What is the Adductor Pollicis?

The adductor pollicis is a muscle in the hand that’s involved in movements of the thumb. Specifically, the muscle is used in thumb adduction, which is movement toward the plane of the palm .The adductor pollicis is made up of two separate heads which work together but have different origins. These are known as the oblique and transverse heads.

Due to the two heads that make up the adductor pollicis, there are two different origins for the muscle. The transverse head has its origin on the third metacarpal bone, which is found in the hand. In contrast, the oblique head of the muscle originates via several different small bits of tissue, which attach to several metacarpals and the capitate bone. The capitate is a small bone found in the wrist.

The different heads of the muscle have different shapes and locations. For example, the transverse head of the muscle is located deeper in the hand. It also has a more triangular shape than the oblique head.

Before insertion, the different heads of the muscle come together and attach to several places. One of these is the ulnar sesamoid, which is a bone in the thumb. Both heads also attach to the proximal phalanx — the first bone of the thumb after the knuckle. The innervation of the muscle is via the ulnar nerve.

The primary action of the muscle is adduction of the thumb, but it is also involved in moving the thumb toward the index finger. Adduction occurs when the thumb is brought back in line with the palm of the hand, usually when it was already abducted away from this plane. Although the muscle helps to pull the thumb in line with the index finger, it does this in conjunction with other muscles of the hand.

Different muscles of the hand work together to achieve movement. Two muscles that the adductor pollicis works with include the adductor pollicis longus and adductor pollicis brevis. Both these muscles are specifically involved in movement of the thumb.

If there is a problem with the adductor pollicis, a test known as Froment’s sign is used to check for an issue with the attaching nerve. To perform this test, the patient holds a thin object with the index finger and thumb and attempts to hold on while the object is pulled away. A healthy adductor pollicis will allow the patient to maintain grip, while an issue with the nerve will cause this to be more difficult.