Predictive Value of Preoperative Paraspinal Muscle Degeneration Parameters for Clinical Outcomes After Unilateral Biportal Endoscopy for L5/S1 Lumbar Disc Herniation

Abstract Objective To investigate the predictive value of preoperative paraspinal muscle degeneration parameters for clinical outcomes after unilateral biportal endoscopy (UBE) in patients with single-level L5/S1 lumbar disc herniation (LDH), and to provide evidence for preoperative risk assessment and individualized rehabilitation planning. Methods A retrospective analysis was conducted on 108 patients who underwent UBE for single-level L5/S1 LDH from January 2024 to December 2025. On preoperative axial T2-weighted MRI images at the L5/S1 disc level, the total cross-sectional area (tCSA) and functional cross-sectional area (fCSA) of the bilateral multifidus (MF) and erector spinae (ES) muscles were measured, and the fat infiltration rate (FIR) was calculated. The Goutallier classification system was used for semi-quantitative assessment of paraspinal muscle fatty infiltration. Visual analog scale (VAS) scores for low back and leg pain and Oswestry Disability Index (ODI) were recorded preoperatively and at 3, 6, and 12 months postoperatively. Clinical outcomes were evaluated using the modified MacNab criteria at the final follow-up. Patients were divided into excellent/good group (90 cases) and fair/poor group (18 cases) based on outcomes. Preoperative paraspinal muscle degeneration parameters were compared between groups. Multivariate logistic regression analysis was used to identify independent risk factors for poor postoperative outcomes. Receiver operating characteristic (ROC) curve analysis was performed to evaluate the predictive efficacy of preoperative paraspinal muscle degeneration parameters for postoperative outcomes. Results The excellent/good rate was 83.3%. Patients in the fair/poor group had significantly smaller preoperative ipsilateral MF fCSA and relative cross-sectional area (rCSA) (P < 0.001), significantly higher MF FIR (P < 0.001), and a significantly higher proportion of Goutallier grade ≥ 2 (83.3% vs. 32.2%, P < 0.001) compared to the excellent/good group. Correlation analysis showed that preoperative MF FIR was significantly negatively correlated with postoperative ODI improvement rate (r=-0.682) and low back pain VAS improvement rate (r=-0.594) (P < 0.001), but showed no significant correlation with leg pain VAS improvement rate (P > 0.05). Multivariate logistic regression analysis revealed that preoperative MF FIR ≥ 25% (OR = 10.55, 95%CI: 2.55–43.62, P = 0.001) and disease duration ≥ 12 months (OR = 6.45, 95%CI: 1.69–24.56, P = 0.006) were independent risk factors for poor postoperative outcomes, while MF fCSA was a protective factor (OR = 0.986, P = 0.020). ROC curve analysis showed that preoperative MF FIR had the largest area under the curve (AUC) for predicting poor postoperative outcomes (0.856, 95%CI: 0.768–0.944), with an optimal cutoff value of 24.8%, sensitivity of 85.0%, and specificity of 75.0%. Conclusion Preoperative paraspinal muscle degeneration, particularly the degree of multifidus fatty infiltration, is an important predictor of clinical outcomes after UBE for L5/S1 lumbar disc herniation. When MRI shows multifidus fat infiltration rate ≥ 24.8% or Goutallier grade ≥ 2, clinicians should be alert to the risk of poor postoperative outcomes. It is recommended that preoperative paraspinal muscle status be incorporated into the surgical risk assessment system, and targeted postoperative rehabilitation of paraspinal muscle function be strengthened for high-risk populations.