High-resolution ultrasonography measurement of dimensions of median nerve at wrist in asymptomatic adults

ABSTRACT

Background: Ultrasonography (USG) is a cheap, easily available and painless modality for the diagnosis of carpal tunnel syndrome. However, the main sonographic criteria of cross sectional area (CSA) and flattening ratio (FR) of median nerve show a wide normal variation which warrants establishment of normal range of variability in the dimensions of median nerve in different populations. Objective: The main aim of this study was to calculate the mean cross sectional area (CSA) and flattening ratio (FR) of median nerve at wrist in asymptomatic adults. Materials and methods: This prospective observational study included asymptomatic adults visiting our tertiary care hospital for unrelated heath conditions with no symptoms to suggest carpal tunnel syndrome. Ultrasound examination of both wrists was carried out by high frequency linear array transducer with frequency of 10MHz with the arm in supine neutral position on LOGIQ P5 (GE Healthcare, Chicago, Illinois, USA) ultrasound machine. The cross-sectional area (CSA) and flattening ratio (FR) of the median nerve was measured at the level of carpal tunnel inlet and mean values with standard deviation were calculated. Results: Three hundred seventy six (376) wrists of 188 subjects were examined. 36 wrists were excluded owing to presence of anatomic variations of the median nerve in them. 340 wrists of 170 patients were included in the study. Mean cross sectional area of median nerve was 9.2 mm2 (±1.2). Arshed Hussain Parry, Abdul Haseeb Wani, Naseer Ahmad Choh, Tariq Ahmad Gojwari. High-resolution ultrasonography measurement of dimensions of median nerve at wrist in asymptomatic adults. IAIM, 2019; 6(4) 144-149. Page 145 Mean value of flattening ratio was 2.4 (±0.6). Mean CSA (9.26 ±1.2 mm2 ) and FR (2.41 ±0.6) of males was not significantly different from mean CSA (9.16 ±1.2 mm2 ) and FR (2.4±0.55) of females. However, mean CSA of right wrist (9.4 ±1.2 mm2 ) was significantly different from mean CSA of left wrist (9.10 ±1.1 mm2 ). Conclusion: We found a higher mean cross sectional area (CSA) of 9.2 mm2 of median nerve in our population. There was a significant difference in the cross sectional area of median nerve between right and left wrists. However, we did not find statistically significant difference in the CSA and FR between the males and females. Establishment of normative data for the dimensions of median nerve is essential for different populations given the wide range of variations in the dimensions of median nerve