Collateral ligament avulsion of the proximal end segment

Avulsions involving the articular surface of the base of the middle phalanx are partial articular fractures and classified according to AO/OTA as 78.2–5.2.1B, where 2–5 indicates which finger is injured. The fractures may be simple or fragmentary.

An avulsion fracture may be associated with a proximal interphalangeal (PIP) joint dislocation.

Avulsion fractures are the result of side-to-side (coronal) forces acting on the finger, putting the collateral ligament under sudden tension. The ligament is usually stronger than the bone, causing the ligament to avulse a fragment of bone at its insertion.

Avulsion fractures result in marked joint instability.

Animation of the injury mechanism

AP x-ray is needed for assessing a collateral ligament avulsion.