Tendon sheaths, like bursae, develop in response to motion as tendons pull and transmit power. The visceral sheath has a flat synovial lining, and the parietal layer has vesicular and granular patches. There is no basement membrane, only a fatty or collagenous connective tissue. Tendon healing is facilitated by an intact tendon sheath. Snapping or triggering of joint movement can be due to nodular enlargement of the tendon, stenosis of the sheath, or both. Enthesitis involves the area of the tendon that inserts into bone, tendinitis typically involves the area of the tendon closer to the enthesis, peritendonitis involves the area that inserts into muscle, and tenosynovitis represents inflammation of the tendon and its enveloping sheath.
