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Abstract
The brachial plexus innervates the upper limb. It is mainly formed by the anterior primary rami of C5 through T1 and provides sensory and motor innervation of the upper extremity. The brachial plexus is divided proximo-distally into rami/roots, trunks, divisions, cords, and terminal branches.[1] The MN (Median Nerve) is the main nerve of the anterior compartment of the forearm. The formation of the trunk of the MN takes place in front of the third part of the axillary artery by the union of lateral and medial roots, which arise from the respective cords of the brachial plexus and pass towards the forearm without supplying any muscles of the arm.[1] In the forearm, it supplies the muscles of the anterior compartment of the forearm through its direct and anterior interosseous branches, except for the flexor carpi ulnaris and the medial side of the flexor digitorum profundus. In the hand it supplies the thenar and the first two lumbricals. It also gives cutaneous branches to the lateral part of the palm and lateral three and a half digits.
The MCN (Musculocutaneous Nerve) arises from the lateral cord of the brachial plexus and has root values of C5, C6, and C7. The MCN pierces and passes through the coracobrachialis muscle, supplying the muscle in the process. The MCN in the lower part of the arm pierces the deep fascia below the elbow on its lateral side and becomes subcutaneous, where it continues as the lateral cutaneous nerve of the forearm.[2,3] In 3.57–6.6% of cases, there will be an absence of MCN with several unforeseen clinical implications regarding the atypical innervation of the musculature otherwise supplied by the musculocutaneous nerve.[4]
Here we present a case report in which there was an absence of MCN in one arm, low fusion of roots of MN below the level of midarm, and the anterior compartment muscles being supplied by the separate branches from the lateral root of MN.
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References
- Borthakur D, Kumar R, Jain H, et al. Unilateral absence of musculocutaneous nerve and unusual supply of median nerve – a case report. Acta Med Litu 2024;31(2):404-8. DOI: https://doi.org/10.15388/10.15388/Amed.2024.31.2.22
- Lalit M, Piplani S, Mahajan A, et al. Brachial plexus variations in the flexor compartment of arm with its clinical implications and embryological basis: A cadaveric study. Translational Research in Anatomy 2022;28:100203. DOI: https://doi.org/10.1016/j.tria.2022.100203
- Saeed M, Rufai AA. Median and musculocutaneous nerves: variant formation and distribution. Clin Anat 2003;16(5):453-7. DOI: https://doi.org/10.1002/ca.10096
- Hunter DD, Zdilla MJ. The absent musculocutaneous nerve: a systematic review. Translational Research in Anatomy 2021;22:100092. DOI: https://doi.org/10.1016/j.tria.2020.100092
- Beheiry EE. Anatomical variations of the median nerve distribution and communication in the arm. Folia Morphol (Warsz) 2004;63:313-8.
- Gumusburun E, Adiguzel E. A variation of the brachial plexus characterized by the absence of the musculocutaneous nerve: a case report. Surg Radiol Anat 2000; 22:63-5. DOI: https://doi.org/10.1007/s00276-000-0063-x
- Ibrahim C, Adnan E, Cem D. Variation between median and musculocutaneous nerves. Internet J Surg 2004;6:1−3. DOI: https://doi.org/10.5580/2429
- Nakatani T, Mizukami S, Tanaka S. Three cases of the musculocutaneous nerve not perforating the coracobrachialis muscle. Kaibogaku Zasshi 1997;72:191-4. DOI: https://doi.org/10.1046/j.1469-7580.1997.19130459.x
- Pacholczak R, Klimek-Piotrowska W, Walocha JA. Absence of the musculocutaneous nerve associated with a supernumerary head of biceps brachii: a case report. Surg Radiol Anat 2011;33:551-4. DOI: https://doi.org/10.1007/s00276-010-0771-9
References
Borthakur D, Kumar R, Jain H, et al. Unilateral absence of musculocutaneous nerve and unusual supply of median nerve – a case report. Acta Med Litu 2024;31(2):404-8. DOI: https://doi.org/10.15388/10.15388/Amed.2024.31.2.22
Lalit M, Piplani S, Mahajan A, et al. Brachial plexus variations in the flexor compartment of arm with its clinical implications and embryological basis: A cadaveric study. Translational Research in Anatomy 2022;28:100203. DOI: https://doi.org/10.1016/j.tria.2022.100203
Saeed M, Rufai AA. Median and musculocutaneous nerves: variant formation and distribution. Clin Anat 2003;16(5):453-7. DOI: https://doi.org/10.1002/ca.10096
Hunter DD, Zdilla MJ. The absent musculocutaneous nerve: a systematic review. Translational Research in Anatomy 2021;22:100092. DOI: https://doi.org/10.1016/j.tria.2020.100092
Beheiry EE. Anatomical variations of the median nerve distribution and communication in the arm. Folia Morphol (Warsz) 2004;63:313-8.
Gumusburun E, Adiguzel E. A variation of the brachial plexus characterized by the absence of the musculocutaneous nerve: a case report. Surg Radiol Anat 2000; 22:63-5. DOI: https://doi.org/10.1007/s00276-000-0063-x
Ibrahim C, Adnan E, Cem D. Variation between median and musculocutaneous nerves. Internet J Surg 2004;6:1−3. DOI: https://doi.org/10.5580/2429
Nakatani T, Mizukami S, Tanaka S. Three cases of the musculocutaneous nerve not perforating the coracobrachialis muscle. Kaibogaku Zasshi 1997;72:191-4. DOI: https://doi.org/10.1046/j.1469-7580.1997.19130459.x
Pacholczak R, Klimek-Piotrowska W, Walocha JA. Absence of the musculocutaneous nerve associated with a supernumerary head of biceps brachii: a case report. Surg Radiol Anat 2011;33:551-4. DOI: https://doi.org/10.1007/s00276-010-0771-9