Isolated main thoracic curve fusion in idiopathic scoliosis: optimizing radiographic outcomes using lumbar modifiers to guide correction

Purpose Does differential correction of main thoracic curve (MTC) and instrumented LIV angulation based on lumbar modifiers affect radiographic outcomes, and can preoperative supine AP radiograph be used to guide correction for optimal final radiographic alignment. Methods Retrospective analysis of idiopathic scoliosis patients who underwent selective thoracic fusions (LIV T11-L1) for Lenke 1 and 2 curve patterns, < 18 years of age. 2-year minimum follow-up. Optimal outcome meant LIV + 1 of < 5 degrees disk-wedging and C7-CSVL < 2 cm. 82 patients met inclusion criteria (70% female), mean age 14.1 years. Results 24 patients were A modifier, 21 B modifier, and 37 C modifier. There were 52 optimal and 30 suboptimal outcomes. LIV was not associated with outcome ( p = 0.08). For optimal outcomes, A modifiers’ MTC improved 65%, B modifiers 65%, and C modifiers 59%. C modifiers’ MTC correction was less than A modifiers ( p = 0.03) but equivalent to B modifiers’ ( p = 0.10). A modifiers’ LIV + 1 tilt improved 65%, B modifiers 64%, and C modifiers 56%. C modifiers’ instrumented LIV angulation was greater than A modifiers’ ( p < 0.01) but equivalent to B modifiers’ ( p = 0.06). Preoperative supine LIV + 1 tilt was 16 o in optimal outcomes and 15° in suboptimal outcomes. Instrumented LIV angulation was 9° for both. The correction between preoperative LIV + 1 tilt and instrumented LIV angulation was not significantly different between groups ( p = 0.67). Conclusion Differential MTC and LIV tilt correction based on lumbar modifier may be a valid goal. Optimizing radiographic outcome by matching instrumented LIV angulation to preoperative supine LIV + 1 tilt could not be proven. Level of evidence IV.