidism, and diabetes mellitus may have an increased incidence of plantar fibroma.”
Though it may not be among the most common foot problems known to runners, it can be a real pain in the…foot. Here’s what you need to know about plantar fibroma.
Plantar Fibroma vs. Plantar Fasciitis: What is the Difference?
As a runner, you may be more familiar with plantar fasciitis. But if you’re seeking treatment on your feet, you’ll want to know the difference between it and the less common plantar fibroma.
“[Plantar fasciitis] is an inflamed tissue and not associated with a mass being present,” says Dr. Scott Nelson, president of the American College of Foot and Ankle Surgeons. Plantar fasciitis is more connected to heel pain, while plantar fibroma is felt in the middle part of the foot.
Plantar fibroma is the name of a nodule, growth, triggerpoint, or knot embedded in the plantar fascia on the bottom of the foot. The plantar fascia is the band of tissue that is under the bottom of the foot, extending from the toes to the heel. The condition is caused when the plantar fascia tightens up.
“Plantar fibromas are not very common, as the majority of runners are way more likely to be impacted by plantar fasciitis as opposed to a fibroma,” says Dr. Zachary Flynn, a board-certified foot and ankle surgeon.
Plantar Fibroma Symptoms
Rebecca Goldstein, physical therapist with Professional Physical Therapy, describes the symptoms as follows:
- Tightness on the bottom of the foot
- Pain and stiffness with walking
- Morning stiffness when taking that first step out of bed
- Calf tightness
- Pain when walking barefoot
Though they don’t know exactly what causes plantar fibroma, specialists have some ideas about how runners can prevent them.
For one, switching out your running shoes or investing in orthotics can help prevent the nodule from developing. The goal, says Dr. Flynn, is to “support the plantar fascia as much as possible to protect against the trauma of running.”
Goldstein adds that a tight Achilles or calf muscles may trigger plantar fibroma. “Over time your plantar fascia may tighten up,” she says.
Keeping a consistent stretching routine (perhaps as part of your cool-down) can help to keep that connective tissue loose. “Stretching the calf and foot is very important after running,” says Dr. Parthasarathy.
When to Stop Running and See a Doctor
If you start to notice a nodule developing on the bottom of your foot, Dr. Parthasarathy recommends you make an appointment to see an expert.
Diagnosing plantar fibroma is relatively simple. Your provider will probably make the diagnosis by feeling the enlarged mass, however, “the growth is sometimes evaluated with an X-ray to make sure there are no bone changes or soft tissue calcification,” says Dr. Nelson.
For complete and regular access to more in-depth stories (like this Daily Mobility Challenge to Strengthen Your Stride), plus exclusive interviews and access to one-on-one service from top coaches and experts, join Women’s Running Pass or Active Pass.
All of the experts interviewed for this article said that if the growth is not causing you pain, it’s OK to continue to run on it. “If you notice the nodule grows in size and hurts to run on it, then stop running,” says Dr. Parthasarathy. That’s when it’s time to seek treatment and wait for the foot to heal.
If you choose to keep running, Dr. Flynn advises you keep this in mind: “Repetitive trauma can induce the fibroma to get larger, so it is a calculated risk.” Instead, try switching to a lower-impact cardio regimen (biking, aqua jogging, swimming, for example) temporarily.
But you really should take time off when you experience any sort of foot pain. If not, you may compensate your foot strike, which can lead to other injuries: hip, knee, or low-back pain.
Treating Plantar Fibroma
A few weeks is the typical treatment time for plantar fibroma. Massaging the foot with a foam roller, tennis ball, or frozen water bottle can help release tension in the foot. Stretching the foot is important too. It can lengthen the tissues and increase circulation.
“The goal of treatment is to reduce pain, halt progression of the fibroma, and enhance the health of the surrounding tissue,” says Dr. Flynn. But none of those at-home treatments will make the nodule go away entirely. “The smaller the lesion at the time we initiate conservative treatment, the more likely you will be able to avoid surgery,” he says.
Before surgery becomes an option, you may want to talk with a physical therapist. Physical therapists use effective stretching with strength exercises to treat the condition. Their techniques may be able to break down the buildup of fibers and growths, depending on how advanced the situation.
A podiatrist may prescribe a topical medication to reduce the nodule size or give you a corticosteroid injection to help with the pain. They can also help fit you with custom orthotics to offload the pressure on the nodules.
And, as Dr. Flynn notes, if all else fails and the mass continues to increase in size, surgery may be needed to remove it. But hopefully if you see a specialist and get help early on, that can be avoided.
Remember to take care of those feet so they can keep carrying you all the miles you want to go.