Optimal radiographical criteria after selective thoracic fusion for patients with adolescent idiopathic scoliosis with a C lumbar modifier: does adherence to current guidelines predict success?

STUDY
DESIGN: Retrospective review of prospective data.
OBJECTIVE: To define optimal postoperative coronal parameters after selective thoracic fusions (STFs) and to test these parameters against recommended criteria for when to perform an STF. SUMMARY OF BACKGROUND DATA: Previous studies have provided recommendations for when STF should be performed; however, clear parameters for target outcomes are lacking.
METHODS: Patients with Lenke 1C to 4C curves with adolescent idiopathic scoliosis from a multicenter database who underwent STF with minimum 2 years of follow-up were included. Postoperative parameters included lumbar Cobb angle, trunk shift, coronal balance, percent lumbar correction, and deformity-flexibility quotient. First, the upper 95% confidence interval for each parameter was calculated (queried data threshold) and set as the limit of "optimal" outcomes. Second, an independent surgeon survey was performed, and in patients with unanimous surgeon agreement of "success," the upper 95% confidence interval was determined (surgeon-derived threshold). Scoliosis Research Society-22 scores were compared between those above and below these 2 thresholds. Then, these outcomes were used to determine whether adherence to, or disregard for, previously published guidelines for STF were predictive of final outcome.
RESULTS: A total of 106 patients were analyzed. Target postoperative parameters as determined by the queried data and surgeon-derived thresholds were similar and rounded to: deformity-flexibility quotient less than 4, lumbar Cobb angle less than 26°, lumbar correction more than 37%, coronal balance 2 cm or less, and trunk shift less than 1.5 cm. Patients within target parameters had significantly better Scoliosis Research Society-22 satisfaction scores. Neither preoperative apical vertebral translation ratio more than 1.2 nor Cobb angle ratio more than 1.2 predicted 2-year success. Preoperative lumbar curve less than 45° and lumbar bend less than 25° were associated with increased likelihood of optimal outcomes.
CONCLUSION: Optimal postoperative outcomes for STF should include a lumbar Cobb angle less than 26°, coronal balance 2 cm or less, deformity-flexibility quotient less than 4, lumbar correction more than 37%, and trunk shift less than 1.5 cm. These findings suggest that performing an STF in patients with a preoperative lumbar Cobb angle less than 45° or a preoperative lumbar bend less than 25° will increase one's chances of success. LEVEL OF EVIDENCE: 4.