Thirty patients (21 females, 9 male) were analyzed. Demographics are shown in Table 1. Average age at time of surgery was 14.0 ± 1.8 years (range, 11–17 years) and median length of follow-up was 2.8 years (IQR 2.1-4.0 years). Surgical and radiographic data are presented in Tables 2 and 3. At most recent follow-up, mean percent major curve correction was 54 ± 13% and mean percent minor curve correction was 35 ± 15%. Average implant density was 80 ± 10% and average anchor density was 1.6 ± 0.2 anchors per level. Pedicle screws consisted of 92 ± 8% of all anchors utilized. Mean total anchor cost was $14,463 ± 2683.
Table 1
Age at time of surgery (years; mean ± SD)
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14.0 ± 1.8
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Sex (n [%] female)
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21 (70)
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Preoperative weight (kg; mean ± SD)
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56.5 ± 15.2
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Preoperative height (cm; mean ± SD)
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162.6 ± 9.6
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Preoperative BMI (kg/m2; mean ± SD)
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21.3 ± 4.8
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Preoperative BMI percentile for age (mean ± SD)
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55.0 ± 30.2
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Length of follow-up (years; median [IQR])
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2.8 (2.1-4.0)
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SD, standard deviation; BMI, body mass index; IQR, interquartile range |
Table 2
Number of levels fused
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11.6 ± 1.7
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Total number of anchors
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18.6 ± 3.0
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Implant density (%)
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80 ± 10
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Pedicle screw ratio (%)
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92 ± 8
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Anchor density
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1.6 ± 0.2
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Pedicle coefficient
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1.5 ± 0.3
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Total anchor cost
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$14,463 ± 2683
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All values are shown as the mean ± standard deviation. |
Table 3
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Preoperative
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First postoperative follow-up
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Most recent postoperative follow-up
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Curve magnitude (degrees)
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Percent flexibility
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Curve magnitude (degrees)
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Percent change
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Curve magnitude (degrees)
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Percent change
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Correction index
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Major curve
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63 ± 13
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34 ± 10
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26 ± 6
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58 ± 10
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29 ± 9
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54 ± 13
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2 ± 1
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Minor curve
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43 ± 8
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21 ± 12
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27 ± 10
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38 ± 17
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28 ± 10
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35 ± 15
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3 ± 3
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Thoracic kyphosis
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25 ± 13
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n/a
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23 ± 13
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17 ± 84
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22 ± 9
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4 ± 87
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n/a
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All values are shown as the mean ± standard deviation. |
After controlling for sex, age at time of surgery, preoperative curve magnitude, percent curve flexibility, and number of levels fused, no association was found between implant density, pedicle screw ratio, anchor density, and pedicle coefficient and postoperative major curve magnitude, percent major curve correction, postoperative minor curve magnitude, percent minor curve correction, postoperative thoracic kyphosis, and percent thoracic kyphosis change at most recent follow-up. Although the overall model for major curve magnitude was significant (P = 0.014), none of the independent variables were significant in the analysis. Regression analysis revealed that female sex was statistically significantly associated with postoperative major curve magnitude [P = 0.004, β coefficient 11.08, 95% CI (4.07–18.09)], percent major curve correction [P = 0.003, β coefficient − 18.06, 95% CI (-29.42-6.70)], and thoracic kyphosis [P = 0.020, β coefficient 10.17, 95% CI (1.78–18.56)]. Preoperative major curve magnitude was a significant predictor of postoperative major curve magnitude [P = 0.010, β coefficient 0.40, 95% CI (0.11–0.70)].
Elimination analysis (Table 4) demonstrated that the most important predictors of postoperative major curve magnitude at most recent follow-up were female sex [P = 0.001, β coefficient 9.01, 95% CI (3.80-14.21)] and preoperative major curve magnitude (P = 0.0001, β coefficient 0.39, 95% CI (0.19–0.58)]. Predictors of percent major curve correction at most recent follow-up were female sex [P = 0.001, β coefficient − 14.04, 95% CI (-22.21- -5.86)] and age at time of surgery [P = 0.084, β coefficient − 2.00, 95% CI (-4.29- 0.29)]. Predictors of postoperative thoracic kyphosis at most recent follow-up were female sex [P = 0.005, β coefficient 9.05, 95% CI (2.99–15.11)] and percentage major curve flexibility [P = 0.036, β coefficient − 31.52, 95% CI (-60.77- -2.27)].
Table 4
Results of elimination analysis.
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Female sex
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Preoperative major curve magnitude
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Age at time of surgery
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Preoperative percent major curve flexibility
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Postoperative major curve magnitude
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P = 0.001
β = 9.00, 95% CI( 3.80–14.20)
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P = 0.0001
β = 0.39, 95% CI( 0.19–0.58)
|
|
|
Percent major curve correction
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P = 0.001
β =-14.04, 95% CI(-22.21- -5.86)
|
|
P = 0.084
β = -2.00, 95% CI( -4.29- 0.29)
|
|
Postoperative thoracic kyphosis
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P = 0.005
β = 9.05, 95% CI( 2.99–15.11)
|
|
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P = 0.036
β = -31.52, 95% CI( -60.77- -2.27)
|