The adductor pollicis muscle is a key mover of the thumb. This muscle has two heads. The transverse head originates on the third metacarpal. The oblique head originates on the base of the second and third metacarpals and the capitate and trapezoid bones. This muscle inserts on the base of the proximal phalanx and ulnar sesamoid. Adduction and flexion of the thumb are the main actions it produces. Trigger points cause an aching pain along the outside of the thumb and hand. Pain can also be felt in the thenar eminence in extreme cases.