This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Orthopaedics
Swan-neck deformity is - 
Select and explain. 
A. Flexion of Metacarpophalangeal joint and extension at interphalangeal joint, B. Extension at Proximal interphalangeal joint and flexion at Distal interphalangeal joint, C. Flexion at proximal interphalangeal joint and extension at distal interphalangeal joint, D. Extension at Metacarpophalangeal joint and flexion at interphalangeal joint
B: Extension at Proximal interphalangeal joint and flexion at Distal interphalangeal joint
Answer: B: Extension at Proximal interphalangeal joint and flexion at Distal interphalangeal joint 
Explanation: 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.