Mallet Finger

Mallet finger is an injury to the extensor mechanism of the finger at the level of the distal interphalangeal joint, it occurs due to forced flexion of the DIP (stubbing your finger). Sometimes it can be bony (an avulsion at the insertion of the common extensor tendon) others it can be purely a mid tendon injury.

Clinically they both present with the finger in fixed flexion ( inability to extend the finger at the DIP joint).

Above is a simplified illustration of the mechanism leading to either a bony avulsion of mid-tendon injury,

Normal

Rupture of extender tendon

Avulsion fracture at base of distal phalanx