Spinopelvic Alignment as an Associated Factor of Short-Term Diagnostic Response to Lumbar Medial Branch Block: A Prospective Study

Background: Lumbar facet joints are a significant source of chronic low back pain (CLBP), and medial branch blocks (MBBs) are the widely accepted reference diagnostic approach for diagnosis. However, clinical response varies. This study aims to investigate whether sagittal spinopelvic alignment parameters can predict the clinical efficacy of MBB in patients with facet-mediated CLBP. Methods: In this prospective observational study, 110 patients (aged 40–80) with facet-related CLBP underwent diagnostic MBBs using a double-block protocol. Spinopelvic parameters, including pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), and lumbar lordosis (LL), were measured on standing lateral radiographs. Clinical response was defined as a ≥80% reduction in Visual Analog Scale (VAS) scores. Data were analyzed using multivariate logistic regression and Receiver Operating Characteristic (ROC) curves. Results: Responders (n = 68) were significantly younger and had a lower BMI than non-responders (n = 42) (p < 0.05). Non-responders exhibited significantly higher PI–LL mismatch (18.6° ± 7.4 vs. 3.9° ± 4.2, p < 0.001), higher PT (23.6° ± 5.1 vs. 17.4° ± 4.5, p < 0.001), and lower LL (35.8° ± 7.2 vs. 45.2° ± 6.4, p < 0.001). ROC analysis identified a PI–LL mismatch threshold of >12.5° as the strongly associated with negative short-term diagnostic response (AUC = 0.892). Multivariate analysis confirmed that PI–LL mismatch > 12.5° was a potential associated factor within the investigated model of poor response (OR: 4.25, 95% CI: 2.10–8.60, p < 0.001), while age and BMI were not significant in the adjusted model. Conclusions: Sagittal spinopelvic malalignment, specifically an increased PI–LL mismatch, is strongly associated with reduced diagnostic utility of MBB. Integrating biomechanical assessment into clinical decision-making may improve patient selection and treatment outcomes for facet-mediated pain.