Frailty-Modulated Outcomes After Microscopic Versus Unilateral Biportal Endoscopic Decompression for Degenerative Lumbar Spinal Stenosis Without Instability

Study Design. Retrospective observational cohort study. Objective. To compare clinical outcomes and paraspinal muscle preservation between microscopic decompression and unilateral laminotomy for bilateral decompression (ULBD) using unilateral biportal endoscopy (UBE) in degenerative lumbar spinal stenosis (DLSS) without instability, and to assess the influence of frailty. Summary of Background Data. Both microscopic decompression and UBE-assisted ULBD are commonly used for DLSS, but comparative data addressing frailty and muscle preservation are limited. Methods. A total of 180 patients with 1–2 level DLSS without instability were retrospectively analyzed and assigned to microscopic decompression (n=90) or UBE-assisted ULBD (n=90). Frailty was assessed using the modified Frailty Index-11. Outcomes included Oswestry Disability Index (ODI) and Visual Analog Scale (VAS) scores for back and leg pain, evaluated preoperatively and at 12 months. Clinical success was defined as meaningful improvement in ODI. Paraspinal muscle injury was assessed on MRI by multifidus muscle atrophy and fatty infiltration. Inverse probability of treatment weighting was used for adjustment. Results. Both techniques significantly improved ODI and VAS scores at 12 months ( P <0.001). ODI improvement and clinical success were higher in the UBE group (92.2% vs. 78.9%; P =0.012). MRI demonstrated less multifidus atrophy and fatty infiltration after UBE. Frailty was negatively associated with functional improvement, with a significant interaction favoring UBE in frailer patients ( P =0.018). Conclusions. Both techniques are safe and effective for DLSS without instability. However, UBE-assisted decompression provides superior functional outcomes and better paraspinal muscle preservation, particularly in frail patients.