Abstract: Background Sagittal imbalance is an important pathogenic mechanism of low back pain in clinical practice. Patients with lumbosacral transitional vertebrae (LSTV) may experience altered spinopelvic parameters due to spinal imbalance. However, it remains unclear whether such changes correlate with increased incidence of low back pain.  Objective　To investigate the prevalence and severity of low back pain in LSTV patients, identify differences in spinopelvic sagittal parameters affecting spinal sagittal balance among distinct LSTV subtypes, analyze key biomechanical mechanisms underlying low back pain from spinopelvic alignment perspectives, and establish an initial predictive model. Methods　 A retrospective analysis was conducted on individuals who underwent spinal examinations during health checkups at the First Medical Center of PLA General Hospital from January 2023 to January 2024. Based on Castellvi classification criteria, participants were categorized into a normal control group and LSTV subgroups with different subtypes. Comparative analysis assessed intergroup differences in low back pain prevalence, Oswestry Disability Index (ODI) scores, and pelvic sagittal parameters, followed by correlation testing between back pain severity and spinopelvic alignment parameters with subsequent multivariate regression to identify contributing factors.Results　The study cohort comprised 971 patients (204 LSTV cases vs 767 normal controls), revealing significantly higher low back pain prevalence (57.8% vs 15.6%, P<0.001), elevated ODI scores (15.32± 8.45 vs 9.67±5.06, P<0.001), and increased spinopelvic parameters in LSTV patients-specifically pelvic incidence (PI: 50.58±10.71 vs 49.18±7.12, P=0.027) and PI-lumbar lordosis mismatch (PI-LL: -6.41±11.37 vs -8.69±10.76, P=0.008) -suggesting inadequate lumbar curvature to accommodate pelvic morphology potentially drives sagittal imbalance. Notably, ODI scores in Castellvi types Ⅱ/ Ⅳ correlated significantly with PI (r=0.24, P=0.007), LL (r=-0.28, P<0.001), and PI-LL (r=0.37, P<0.001). Multivariate regression identified BMI ≥28 (OR=2.592, 95% CI: 1.190-5.641), LSTV diagnosis (OR=7.060, 95% CI: 2.488-20.020), and physically demanding occupations (OR=1.659, 95% CI: 1.030-2.671) as independent risk factors for impaired recovery (P<0.05), with the derived predictive model demonstrating moderate discrimination (ROC-AUC=0.7058; 95% CI: 0.6644-0.7473). Conclusion　In patients with (LSTV, particularly those classified as Castellvi types Ⅱ and Ⅳ, significant impairment of local sagittal spinal stability occurs, accompanied by alterations in spinopelvic sagittal parameters-these biomechanical disturbances may constitute a significant contributor to the pathogenesis of low back pain.  Sagittal imbalance is an important pathogenic mechanism of low back pain in clinical practice. Patients with lumbosacral transitional vertebrae (LSTV) may experience altered spinopelvic parameters due to spinal imbalance. However, it remains unclear whether such changes correlate with increased incidence of low back pain.