(English captions by Jade Cheng from the Universtiy of Michigan)

Ulnar collateral ligament testing of the thumb
is performed to evaluate for instability found

on a gamekeeper's or skier's thumb.

After stabilizing the first metacarpal, a
valgus stress is applied to the thumb at the

metacarpophalangeal joint.

Laxity indicates a partial or complete ulnar
collateral ligament tear.