Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disorder that causes soft tissues to transform permanently into bone. These bones grow abnormally in the muscles, tendons, ligaments and other connective tissues, forming bridges of extra bone across the joints. As a result, movement in the areas affected by FOP is greatly restricted and sometimes impossible. The condition affects many areas of the body including, but not limited to, the neck, spine, chest, shoulders, elbows, wrists, hips and knees.