What is the primary condition involved in De Quervain's tenosynovitis?

De Quervain's tenosynovitis primarily involves the inflammation of the tendons that control the movement of the thumb, specifically the extensor pollicis brevis and abductor pollicis longus. This condition typically results in pain around the wrist, especially during hand and thumb movements, due to swelling in the compartment that houses these tendons as they pass through the radial styloid.

The correct understanding of this condition revolves around the mechanical and anatomical relationship between these tendons and the wrist joint, which often leads to irritation and pain due to repetitive motion or overuse. This inflammation creates a characteristic thickening of the tendons and their surrounding sheath, leading to restricted movement along with sharp pain that may radiate up the arm.

Other conditions mentioned do not relate to De Quervain's tenosynovitis. For instance, inflammation of the extensor digitorum pertains to a different set of symptoms associated with the fingers, while rupture of the flexor digitorum superficialis affects finger flexion. Tendinitis of the supraspinatus is associated with shoulder issues, specifically involving the rotator cuff. Understanding these distinctions is crucial for effective diagnosis and treatment.