Mallet finger is caused by injury to extensor tendon inseion at:

MALLET FINGER/BASEBALL FINGER- avulsion of extensor tendon of the distal interphalangeal joint from its inseion at the base of distal phalanx. Cause due to direct trauma, occurs when the finger tip is forcibly bent during active extension Treatment An acute mallet finger should be splinted and the DIP joint is kept in hyperextension for 6-8 weeks. Old lesion need treatment if deformity is marked, hand functions seriously impaired, and joint still mobile. The options include fusion, tendon reconstruction or fowler' central slip tenotomy.