Image 2. (coronal T2 SPIR): The ulnar collateral ligament (arrowhead) is torn at its distal end where it no longer attaches to the proximal phalanx, and is buckled and proximally displaced. The adductor aponeurosis (arrow) is interposed between the torn ulnar collateral ligament and the proximal phalanx, blocking healing of the UCL to its normal site of attachment to the proximal phalanx.
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Diagnosis:
Ulnar collateral ligament injury (Gamekeeper’s thumb) with a Stener lesion.
Discussion:
The ulnar collateral ligament (UCL) of the thumb attaches to the distal end of the first metacarpal and to the base of the proximal phalanx of the thumb at the metacarpophalangeal joint. This ligament is a low signal intensity band on MR located deep to the similar vertically oriented low signal intensity adductor aponeurosis. The UCL is the major stabilizer of the ulnar side of the thumb.
An abduction injury to the first metacarpophalangeal joint my cause an avulsion fracture at the site of attachment of the UCL to the base of the proximal phalanx of the thumb, or it may injure only the UCL without an osseous abnormality. The injury was originally termed “game-keeper’s thumb” because it occurred in Scottish gamekeepers as a result of the method used to kill rabbits. Nowadays, the injury most commonly occurs in skiers. The UCL can be incompletely or completely ruptured. Tears usually occur near the distal phalangeal insertion. When the UCL is retracted and displaced superficial to the adductor aponeurosis, it is referred to as a Stener lesion. Stener lesions occur in about one third of all gamekeeper’s thumb injuries. The interposition of the adductor aponeurosis between the torn ulnar collateral ligament and the bone will prevent normal healing.
The Stener lesion has been described as having the appearance of a “yoyo on a string” on MRI. The “yoyo” is the balled-up and retracted UCL, while the “string” is the adductor aponeurosis. The most important imaging plane for diagnosing UCL injuries is the true coronal orthogonal plane through the MCP joint. A tear of the UCL without a Stener lesion on MRI would appear as discontinuity of the UCL with hemorrhage and edema surrounding the torn end of the ligament. The ligament would remain deep to the adductor aponeurosis.
Either partial tear or non-displaced complete rupture of the UCL are treated conservatively. However, complete rupture of the UCL with displacement or Stener lesion requires surgical intervention. Since treatment in the first three weeks after injury has a better outcome, it is critical to correctly diagnose a Stener lesion.
