Dural Entrapment by Facet Joint after Unilateral Biportal Endoscopic Lumbar Decompression Surgery: Incidence, Risk Factors, and Biomechanical Considerations

Objective Dural entrapment by the facet joint is a rare but potentially serious complication following unilateral biportal endoscopic (UBE) lumbar decompression. However, its incidence, risk factors, and biomechanical mechanisms remain unclear. This study aimed to investigate the incidence, clinical characteristics, and predictive factors for dural entrapment following UBE lumbar decompression, with a particular focus on anatomical and biomechanical considerations. Methods This retrospective cohort study included 181 patients (257 spinal segments) who underwent UBE lumbar decompression at a single institution between January 2023 and January 2024. Patients with prior lumbar surgery, deformity, severe instability, or incomplete imaging were excluded. Clinical and radiological parameters, including facet joint gap, facet joint angle, and dural sac-to-canal ratio, were evaluated. Multivariate logistic regression and receiver operating characteristic (ROC) curve analyses were performed to identify independent risk factors and their predictive performance. Results Dural entrapment occurred in 15 of 257 segments (5.8%). Symptomatic entrapment was observed in 2 cases (0.8%), one requiring revision surgery. Multivariate analysis identified degenerative spondylolisthesis (adjusted OR 46.88, p < 0.001), postoperative ipsilateral facet joint gap (adjusted OR 8.02, p = 0.003), and dural sac-to-canal ratio (adjusted OR 3.21, p = 0.031) as independent risk factors. ROC analysis demonstrated good predictive accuracy for the facet joint gap (AUC 0.786) and dural sac-to-canal ratio (AUC 0.705), with excellent performance for the combined model (AUC 0.925). Conclusion Dural entrapment after UBE lumbar decompression, though uncommon, may cause significant morbidity. Anatomical and biomechanical factors, including facet joint gap widening, play a critical role. Careful surgical techniques and targeted preventive strategies are essential to minimize this complication.