Does the amount of spontaneous thoracic curve correction after selective lumbar fusion for Lenke type 5C adolescent idiopathic scoliosis affect outcomes of posterior deformity correction?

Selective lumbar fusion (SLF) is commonly performed for Lenke type 5C adolescent idiopathic scoliosis (AIS). However, whether a greater amount of spontaneous thoracic curve correction (STCC) could lead to better surgical outcome remains unclear. This retrospective cohort study was conducted to identify whether the amount of STCC after SLF for Lenke 5C AIS is associated with outcomes of posterior deformity correction and to clarify factors that could predict greater STCC. A total of 62 patients who underwent posterior-only SLF and were followed up for > 2 years were reviewed. Radiographic measurements and Scoliosis Research Society (SRS)-22 scores were analyzed. Patients with an STCC rate of > 50% at postoperative 2 years were classified as the middle thoracic (MT)-corrected group, while those with an STCC rate of ≤ 50% were included in the MT-uncorrected group. In total, 62.9% (39/62) of patients reached an STCC rate of > 50%, while the remaining 37.1% (23/62) failed to achieve an STCC rate of > 50%. The Cobb angle of MT significantly increased during the postoperative 2-year follow-up in the MT-uncorrected group (mean difference [MD] 2.279, 95% CI 0.681-3.877, p = 0.002), while it did not increase in the MT-corrected group (p = 0.820). Patients with an STCC rate of > 50% demonstrated significantly higher self-image (MD 1.513, 95% CI 0.943-2.854, p = 0.001), satisfaction (MD 1.322, 95% CI 0.529-2.231, p = 0.001), and overall (MD 0.611, 95% CI 0.321-1.219, p = 0.004) SRS-22 scores at the postoperative 2-year follow-up. Furthermore, greater MT curve flexibility (p = 0.042, cutoff value 55%) and less apical vertebral translation (AVT) of MT (p = 0.003, cutoff value 7 mm) demonstrated significant results for predicting an STCC rate of > 50% at the 2-year postoperative follow-up. Patients with an STCC rate of ≤ 50% demonstrated worse outcomes compared to those with an STCC rate of > 50%. Patients with greater preoperative MT curve flexibility and less AVT of MT were more likely to achieve an STCC rate of > 50% with SLF. Inclusion of thoracic curve within the fusion construct could be considered for those who do not meet these criteria.