Ideal Lumbar Lordosis Correction in Patients with Adult Spinal Deformity Without Adversely Impacting Pelvic Tilt and Pelvic Incidence Minus Lumbar Lordosis

Study Design. Retrospective study. Objectives. To determine the ideal pelvic incidence (PI) – lumbar lordosis (LL) range to prevent pelvic tilt (PT) undercorrection while avoiding PI-LL overcorrection following adult spinal deformity (ASD) surgery. Summary of Background. PI-LL and PT are the important sagittal parameters to be restored to an adequate range by surgery. Ideal PI-LL target without causing PI-LL overcorrection and PT undercorrection has not been documented. Methods. We included patients with ASD undergoing ≥5-level fusion including the sacrum. Receiver operating characteristic (ROC) curve analysis was performed to calculate the lower limit of the ideal PI-LL without causing PI-LL overcorrection and the upper limit of ideal PI-LL without causing PT undercorrection. The calculated ideal PI-LL was validated in terms of proximal junctional kyphosis and failure (PJK and PJF) rates and clinical outcomes. Analyses were performed according to age subgroups (<70 and ≥70 y). Results. In total, 426 patients were included in the study. Female patients were predominant (85.4%), with a mean age of 69.8 years. The lower limits of PI-LL were calculated as 4.9° for all patients, 2.3° for patients aged <70 years, and 7.9° for patients aged ≥70 years. Meanwhile, the upper limits of PI-LL were calculated as 12.7° for all patients, 12.5° for patients aged <70 years, and 13.3° for patients aged ≥70 years. There were no significant differences in the PJK and PJF rates among the new three PI-LL groups. Clinical outcomes were significantly better in patients with the ideal PI-LL group than those in patients with overcorrection or undercorrection groups for all age groups. Conclusion. The ideal PI-LL correction target without adversely impacting PT and PI-LL was calculated at 2.3°–12.5° for patients aged <70 years and 7.9°–13.3° for patients aged ≥70 years. These guideline parameters may help ensure optimal clinical outcomes without increasing the risk of PJK/F.