Supination and pronation occurs at which of the following joint: September 2006

Ans. C: Radio-ulnar Joint Supination and pronation occurs at the radio-ulnar joint. The radius revolves on the ulna about an axis which passes through the centre of the head of the radius above and the styloid process of the ulna below, which line if prolonged would pass through the ring finger. In pronation, the hand lies with the palm down and the radius is crossed diagonally over the ulna; the bones are close together. In supination the hand lies with the palm up, the bones lie parallel to one another and widely separated. In the mid-position the radius lies above the ulna and the space between them is at its maximum. The head of the radius rotates in the orbicular ligament, the lower end of the radius revolves around the head of the ulna and rests on the interaicular triangular fibrocailage. The radius is pronated by the pronator teres and pronator quadratus muscles. It is supinated by the brachioradialis, supinator (brevis), and biceps muscles. Some of the other muscles also aid slightly in these movements, especially the flexor carpi radialis in pronation. In fractures the preservation of the interosseous space is essential for the proper performance of pronation and supination.