Clinical Implications of Spino-pelvic Parameters for the Outcome of Spinal Surgery for Lumbar Degenerative Diseases

Study Design: A review of the literature. Objectives: To discuss how to evaluate, interpret, and utilize measurements of spino-pelvic alignment before and after spinal surgery in patients with lumbar degenerative disease. Summary of Literature Review: Various spino-pelvic parameters are currently utilized in the evaluation of spinal patients; however, interpretation of these parameters is not easy. Materials and Methods: Each spino-pelvic parameter and factors affecting its value, and how to interpret and utilize the spino-pelvic parameters before and after spinal surgery were discussed for patients with lumbar degenerative disease with and without sagittal spinal deformity. Results: Sagittal modifiers in the SRS-Schwab classification including pelvic incidence minus lumbar lordosis (PI-LL), sagittal vertical axis (SVA), and pelvic tilt (PT) are widely accepted in the evaluation of lumbar degenerative disease with sagittal deformity. Surgery for sagittal realignment is meant to restore both the SVA and PT by restoring the LL in reference to the PI. However, patients with an extremely high SVA and PT or those with a high SVA and low PT can end up with postoperative residual malalignment. In patients without deformity, PI-LL mismatch (> 10°) should be highlighted and should be actively corrected by restoring the lordosis of the pathologic segment. Conclusions: Sagittal modifiers are beneficial for their simplicity and comprehensibility; however, they are insufficient for evaluating sub-regional spinal deformity. Spino-pelvic parameters can be useful for evaluating spinal patients in a clinical setting, but the measurements are greatly affected by confounding factors such as poor patient posture, unqualified testers, and manual measurement techniques.