Swan-neck deformity is -
Important hand deformities of hand in RA

Boutonniere deformity: Flexion contracture of PIP joint and extension of the DIP joint.
Swan neck deformity: Hyperextension of PIP joint and flexion at DIP joint.
Z-deformity: Radial deviation of the wrist with ulnar deviation of fingers.
Hyperextension of 1st interphalangeal joint and flexion of MP joint.