Biplanar vs. uniplanar pedicle subtraction osteotomy for rigid adult spinal deformity: trading safety for correction?

Purpose: Pedicle subtraction osteotomies (PSOs) are well-established for rigid sagittal deformities, but the efficacy and safety of biplanar PSOs (BiPSOs) remain uncertain. This study aims to evaluate whether BiPSOs compromise sagittal correction or elevate surgical morbidity or complication rates. Methods: A retrospective analysis of a prospective multicentric adult spinal deformity database included patients who underwent a single Schwab-3/4 PSO with at least two years of follow-up. BiPSOs were defined by segmental angular changes (SAD) greater than 5° in both the sagittal and coronal planes, while uniplanar (UPSOs) had SAD greater than 5° in one plane. Demographic, surgical, and outcome variables were compared. Results: The study included 33 BiPSOs and 123 UPSOs. No differences were found for baseline demographic characteristics. UPSOs were more common in patients with prior spinal surgery (57.6% vs. 80.5%) with less L4-S1 lordosis (29.5° vs. 22°), meanwhile BiPSOs’ patients showed worse preoperative coronal alignment (C7-SVL 37.2 vs. 25.2 mm) and greater Cobb angles (44.6° vs. 24°). Comparable coronal and sagittal alignment were obtained postoperatively according to C7-CSVL (19.1 vs. 17.0 mm) and GAP Score (5.1 vs. 5.6 points, − 48.6% vs. − 43.8%). Comparable surgical aggressiveness including surgical time, blood loss, or hospitalization stays was observed. Neurological complications were comparable between the groups (15.2% BiPSOs vs. 19.5% UPSOs), with no significant differences in motor deficits. Overall complication rates and patient-reported outcomes were comparable, though BiPSOs had higher satisfaction at final follow-up. Conclusions: BiPSOs effectively treat rigid biplanar deformities, achieving optimal coronal correction without compromising sagittal alignment restoration or increasing surgical morbidity and neurological risks.