Figure 2.

3D representation of an anatomically normal spine according to White and Panjabi (25), and its projections in the three spatial planes – according to the spinal Top View. The normal spine is straight in the frontal plane (xoy), while the sagittal (yoz) physiological curves (kyphosis and lordosis) make it appear, in the Top View (Horizontal – xoz), as a straight line and not as a point, as it would have been in case of absence of sagittal curves. Drawing the TopView from C7 to S1 in a normal situationwould make appear a line first moving backward from C7 to the apex of kyphosis, then forward to the apex of lordosis, and finally backward to the starting point (by definition, in the spinal Top View there is vertical coincidence of C7 and S1) in the middle of the graph.