|Year : 2020 | Volume
| Issue : 2 | Page : 66-71
Communication between the median nerve and the musculocutaneous nerve: Occurrence and significance
BN Shruthi1, Shreya Krishnamurthy2, K Ruthvik2, B Rahul2
1 HOD, Department of Anatomy, Rajarajeswari Medical College and Hospital, Kambipura, Karnataka, India
2 UG Student, Rajarajeswari Medical College and Hospital, Rajarajeswari Medical College and Hospital, Kambipura, Karnataka, India
|Date of Submission||16-Dec-2019|
|Date of Decision||11-Mar-2020|
|Date of Acceptance||23-May-2020|
|Date of Web Publication||10-Sep-2020|
UG student, Rajarajeswari Medical College and Hospital, Kambipura, Karnataka
Source of Support: None, Conflict of Interest: None
Background: The median nerve and musculocutaneous nerve are nerves arising from the brachial plexus supplying the muscles of the arm and forearm. The communication between these nerves is of clinical importance in the traumatology of the shoulder joint and upper arm and in situations where a surgeon needs to isolate and trace the median and musculocutaneous nerves distally. Aims and objectives: The study was conducted to observe and discuss the communications between the median and musculocutaneous nerves. The data was statistically analysed. Materials and Methods: The present study was conducted on 60 cadaveric upper limbs (left: right=30:30) obtained from the department of Anatomy, Rajarajeswari Medical College and Hospital, Bengaluru. The brachial plexus was dissected according to standard dissection procedures and the median nerve and musculocutaneous nerve were exposed. Results: The musculocutaneous nerve did not pierce the coracobrachialis in 5 limbs. However, the nerve did supply the coracobrachialis muscle in all cases. In 5 upper limbs (8.3%), a single communicating nerve was observed between the median nerve and the musculocutaneous nerve. In one case (1.67%), two communicating nerves were observed between the median nerve and the musculocutaneous nerve. Conclusion: Variations in the formation and branching of the brachial plexus have been reported by several researchers. The anatomical variations of musculocutaneous nerve and median nerve are important to neurosurgeons ,orthopaedicians and general surgeons who deal with cases of neurofibromatosis and neurotization procedures. Surgeons must consider the possible presence of the communication between the median nerve and musculocutaneous nerve in such cases.
Keywords: Anatomical variation, brachial plexus;, median nerve, musculocutaneous nerve, nervous communication
|How to cite this article:|
Shruthi B N, Krishnamurthy S, Ruthvik K, Rahul B. Communication between the median nerve and the musculocutaneous nerve: Occurrence and significance. Natl J Clin Anat 2020;9:66-71
|How to cite this URL:|
Shruthi B N, Krishnamurthy S, Ruthvik K, Rahul B. Communication between the median nerve and the musculocutaneous nerve: Occurrence and significance. Natl J Clin Anat [serial online] 2020 [cited 2020 Nov 28];9:66-71. Available from: http://www.njca.info/text.asp?2020/9/2/66/294751
| Introduction|| |
The muscles, joints, and skin of the upper limb are innervated by a network of nerves called brachial plexus. The anterior primary rami of 5th, 6th, 7th, 8th cervical and 1st thoracic spinal nerves contribute in the formation of brachial plexus. The above said nerves called as roots with respect to brachial plexus, combine in particular manner to form three trunks. They are upper trunk (C5–C6), the middle trunk (C7), and the lower trunk (C8-T1). These trunks bifurcate to form the anterior and posterior divisions. Anterior divisions of upper and middle trunks unite to form lateral cord, anterior division of the lower trunk continues as medial cord and the posterior divisions of all the trunks unite to form posterior cord. These cords give branches which supplies the upper limb.
Median nerve is formed by the union of medial and lateral roots (of median nerve) contributed by medial and lateral cords (root values C5–C6 and C8-T1), respectively. Whereas the musculocutaneous nerve is one of the terminal branches of the lateral cord of the brachial plexus with root value C5-7.
After exiting from the axilla, it pierces the coracobrachialis muscle, near its insertion then supplies biceps brachii and the Coracobrachialis muscles of flexor compartment of arm. Later, it terminates by innervating the skin over the lateral aspect of forearm, hence called lateral cutaneous nerve of antebrachium.
