This case demonstrates an excellent example of the cartilage interface sign which refers to the sonographic presence of a thin markedly hyperechoic line at the interface between the hyaline articular cartilage of the humeral head and an abnormally hypoechoic supraspinatus tendon. The sign indicates the presence of partial or complete supraspinatus tear and has been shown to be 100% specific.  The sign however is not often present and therefore has a low sensitivity of around 30%.