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The muscles allow for flexion, extension, adduction, abduction and opposition of the thumb. The muscles acting on the thumb can be divided into two groups: The extrinsic hand muscles, with their muscle bellies located in the forearm, and the intrinsic hand muscles, with their muscles bellies located in the hand proper.
Abduction of the thumb is defined as the movement of the thumb anteriorly, a direction perpendicular to the palm. The abductor pollicis brevis does this by acting across both the carpometacarpal joint and the metacarpophalangeal joint. It also assists in opposition and extension of the thumb.
The radial nerve innervates the finger extensors and the thumb abductor; that is, the muscles that extend at the wrist and metacarpophalangeal joints (knuckles) and abduct and extend the thumb. The median nerve innervates the flexors of the wrist and digits, the abductors and opponens of the thumb, the first and second lumbricals. The ulnar ...
Abductor pollicis brevis abducts the thumb. This muscle is the most superficial of the thenar group. Flexor pollicis brevis, which lies next to the abductor, will flex the thumb, curling it up in the palm. (The flexor pollicis longus, which is inserted into the distal phalanx of the thumb, is not considered part of the thenar eminence.)
In the thenar eminence, the recurrent branch of the median nerve provides motor innervation to: [4] opponens pollicis muscle; abductor pollicis brevis muscle; superficial part of flexor pollicis brevis muscle; A separate, more proximal branch of the median nerve additionally provides motor innervation to the 1st and 2nd lumbricals of the hand.
An accessory abductor pollicis longus (AAPL) tendon is present in more than 80% of people, and a separate muscle belly is present in 20% of people. In one study, the accessory tendon was inserted into the trapezium (41%); proximally on the abductor pollicis brevis (22%) and opponens pollicis brevis (5%); had a double insertion on the trapezium and thenar muscles (15%); or the base of the first ...
Sensory loss in the thumbs, index fingers, long fingers, and the radial aspect of the ring fingers. Weakness in forearm pronation and wrist and finger flexion [ 2 ] Activities of daily living such as brushing teeth, tying shoes, making phone calls, turning door knobs and writing, may become difficult with a median nerve injury.
The lateral portion supplies a short, stout branch to certain of the muscles of the ball of the thumb, viz., the abductor pollicis brevis, the opponens pollicis, and the superficial head of the flexor brevis, and then divides into three proper palmar digital nerves of median nerve (proper volar digital nerves):