Using Lordotic Cages at the L5–S1 Level Does Not Guarantee the Improvement of Sagittal Alignment in Patients Who Underwent Posterior Lumbar Interbody Fusion

Study Design Retrospective comparative study. Purpose This study aimed to investigate the effects of the lordotic angle of cages on sagittal alignment in patients who underwent 1- or 2-level posterior lumbar interbody fusion (PLIF), including the L5–S1 level. Overview of Literature Few studies have addressed the effects of the lordotic angle of cages on regional and global sagittal balance in patients undergoing PLIF at the L5–S1 level. Methods Sixty-one patients who underwent 1- or 2-level PLIF, including the L5–S1 level, were divided into two groups based on the lordotic angle of cages (4° and 8° in 41 and 20 patients, respectively). Clinical and radiological parameters were compared. Correlation analyzes were performed to reveal the effect of flexibility and position of cages on the regional sagittal parameters. Results Pre- and postoperative clinical and radiological parameters were not different between the two groups. Although clinical outcomes improved postoperatively, sagittal parameters did not improve postoperatively in both groups. Patients who underwent 1-level PLIF at the L5–S1 level with the use of 8° cages showed no postoperative improvement (segmental angle: 16.1°–15.9°, p=0.140; lumbar lordosis: 44.8°–47.8°, p=0.740) of regional sagittal parameters. The degree of anterior location of cages showed a positive correlation with the postoperative restoration of the segmental angle (p=0.012 and p=0.050 at 1 and 2 years postoperatively, respectively). Conclusions Clinical and radiological outcomes based on the lordotic angle of cages were not different. Even with the use of 8° cages and regardless of the more anterior position of cages, sagittal alignment did not improve in cases involving the L5–S1 level. PLIF at the L5–S1 level should be used with caution because improvement in sagittal alignment did not occur.