GameKeeperslabelA common thumb injury is the “gamekeeper’s thumb or “skier’s thumb”, which involves an injury to the ulnar collateral ligament (UCL) of the first MCP joint. It is caused by forced abduction and hyperextension of the thumb, such as from a ski pole. But did you know that there are two branches of the ligament that you should test?

There exists both a proper and accessory UCL of the thumb MCP. When both are ruptured, this is a complete UCL tear and generally will require operative repair. Only one of of the two ligamentous branches, however, can be subtly injured and should be tested individually. Despite proper examination techniques, subtle injuries can be missed and for this reason, all patients with any suspicion for an UCL injury should be placed in a thumb spica splint and followed closely by an orthopedist.

Anatomy of the UCL ligaments1

  • Proper UCL: Connects the dorsal 1st metacarpal head to the ulnar base of the proximal phalanx
  • Accessory UCL: Connects the 1st metacarpal head (more volar than the proper UCL)  to the ulnar base of the proximal phalanx

Examination technique []

1. Apply valgus force to the 1st MCP to test the PROPER UCL with the thumb MCP in flexion.

  • This position keeps the proper UCL taut and the accessory UCL loose.
  • The blue line denotes the proper UCL which inserts along the dorsal/ulnar aspect of the 1st metacarpal head.

UCLproper Med


2. Apply valgus force to the 1st MCP to test the ACCESSORY UCL with the thumb MCP in extension.

  • This position keeps the accessory UCL taut and the proper UCL loose.
  • The dotted line is the accessory UCL, which inserts “under” or on the volar/ulnar aspect of the 1st metacarpal head.

UCLaccessory Med


Image 1

McKeon K, Gelberman R, Calfee R. Ulnar collateral ligament injuries of the thumb: phalangeal translation during valgus stress in human cadavera. J Bone Joint Surg Am. 2013;95(10):881-887. [PubMed]
Michelle Lin, MD
ALiEM Founder and CEO
Professor and Digital Innovation Lab Director
Department of Emergency Medicine
University of California, San Francisco
Michelle Lin, MD


Professor of Emerg Med at UCSF-Zuckerberg SF General. ALiEM Founder @aliemteam #PostitPearls at Bio:
Michelle Lin, MD