Final answer:
The close packed position of the proximal radioulnar joint is typically during supination, where the radius and ulna are parallel and the palm faces anteriorly. This position provides maximal stability to the joint.
Step-by-step explanation:
The close packed position of the proximal radioulnar joint is not explicitly mentioned in the reference information provided. However, the close packed position of a joint generally refers to the joint configuration where the articulating bone ends are maximally congruent, and the ligaments and capsule are taut, resulting in maximal stability. In the case of the proximal radioulnar joint, this position is typically achieved during supination. This joint is a uniaxial pivot joint that permits the rotation of the head of the radius as it articulates with the radial notch of the ulna. During supination, the radius and ulna are parallel, and the palm faces anteriorly, which is also referred to as the anatomical position. Conversely, pronation involves the forearm moving to a pronated position where the palm faces backward, and the radius crosses over the ulna, forming an X-shape with the ulna at the distal radioulnar joint.