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ORIGINAL ARTICLE
Year : 2007  |  Volume : 10  |  Issue : 2  |  Page : 100-104
 

Various types of intercommunications between musculocutaneous and median nerves: An analytical study


Department of Anatomy, Assistant Professor, NRI Medical College, Chinakakani. Guntur Dist., Andhra Pradesh, India

Correspondence Address:
R Chitra
17-15-33, Ramasamy Nadar Street, Purnanandampet, Vijayawada
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0972-2327.33217

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   Abstract 

Intercommunications between musculocutaneous nerve and median nerve deserve important interest in view of their clinical significance. In the study of 50 upper limb specimens, the various communications between the musculocutaneous and median nerve in the arm were observed carefully. The communications between the two nerves were found in 13 arms. Variations in the present study involving the median nerve and musculocutaneous nerve are important in repairs for trauma to the shoulder and the understanding of the median nerve and the musculocutaneous nerve dysfunction.


Keywords: Intercommunications, musculocutaneous and median nerves


How to cite this article:
Chitra R. Various types of intercommunications between musculocutaneous and median nerves: An analytical study. Ann Indian Acad Neurol 2007;10:100-4

How to cite this URL:
Chitra R. Various types of intercommunications between musculocutaneous and median nerves: An analytical study. Ann Indian Acad Neurol [serial online] 2007 [cited 2020 Feb 24];10:100-4. Available from: http://www.annalsofian.org/text.asp?2007/10/2/100/33217



   Introduction Top


The musculocutaneous nerve is normally the terminal branch of lateral cord of brachial plexus and it pierces the coracobrachialis muscle. Before it pierces the coracobrachialis, it supplies the muscle. After piercing the coracobrachialis, it descends in between the biceps muscle and brachialis muscle and supplies the above muscles and descends as lateral cutaneous nerve of forearm. Number of variations in the course and distribution of the musculocutaneous nerve have been reported. Instead of piercing the coracobrachialis muscle, the nerve may adhere to the median nerve for some distance down the arm and then, either as a single trunk or as several branches, pass between the biceps and brachialis muscles to supply all three muscles (about 22% of arms). Sometimes only a part of the nerve follows this course; this part then rejoins the main trunk after it transits through and supplies coracobrachialis. In some cases, instead of the whole trunk of the nerve piercing coracobrachialis, only its muscular branch or only its cutaneous branch pierces the muscle. The musculocutaneous nerve may be accompanied by fibers from the median nerve as it transits coracobrachialis; a communicating branch passes from the musculocutaneous to the median nerve.[1]

The median nerve is normally formed by two roots, the lateral root and the medial root from the corresponding cords of the brachial plexus. It descends crossing the brachial artery from lateral to medial side and descends without giving any branch in the arm. The following variations in the formation, course and distribution of this nerve have been reported. The combination from the first thoracic nerve to the formation of the median nerve may be missing. The site of union between the lateral and medial branches is quite variable and has been found as far down as the elbow. The two branches may enclose the axillary vein as well as the axillary artery.[1]


   Materials and Methods Top


This study was conducted in 50 upper limb specimens (25 cadavers) dissected by the undergraduate students of our college. The bodies were embalmed with femoral arterial perfusion of 4% formaldehyde and bodies were then preserved in weak solution of formalin for one year before dissection. The brachial plexus of both sides were dissected carefully with particular importance to the communications between the musculocutaneous and median nerves and the deviations from the normal pattern were noted, sketched and photographed.


   Results Top


The communications between the two nerves were observed under the following protocol:

  1. Whether the formation of two nerves were normal.
  2. Direction of the communication- from musculocutaneous to median nerve or from the median nerve to musculocutaneous nerve
  3. Site of communication in relation to bony processes such as coracoid process of scapula, condyles of the humerus.
  4. Length of communicating branch.
  5. Number of communicating branches.


This protocol was based on Le Minor's[2] observations. In the present study, the communications were present in 13 upper limbs. Three cadavers had bilateral variations. All the communications that we observed in this study were single and from the musculocutaneous nerve to the median nerve. These observations are tabulated and compared with the classification of LeMinor[2] in [Table - 1]


   Discussion Top


Although communications between the nerves in the arm are rare, the communication between the median nerve and the musculocutaneous nerve were described by many authors[3],[4],[5] from nineteenth century.

The communications between the musculocutaneous nerve and the median nerve have been classified by earlier workers.[2],[6]

The variations of the musculocutaneous and median nerve may be classified into five types [Figure - 6] by Le minor.[2]

Type I: There are no connecting fibers between the musculocutaneous and median nerve as described in classic textbooks. The musculocutaneous nerve pierces the coracobrachialis muscle and innervates the coracobrachialis, the biceps brachii and brachialis muscle.

Type II: Although some fibers of the medial root of the median nerve unite with the lateral root of the median nerve and form the main trunk of median nerve, remaining medial root fibers run in the musculocutaneous nerve leaving it after a distance to join the main trunk of median nerve.

Type III: The lateral root of the median nerve from the lateral cord runs in the musculocutaneous nerve and leaves it after a distance to join the main trunk of median nerve.

Type IV: The fibers of the musculocutaneous nerve unite with the lateral root of the median nerve. After some distance, the musculocutaneous nerve arises from the median nerve.

Type V: The musculocutaneous nerve is absent. The fibers of the musculocutaneous nerve runs within the median nerve along its course. In this type the musculocutaneous nerve does not pierce the coracobrachialis muscle.

It is interesting that all the types described by Le Minor[2] were observed in our study. There is no past study describing all types of communications.

