One cause of a lump on the arch of the foot is a plantar fibroma, which is a non-cancerous tumor, notes the American College of Foot and Ankle Surgeons. Once it appears, the plantar fibroma does not go away or shrink without treatment. The exact reason why a plantar fibroma forms is not clear, as of 2015, but it is most likely genetic, states the American Orthopaedic Foot & Ankle Society.
A plantar fibroma is a lump that consists of cells found in the ligaments of the foot. It grows in the plantar fascia, which extends from the toes to the heel, notes the American College of Foot and Ankle Surgeons. Plantar fibromas typically occur in adults aged 20 to 70.They are slow growing and measure less than an inch. Some lumps in the arch of the foot are rapid-growing benign nodules known as plantar fibromatosis, notes the American Orthopaedic Foot & Ankle Society. The first sign that a plantar fibroma is forming is a noticeable firm lump in the foot. Patients can have more than one plantar fibroma, and may or may not feel pain. Pain generally occurs when the shoe pushes against the plantar fibroma.
There are several forms of non-surgical treatment available, states the American College of Foot and Ankle Surgeons. Steroid injections may help decrease the size of the lump and relieve pain. Shoe inserts can also help with pain if the lump is not increasing. Patients who do not want to receive injections may also may be able to relieve pain with physical therapy. If the pain does not go away or the plantar fibroma increases in size, it may be necessary to undergo surgery.