All joint movements are measured on a half-circle arc from 0° to 180°.
The zero end of this arc is toward the head and the neutral position is 180° for all movements except rotation. For rotation, including pronation and supination, the zero end is toward the median body line (on the left for the spine) and the neutral position is 90°.
Extension is a movement toward 180° and flexion toward 0° on the flexor half-circle arc in the anteroposterior plane.
Hyperextension is a movement toward 0° on the half-circle arc on the extensor side of the joint in the anteroposterior plane.
Abduction and adduction are both movements toward 0° in the lateral plane, the former on the half-circle arc lying external to the joint, and the latter on the half-circle arc lying internal to the joint.
Internal rotation is toward 0° and external toward 180° on the anterior half-circle arc in the transverse plane. For the spine rotation to the patient's left is toward 0° and to his right toward 180°.
The number of degrees stated in records by this system indicates the limit of motion on the half-circle scale and not the amount of motion.