Posterior tibial nerve stimulation: is ultrasound guided needle placement more accurate?

Introduction: To compare the accuracy of the transcutaneous ultrasound (US) in detecting the tibial nerve (TN) as opposed to digital palpation in the performance of posterior tibial nerve stimulation (PTNS). Materials and methods: After Institutional Review Board (IRB) approval, 25 adults were enrolled to quantify the difference in position of the distal TN by the use of US as opposed to cutaneous palpation. The position of the TN was determined first by the palpation method and then by using a L12-4MHz high frequency Linear Array Transducer. The difference in position between the two methods was determined in both proximal distal (PD [Knee-Sole]) and anterior-posterior planes (AP). Statistical analysis was completed with numeric variables summarized with the sample median, range, and interquartile range (IQR). Categorical variables were summarized with the number and percentage of patients. Comparisons between AP and PD distances were performed using a nonparametric Wilcoxon signed rank test. Box and whisker plots were used to display individual observations graphically. All analyses and graphics were performed using SAS statistical software (version 9.4M5, SAS Institute Inc., Cary, NC, USA). Results: Twenty-five patients were studied. The median AP distance between US and digital palpation was 2 mm (range, 0-5 mm; IQR, 2-3 mm). The median PD distance between US and digital palpation was 4 mm (range, 0-9 mm; IQR, 3-5 mm). The median difference between the AP and PD distances was 2 mm (range, -3-7 mm; IQR, 0-4 mm, p < 0.001). Conclusion: The use of US identifies the nerve with statistically significant greater accuracy than palpation technique along the PD plane.