Tenosynovitis is inflammation of the paratendon, which is the outermost sheath that is lined in some tendons by a synovial membrane (e.g., extensor tendons of the thumb in De Quervain’s tenosynovitis). It may or may not coexist with tendinitis.
Most of these conditions can be classified as “overuse” syndromes. Aging can decrease the integrity of the tendon, making it more prone to injury.
