O2093: T1 Tilt and Clavicle Angle Are the Most Reliable Predictors of Postoperative Shoulder and Neck Balance, Defined by RSH, in Patients with Adolescent Idiopathic Scoliosis (AIS)

Background: Shoulder imbalance following Posterior Spinal Fusion (PSF) is a significant concern, and while numerous studies have examined various radiographic parameters associated with uneven shoulders postoperatively, there is a lack of research investigating predictors for balanced shoulders. This study aimed to identify radiographic predictors of shoulder balance by analyzing X-rays of patients with Adolescent Idiopathic Scoliosis (AIS) who underwent PSF, as well as control patients with no spinal curvature.

Methods: The study used Radiographic Shoulder Height (RSH) as a proxy for shoulder height, with RSH less than 2cm considered normal. T1 tilt and clavicle angle (CA) in the same orientation as RSH were defined as concordant. The study was divided into three parts:
Part I: X-rays of control patients were evaluated, with T1, CA, and RSH recorded to determine "normal" values. Kruskal-Wallis tests were performed to analyze the results.
Part II: Preoperative, postoperative, and final follow-up X-rays of AIS patients who underwent PSF were measured. Spearman's correlation was used to assess the correlation between radiographic parameters and RSH. Fisher's exact test was used to evaluate the distribution of abnormal postoperative RSH.
Part III: X-rays from multiple surgeons were evaluated to predict RSH, and Fisher's exact test was used to evaluate the distribution of abnormal postoperative RSH.

Results: Part I: 211 control patients were evaluated. 191 had normal RSH and 20 were abnormal. T1 tilt (2.0 vs 4.1) and CA (1.1 vs 4.95) were significantly different between the two groups (p <.05).
Part II: In 324 patients, preoperative and postoperative CA correlated very strongly with RSH (r = 0.857). T1 tilt correlated moderately with RSH (r = 0.451), but was better when concordant (r = 0.601). CA below 3 degrees yielded normal RSH postop (p < 0.001). Restoring Concordant T1 tilt below 3 degrees yielded normal RSH in nearly all cases (p < 0.001). RSH did not change significantly from immediate postop to final follow up (p=0.53). Restoring
Part III: In 59 patients across 4 surgeons, restoring CA below 3 degrees yielded normal RSH at postop in all cases. Restoring concordant T1 tilt below 3 degrees yielded normal RSH at postop in nearly all cases.

Conclusion: In order to prioritize shoulder balance following PSF, our findings suggest restoring CA < 3° yields normal RSH postoperatively. In addition, when T1 is concordant, restoring it to < 3 degrees can yield normal RSH. Additionally, proximal thoracic fusion did not correlate with post op RSH.