OBLIGATORY ALTERATIONS IN THE MORPHOLOGY OF MEDIAN NERVE: A SONOGRAPHIC STUDY IN ASYMPTOMATIC INDIVIDUALS

Abstract

Introduction: Median nerve is formed in axilla by contributions from medial and lateral cords of brachial plexus. It descends in the arm, forearm and then through carpal tunnel in close conjunction with flexor tendons of forearm. Carpal tunnel syndrome (CTS) is a common entrapment neuropathy. Median nerve cross sectional area (CSA) and ratio of nerve major axis to minor axis (flattening ratio) serve as potential diagnostic criteria for carpal tunnel syndrome. Median nerve cross sectional area and flattening ratio (FR) can be assessed by ultrasonography (US). Aim of the study was to assess median nerve by US and tabulate mean values for CSA and FR in asymptomatic population. This would serve to limit the cut-off values that differentiate asymptomatic nerves from neuropathic nerves. Material & Methods: Study was conducted in the Department of Anatomy, KGMU, Lucknow. Fifty randomly selected asymptomatic volunteers (undergraduate students: 30 males, 20 females) participated in the study. Sonography was performed to evaluate certain morphological dimensions of median nerve. Height, weight and wrist circumference of participants were also noted. Ultrasonography was performed using high frequency linear probe and observations were made at two pre-determined sites. Observations were recorded, tabulated and analyzed. Results: Median nerve was easily observable at both sites. It was round in shape in forearm (Fo), and flattened as it reached the carpal tunnel (Ct). Among all 50 study subjects, at both sites, flattening was more on right side (FRFoRt-1.71; FRCtRt-3.08) than on left side (FRFoLt-1.66; FRCtLt-2.78). In right forearm, nerve was flatter in females (FRFoRt-1.77) as compared to males (FRFoRt-1.68). In left forearm, median nerve was slightly rounder in females (FRFoLt-1.65) as compared to males (FRFoLt-1.67). At the distal wrist crease on right side, increased flattening was observed in females (FRCtRt-3.30) as compared to males (FRCtRt-2.94), whereas on left side, at same site flattening was more in females (males FRCtLt-2.74; females FRCtLt-2.83). Conclusion: Altered FR has both diagnostic as well as prognostic values in carpal tunnel syndrome. The database generated from the study will help in facilitating comparisons between normal, asymptomatic and pathological, asymptomatic individuals.