Exploring the impact of mild-to-moderate foraminal stenosis at L5-S1 on clinical outcomes following L4-5 posterior lumbar interbody fusion

BACKGROUND CONTEXT: Patients scheduled for L4 - 5 PLIF often have FS at L5 -S1. However, data on the clinical and radiographic outcomes of cases with mild-to-moderate L5 - S1 FS are lacking, which may affect clinical outcomes or require additional surgery after L4 - 5 fusion. PURPOSE: To evaluate the clinical and radiographic outcomes of L4 - 5 PLIF in patients with and without mild-to-moderate L5 - S1 FS, with a primary focus on the association between L5 - S1 FS and postoperative clinical outcomes including back pain, leg pain, and scores on the oswestry disability index (ODI) and EuroQol 5-dimension (EQ-5D). STUDY DESIGN: Retrospective comparative study. PATIENT SAMPLE: A retrospective review of patients who underwent L4 - 5 PLIF from 2014 to 2018. The patients were divided according to the presence of mild-to-moderate FS at L5 - S1. OUTCOME MEASURES: Clinical assessment included the pain visual analog scale (VAS), ODI, and EQ-5D score. Radiographic assessments included spinopelvic parameters and grades for central and foraminal stenosis. METHODS: Clinical outcomes were assessed using validated outcome measures at preoperative, 6-month, 12-month, and 36-month follow-up visits. Radiographic evaluations were performed using preoperative and postoperative radiographs. Foraminal stenosis was assessed qualitatively using MRI with a grading system from none to severe and quantitatively by measuring changes in the foraminal area on CT. RESULTS: Among 186 patients, 55 were categorized as the FS group and 131 as the non-FS group. The FS group was older (p=0.039) and had more severe central stenosis at L5 - S1 (p=0.007) as well as more severe FS at both L4 - 5 and L5 - S1 (both p < 0.001). Preoperative disc height (p < 0.001), C7S1 sagittal vertical axis (p=0.003), lumbar lordosis (p=0.005), and pelvic incidence - lumbar lordosis mismatch (p=0.026) were more aggravated in the FS group. The FS group showed inferior clinical outcomes at the final follow-up in terms of back pain (p=.010) and ODI score (p=.003). CONCLUSION: The presence of mild-to-moderate FS at L5 - S1 was associated with more aggravated sagittal balance in terms of smaller preoperative disc height, larger sagittal vertical axis, smaller lumbar lordosis, and larger pelvic incidence - lumbar lordosis mismatch. Patients with L5 - S1 FS also had poorer clinical outcomes including back pain and ODI score after L4 - 5 PLIF. Patients with L5 - S1 FS need to be carefully examined before L4 - 5 fusion considering their adverse outcomes due to underlying degenerative changes. (c) 2024 Elsevier Inc. All rights reserved.