De Quervain's tenosynovitis: Inflammation of tendons on the side of the wrist at the base of the thumb. These tendons include the extensor pollicis brevis and the abductor pollicis longus tendons. De Quervain's tenosynovitis is typically associated with pain when the thumb is folded across the palm and the fingers are flexed over the thumb as the hand is pulled away from the involved wrist area (the Finklestein sign). Treatment includes a combination of rest, splinting, ice, anti-inflammation medication, and/or cortisone injection. Surgery is rarely necessary.