Axis of motion of the humero-ulnar joint
The humero-ulnar joint is composed of the trochlear of humerus and the trochlear notch of ulna. The axis of motion is the intercondylar axis, which connects the medial and lateral epicondyles. The forearm can be flexed and extended around this axis. The angle of flexion is 140° and extension is 0°. However, in women and children, hyperextension of 5 to 10 degrees is observed due to laxity of the ligaments.
The groove of the trochlea is not vertical but oblique. Therefore, the forearm is tilted downward and outward relative to the upper arm. This is the carrying angle. The carrying angle is more pronounced in women than in men.