An uncommon injury of the thumb.

Ulnar collateral ligament rupture of the thumb is a relatively common injury that is often missed in the emergency department. This in combination with an interphalangeal joint dislocation of the ipsilateral thumb is rare and we report such a case. The importance of looking specifically for an associated ulnar collateral ligament laxity in any injury to the thumb is highlighted. The force producing a combination of ulnar collateral ligament rupture with ipsilateral simultaneous injury to the thumb is often severe enough to cause complete rupture of the ligament, necessitating open repair.