A Lump in the Sole of the Foot – Plantar Fibromas Explained

Anytime one feels a lump in the body, mental alarm bells ring out with fears of cancer. This natural reaction is fairly universal for most people. When the lump is felt in the bottom of the foot, where it can cause pain with every step, the fear can be even greater owing to the noticeable symptoms the lump has when walking or standing. Fortunately, true malignant tumors of deep tissue in the foot are very rare. However, it is not uncommon for many people to develop a benign firm mass on the bottom of the foot arch called a plantar fibroma (or superficial fibromatosis).

Plantar fibromas develop from a part of the foot known as the plantar fascia. The plantar fascia is a thick, strap-like dense tissue that connects the heel bone and the ball of the foot. This tissue is broad, traversing across the entire width of the foot in three distinct bands. It is essentially a thick ligament, and provides some rigidity to the arch of the foot. In some people, small nodules, or growths, can develop along the surface of the fascia, and can slowly expand over time. These growths can be single, multiple in number, or one mass with numerous areas of bulging. The nodules are well affixed to the fascia, and do not move when one tries to move the overlying skin around. In general, these nodules grow very slowly, and do not appear ‘overnight’. However, they may seem to suddenly appear as most people cannot feel them until they become very large or develop pain. At times, people who rub their feet might notice them early on, but most people only notice the mass all of a sudden when it is big enough to expand the underlying skin or is tender to pressure. One can rest assured that these masses are benign, and conversion to a malignant cancer (fibrosarcoma) is almost unheard of.

Symptoms are usually related to irritation of the fascia tissue and inflammation around the nodule when one stands on the foot and places pressure on the fibroma. Many of these plantar fibromas are painless masses that are not irritated by pressure on the sole of the foot. Some are painful, though, and can limit one’s ability to comfortably walk. This is especially true when the mass pushes into a sensitive tissue, such as one of the many nerves found traversing the bottom of the foot above or below the plantar fascia. Barefoot walking and shoe use can be uncomfortable due to the ‘lump’, and other parts of the plantar fascia can become irritated as a result.

Treatment is geared towards either accommodating the mass to make those who suffer with it more comfortable, or removing it all together. It should be noted that if the mass does not cause any discomfort, it does not need to be treated. Its growth cannot be slowed or prevented with early treatment, and aggressive treatment of a non-painful plantar fibroma is not necessary. When there is pain involved, treatment with accommodation or removal is clearly recommended. Accommodating the mass involves the use of stretches to keep the fascia limber, anti-inflammatory medication, and accommodative inserts that pad and protect the area around the mass. In some people with painful plantar fibromas, this can help relieve, or at least temporarily control, the pain. If this is not effective, then surgery is typically needed to remove the mass itself. This surgery can run the range from simple to highly complicated depending on the size of the mass. Small plantar fibromas are easily removed with out too much tissue loss, and the resulting tissue gap can eventually fill with scar tissue to keep the structure of the plantar fascia intact. In any removal procedure, it is vital that all of the fibroma, along with a margin of normal fascia and the overlying under surface of the skin be removed to help prevent recurrence. Medium and large size fibromas are much more difficult to remove. Their removal causes large gaps in the plantar fascia, and can effect the stability of the bottom of the foot to a certain degree. This also leaves open an internal area that can be apt to developing scars and adhesions in the surface under and on the skin. At times, the resulting tissue can potentially be more painful than the original fibroma if healing is poor. These gaps need to be filled in if possible to maintain integrity of the fascia and limit scar tissue. Newer tissue grafts that act as scaffolds for whatever tissue is attached to them can help with this problem. The remaining fascia tissue will creep into these grafts, effectively restoring the fascia to a similar state as before surgery (and before the mass). Whether large or small, all plantar fibromas have a fairly high rate of recurrence, and even the best surgical technique cannot necessarily prevent this from happening. Simply put, some people quickly regrow these masses even after removal. This is not a sign so much for malignancy as much as it’s a sign of a common problem after excision surgery for plantar fibromas. There is no way to effectively control this potential for regrowth after surgery unfortunately.

One final note should be made regarding plantar fibromas, and foot masses in general. As stated previously, true deep foot malignant tumors are very rare…but they do occur. It is recommended that a medical evaluation by a foot specialist (podiatrist) be performed to ensure that the mass felt is simply a common plantar fibroma. An MRI may need to be performed if there are unusual characteristics to the shape or location of the mass (or even if surgery to remove it is being planned). Less commonly, a biopsy may be considered if there is great abnormality or questionable findings on the exam. While all this may seem like a lot of time and money for a little mass, it can potentially make the difference between a healthy foot and a leg amputation if there truly is something more abnormal to begin with.