Why use the “stretch film”. The fundamental measurement made on the “stretch film” is the Cobb angle of the major curve while the spine is being stretched. The unique value of the “stretch film” is that is clearly identifies the area of major deformity, while the spinal column is compensated, over the pelvis, and the compensatory curves are well corrected. In the author’s experience, this type film is much easier to interpret than bending films, which, by their nature, are NOT made with the patient’s spine fully compensated and the compensatory curves minimized. Analyzing/measuring the “stretch film”. From the Cobb angle on the “stretch film,” a measurement (in mm) is made from the top edge of the top vertebra to the bottom edge of the bottom end vertebra on the concave side of the curve. An identical measurement is made from the same vertebrae on the convex side of the curve. The thicknesses of the intervertebral discs were then measured on the concave and convex sides of the curve. The thicknesses of the discs were summed together on the concave and convex sides, and then subtracted from the longitudinal measurement made on the concave and convex sides of the curve. If the subtracted sums were within 5 to 10 mm of one another, then it was assumed that the reconstructed spine would approach “straight” after the discs were removed. If the difference in the subtracted measurements was more than 10 mm, this indicated the need to either add another disc to the preoperative plan or take off bony wedges from the endplates to get the spine straight.