A Positive (+ve) Postoperative Upper Instrumented Vertebra Tilt Angle (≥0°) Significantly Increases the Risk of Medial Shoulder and Neck Imbalance in Lenke 1 and 2 Adolescent Idiopathic Scoliosis Patients.

Study Design. Retrospective study. Objective. To investigate the relationship between a +ve postoperative Upper Instrumented Vertebra (UIV) (>= 0 degrees) tilt angle and the risk of medial shoulder/neck and lateral shoulder imbalance among Lenke 1 and 2 Adolescent Idiopathic Scoliosis (AIS) patients following Posterior Spinal Fusion. Summary of Background Data. Current UIV selection strategy has poor correlation with postoperative shoulder balance. The relationship between a +ve postoperative UIV tilt angle and the risk of postoperative shoulder and neck imbalance was unknown. Methods. One hundred thirty-six Lenke 1 and 2 AIS patients with minimum 2 years follow-up were recruited.For medial shoulder and neck balance, patients were categorized into positive (+ve) imbalance (>=+4 degrees), balanced, or negative (-ve) imbalance (<=-4 degrees) groups based on T1 tilt angle/Cervical Axis measurement. Forlateral shoulder balance, patients were classified into +ve imbalance (>=+3 degrees) balanced, and -ve imbalance (<=-3 degrees) groups based on Clavicle Angle (Cla-A) measurement. Linear regression analysis identified the predictive factors for shoulder/neck imbalance. Logistic regression analysis calculated the odds ratio of shoulder/neck imbalance for patients with +ve postoperative UIV tilt angle. Results. Postoperative UIV tilt angle and preoperative T1 tilt angle were predictive of +ve medial shoulder imbalance. Postoperative UIV tilt angle and postoperative PT correction were predictive of +ve neck imbalance. Approximately 51.6% of patients with +ve medial shoulder imbalance had +ve postoperative UIV tilt angle. Patients with +ve postoperative UIV tilt angle had 14.9 times increased odds of developing +ve medial shoulder imbalance and 3.3 times increased odds of developing +ve neck imbalance. Postoperative UIV tilt angle did not predict lateral shoulder imbalance. Conclusion. Patients with +ve postoperative UIV tilt angle had 14.9 times increased odds of developing +ve medial shoulder imbalance (T1 tilt angle >=+4 degrees) and 3.3 times increased odds of developing +ve neck imbalance (cervical axis >=+4 degrees).