Answer to the Letter to the Editor of A. Gardner concerning “Loss of apical vertebral derotation in adolescent idiopathic scoliosis: 2-year follow-up using multi-planar reconstruction computed tomography” (by G. Cui, K. Watanabe, Y. Nishiwaki, N. Hosogane, T. Tsuji, K. Ishii, M. Nakamura, Y. Toyama, K. Chiba, M. Matsumoto; Eur Spine J (2012) Jun;21(6):1111–20. doi:10.1007/s00586-012-2633-0)

Excerpt

We thank Dr. Gardner for the interest in our work and the letter to the editor. In the letter, Dr. Gardner commented that the correction loss in Cobb angle should be less significance, since the value was within the range of error based on the previous reports [1‐4]. In our study, the mean correction loss between the Cobb angle of immediate after surgery and that of postoperative 2 years was 2.5 ± 1.5º [5]. The loss was significant when analyzed using paired t test. However, the change had no clinical impact when evaluated by SRS-22 scores. Based on our previous study, the coefficient of variations for intra-observer measurement was 2.3 % for the MT curve [6] using a digital measurement software on appropriately adjusted X-ray films [7, 8], and by selecting the same end vertebra in each patient at different time course [9]. In this study, we also used CT scans to demonstrate the correction loss in the axial plane and, in doing so, we tried to minimize measurement errors caused by patient positioning during CT examination using the relative AVR (rAVR), which was defined as the difference between the axial rotation angle of the upper instrumented vertebra and the apical vertebra. As a result, we also found a small but significant time-interval difference in rAVR. …