Risk Factors for Conversion to Open Spinal Surgery after Percutaneous Epidural Neuroplasty

Study design: Retrospective case-control study. Objective: To evaluate the risk factors for conversion to open spinal surgery after percutaneous epidural neuroplasty (PEN) and suggest appropriate indications for PEN. Summary of Literature Review: PEN is a minimally invasive therapy wherein a catheter is directly placed into various spine pathologies, and it has reported to be safe and effective. However, the incidence and risk factors of conversion to open spinal surgery have not been reported. Materials and Methods: This study included patients who underwent PEN from 2019 to 2020, for lumbar spinal stenosis on magnetic resonance imaging (MRI), with at least 6-month follow-up and computed tomography (CT) scans to evaluate spinal hard-tissue pathologies. Radiologic parameters included the degree of central and foraminal stenosis on MRI, the presence of spondylolisthesis, and hard-tissue pathologies including calcified ligamentum flavum and discs on CT. Clinical outcomes included the numeric rating scale (NRS) for back pain and leg pain, and the Oswestry Disability Index (ODI). Results: Among 63 patients, 7 (11.1%) underwent open surgery within 6 months after PEN. The mean time from PEN to open surgery was 49.7±32.4 days. Risk factors for conversion to open surgery were the grade of central stenosis, calcification of ligamentum flavum, and limited contrast spread within the canal (p<0.05 for all). Multivariate analysis revealed that the independent risk factors were calcification of the ligamentum flavum (odds ratio [OR]=8.4, p=0.045) and intra-canal contrast spread (OR=16.3, 95% CI, 2.3–114.9; p=0.005). The NRS for back pain and leg pain and ODI at 1 and 3 months postoperatively were significantly greater in the surgery group than in the non-surgery group, despite similar preoperative values. Conclusions: The rate of conversion to spinal surgery after PEN within 6 months was 11.1%. Calcified ligamentum flavum and intra-canal contrast spread were risk factors for conversion to open spinal surgery. Thus, preoperative CT scans should be conducted and careful consideration should be taken for patients at high risk for open spinal surgery.