Fig. 6

Sign convention for measurement of inter-endplate rotations; clockwise endplate rotations are positive viewed from above. Endplate rotations are measured relative to the scanner bed reference normal. Inter-endplate rotation = φu-φl where φu and φl denote upper and lower endplate rotations, respectively. In the example given, inter-endplate rotation at a vertebra/disc level below the curve apex increases from +3° at 6 months post-surgery to +4° at 24 months post-surgery, representing a small (non-significant in this example) loss of correction over time at the level in question