One of the most common masses in the foot is a plantar fibromatosis. Commonly called a plantar fibroma, this benign mass is an enlargement of the tissue that is found in a structure called the plantar fascia. This strap-like band of tissue runs from the bottom of the heel to the ball of the foot. Occasionally, the material that composes this tissue begins to grow rapidly, and results in a round to oval shaped mass. This mass is usually found in the middle of the arch, but can be present in numerous areas on the bottom of the foot. Plantar fibromas can grow quite large, and can have multiple surfaces or lumps. More than one mass can also develop.

The cause of these masses may be genetic, and also may be related to trauma or injury to the fascia. Symptoms include a mass that can be felt under the skin, that may cause pain when bearing weight on that foot. Barefoot walking can become uncomfortable, and sometimes even well cushioned shoes can be painful to wear and walk in. This condition can be compounded if the mass pushes against one of the numerous nerves that lie within the foot, and large masses can stretch the skin out.

Treatment depends on further diagnostic study beyond the physical exam to ensure the mass is a simple fibroma, and not a more serious malignant mass. Usually an MRI is performed, which can verify where the mass is coming from. If it is clearly from the plantar fascia, and does not exhibit aggressive expansion or atypical shape, then one can likely assume the mass is a benign plantar fibroma. If the MRI findings are inconclusive or atypical, or if the mass demonstrates unusual syptoms or characteristics, then a biopsy needs to be performed to ensure the mass is not a malignant tumor (which is very uncommon). Malignant masses require extensive treatment, including extensive surgical excision or possibly amputation. In contrast, treatment for plantar fibromas is much simpler. The two treatment options for plantar fibromas include padding and shoe accomodation to make the mass easier to walk on, or surgery to remove it. Minor masses and larger ones that are not very painful can be simply treated with padded shoe inserts or custom made padding to reduce pressure. The continued presence of the mass generally does not pose a risk, and it can remain in the foot as long as there are no symptoms. However, the only way to resolve the condition once and for all is to surgically remove it. This is certainly the treatment of choice for painful plantar fibromas. Unfortunately, there is a risk that the masses will return elsewhere in the remaining fascia, as regrowth following surgery is not uncommon. Large masses can leave a big deficit of tissue under the bottom of the arch when removed, and a tissue graft is usually placed in the space to help maintain the integrity of the plantar fascia as a whole. Newer graft materials allow fascia tissue to integrate into the graft, eventually turing the graft into fascia tissue and restoring the length of the fascia. This surgery is generally performed on an outpatient basis.