Swan-neck deformity is a bending in (flexion) of the base of the finger, a straightening out (extension) of the middle joint, and a bending in (flexion) of the outermost joint. The most common cause is Rheumatoid Arthritis
Boutonnière deformity (buttonhole deformity) is a deformity in which the middle finger joint is bent in a fixed position inward (toward the palm) and the outermost finger joint is bent excessively outward (away from the palm). Most common causes are Rheumatoid Arthritis and trauma
In trigger finger (flexor digital tenosynovitis), a finger becomes locked in a bent position. The finger locks when one of the tendons that flex the finger becomes inflamed and swollen.
A mallet finger is a deformity of a finger caused when a certain tendon (the extensor tendon) is damaged. When a ball or other object strikes the tip of the finger or thumb, the force damages the thin tendon that straightens the finger giving the patient difficulty straightening the tip of the finger