By 5th week of intrauterine life of embryo, the upper limbs appear as paddle-shaped limb buds. During the 6th week, the ends of the limb buds become flattened to form hand plates. Digits develop from these hand plates. By the 7th week of embryonic life, the upper limb rotates such that the thumb lies laterally. By the 3rd month of embryonic development, skeletal muscles in the upper limb begin to develop striations. The development of the nervous system is coordinated with the development of the rest of the structures of the upper limb. The communicating segment between median nerve and musculocutaneous nerve may have developed at the same time as the rest of the named nerves of the brachial plexus.
Variations in the origin and formation of the nerves of the brachial plexus, such as the median nerve and musculocutaneous nerve, are considered normal. The most frequent variation observed in man is the musculocutaneous nerve being absent. The communication between the nerves is of clinical importance in situ ations where the median and musculocutaneous nerves have to be isolated and traced distally.,,
A proximal lesion in the brachial plexus after the origin of the musculocutaneous nerve could possibly affect the functionality of the arm. The anatomical variations of the median and musculocutaneous nerves are important to neurosurgeons, orthopedists, and general surgeons who deal with cases of neurofibromatosis and neurotization procedures. Such communications between the nerves are of significant importance to the surgeons while treating above cases.
The current study was undertaken to
- Discuss the topography of the variation between the median nerve and musculocutaneous nerve
- Discuss the clinical importance of the variations.
| Materials and Methods|| |
The study was undertaken in the Department of Anatomy, Rajarajeswari Medical College and Hospital. Sixty upper limbs of adult human cadavers (age approximately 18–60 years), 30 left and 30 right, irrespective of sex were studied. Cadavers outside the age range, cadavers with congenital anomalies, obese cadavers, and cadavers with damaged brachial plexus were excluded from the study.
Ten percent formalin was used to preserve the limbs and were dissected following the Cunningham's manual, 16th edition by incising along the anterior axial upper limb. Roots, trunks, divisions, cords, and branches of the brachial plexus were cleared. The following observations/measurements were photographed/tabulated, and statistically analyzed;
- Musculocutaneous nerve and median nerve-whether present or not
- Whether the musculocutaneous nerve pierces the coracobrachialis or not
- Existence of a communicating segment between musculocutaneous and median nerve
- Distance of communicating segment calculated from the tip of acromion process
- The length of the communicating segment
- The pattern of branching.
The distance between the points of formation of communicating segment (between the two nerves) from the tip of the acromion process was measured using a thread and measuring tape. All measurements were made in centimeters.
All the tabulated measurements were analyzed for statistical significance.
Each case of communication was carefully studied and classified according to Le Minor and Choi et al. system of classification.
Le Minor in his study, classified the variations into five types:
- Type I: No communicating segment between the two nerves
- Type II: The fibers of lateral root of median nerve joins the musculocutaneous nerve initially and in the middle of the arm finally joins with the main median nerve
- Type III: The fibers of lateral root fibers of the median nerve initially runs along with musculocutaneous nerve for a short length and then change their course ultimately continue as lateral root of the median nerve
- Type IV: Few of the fibers musculocutaneous nerve included in the lateral root which separate out and pass along their course after a short distance
- Type V: Fibers of musculocutaneous nerve entirely joins with the lateral root of median nerve supply the muscles of anterior compartment of arm. Hence, there is absence of musculocutaneous nerve altogether [Figure 1].
|Figure 1: Li Minor classification of communication between median nerve and musculocutaneous nerve|
Click here to view
According to Choi et al., there are three different types of communication between the nerves (median and musculocutaneous):
- There is fusion of both the nerves
- A supplementary segment exists between the two nerves
- Single root extending from the musculocutaneous nerve
- Their exists two roots from the musculocutaneous nerve, contributing to the connection.
- Two branches are present from both nerves [Figure 2].
|Figure 2: Choi classification of communication between median nerve and musculocutaneous nerve|
Click here to view
| Results|| |
In this study, the following variations of the median and musculocutaneous nerves were observed and studied separately on the right and left limbs.
