Variation of sciatic nerve cross-sectional area in different positions of the flexion-distraction table: a cross-sectional study

Abstract

Objective: To compare the cross-sectional area (CSA) of the sciatic nerve in different positions of the flexion-distraction table (FDT). Methods: A cross-sectional study was performed on 30 healthy subjects. The CSA of the sciatic nerve was measured with Ultrasound Imaging (USI) in transverse sections in the posterior medial region of the left thigh. Six different FDT positions with variation of lumbar, knee and ankle positioning were performed. Participants remained in three positions with the lumbar in the neutral position
(initial positions: A with knee extended, B with knee flexed and C with knee extended and ankle dorsiflexion) and other three positions with the lumbar flexed (final positions: D with knee extended, E with knee flexed and F with knee extended and ankle dorsiflexion). The CSA values measured at each position were compared. Results: 30 healthy subjects (16 women – 53.3%) participated in the study with a mean and standard deviation of age of 35.5 ± 6.2 years, height of 1.71±0.9 m, weight of 72.1±16.1 kg and body mass index of 24.4±3.8. We analyzed 180 USI and the results of CSA of the sciatic nerve (in mm2) were described in
descending order of FDT positions, in mean and with a confidence interval of 95% (M; 95% CI) for initial position B (59.71; 53.21-66.21), initial position A (54.34; 49.21-59.47), final position E (53.57; 48.57-58.56), final position D (51.18; 46.03-56.34), final position F
(48.71; 43.05-54.37) and initial position C (48.37; 42.26-54.47). The results were described in with mean and standard deviation, mean difference, confidence interval and p-value (M±SD, ≠M, CI95%, p), the initial position B (with neutral lumbar and knee flexion) (59.71±17.41), presented higher CSA when compared to the final position D (with lumbar flexed and knee extended) (51.18±13.81; 85.27(18.78/151.76); p=0.005), to final position F (with lumbar flexed and ankle dorsiflexion) (48.71±15.16; 110.02(24.41/195.63); p=0.004) and to the initial position C (with neutral lumbar and extended knee) (48.37±16.35; 113.46(19.35/207.56); p=0,009). Conclusion: The sciatic nerve can change its CSA in different positions in the FDT, with reduction of its CSA in combination of knee extension and ankle dorsiflexion. Flexing the knee and keeping the ankle in the neutral position increase CSA sciatic nerve.