Effect of one- or two-level posterior lumbar interbody fusion on global sagittal balance.

BACKGROUND CONTEXT: Sagittal imbalance is associated with poor clinical outcomes in patients with degenerative lumbar disease. However, there is no consensus on the impact of posterior lumbar interbody fusion (PLIF) on local and global sagittal balance.

PURPOSE: To reveal the effect of one- or two-level PLIF on global sagittal balance.

DESIGN/SETTING: A retrospective case-control study.

PATIENTS SAMPLE: This study included 88 patients who underwent a one- or two-level PLIF for spinal stenosis with spondylolisthesis.

OUTCOME MEASURES: Clinical and radiological parameters were measured pre- and postoperatively.

METHODS: All patients were followed up for >2 years. Clinical outcomes included a visual analog scale, Oswestry Disability Index, and EuroQol 5-dimension questionnaire (EQ-5D). Radiological parameters were measured using whole-spine standing lateral radiographs. Fusion, loosening, subsidence rates, and adverse events were also evaluated. Patients were divided into two groups according to their preoperative C7-S1 sagittal vertical axis (SVA): Group N: SVA≤5 cm vs Group I: SVA>5 cm; they were also divided according to postoperative changes in C7-S1 SVA. Clinical and radiological outcomes were compared between the groups.

RESULTS: All clinical outcomes and radiological parameters improved postoperatively. C7-S1 SVA improved (-1.6 cm) after L3-L5 fusion, but it was compromised (+3.6 cm) after L4-S1 fusion (p=.001). Preoperative demographic and clinical data showed no difference except in the anxiety or depression domain of EQ-5D. No differences were found in postoperative clinical outcomes. Lumbar lordosis, pelvic tilt, and thoracic kyphosis slightly improved in Group N, whereas C7-S1 SVA decreased from 9.5 cm to 3.8 cm (p<.001) in Group I. Furthermore, all sagittal parameters improved in Group I. On comparing the postoperative changes in C7-S1 SVA, we found that the decreasing trend in the postoperative C7-S1 SVA was related to a larger preoperative C7-S1 SVA (p=.030) and a more proximal level fusion (L3-L5 vs L4-S1, p=.033).

CONCLUSIONS: Global sagittal balance improved after short-level lumbar fusion surgery in patients having spinal stenosis with spondylolisthesis who showed preoperative sagittal imbalance. Restoration of sagittal balance predominantly occurred after L3-L4, L4-L5, or L3-L5 PLIF. However, no such restoration was observed after L5-S1 or L4-S1 PLIF. Thus, we could anticipate sagittal balance restoration after performing PLIF at L3-L4 or L4-L5 level. However, caution is required when planning for L5-S1 fusion if preoperative sagittal imbalance is present.