Origin: Flexor retinaculum, tubercle of the trapezium bone and tubercle of the scaphoid bone.

Insertion: Base of the proximal phalanx of the thumb, radial side and extensor expansion.

Action: Abducts the carpometacarpal and metacarpophalangeal joints of the thumb in a ventral direction perpendicular to the plane of the palm. By virtue of its attachment into the dorsal extensor expansion, extends the interphalangeal joint of the thumb. Assists in opposition, and may assist in flexion and medial rotation, of the metacarpophalangeal joint.

Patient: Sitting or supine.

Fixation: The examiner stabilizes the hand.

Test: Abduction of the thumb ventrally from the palm.

Pressure: Against the proximal phalanx, in the direction of adduction toward the palm.

Weakness: Decreases the ability to abduct the thumb, making it difficult to grasp a large object. An adduction deformity of the thumb may result from marked weakness.


Origin: Flexor retinaculum and tubercle of the trapezium bone.

Insertion: Entire length of the first metacarpal bone, radial side.

Action: Opposes (i.e., flexes and abducts with slight medial rotation) the carpometacarpal joint of the thumb, placing the thumb in a position so that, by flexion of the metacarpophalangeal joint, it can oppose the fingers. For true opposition of the thumb and little finger, the pads of these digits come in contact. Bringing the tips of these digits together can be done without action of the opponens.

Patient: Sitting or supine.

Fixation: The examiner stabilizes the hand.

Test: Flexion, abduction, and slight medial rotation of the metacarpal bone so that the thumbnail shows in the palmar view.

Pressure: Against the metacarpal bone, in the direction of extension and adduction with lateral rotation.

Weakness: Results in a flattening of the thenar eminence, extension and adduction of the first metacarpal, and difficulty in holding a pencil for writing or in grasping objects firmly between the thumb and fingers.

Note." 77ie attachment of the palmaris longus and the opponens pollicis to the flexor retinaculum accounts for contraction of the palmaris longus during the opponens test.

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