Impact of Cage Angle on Spinal Alignment in Posterior Lumbar Interbody Fusion: A Comparison of 12°, 16°, and 22° Cages.

INTRODUCTION

We evaluated the effect of 3 high-angle cages on spinal alignment and clinical outcomes following posterior lumbar interbody fusion (PLIF).

METHODS

A retrospective analysis was performed on 104 patients who underwent PLIF at the L4/5 level between January 2021 and August 2023. Patients were divided into 3 groups: 12° (L), 16° (M), and 22° (H) cage groups. Lumbar spine radiographs were taken preoperatively and one year postoperatively to assess slip rate (% slip), segmental lumbar lordosis (SLL), segmental intervertebral angle (SIA), lumbar lordosis (LL), pelvic incidence-LL, sagittal vertical axis (SVA), Japanese Orthopedic Association score, and lower back pain visual analog scale score. Bone union and cage subsidence rates were evaluated using computed tomography 6 months postoperatively. Statistical analyses were performed using either the Wilcoxon signed rank test, Kruskal-Wallis test, or z-test.

RESULTS

Intragroup analysis showed significant improvements in local alignment, with notable SVA improvement in the H group. Intergroup comparisons revealed no significant differences in preoperative evaluation items. Postoperatively, the H group showed significantly greater improvements in SLL and SIA than the L group. Although no significant difference was observed in bone union, the cage subsidence rate was significantly higher in the H group than in other groups.

CONCLUSIONS

PLIF using high-angle cages (≥12°) significantly improved local alignment in all groups. The 22° cage showed greater improvements in SLL and SIA but a higher incidence of cage subsidence. No significant clinical differences were observed between groups. LL in the lower lumbar spine can be achieved relatively easily using a cage with a larger angle in PLIF. However, although a cage with a larger angle may be advantageous for lordosis formation, postoperative clinical outcomes do not differ; therefore, cage selection should consider the surgeon's skill and patient factors, such as the degree of preoperative lumbar disc degeneration, instability, and alignment.