VARIATIONS IN FORMATION OF MEDIAN NERVE: A CADAVERIC STUDY

Background: Median nerve is generally formed in axilla, as one of the branch of brachial plexus. It is formed by the union of medial and lateral roots which are the branches of medial and lateral cord respectively. The knowledge of origin, course and area of distribution of median nerve is important for the anatomist, the neurologist and also for correction of traumatic injuries that are related to brachial plexus. The main objective of this study is to observe different variations in median nerve formation in cadavers.


INTRODUCTION
Median nerve is one of the branches of brachial plexus formed by the union of two roots, lateral root from lateral cord and medial root from medial cord. It is present in front or to the lateral aspect of axillary artery in the axilla. 1 Variations in the arrangement and distribution of brachial plexus are common. The unusual branches are more prone to injury during the surgical operations in axilla and are also vulnerable in routine nerve repair. 2 The knowledge about the variations is significant for the neurologists, surgeons, anesthetists and the anatomists. This may contribute in explaining the diagnosis and surgical treatment around axilla and upper limb which can prevent operative as well as post operative complications. 3 The main objective was to study the variation in formation of the median nerve and its location.

METHODS
A descriptive cross-sectional study was conducted in the Department of Anatomy, KIST Medical College and Teaching Hospital, Lalitpur, Nepal. Data collection was done from 18/04/2019 to 29/01/2020 after obtaining ethical approval from Institutional Review Committee (IRC NO. 2075/76/66). Properly embalmed and well preserved 25 adult human cadavers of both sexes with intact nerves were included in the study. Cadavers with any kind of upper limb anomalies and cut branches of brachial plexus were excluded from the study. The fixed specimens (50 limbs) were dissected following the steps of Cunningham's Manual of Practical Anatomy vol.1. 4 The ethical standards of handling cadaver for teaching and learning purpose were followed during the procedures. According to this calculation, at least 51 samples were required. Altogether, 50 specimens were enrolled in the study by convenient sampling method. The cadavers were numbered from 01 to 25. Median nerve was studied in respect to its location and formation. The median nerve with additional roots were tagged and photographs were taken. All the observations were recorded and tabulated. The data was analyzed with the help of SPSS version 20 software.

RESULTS
The location of median nerve was axilla in 92% of specimen. In 78% (39/50) cases, the formation of median nerve was observed to be normal with two roots (Table 1).   In 20% (10/50) of cases median nerve had three roots among these 18% (9/50) cases had additional root arising from the lateral cord of brachial plexus (Figure 1). In 2% (1/50) of the cases four roots were forming the median nerve ( Figure 2) and both the additional roots were branches of the lateral cord.
The variations were mostly seen in right upper limb which was 24% (6/25) and on the left upper limb it was present in 16% (4/25) cases.
Only in 2 cadavers the additional roots in median nerve were present in both limbs. Both cadavers had 3 roots in both limb and the additional root was the branch from lateral cord.

DISCUSSION
Brachial plexus is associated with several variations such as in its formation, branches and communication. 5 Median nerve is one of the branches of brachial plexus whose variations regarding its formation and its communication with other nerves has been reported by many authors. Different authors have reported the formation of median nerve with additional roots. [6][7][8] In present study we observed variation in 22% (11/50) cases. Mostly the variations with three roots were seen. Due to the difference in the sample size the percentage in this study was different from other studies.
Buddhiraja et al reported the presence of three roots in 22.4% (44/196) cases, where additional roots were given by lateral cord in 14.2% cases and in 8.16% cases from musculocutaneous nerve. Similarly, four roots were present in 3.75% (7/196) cases with additional roots from both lateral and musculocutaneous nerve. 9 Similar type of observation with trifurcated origin in 26.41% and median nerve with four roots in 1.88% cases was present in study by Laxmi Kumari et al. 10 Among the four roots two roots were from lateral cord and two from the me- In this study 8% of cases presented formation of median nerve in the arm instead of axilla. Laxmi Kumari A et al 10 reported the formation of median nerve in arm in 8.49% cases. Similarly, in another study in 17.3 % cases formation was taking place in the arm. 9 The presence of median nerve in arm with the additional branches has also been reported. 6 This study has been conducted in limited number of cadavers. Out of 25 cadavers only 3 cadavers were of female, because of this reason it was not possible to include the study of sexual dimorphism.

CONCLUSION
There might be variation in number of root as well as location of formation of median nerve. Knowledge regarding such variation is important during the surgical operations to prevent operative as well as postoperative complications.

ACKNOWLEDGEMENT
The author would like to extend heartfelt gratitude towards Professor Dr. Prakash Man Singh Dangol for his constant guidance and support throughout this research.