Venieratos and Anagnostopoulou[6] reported three types of communications between median and musculocutaneous nerves considering the coracobrachialis muscle as the reference point. In type one, the communication was proximal to the entrance of the musculocutaneous nerve into coracobrachialis. In type two, the communication was distal to the muscle and in type three, the nerve and the communicating branch did not pierce the muscle.

Venieratos[6] found 22 communications between the musculocutaneous and median nerves in 16 out of 79 cadavers. In six subjects they were present bilaterally. Nine of these 22 communications were proximal to the entrance of the musculocutaneous nerve into the coracobrachialis.

In the most recent observations recorded by Choi[7] such communications have been broadly classified into three patterns. In pattern 1, the two nerves are fused. In type 2, there was one communicating branch between the musculocutaneous nerve and the median nerve. In pattern 3, two connecting branches are between the two nerves.

Our observations of communications between musculocutaneous and median nerves were compared with various classifications and they are tabulated in [Table - 2].

Eglseder and Goldman[8] dissected 54 cadaver arms to determine the course and anatomic relationships of the musculocutaneous nerve in the arm. They noticed interconnections between the musculocutaneous nerve and median nerve in 36% of dissections. The mean length of these interconnections was 1.77 cm. Connections from median nerve to musculocutaneous nerve in the opposite direction are rarely found.[6]

Incidence of communication between musculocutaneous and median nerves in the present study is compared with previous authors and tabulated in [Table - 3].

Communication between the musculocutaneous and median nerves in the arm is considered as remnant from the phylogenetic or comparative point of view. Kosugi[10] suggested that there was one trunk equivalent to the median nerve in the thoracic limb of the lower vertebrates (amphibians, reptiles. birds). In man, the forelimb muscles develop from the mesenchyme of the paraxial mesoderm during the fifth week of intrauterine life.[11] The axons of the spinal nerves grow distally to reach the mesenchyme. As the guidance of the developing axons is regulated by the expression of chemoattractants and chemorepulsants in a highly coordinated site specific fashion, significant variations in nerve patterns may be a result of altered signalling between mesenchymal cells and neuronal growth cones[12] or circulatory factors at the time of fusion of brachial plexus cords.[10] Studies of comparative anatomy have observed the existence of such connections in monkeys and in some apes; the connections may represent the primitive nerve supply of the anterior arm muscles.[13]

Such variations have also clinical importance especially in posttraumatic evaluations and exploratory innervations of the arm for peripheral nerve repair. The knowledge of the variations of this communication between the musculocutaneous and median nerves in the distal third of the arm is important in the anterior approach for the fracture of the humerus. This knowledge is also important for the clinicians to avoid unnecessary release of the carpal tunnel by them. Lesions of the communicating nerve may give rise to patterns of weakness that may impose difficulty in diagnosis. Clinical implication of this could be that injury of musculocutaneous nerve proximal to the anastomotic branch between musculocutaneous and median nerve may lead to unexpected presentation of weakness of forearm flexors and thenar muscles.[14] There is a need for newer classification of the communication types between musculocutaneous and median nerves incorporating the different classifications.

 
   References Top

1.Bergman RA, Thompson SA, Afifi AK, Saadeh FA. Compendium of human anatomic variation. Munich and Baltimore: 1988. p. 139-43.   Back to cited text no. 1    
2.Le Minor JM. A rare variation of the median and musculocutaneous nerves in man. Arch Anat Histol Embryol 1990;73:33-42.  Back to cited text no. 2  [PUBMED]  
3.Harris W. The true form of the brachial plexus. J Anatomy Physiol 1904;38:399-422.  Back to cited text no. 3    
4.Testut, Trait: d" Anatomie, 4th ed. Vol 3, TI Liabrairie Octave Doin: Paris; 1899. p. 176.  Back to cited text no. 4    
5.Villar F. Quelques recherches sur lesanastomoses des nerfsdu member superieur. Bull Scoc Anat De: Paris; 1888. p. 607-15.  Back to cited text no. 5    
6.Venieratos D, Anagnostopoulou S. Classification of communications between the musculocutaneous and median nerves. Clin Anat 1998;11:327-31.  Back to cited text no. 6  [PUBMED]  [FULLTEXT]
7.Choi D, Rodriguez-Niedenfuhr M, Vazquez T, Parkin I, Sanudo JR. Patterns of connections between the musculocutaneous and median nerves in the axilla and arm. Clin Anat 2002;15:11-7.  Back to cited text no. 7    
8.Eglseder WA, Goldman M. Anatomic variations of the musculocutaneous nerve in the arm. Am J Orthop 1997;26:777-80.  Back to cited text no. 8  [PUBMED]  
9.Kerr AT. The brachial plexus of nerves in man. The variations in its formation and branches. Am J Anat 1918;23:285-395.  Back to cited text no. 9    
10.Kosugi K, Mortia T, Yamashita H. Branching pattern of the musculocutaneous nerve 1 case possessing normal biceps brachii. Jikeakai Med J 1986;33:63-71.  Back to cited text no. 10    
11.Larsen WJ. Human embryology in development of limbs. 2nd ed. Churchil Livingstone: Edinburg; 1997. p. 311-39.  Back to cited text no. 11    
12.Sannes HD, Rey TA, Harris W. Development of the nervous system in: Axon growth and guidance. Academic Press: New York; 2000. p. 189-97.  Back to cited text no. 12    
13.Miller RA. Comparative studies upon the morphology and distribution of the brachial plexus. Am J Anat 1934;54:143-7.  Back to cited text no. 13    
14.Sunderland S. Nerves and nerve injury. In : The median nerve: Anatomical and physiological features: 2nd ed. Churchil Livingstone: Edinburg; 1978. p. 672-7, 691-727.  Back to cited text no. 14    


    Figures

  [Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5], [Figure - 6]
 
 
    Tables

  [Table - 1], [Table - 2], [Table - 3]


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