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Abductor Pollicis Longus (APL)

Key Points:
• Abductor pollicis longus abducts the thumb.
• Extrinsic muscle.
• Located in the first dorsal/extensor compartment.
• Often has multiple tendon slips.
• Inflamed in DeQuervain’s tenosynovitis.
Muscle Function:
Extends and abducts the carpal-metacarpal joint of the thumb. Assists with radial deviation of the wrist.
Palpation: Palate the first dorsal compartment on the radial aspect of the wrist during abduction and slight extension of the thumb metacarpal. The abductor pollicis longus tendon is radial to the extensor pollicis brevis and proximal to the first metacarpal.
Strength Testing: Position - the thumb metacarpal-phalangeal joint in slight flexion. Stabilize – the wrist. Resist - thumb abduction by applying force over distal, dorsal and radial thumb metacarpal (in the direction of adduction and flexion of the thumb).
Relevant Anatomy:
• Roots: C7, C8.
• Nerve: Radial nerve, posterior interosseous nerve.
• Innervation Route: C7, C8 → radial nerve → posterior interosseous nerve → abductor pollicis longus branch.
Origin: Dorsal ulna, interosseous membrane, and dorsal radius.
Insertion: Radial tubercle at base of thumb metacarpal.