A 32 years old female present’s to ED, c/o sore left thumb after she slipped while mopping the floor causing her thumb to abduct against the mop handle. On examination the thumb is swollen and bruised over the MCP joint, with marked laxity on flexion and extension of the MCP joint. You give the patient analgesia then send them to X-ray to rule out  a fracture.
 

What is the diagnosis?

Injury to ulnar collateral ligament:
Injury to the ulnar collateral ligament can occur acutely or chronically, and is an easy to miss injury that can lead to chronic instability if not identified and treated early.

• Acute injury known as skier’s thumb occurs due to a fall on outstretched hand with thumb forced into abduction.
• Gamekeeper’s thumb is a chronic lesion which develops  from repetitive strain on the UCL.
• The UCL which prevents abnormal opening of the MCPJ of the thumb on the ulnar side is over-stretched and torn, rendering the joint unstable. The ligament on radial side can occasionally suffer a similar injury.
• Injury to the ulnar collateral ligament injury is often associated with an avulsion fracture of the proximal base.

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