A patch made of polyester that ‘draws in’ water, could be an effective treatment for shoulder pain, a new study suggests. The UK-developed patch is used to augment the surgical repair of a damaged rotator cuff, and is designed to help prevent recurrence of the problem. The shoulder is a complex ball and socket joint. It is formed by three main bones: the collarbone, shoulder blade and upper arm bone — the latter forms a ball, called the humeral head, which rests against a socket in the shoulder blade. Although it is a ball and socket joint like the hip, the shoulder socket is shallower as it has to allow a wider range of movement. In contrast, the main purpose of the hip is to provide stability.