Discontinuities of the extensor insertion are often referred to as “mallet injury” or “baseball finger”. They can be purely tendinous or bony avulsion fractures.
The injuries can result in subluxation or total dislocation of the joint.
Large fragment remains minimally displaced because of the volar plate attachment, the collateral ligament, and the IV annular pulley.
An avulsion injury destroys the synergistic balance of the pull exerted by flexor and extensor tendons. The continuity of the flexor tendon is lost. This results in inability to flex the DIP joint.