Final answer:
The loose packed position of the proximal radioulnar joint is when the forearm is in mid-pronation, neither fully pronated nor fully supinated, allowing the bones to be partially crossed with the ligaments being relatively lax.
Step-by-step explanation:
The loose packed position of the proximal radioulnar joint refers to the most relaxed or unstressed position for the joint, where the articular surfaces are not maximally congruent and the supporting ligaments are relatively lax. This joint is a pivot joint, which permits rotation of the radius around the ulna during pronation (forearm rotation so the palm faces backward) and supination (forearm rotation so the palm faces forward). The loose packed position of the proximal radioulnar joint is generally considered to occur in mid-pronation, where the forearm is neither fully pronated nor fully supinated. In this position, the radius and ulna appear partially crossed but not as distinctly as they do in full pronation, where the bones form an obvious X-shape.