Final answer:
The proximal radioulnar joint is a pivot joint allowing for forearm pronation and supination, with the annular ligament and collateral ligaments aiding in stability and movement.
Step-by-step explanation:
The proximal radioulnar joint is crucial for the rotation of the forearm and is classified as a uniaxial pivot joint. It involves the articulation between the head of the radius and the radial notch of the ulna. This joint allows for forearm movements such as pronation and supination. The annular ligament is instrumental in securing the head of the radius within the radial notch, enabling this rotational movement. When the forearm is pronated, the radius rotates over the ulna, forming an X-shape with it. Conversely, during supination, the radius returns to a parallel position relative to the ulna. It is important to note that the proximal radioulnar joint works in conjunction with the distal radioulnar joint during these motions. The collateral ligaments provide stability by preventing side-to-side movement and resisting hyperextension.