Patient and curve characteristics
Out of the 116 included patients, 34 operated during 2005-2006, 21 during 2007, 25 during 2008, and 36 during 2009, with mean age of 15.9 ± 2.8 years, median 15 years and range 12-24 years. The types of scoliotic curves according to Lenke classification [11] was 60 Lenke type 1 (52%), 7 Lenke type 2 (6%), 19 Lenke type 3 (16%), 5 Lenke type 4 (4%), 15 Lenke type 5 (13%), and 10 Lenke type 6 (9%). The Lenke curve types were evenly distributed among patients of the different study groups. The major structural curve was thoracic in 90 patients (78%) and lumbar in 26 (22%). No vascular or infectious complications were recorded after surgery. One patient reported postoperatively pain and paraesthesia in the T8-T10 dermatome. The neurological deficit was believed to be caused by local extraforaminal nerve injury as low-dose spine CT showed no screw misplacement.
Deformity correction for the whole study cohort
The mean reduction of Cobb angle was 38.4 ± 8.9° (69%), LEVT 19 ± 6.9° (68%), and vertebral rotation 6.5 ± 3.9° (37%) (all P < 0.001, respectively). The mean restoration of thoracic kyphosis was 4 ± 5° (24%) (P < 0.001), Table 1.
Table 1 The results of the linear regression analyses of the deformity correction during the study period (2005-2009)
Deformity correction during different study periods
The linear regression showed that the correction of the deformities in coronal plane improved from 37.4° (66%) in 2005-2006 to 39.6° (74%) in 2009 (P = 0.325), Figure 1A, and Table 1, and the correction of LEVT from 17.9 ° (66%) in 2005-2006 to 19.9° (71%) in 2009, (P = 0.237), Figure 1B, and Table 1. The measurement of the sagittal Cobb angle showed no restoration of thoracic kyphosis in 2005-2006 compared to restoration of kyphosis of 5.9° in 2009, (P < 0.001), Figure 1C, and Table 1. The correction of apical vertebral rotation was improved from 4.2° (29%) in 2005-2006 to 7.8° (45%) in 2009, (P < 0.001), Figure 1D, and Table 1.
On group level, there was no significant difference between the correction of the Cobb angle (P = 0.425), and LEVT (P = 0.298) in patients operated on during the first period (2005-2006) compared with that in patients operated on during the remaining periods (2007-2009). In contrast, the mean restoration of the sagittal profile (P < 0.001) and the mean correction of the vertebral rotation (P < 0.001) was significantly better in patients operated 2007-2009 than in patients operated 2005-2006, Table 2.
Table 2 The results of the independent sample t-test to find out if there were break points (significant differences in the deformity correction) between the first period i.e. at the end of 2006 compared with 2007-2009
Correlation between the deformity correction and the order of the operation
For the whole study population, there was statistically significant correlation between the order of the operation (patient number) and the restoration of the thoracic kyphosis (r = -0.344, P = 0.001), as well as the correction of vertebral rotation (r = 0.370, P < 0.001) Figure 2A and 2C. There was when using the 5.5 mm rod no significant correlation between the order of the operation and the restoration of the thoracic kyphosis (r = -0.232, P = 0.286) or the vertebral rotation (r = 0.174, P = 0.340), Figure 2B and 2D. Furthermore, there was when using the 5.5 mm rod no mean difference in the restoration of the thoracic kyphosis or the vertebral rotation when the first 17 operated patients were compared with the last 17 patients (P = 0.621, and 0.941, respectively), Table 3.
Table 3 The results of the independent sample t-test between first 17 patients and the last 17 patients operated with 5.5 mm rods and one surgeon Age, gender, and curve type
There was no gender difference in the correction of the Cobb angle (p = 0.811) or vertebral rotation (p = 0.225). The age of the patients correlated inversely with correction of the Cobb angle (r = -0.508, p < 0.001) and LEVT (r = -0.375, p < 0.001). There was statistically significant correlation between the correction of the Cobb angle and the correction of vertebral rotation (r = 0.228, p = 0.016) and the LEVT (r = 0.702, p < 0.001) but not with the restoration of the thoracic kyphosis (r = -0.121, p = 0.254). The Cobb angle of the thoracic curves was corrected with 39.4 ± 8.7° compared with 35 ± 9.4° for the thoracolumbar or lumbar curves (P = 0.017). The vertebral rotation of the thoracic curves was corrected with 6.1 ± 4.1° compared with 7.6 ± 2.9° for the thoracolumbar or lumbar curves (P = 0.037).