Long Island Foot and Ankle Group July 2, 2018 foot conditions, foot pain Treating a Plantar Fibroma Long Island Foot and Ankle Group July 2, 2018 foot conditions, foot pain Finding a lump in your foot can be alarming. At Long Island Foot & Ankle Group, PC, patients are relieved when we tell them a fibrous knot in the arch of their foot is a plantar fibroma, which is not malignant.