For example, Lee and Dauphinée ( 11) found an increased CSA using ultrasound in patients with DPN (24 mm 2) compared with healthy control subjects (12 mm 2). Variations in methods in the current literature give a variation in results and make the studies difficult to compare ( 11, 12, 16– 21). Resultsįirst our study demonstrates that the CSA in the tarsal tunnel is significantly larger in patients with painful DPN (8.4 ± 3.9 mm 2) than in healthy control subjects (6.4 ± 1.3 mm 2), P = 0.007. Using 38 control subjects and 42 patients, we have 80% power to detect differences between the groups of 0.65 SDs (=Cohen’s D) per variable, which is a medium size difference. The sample size of the study was therefore not tailored to the current research question. The current study was performed as a substudy from a randomized controlled trial. Statistical significance was assessed as P < 0.05. To test the reliability of the ultrasound measurements, intraclass correlation coefficients (ICCs) were calculated using a two-way mixed model and consistency measures. To identify potential confounding effects, multivariate analysis was performed using MANOVA. For comparison of values within patients, a paired Student t test was applied. To determine whether there were significant differences between the patients and control subjects, an independent samples Student t test was applied for continuous variables and the χ 2 test for categorical variables. The mean and SDs for the CSA, T/W ratio, and thickness of the retinaculum were assessed. All measured values were compared between the patients with DPN and the control subjects. The thickness-to-width (T/W) ratio was determined by dividing the shortest axis by the longest axis.Īnalyses were performed in IBM SPSS statistics version 20.0. CSA was calculated by major axis × minor axis × pi × 1/4. At follow-up, the radiologist was not blinded for the groups. At baseline, the radiologist randomly examined healthy control subjects and patients with DPN. All subjects underwent ultrasonography at baseline, and patients at follow-up as well. The thickness of the flexor retinaculum itself was measured as well. Measurements were performed by drawing an ellipse around the nerve, after which the program calculated the minor and major axis and the CSA ( Fig. The short axis and long axis of the tibial nerve were measured at two specific locations: the medial plantar branch of the tibial nerve under the flexor retinaculum and the tibial nerve cranial to flexor retinaculum, 3 cm proximal to the malleolar calcaneal line. One single radiologist (I.t.K.) performed an ultrasound in both legs of the tibial nerve at the medial ankle, with the patient in supine position and the hip in exorotation, using a Philips iU22 with a 15-7–MHz transducer.
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