de Quervains tenosynovitis is the thickening and inflammation of the sheath containing the tendons of the inner wrist and thumb area (extensor pollicis brevis and abductor pollicis longus tendons). de Quervain's Tendonitis results from inflammation or constriction of the tendons of the muscles of the thumb at the point where they pass into the wrist. In many cases both tenosynovitis and tendonitis occur, a condition known as tendinopathy.