The musculocutaneous nerve was present in all 60 limbs. It pierced the coracobrachialis in 93.33% (28) of the limbs on the left side and in 90% (27) of the limbs on the right side. Altogether the musculocutaneous nerve did not enter the coracobrachialis in 16% (5 limbs–2 left and 3 right) of the cases. It crossed the superficially and supplied the muscles of flexor compartment of arm before continuing as the lateral cutaneous nerve of arm.
The median nerve was present in all the limbs studied.
Lateral cord contributed lateral root of median nerve and musculocutaneous nerve in all of the limbs studied. Of the 60 limbs dissected, 54 (90%) limbs had normal anatomy, and 6 (10%) limbs were found to have a communicating segment between the two nerves.
They were of varied shapes-some of the communications were flat, wide (4 out of 6) and others were cylindrical and narrow (2 out of 6).
In the present study, the mean distance of communicating segment from the acromion process of the scapula was 15.35 cm on left, 20.86 cm on right side and average being 19.28 cm, and the t-test was significant with a P = 0.0014, at a significance of P < 0.05.
The mean length of communicating segment in the observed cases was 5.15 cm on left, 7.66 cm on right and the average was 6.942 cm with standard deviation being 6.37 cm. t-test for the length of the communicating segments of left versus right was significant at P < 0.0001 for a significance of P < 0.05.
No fusion was observes between the two nerves in any of the upper limbs studied.
In this study, the most common alterations observed were that the lateral root fibers of median nerve joined with musculocutaneous nerve initially and later altered its course to join the main median nerve. Five of the observed cases were found to have a Le Minor type II communication between the two nerves. One limb was observed to have a rare Le Minor Type IV communication between the two nerves.
According to Choi system of classification, three of the observed cases had communications of the Type 2a, one case had a Type 2b communication, and one case had a Type 3 communication. The Type 2b and Type 3 communications were seen only in the right limb.
The growth pattern, branching, and remaining course of musculocutaneous nerve and median nerve was normal and unremarkable. There was no significant difference observed in the morphology or anatomy of the upper limbs in cases where communication was observed between the two nerves studied. There was observed no deformity of upper limb in any case and no apparent loss of function.
| Discussion|| |
In our study, communication between the median nerve and musculocutaneous nerve was found in 6 of the 60 cases.
The alterations of the median nerve, and its communications with the musculocutaneous nerve has been documented in various studies.,,,,,
In the 20th right and 3rd left upper limb, the musculocutaneous nerve was not seen to enter and pass through the coracobrachialis after forming a communicating segment.
In a study by Kerr, where the absence of musculocutaneous nerve was studied, the author noticed that the absence of multicystic nephroma could be unilateral or bilateral. In the same study the median nerve innervated all the anterior compartment muscles (5.14%) or the biceps and the brachialis supplied by median nerve and the coracobrachialis by the branches of lateral cord.
Similar to our findings in the right arm, Venierators and Anagnostopoulou observed communications between the two nerves in 16 limbs out of 79 studied. Communication was present bilaterally in 6 cadavers, altogether there were 22 communications. In 10 out of 22 cases, communication was distal to the coracobrachialis muscle. Venieratos and Anagnostopoulou believed it to be the most frequent type of variation of musculocutaneous nerve.,
Considering the large number of variations in the formation of the median and musculocutaneous nerves discussed, many attempts have been made to categorize such variations. Among them, the most widely used is the one advocated by Le Minor, which has five types of variations.,
In our study, the most common variant noted was that, the fibers of lateral root of median nerve joining with the fibers of musculocutaneous nerve initially and then changing its course to merge with the median nerve.
Five of the observed cases were found to have a Le Minor Type II communication between the two nerves. One case was observed to have a rare Le Minor Type IV communication between the two nerves studied [Figure 3].
|Figure 3: Choi type 3 Communication between the median nerve and musculocutaneous nerve in the arm|
Click here to view
Also four observed cases had communications of the Type 2a, one case had a Type 2b communication and one case had a Type 3 communication, in terms of Choi et al. classification [Figure 4] and [Figure 5].
|Figure 4: Choi type 2B communication between the median nerve and musculocutaneous nerve in the arm|
Click here to view
|Figure 5: Choi type 2A communication between the median nerve and musculocutaneous nerve in the arm|
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Some authors also have classified the variations in the musculocutaneous nerve taking into consideration the number of communicating segments and the length of such segments.
