Ultrasound estimates of the epidural depth in the paramedian sagittal oblique and transverse median planes: the correlation between estimated and actual depth to the epidural space in children with scoliosis

Introduction The present study aimed to compare the correlation and agreement of epidural depth estimation using ultrasound in the paramedian sagittal oblique (PSO) versus the transverse median (TM) plane relative to the actual epidural depth observed during midline epidural punctures in children with scoliosis.Methods In this prospective observational study, we enrolled 55 children aged 3-14 years with thoracolumbar scoliosis (Cobb angle >10 degrees) requesting postoperative epidural analgesia. Ultrasound imaging was performed to estimate the distance from the skin to the epidural space in the bilateral PSO and TM planes. An anesthesiologist performed midline epidural puncture and measured the actual epidural depth from the skin to the epidural space. The correlation and degree of agreement between the ultrasound-estimated and actual epidural depths were investigated using Pearson's and concordance correlation coefficients. The image quality of the ligamentum flavum and posterior dura mater was compared.Results In the PSO view, where the larger of the two measurements from both sides was used, both Pearson's and concordance correlation coefficients for comparing the actual epidural and ultrasound-estimated depths were significantly higher than those in the TM view (0.964 vs 0.930, p value=0.002; 0.952 vs 0.892, p value=0.004, respectively). The ligamentum flavum-posterior dura mater unit was more easily distinguished in the PSO view than in the TM view (72.7% vs 38.2%, p value<0.001).Conclusions The PSO view can be a reliable guide to facilitate epidural puncture in children with scoliosis with better visualization.