When the forearm is extended and supinated, the axis of the arm and forearm are not in the same line; the arm forms an obtuse angle with the forearm, known as the carrying angle. During flexion, however, the forearm and the hand tend to approach the middle line of the body, and thus enable the hand to be easily carried to the face.
The accurate adaptation of the trochlea of the humerus, with its prominences and depressions, to the trochlear notch of the ulna, prevents any lateral movement.
