This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Joint disorders, Subject name: Orthopaedics
A lady having flexion at proximal interphalyngeal joint and hyperextension at distal interphalyngeal joint of index finger is called- 
Select and explain. 
A. Boutonniere deformity, B. Swan neck deformity, C. Wind swept deformity, D. Z deformity
A: Boutonniere deformity
Answer: A: Boutonniere deformity 
Explanation: ref : maheswari 9th ed