Comparative Efficacy of L3 Versus L4 As the Lowest Instrumented Vertebra for Lenke 5/6 Adolescent Idiopathic Scoliosis: A Systematic Review and Meta‑Analysis

The most optimal lowest instrumented vertebra (LIV) selection in Lenke 5/6 adolescent idiopathic scoliosis (AIS) is controversial. We aimed to compare the radiographical and clinical outcomes between L3 and L4 as LIV, the two most frequent selections. This research encompassed studies comparing outcomes of L3 versus L4 as the LIV in Lenke 5/6 AIS released from August 2001 to June 2025 in the PubMed, Embase, Cochrane Library, and Web of Science databases. The Cochrane risk of bias assessment tool and the Newcastle‒Ottawa Scale were used to assess the quality of the randomized controlled trials and the retrospective cohort studies respectively. Meta-analysis of coronal parameters, sagittal parameters and adding-on phenomenon was performed. Data were pooled using random-effects or fixed-effect models to obtain mean differences (MD) for continuous variables and odds ratios (OR) for categorical variables, along with matching 95% confidence intervals (CI). Six studies with 228 patients in L3 group and 184 patients in L4 group were included. The preoperative thoracolumbar/lumbar curves were 48.13 ± 8.25 ^。 in L3 group and 47.38 ± 7.96 ^。 in L4 group. There was no difference in correction of thoracic curve (MD = 0.45, 95% CI: -1.00 to 1.90, P  = 0.54), C7-central sacral vertical line (MD = 2.16, 95% CI: -0.29 to 4.61, P  = 0.08), thoracic kyphosis (MD = -0.39, 95%CI: -2.49 to 1.71, P  = 0.72), lumbar lordosis (MD = 1.8, 95% CI: -1.14 to 4.75, P  = 0.23) and sagittal vertebral axis (MD = 1.01, 95% CI: -3.47 to 5.50, P  = 0.66) between L3 group and L4 group. L3 group showed a better effect in correcting thoracolumbar/lumbar curve (MD = 3.97, 95% CI: 2.31 to 5.63, P  < 0.01) than L4 group. With respect to the adding-on phenomenon, L3 group had a higher incidence compared with L4 group (OR = 3.39, 95% CI: 1.49 to 7.74, P  = 0.004). In summary, in patients with mild to moderate Lenke 5/6 AIS, outcomes may be comparable or superior when the LIV is stopped at L3 compared with L4. However, caution is advised for adding-on phenomenon during follow-up assessments.