In the present study, anastomosis of the musculocutaneous nerve occurred before the origin of muscular branch to coracobrachialis muscle, in the cases where there were Choi Type 2a communications observed.
Abhaya et al. classified it as the dual origin of musculocutaneous nerve in their studies. The incidence of occurrence of communicating segments between the two nerves as reported by different studies is represented in [Table 1].
|Table 1: Occurrence of communication between median nerve and musculocutaneous nerves as reported by different studies,,,,,,,,,,,,,|
Click here to view
In a study undertaken by Chaudhary et al., it was found that in all of the limbs in which communicating segments were found, the branching pattern was categorized as type II (Le Minor) and Type 2a (Choi). The mean length of the communicating segment was 4.3 cm in comparison with 6.95 cm in the present study.
With respect to Choi et al. classification, the incidence of type 1 communications was 13.1%, type 2 was 75.4% and type 3 was 8.5%. This is in comparison with the findings of the present study, where there were no type 1 variants, 83.33% type 2 variants, and 16.66% type 3 variants.
In the studies cited above, there was relationship of statistical significance observed between the incidence variations and gender.
However, it is not possible to apply these statistical findings to a larger population, due to a greater variation in genetic and environmental factors that might cause a predisposition to this anomaly.
Thus, it is vital that surgeons and anesthetists consider the possibility of such a variation in nerve structure while performing a Bier's block or a single nerve block anaesthesia [Table 2].
|Table 2: Average length of communicating segment between median and musculocutaneous nerves,,|
Click here to view
The variations in the formation of median nerve and its communications with the musculocutaneous nerve in the arm have also been documented by various researchers.
The findings of this study were found to be in accord with the findings of the studies conducted by Chaudhary et al., Aktan et al., Ferriera H, and Yang et al., and the average length of communicating segment was found to be closest to the findings in the study conducted by Prasada Rao and Chaudhary.,,,
These variations are considered to be of clinical importance in the evaluation of the upper limb following trauma and in exploratory innervation of the arm for peripheral nerve repair procedures. An unexpected presentation of weakness of forearm flexor muscles and thenar muscles of hand may be a consequence of the injury to the musculocutaneous nerve proximal to the communicating branch between the two nerves.
Understanding of the variations of this communication between the two nerves in the middle of the upper limb is quite important during the anterior approach for the treatment of humerus fractures.
In this study, the communication between the two nerves was not similar in left and right upper limbs, in incidence or formation.
With respect to phylogeny, the communicating segment between the two nerves is considered as remnant of fetal development processes. Imokawa observed that in lower vertebrates (reptiles, birds, and amphibians) there was only one trunk that could be equated to the median nerve in the thoracic limb.
Ernst Haeckel's quote “ontogeny recapitulates phylogeny” is used to explain the recapitulation theory. According to this theory of embryological parallelism, the presence of communicating segment between the two nerves such as that seen in this study is attributed to a developmental/congenital anomaly.
In humans, the upper limb muscles develop from the paraxial mesoderm around 5th week of intrauterine life. The fibers of the designated spinal nerves reach the limb bud mesenchyme by growing distally. The development of nerve fibers is controlled by chemicals in a highly coordinated manner. Any variation in this coordination between the mesenchymal cells and growing nerve fibers can lead to alteration in the path of the nerve. This type of anomaly in the growth of axons in coracobrachialis muscle can lead to a condition where the coracobrachialis muscle is not pierced by the musculocutaneous nerve.
Alternatively, the presence of the communication could be due to variations in circulation during the event of fusion of the cords to form the brachial plexus.
| Summary and Conclusion|| |
The morphological and anatomical variations of the two nerves studied that are musculocutaneous nerve and median are relatively well known. Acknowledgement of such anatomical variations is essential in neurophysiological studies, and for surgeons and orthopedicians while treating fracture of humerus (anterior approach) or diagnosing entrapment syndromes; as such variations can lead to entrapment syndromes in rare cases.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2]