Final answer:
The close packed position of the sternoclavicular joint is when the arm is maximally elevated, providing maximum joint stability.
Step-by-step explanation:
The close packed position of a joint refers to the position in which the joint surfaces are maximally congruent and the ligaments and capsule are taut, providing maximum stability. In the sternoclavicular joint, which is the articulation between the manubrium of the sternum and the medial end of the clavicle, the close packed position occurs with the arm maximally elevated. This joint, playing a pivotal role in the movement of the upper limb, allows for a wide range of motion in multiple planes and is stabilized by several ligaments, including the costoclavicular ligament that connects the first rib to the underside of the clavicle.