Overcorrection of lumbar lordosis for adult spinal deformity with sagittal imbalance: comparison of radiographic outcomes between overcorrection and undercorrection.

PURPOSE: To determine the correlation of the difference between postoperative lumbar lordosis (LL) and ideal LL with the sagittal vertical axis (SVA) at the final follow-up in patients with adult spinal deformity (ASD).

METHODS: Fifty-one patients with degenerative lumbar kyphosis (DLK) (mean age 66.5 years) who underwent surgical correction with a minimum 2-year follow-up were evaluated. Based on the difference between postoperative LL and ideal LL using the Korean version of Legaye's formula, we divided the 51 patients into two groups: overcorrection (degree of postoperative LL > ideal LL) and undercorrection (degree of postoperative LL < ideal LL).

RESULTS: Our clinical series of patients comprised 24 in the overcorrection and 27 in the undercorrection group. No significant differences were found in preoperative pelvic incidence (PI 52.6° vs. 57.3°), sacral slope (SS 23.3° vs. 18.3°), LL (-6.9° vs. -2.3°), thoracic kyphosis (TK 4.7° vs. 4.9°) and SVA (140 vs. 139 mm) except pelvic tilt (PT 29.4° vs. 39.0°), between the two groups. All the patients in the overcorrection group and 16 in the undercorrection group achieved postoperative optimal sagittal balance based on SVA ≤ 50 mm. In addition, significant differences in PT (10.5° vs. 26.7°), SS (42.1° vs. 30.6°), LL (-64.3° vs. -37.1°), TK (22.6° vs. 15.8°), and SVA (-1 vs. 41 mm) between the two groups were observed postoperatively. Furthermore, four patients (16.7 %) in the overcorrection group and eight (50 %) in the undercorrection group had sagittal decompensation at the final follow-up. Our results showed that the difference between postoperative LL and ideal LL had a significant correlation with postoperative and final follow-up SVA in our clinical series.

CONCLUSION: Overcorrection of LL is an effective treatment modality to maintain optimal sagittal alignment in patients with DLK; this suggests that it should be considered in preoperative planning for patients with ASD with sagittal imbalance.