High grade partial tear ucl and common flexor tendon what does this mean?

Thumb or Elbow?: The ulnar collateral ligament (ucl) is a primary stabilizer to one of your thumb joints. It provides stability to the thumb when you pinch something between your thumb and index finger. It is injured when the thumb is bent backwards and outwards. It is unlikely that you injured the actual flexor tendon to the thumb but rather the insertion of some thumb muscles that attach near the ucl.