Variations in the Formation of the Median Nerve and Its Clinical Correlation

Introduction:The median nerve is commonly formed by the fusion of two roots, i.e., the lateral root arises from the lateral cord and the medial root from the medial cord. These roots embrace the axillary artery (third part) and then unite with each other slightly below the level of pectoralis minor, just anterior or anterolateral to the axillary artery. It is associated with different variations like origin from more than two roots, splitting of the nerve and abnormal connections with neighbouring nerves like musculocutaneous or ulnar nerve. Objectives:To explore the different anatomical variations in the formation of the median nerve in the North Indian population. Material and methods:We studied different variations in the formation of the median nerve during routine dissection classes of the upper limb which was for the undergraduate medical students at the Department of Anatomy of Indira Gandhi Institute of Medical Sciences, Patna, Bihar, India. The present study was conducted on a total of 84 upper limbs, of 42 formalin-preserved cadavers, of which 28 belonged to males and 14 to females. Results:We observed several variations in the formation of the median nerve. Three roots contributed to the formation of the median nerve in 25% of male subjects, among which the third root arose from the lateral cord of the brachial plexus in 16.07% of cases, and from the musculocutaneous nerve in 8.93% of cases. In females, three roots were found in 21.42% of cases, among which the root arose from the lateral cord of the brachial plexus in 14.28% of cases and from the musculocutaneous nerve in 7.14% of cases. Four roots were found in 5.36% of male cases, while in females they were found in 7.14% of cases. The formation of the median nerve occurred in the arm in 11.91% of cases (8.33% belonging to males and 3.58% to females), while in the axilla, it is formed anterior to the axillary artery in 4.76% of cases (3.57% belonging to males and 1.19% to females), medial to the axillary artery in 2.38% of cases (1.19% were found in both male and female cadavers). We also observed an abnormal connection between the median nerve and musculocutaneous nerve in two upper extremities (2.38% of cases) in one male and one female cadaver and one upper extremity of a female cadaver (1.19% of cases) in which the median nerve is present lateral to the brachial artery at the level of the cubital fossa. Conclusion:The knowledge about variations in the formation of the median nerve is relevant to both anatomists and surgeons. It is useful during different surgical procedures around the axilla and also helps in reducing the failure rate of nerve blocks around the infraclavicular part of the brachial plexus during surgeries involving this area.