The shoulder joint is one of the most mobile in the body, at the expense of stability. Here, we shall consider the factors the permit movement, and those that contribute towards joint structure. Factors that contribute to mobility: 1  Type of joint â It is a ball and socket joint.ig 1.0 â The articulating surfaces of the shoulder joint. The shoulder joint is formed by the articulation of the head of the humerus with the glenoid cavity (or fossa) of the scapula. This gives rise to the alternate name for the shoulder joint â the glenohumeral joint.