The radius and ulna of equine species function as which type of joint?

• A. Pivot
• B. Ball-and-socket
• C. Hinge
• D. Gliding

Answer: (A)

The radioulnar joint is designed for rotation of the forearm around a single axis, which is the hallmark of a pivot joint. In this arrangement, the head of the radius rotates around the ulna (via the annular ligament), allowing pronation and supination of the limb. In horses, the ulna and radius are closely linked and movement between them is limited, but the functional concept remains a pivot-type relationship at the radioulnar articulation. Other joint types describe different movement patterns: hinge joints flex and extend in one plane, ball-and-socket joints allow multi-directional movement, and gliding joints involve sliding between smooth surfaces. Thus, the radius and ulna in equines function as a pivot joint.