MRI-defined Lumbar Fasciitis Is Associated With Inferior Subjective Outcomes After Endoscopic Decompression for Lumbar Spinal Stenosis

Purpose To examine factors associated with unfavorable subjective outcomes at 12 months after endoscopic decompression for LSS, with a specific focus on the role of MRI-defined lumbar fasciitis, and to explore potential mechanistic implications. Methods Baseline clinical characteristics, perioperative laboratory parameters, CT-based radiographic indices, and MRI-derived paraspinal muscle measurements were collected. Lumbar fasciitis was defined as an imaging-based phenotype characterized by edema-like signal alterations within the lumbar fascia on preoperative MRI. Univariate analyses were performed to compare variables between outcome groups. Variables with p < 0.05 were entered into a multivariate binary logistic regression model to identify factors independently associated with unfavorable outcomes. Results Ninety-two patients (87.6%) achieved favorable outcomes, whereas 13 patients (12.4%) had unfavorable outcomes. Lumbar fasciitis was significantly more frequent in the unfavorable outcome group (p = 0.003). In multivariate analysis, concomitant lumbar fasciitis remained independently associated with unfavorable MacNab outcomes (odds ratio = 15.463, 95% confidence interval: 1.63–146.7, p = 0.018). Age, operation time, medial facetectomy angle, postoperative red blood cell count, and muscle-to-disc area ratios were not independently associated with postoperative outcomes. Conclusions MRI-defined lumbar fasciitis was strongly associated with inferior subjective outcomes at 12 months after endoscopic decompression for lumbar spinal stenosis. These findings suggest that fascia-related pain phenotypes may contribute to postoperative dissatisfaction despite technically adequate neural decompression. Preoperative recognition of lumbar fasciitis may therefore enable more accurate risk stratification and more realistic expectation management. These findings underscore the importance of moving beyond radiographic decompression adequacy toward a more holistic, pain-oriented preoperative assessment framework.