Hak Sun Kim, et al. tion (p = 0.04) as well as at the time of last follow-up (p = 0.01) (Table 2) (Figs. 1 and 2). Coronal balance, as measured with a plumb line drawn from T1, was corrected within 1 cm of the midpoint of the sacrum in both thick and thin groups (1.3 ± 1.1 and 1.2 ± 0.7 cm respectively). The tilt angle of the most caudal ins- trumented vertebra (that is, the angle of tilt of thevertebra from the horizontal) was corrected to less than 10O in both groups as well (Table 3). Post-operatively, thoracic kyphosis was slightly increased (mean 2.9O) in the thick rod group and was slightly dec- reased (mean 1O) in the thin rod group, but it remained within normal limits with no significant statistical differ- ence (p = 0.08). C7 sagittal plumb line measurements also improved in both groups and there was no statistical differ- ence between their values (Table 3). Table 2. Major Thoracic Curve Correction Thin rod group Pre-operative (degree)* 49.8 ± 9.3 (40 - 70) Immediate post-operative at supine position 15.8 ± 7.3 (6 - 36) Post-operative 2 weeks at standing position 23.2 ± 6.8 (11 - 40) Final follow-up 24.5 ± 706 (8 - 41) *The data are given as the mean and the standard deviation, with the range in parentheses. Table 3. Coronal and Saggital Measurements Thin rod group Thick rod group p value Coronal balance (cm)* Pre-operative 1.3 ± 1.1 (0 - 3.8) 1.2 ± 0.7 (0.3 - 2.4) 0.57 Follow-up 0.6 ± 0.8 (0 - 2.2) 0.7 ± 0.8 (0 - 3.1) 0.48 Tilt angle of most caudal instrumented vertebra (degree)* Pre-operative 21.6 ± 6.7 (15 - 32) 19.3 ± 7.7 (2 - 24) 0.15 Follow-up 6.7 ± 4.58 (2 - 16) 7.4 ± 5.5 (3 - 15) 0.57 Thoracic kyphosis (degree)* Pre-operative 18.8 ± 7.3 (8 - 28) 17.7 ± 7.0 (8 - 33) 0.43 Follow-up 17.8 ± 6.4 (5 - 30) 20.6 ± 5.4 (8 - 30) 0.08 C7 sagittal plumb line* Pre-operative - 24.9 ± 24.0 (- 50 - 13) - 14.6 ± 25.7 (- 24 - 24) 0.12 Follow-up - 19.0 ± 25.8 (- 74 - 39) - 18.4 ± 25.6 (- 80 - 30) 0.47 *The data are given as the mean and the standard deviation, with the range in parentheses. Thick rod group 47.2 ± 9.9 (40 - 61) 14.1 ± 6.5 (6 - 28) 18.8 ± 6.8 (8 - 31) 18.7 ± 7.6 (7 - 32) p value 0.31 0.43 0.04 0.01 A 756 B C Fig. 1. Radiographs of the spine in a patient instrumented with thin 4.5 mm diame- ter rod. (A) Pre-operative anteroposterior radiograph. (B) Immediate post- operative anteroposterior supine radiograph. (C) The anteroposterior standing radiograph made thirty months after surgery, showing the large degree correc- tion loss compared to immediate post-operative radiograph. A B C Fig. 2. Radiographs of the spine in a patient instrumented with thick 5.5 mm diameter rod. (A) Pre-operative anteroposterior radiograph. (B) Immediate post- operative anteroposterior supine radiograph. (C) The anteroposterior standing radiograph made thirty-eight months after surgery, showing no loss of correction compared to immediate post-operative radiograph. Yonsei Med J http://www.eymj.org Volume 51 Number 5 September 2010