Radiologic and clinical outcomes of unilateral biportal endoscopic decompression for thoracic ossification of the ligamentum flavum.

Abstract

Thoracic ossification of the ligamentum flavum (OLF) is a major cause of thoracic myelopathy requiring surgical decompression. While unilateral biportal endoscopy (UBE) has been increasingly applied to thoracic decompression, quantitative radiologic evidence regarding decompression adequacy and posterior structure preservation remains limited. This retrospective single-center study included consecutive patients who underwent thoracic UBE decompression for OLF. Radiologic outcomes were assessed at the segment level using magnetic resonance imaging and computed tomography. Dural sac cross-sectional area (DSCA), facet joint length and area, and segmental kyphosis were quantitatively measured preoperatively and postoperatively. Clinical outcomes were evaluated using the modified Japanese Orthopaedic Association (mJOA) score, Nurick grade, and visual analog scale (VAS). Postoperative residual OLF and complications were recorded. A total of 45 patients (55 segments) were analyzed with a mean follow-up of 16.0 months. Mean DSCA increased significantly from 70.4 ± 20.4 mm² preoperatively to 119.8 ± 31.0 mm² postoperatively, corresponding to a mean expansion ratio of 75.0%. Facet preservation was asymmetric, with significantly greater preservation on the contralateral side compared with the ipsilateral approach side (facet area preservation: 79.4% vs. 64.2%, p < 0.001). Segmental kyphosis increased modestly at 1-year follow-up (mean change, 1.5°), while clinically significant kyphotic progression requiring surgical stabilization was rare. Clinical outcomes improved significantly, with a mean mJOA recovery rate of 71.2%. Residual OLF was observed in a subset of segments and primarily reflected an intentional floating strategy rather than incomplete decompression. Thoracic UBE decompression for OLF achieves substantial dural sac expansion and favorable clinical outcomes while preserving posterior stabilizing structures. In this retrospective single-arm cohort, adequate decompression was accomplished without routine fusion or extensive posterior element disruption. Thoracic UBE may be a feasible, tissue-preserving option in carefully selected patients with thoracic OLF, although comparative studies are needed to define its role relative to conventional surgery.