This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Forearm wrist and hand injuries, Subject name: Orthopaedics
Game Keeper's thumb is injury to ? 
Select and explain. 
A. Ulnar collateral ligament injury of MCP Joint, B. Radial collateral ligament injury of MCP joint, C. Radial collateral ligament injury of CMC joint, D. Ulnar collateral ligament injury of CMC joint
A: Ulnar collateral ligament injury of MCP Joint
Answer: A: Ulnar collateral ligament injury of MCP Joint 
Explanation: GAMEKEEPER&;S THUMB/SKIER&;S THUMB The ulnar collateral ligament inses paly inyo the palmar plate. In PAIAL RUPTURE,only the ligament proper is torn and the thumb is unstable in flexion.Here the palmar plate is intact. In COMPLETE RUPTURE,both the ligament proper and the palmar plate are torn and the thumb is unstable in all positions. C/F:Tenderness and swelling precisely over the ulnar side of the thumb metacarpophalangeal joint. X-ray is essential,to exclude a fracture berfore carrying out any stress tests. TREATMENT: Paial tears can be treated by a sho period (2-4weeks)of immobilisation in a splint followed by icreasing movement. Complete tears need operative repair.Post operatively,the joint is immobilized in a thumb slint for 6 weeks,but can be moved early in the flexion-extension phase. Ref: Maheshwari and Mhaskar 9th ed pg 122