The causes for consistent coronal alignment and the risk factors for coronal imbalance after corrective surgery in degenerative lumbar scoliosis

English Keywords:Degenerative lumbar scoliosis  Coronal imbalance  Coronal balance distance  Correlated factors  Receiver operating characteristic curve

English Abstract:

  【Abstract】 Objectives: To explore the parameters associated with trunk shifting and scoliosis in the same direction-consistent coronal alignment(CA), and to investigate the risk factors associated with early postoperative coronal imbalance(CIB) after corrective surgery in patients with degenerative lumbar scoliosis(DLS). Methods: A total of 75 DLS patients underwent the posterior osteotomy and orthopedics surgery of long-segment fusion(fixed vertebras≥5) with instrumentations from May 2015 to January 2020 were enrolled. According to relations of the C7 plumb line(C7PL) and major curve direction, the patients were divided into type Ⅰ(C7PL locating at the convex side of the major curve) and type Ⅱ(C7PL locating at the concave side of the major curve). The distance from C7PL to the midpoint of S1 was defined as the coronal balance distance(CBD), and coronal imbalance(CIB) was concerned if the CBD≥30mm. All the patients with type Ⅰ CIB were divided into group A(CBD≥30mm) and group B(CBD<30mm) according to the CBD postoperatively. The age, gender, and body mass index(BMI); radiographic parameters before and after surgery, including CBD, major curve Cobb(MCC), lumbosacral fractional Cobb(FC), L4 and L5 coronal tilt, coronal apical lateralisthesis degree(proximal vertebra sliding to the convex side was recorded as +； if not as -), and the vertebras including in the major curve; and surgical data including major curve correction degree and correction rate, number of fixed vertebras, upper instrumented vertebra(UIV), and lower instrumented vertebra(LIV) were recorded. The apical lateralisthesis degree and the MCC correction in patients with the type I CIB were analyzed using the receiver operating characteristic(ROC) curve analysis, the best cutoff value and 95% confidence interval(CI) were obtained by the area under the curve(AUC). The normal distribution parameters were analyzed using the independent sample t test, the Mann-Whitney U test was for non-normal distribution data, and qualitative data were tested using chi-square test or Fisher test, and the odds ratio (OR) was calculated subsequently. Results: The 75 DLS patients consisted 60 females and 15 males, averaged 62.93±8.42 years. There were 33 and 42 patients in type Ⅰ and Ⅱ respectively, and among them, 12 typeⅠ patients suffered from CIB before operation and 12 after operation, while 5 type Ⅱ patients suffered from CIB before operation and 6 after operation. The incidence of CIB in type Ⅰ was significantly higher than that in type Ⅱ(P<0.05). Preoperative CBD(P=0.01), the apical lateralisthesis degree(P<0.001) and L4 tilt(P=0.015) of type Ⅰ patients were much bigger than those of type Ⅱ patients. ROC analysis showed that the best cutoff value for the apical lateralisthesis was 6.5mm, the sensitivity=91.7%, specificity=85.7%; AUC=0.903, 95%CI: 0.793-1.000. There were 12 and 21 patients in groups A and B respectively. The preoperative apical lateralisthesis degree(P=0.037), L4 tilt(P=0.001), and L5 tilt(P=0.038) in group A were much greater than those in group B. There were no significant differences in number of fixed segments, UIV and LIV between groups, however, the CIB correction degree(P=0.001) and correction rate(P<0.001) in group A were much more than those in group B. ROC curve analysis showed that the best cutoff value of major curve correction rate of type Ⅰ patients was 65%, the sensitivity=75.0%, specificity=81.0%; AUC=0.861, 95%CI: 0.739-0.984. The correction rate of MCC over 65% in type Ⅰ patients, the incidence of postoperative CIB increased significantly(OR: 9.6; 95%CI: 1.847-49.884; P=0.009). Conclusions: In DLS patients, the preoperative CBD and the apical vertebra gliding towards convex side may correlate significantly with type Ⅰcoronal alignment, and a slippage of ≥6.5mm will lead to coronal imbalance. In addition, the greater L4/L5 tilt preoperatively and overcorrection of MCC in patients with type Ⅰmay result in bigger posibility of postoperative CIB, and the MCC correction rate surpassing 65% may increase postoperative CIB significantly.