Anatomy Of The Adductor Pollicis Muscle - Everything You Need To Know - Dr. Nabil Ebraheim

Dr. Ebraheim’s educational animated video describes the anatomy of the adductor pollicis muscle.

The abductor pollicis muscle is a small muscle of the hand and it is very important.
Origin: there are two heads
Transverse head arises from the anterior radial surface of the body of the third metacarpal.
Oblique head arises from the base of the second and third metacarpals. It also arises from the capitate bone and the adjacent carpals.
Insertion: the two heads converge into a tendon that inserts along with fibers from the adjacent flexor pollicis brevis into the medial side (ulnar aspect at the base of the proximal phalanx) of the thumb. There is a sesamoid bone passing in the tendon. The tendon inserts into the ulnar sesamoid bone of the thumb. It also inserts into the dorsal apparatus.
Function: the predominant action of the adductor pollicis is adduction of the thumb metacarpal. It draws the first metacarpal laterally to oppose the thumb towards the center of the palm and rotate it medially. The adductor pollicis also works on the interphalangeal (IP) joint causing extension of that joint. It also works on the metacarpophalangeal (MCP) joint causing flexion of that joint.
The action of the adductor pollicis muscle is complicated:
1.First metacarpal adduction
2.MCP flexion
3.IP extension
Innervation: deep branch of the ulnar nerve (C8, T1).
Anatomical Consideration with Clinical Significance
Gamekeeper’s Thumb (skier’s thumb): tear of the ulnar collateral ligament.
Stener Lesion: torn ulnar collateral ligament or avulsion may become entrapped by the aponeurosis of the adductor pollicis muscle.
Oblique Pulley of the Thumb: adductor pollicis tendon may be inserted into the oblique pulley of the thumb or attached close to it. The oblique pulley is the most important pulley in the thumb. It prevents bowstringing of the flexor pollicis longus tendon.
Trigger Thumb (stenosing tenosynovitis): the A1 pulley will cause the condition of trigger thumb. Sometime release of the A1 pulley is needed when conservative treatment fails.
The Froment’s Sign is used to test the function of the adductor pollicis muscle (ulnar nerve motor weakness). When pinching a piece of paper between the thumb and index finger against resistance, the thumb IP joint will flex if the adductor pollicis muscle is weak. This occurs in cases of ulnar nerve palsy due to weakness of the adductor muscle which is supplied by the ulnar nerve. IP flexion of the thumb occurs by the flexor pollicis longus which is innervated by the median nerve.
If you do flexion of the IP joint (bad for an ulnar nerve diagnosis), this means the ulnar nerve is injured or involved. But it is good if you examine for the anterior interosseous nerve, which means the patient can perform the ok sign, ben d the tip of the thumb and index finger, this means the anterior interosseous nerve is good.
If it is bad for the ulnar nerve, it is good for the anterior interosseous nerve.
Metacarpal Base Fracture:
Bennett Fracture: Fracture dislocation that extends into the carpometacarpal (CMC) joint articulation. There is usually two parts to this fracture. The key is the volar-ulnar beak fracture fragment attached to the volar oblique ligament. The second part is the first metacarpal shaft. It will show lateral displacement by the APL and the adductor pollicis muscles. The metacarpal is displaced dorsally, radially and supinated. The small volar lip ulnar beak fragment remains in its position attached to the trapezium by the oblique ligament. Reduce the first metacarpal to restore the articular surface. How do we reduce it?
Reduction: traction longitudinal. Pronation of the metacarpal. Pressure on the thumb base to push it back to its place by abduction and extension of the metacarpal.

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