The pectoralis major's primary functions are flexion, adduction, and internal rotation of the humerus. The movements permitted in the metatarsophalangeal joints are flexion, extension, abduction, adduction and circumduction. The muscles allow for flexion, extension, adduction, abduction and opposition of the thumb. This permits movement in two planes, allowing flexion, extension, adduction, abduction, and circumduction. Hip adduction occurs when the femur moves back to the midline. The iliofemoral ligament prevents excessive adduction and internal rotation of the hip. When at an approximately 110 degree angle, it contributes to adduction of the humerus. The trigger mechanism of unlocking is debated, but is probably in lateral adduction. Risk factors in women include increased hip adduction, knee internal rotation. Risk factors seen in men are increased hip internal rotation and knee adduction. Its action on the shoulder joint are internal rotation, adduction, and retroversion. The affected eye shows impairment of adduction. This is achieved by a deep inhalation followed by the adduction of the vocal folds. Reactions with organomagnesium compounds, alcohols, amines, and ammonia yield adduction compounds. Dropping the arms to the sides, and bringing the knees together, are examples of adduction.