Doctors do no know the cause of plantar fibroma, though they think it is related to genetics, according to the American Orthopaedic Foot & Ankle Society. Foot trauma does not seem to be a cause.
A plantar fibroma is a benign, slow-growing nodule on the bottom of the foot, explains the American Orthopaedic Foot & Ankle Society. It generally is less than an inch in size and is composed of cells from ligaments. Plantar fibroma generally occurs in individuals between age 20 and age 60. A plantar fibroma nodule is painful, especially with pressure or wearing shoes. The nodule is typically located in the middle of the arch or instep of the foot, between the forefoot pad and the heel pad.