What causes a trigger thumb?
Trigger thumbs are caused by a size mismatch between the flexor tendon of the thumb and the A1 pulley, a fibrous band under which the tendon normally glides. When the A1 pulley is too tight to allow for easy tendon gliding, the tendon can become swollen and inflamed, ultimately leading to triggering or inability to fully extend the thumb. Trigger thumbs occur sporadically and are not associated with other hereditary or congenital disorders.
