👉 The thumb fluid, also known as the palmar aponeurosis or flexor retinaculum's tendon sheath, is a thick, fibrous sheet that spans the base of the thumb, playing a crucial role in thumb stability and movement. It acts as a protective layer over the tendons of the flexor digitorum profundus and flexor pollicis longus muscles, preventing them from slipping through the carpal tunnel. This fluid-filled structure also allows for smooth gliding of these tendons, facilitating precise and coordinated thumb motions essential for gripping, pinching, and other fine motor tasks.
