Background: Isolated thoracic fusion (ITF) for idiopathic scoliosis preserves lumbar segment motion but risks lumbar curve progression. This study examined if Lenke classification, residual disc wedging, or tilting at the lowest instrumented vertebrae (LIV) are associated with lumbar curve progression or adding-on after ITF.

Methods: A retrospective analysis of idiopathic scoliosis patients aged 8 to 12 years treated with primary ITF was conducted. Inclusion criteria were a diagnosis of idiopathic scoliosis, LIV T10-L1, and ≥2 years of postoperative follow-up. Growth, Lenke classification, lumbar magnitude, angle of disc wedging below the LIV, and LIV tilt were assessed preoperatively, at 6 weeks postoperative, and at final follow-up. Standard descriptive statistics and repeated measures ANOVA were performed, with significance set at P <0.05.

Results: Fifty-seven patients were included, with a mean follow-up of 4.6 years (2 to 12 y). At surgery, 67% (38 patients) were Risser 0. There was no significant lumbar curve increase from the first (24 degrees±12) to the final follow-up (22 degrees±14, P =0.21). Patients with a lumbar curve ≥30 degrees at first follow-up (n=16) also showed no increase in curve magnitude (40 degrees±8 at first follow-up vs. 37 degrees±17 at final follow-up, P =0.47). Disc wedging ≥5 degrees and LIV tilt ≥5 degrees were not associated with lumbar curve progression (29 degrees±14 at first follow-up vs. 28 degrees±17 at final follow-up for disc wedging, P =0.52; and 30 degrees±12 at first follow-up vs. 27 degrees±16 at final follow-up for LIV tilt, P =0.28) or adding-on. Lenke classification was not associated with lumbar curve progression. However, Lenke 3 and 4 patients had larger curves immediately after surgery and final lumbar curves ≥45 degrees. Of 9 Lenke 3 and 4 patients, 3 had lumbar curves ≥45 degrees at the final follow-up. No Lenke 1 or 2 patients (0 out of 41) had lumbar curves ≥45 degrees at the final follow-up ( P <0.01).

Conclusions: In pediatric ITF patients, disc wedging and LIV tilt were not associated with adding-on or lumbar curve progression. Methods: Level III.