(English captions by Andrea Matsumoto from the University of Michigan)
To perform O'Brien's Test point the thumb down and flex shoulder to 90 degrees.
Adduct the arm across midline, provide resistance against further shoulder flexion and evaluate
for pain.
Repeat with the thumb pointing up and again evaluate for pain.
If pain was present with the thumb down but relieved with the thumb up, it is considered
a positive test, suspicious for a labral tear.