Tendinitis and tenosynovitis most commonly affect tendons associated with the shoulder (rotator cuff), the tendon of the long head of the biceps muscle (bicipital tendon), flexor carpi radialis or ulnaris, flexor digitorum, popliteus tendon, Achilles tendon (see Achilles Tendinitis), and the abductor pollicis longus and extensor pollicis brevis, which share a common fibrous sheath (the resulting disorder is De Quervain syndrome).