Rotator cuff tear infraspinatus, teres minor, and subscapularis, may also be injured. The amount of stress needed to tear a rotator cuff tendon acutely will depend on the underlying condition of the tendon prior to the stress. In the case of a healthy tendon, the stress needed will be high, such as a fall on the outstretched arm. This stress may occur coincidentally with other injuries such as a dislocation of the shoulder, or separation of the acromioclavicular joint. In the case of a tendon with pre-existing degeneration, the force may be surprisingly modest, such as a sudden lift, particularly with the arm
Synovial sheath Synovial sheath A synovial sheath is one of the two membranes of a tendon sheath which covers a tendon. The other membrane is the outer fibrous tendon sheath. The tendon invaginates the synovial sheath from one side so that the tendon is suspended from the membrane by the mesotendon, through which the blood vessels reach the tendon, in places where the range of movement is extensive. The mesotendon disappears or remains in the form of narrow tendinous bands as threads known as vincula tendina. The synovial sheath is found where the tendon passes under ligaments and through osseofibrous tunnels; their