A baseball player is hit on the tip of his long finger by a baseball. He tears a tendon and is unable to straighten the last joint of his long finger. What is the diagnosis?

The correct answer is E. Mallet finger.

• Mallet finger is an injury to the extensor tendon at the distal interphalangeal (DIP) joint, which is the last joint of the finger. It typically occurs when the fingertip is struck, causing the tendon to tear or avulse from the bone, resulting in the inability to straighten the last joint of the affected finger. The description of the baseball player being hit on a fingertip, tearing a tendon, and being unable to straighten the last joint of his long finger perfectly matches the characteristics of a mallet finger.