A while ago, I discussed a case of a tear of the ulnar collateral ligament (UCL) of the first MCP joint, an injury also known as Gamekeeper's thumb. The radial collateral ligament of the thumb can also be injured. Here is a case of a patient who sustained an injury to his thumb while doing karate.
Oblique coronal intermediate-weighted images, anterior to posterior. There is a frank tear of the RCL (red arrow). Note the UCL (green arrow), which contains subtle abnormal signal, representing a concurrent grade 1 sprain of the UCL.
Vic David MD