What is a mallet finger?

Mallet finger is characterized by a flexion deformity at the distal interphalangeal (DIP) joint of a finger. This occurs when there is an injury to the extensor tendon that affects its ability to extend the finger at this joint, often caused by a forceful impact that bends the fingertip downwards. As a result, the fingertip cannot be straightened voluntarily, leading to the defined flexion deformity at the DIP joint.

In the context of the question, the answer correctly identifies mallet finger as a condition where there is persistent flexion at the DIP joint, highlighting how the injury results in the typical presentation associated with this condition.