Lumbar Neuraxial Ultrasound Corrrelation With MRI

Ultrasound is used increasingly to aid placement of neuraxial blocks. Good visibility of ligamentum duramater complex and posterior longitudinal ligament (LF, PLL) has a positive predictive value of 85% for successful neuraxial block. Dural puncture could still be feasible despite the absence of a good view, as reflected by a negative predictive value of 30%. Poor neuraxial ultrasound view could be due to limitations of ultrasound or various other anatomical reasons which might include absent LF, calcification of ligaments, spinous process contact and presence or absence of epidural or subdural fat. This will be the first study of its kind to compare neuraxial ultrasound with MRI. The aim of this study is to look for anatomical correlation between neuraxial ultrasound and MRI at various lumbar interspinous levels and to look at factors that contribute to abnormal neuraxial imaging. Assuming the predicted abnormal ultrasound images to be around 30% and predicted abnormal MRI images to be 5%, 79 images should give a power of 0.9 and alpha 0.01 to analyse the association between the two. Sample Size Calculations were performed using statistical software R version 2.15.2