Early MRI-Detected Interspinous Ligament Region Edema Is Associated With Delayed Pain Recovery and Persistent Low Back Pain After Unilateral Biportal Endoscopic Surgery
TL;DR
The extent of postoperative ISLRE, particularly grade 2 edema, may be useful for postoperative risk stratification and targeted patient management after UBE surgery and Linear mixed-effects modeling demonstrated significantly delayed pain recovery trajectories in higher-grade edema groups.
Abstract
Persistent postoperative low back pain remains a concern after unilateral biportal endoscopic (UBE) surgery, but the impact of surgery-related interspinous ligament edema is unclear. This study investigated whether magnetic resonance imaging (MRI)-detected interspinous ligament region edema (ISLRE) was associated with delayed pain recovery and persistent postoperative low back pain after UBE surgery. This retrospective cohort study included patients who underwent single-level UBE surgery between October 2021 and October 2024. On the basis of MRI within 3 days postoperatively, ISLRE was graded as grade 0 (no/minimal edema), grade 1 (localized edema), or grade 2 (diffuse or confluent edema involving most of the operated interspinous region). Clinical outcomes included visual analogue scale scores for low back pain (VAS-LBP), Oswestry disability index (ODI), and persistent postoperative low back pain, defined as 12-month VAS-LBP > 3. Multivariable linear and logistic regression analyses were performed to assess independent associations, and linear mixed-effects modeling was used to evaluate longitudinal pain recovery trajectories. A total of 245 patients were included (grade 0: n = 117; grade 1: n = 74; grade 2: n = 54). Interobserver agreement for MRI grading was substantial (κ = 0.802). At 12 months, VAS-LBP scores increased progressively across edema grades (1.66 ± 1.20, 2.34 ± 1.45, and 3.54 ± 1.65 for grades 0–2, respectively; P < 0.001), while persistent postoperative low back pain occurred in 21.4%, 41.9%, and 68.5% of patients, respectively (P < 0.001). Compared with grade 0 edema, grade 2 edema was independently associated with higher 12-month pain scores (β = 1.78, 95% confidence interval [CI] 1.34–2.22; P < 0.001) and more than eightfold increased odds of persistent postoperative low back pain (odds ratio [OR] 8.90, 95% CI 4.01–19.76; P < 0.001). Linear mixed-effects modeling demonstrated significantly delayed pain recovery trajectories in higher-grade edema groups. Although statistically significant, the magnitude of ODI differences at 12 months was below the minimal clinically important difference (MCID) threshold, suggesting limited clinical relevance. The extent of postoperative ISLRE, particularly grade 2 edema, may be useful for postoperative risk stratification and targeted patient management after UBE surgery.