Final answer:
The distal and proximal radioulnar joints are pivot joints that allow for the rotation of the radius during movements like pronation and supination of the forearm. They are classified as uniaxial diarthrosis joints, enabling motion around a single axis.
Step-by-step explanation:
The distal and proximal radioulnar joints are types of synovial joints specifically categorized as pivot joints, which permit rotation. The proximal radioulnar joint is where the head of the radius articulates with the radial notch of the ulna, allowing for the rotation of the radius during pronation and supination of the forearm. This action is facilitated by the annular ligament, which holds the head of the radius in place. The maneuvering of the radius over the ulna brings both bones into an X-shape position during pronation and back to parallel during supination. The distal radioulnar joint involves the head of the ulna and the ulnar notch of the radius. Together, these pivot joints coordinate to enable the hand to turn over at the wrist.
Both joints are considered uniaxial diarthrosis joints, meaning they are freely movable (diarthrosis) but allow motion in one plane or axis (uniaxial). They are essential for movements such as turning a doorknob or using a screwdriver, where the rotation of the forearm is necessary.