C7 pelvic angle: a useful parameter for spinopelvic alignment evaluation in Lenke 1 and 2 adolescent idiopathic scoliosis.

PURPOSE: (1) Analyse the association between C7 pelvic angle (C7PA) and other spinopelvic alignment parameters in patients with Lenke 1 and 2 adolescent idiopathic scoliosis (AIS), and (2) verify its value in predicting pelvic incidence (PI) - lumbar lordosis (LL) mismatch after selective thoracic fusion (STF).

METHODS

A single center retrospective study was undertaken with patients with Lenke 1 and 2 AIS undergoing STF. PI-LL greater than 9° was defined as PI-LL mismatch. Pearson correlation analysis and receiver operating characteristic (ROC) curves analysis were performed to explore the association between variables and outcomes. Multivariable logistic regression analysis was used to identify the independent risk factor for PI-LL mismatch at final follow-up.

RESULTS

A total of 106 patients were enrolled in this study. Patients in the PI-LL match group had higher SVA (-20.26 ± 29.74 mm vs. -33.50 ± 27.16 mm), PI (48.11 ± 8.97 ° vs. 42.64 ± 10.20 °), pelvic tilt (PT) (10.02 ± 6.06 ° vs. 5.74 ± 7.73 °), C7PA (5.83 ± 4.92 ° vs. 0.70 ± 6.78 °) and smaller |PI-LL| (5.3°, 8° vs. 11.2°, 13°) before surgery. The correction of thoracic curve and lumbar curve were comparable between the PI-LL match and mismatch group. There was a strong positive correlation between C7PA and PI-LL both preoperatively (r = 0.736, p < 0.001) and postoperatively (r = 0.903, p < 0.001). The association between SVA, LL and C7PA were also statistically significant (pre-op C7PA-SVA, r = 0.373, p = 0.009; pre-op C7PA-LL, r = -0.251, p < 0.001; po-op C7PA-SVA, r = 0.424, p < 0.001; po-op C7PA-LL, r = -0.396, p < 0.001). When C7PA ≤ 0.3×PT preoperatively, the incidence of sagittal imbalance (p = 0.05) and PI-LL mismatch (p < 0.001) significantly increased at last follow-up. ROC curves analysis revealed that (0.3×PT - C7PA) had the highest area under curve (AUC) when compared with other parameters [(0.3×PT - C7PA), AUC = 0.745; C7PA, AUC = 0.723; PI, AUC = 0.646; PT, AUC = 0.660]. Multivariable logistic regression demonstrated that C7PA ≤ 0.3×PT was the key independent risk factor of PI-LL mismatch at final follow-up [odds ratio = 6.38, 95% confidence interval = 1.85-25.34, p = 0.005).

CONCLUSION

C7PA was strongly correlated with spinopelvic parameters especially with PI-LL both before and after surgery in patients with Lenke 1 and 2 AIS. The C7PA could serve as a crucial factor indicating PI-LL outcome after STF. Specifically, patients were at a significantly higher risk of PI-LL mismatch at final follow-up when preoperative C7PA ≤ 0.3×PT.