Some disorders, such as rheumatoid arthritis, and injuries can cause the fingers to bend abnormally. In swan-neck deformity, the joint at the base of the finger bends in (flexes), the middle joint straightens out (extends), and the outermost joint bends in (flexes). In boutonnière deformity, the middle finger joint is bent inward (toward the palm), and the outermost finger joint is bent outward (away from the palm).