Department ofOrthopedics and Traumatology, Instituto Doutor José Frota de Fortaleza, Fortaleza, CE, Brazil
Introduction
The musculocutaneous nerve (MCN) originates from the lateral fasciculus (roots C5–C7) where it initially sends a branch to the shoulder and then perforates the coracobrachialis muscle, which it innervates, emerges between the biceps brachii and brachialis muscles and sends a muscular branch to each of these muscles. After supplying all three muscles of the arm anterior compartment, the MCN emerges laterally to the biceps brachii muscle tendon, as the lateral cutaneous nerve of the forearm becomes truly subcutaneous when it perforates the muscle fascia proximal to the cubital fossa to initially follow the cephalic vein and in the subcutaneous tissue and, after crossing the anterior surface of the elbow, it continues to supply the skin of the lateral side of the forearm.1
The clinical and surgical importance of the anatomical knowledge of this nerve and its variations is due to the fact that many surgical procedures in the upper limb involve mobilization or displacement of the muscles of the anterior arm compartment and one of the complications of these procedures is MCN lesions.2
Therefore, we report an anatomical variation ofthe musculocutaneous nerve observed during the dissection ofa cadaver from the human anatomy laboratory of our university
Case report
During a routine dissection of the right upper limb of a male cadaver that belonged to the anatomy laboratory collection, we observed an anatomical variation of the musculocutaneous muscle. The corpse, previously preserved in formaldehyde and through the glycerination method of Giacomini, was dissected. All the subcutaneous tissue and superficial fascia were removed. Subsequently, the brachial plexus, starting from its fasciculus, was painted with yellow fabric paint. The trajectory ofthe MCN was analyzed and measured from its origin in the lateral, up to its union with the median nerve, which was also measured from its origin in the medial and lateral fasciculus, to the cubital fossa region. An Absolute Digimatic® digital caliper of Mitutoyo Sul Americana Ltda was used for the measurements.
In our specimen, the MCN originated in the lateral fasciculus, which provides a component for the origin of the median nerve. The MCN followed laterally for 47.38 mm, passed under the coracobrachialis muscle for 32.73 mm to then emerge on the other side of this muscle and then follow for 55.38 mmup to its first branch to the biceps brachii muscle. Then it coursed for 29.56 mm longer and provided two more branches: the lateral cutaneous nerve of the forearm and a branch to the brachial muscle. Subsequently, it followed for 29.34 mm longer and joined the median nerve, which was 145.90 mm
long since its origin up to its union with the musculocutaneous nerve. The median nerve followed medially along the arm for 158.41 mm to the region of the cubital fossa and then gave origin to the anterior intermediate nerve of forearm. The union of the musculocutaneous nerve with the median nerve occurred at approximately the midpoint of the arm and the median nerve (Figs. 1–3).
Discussion
The anatomical associations of MCN have been studied over the past few years aiming to prevent lesions during surgical procedures2 and these variations often involve communication between the musculocutaneous and the median nerves through one or more of the communicating branches.3–8 The MCN can also send an independent branch to the coracobrachialis muscle instead of perforating, remaining parallel to the median nerve by a variable distance until it passes under the biceps brachii, or some of the median nerve fibers may follow for some length in the MCN before joining its own trunk, or the MCN can send muscular branches to the pronator teres muscle or innervate the dorsum of the thumb in the absence of the radial nerve superficial branch.1
Considering the large number of variations found in the literature, there have been attempts to classify such variations. The most often used classification criteria in the comparisons of the variation pattern of the MCN and MN is the one proposed by Le Minor, which describes five types of variation.9,10 Our example did not fit in any of the five types described by the author. Another classification is the one by Venieratos and Anangnostopolou,3 that indicates three types of possible variations. In this case, our variation fits into two proposed types: Type II, in which the union of the MCN with the MN occurs distally to the coracobrachialis muscle, and Type III, in which neither the nerve nor the communicant branch perforate the coracobrachialis muscle.9,10
Some authors classify the variations in the MCN taking into account the number of communicating branches and their height.3–8 In our finding, the anastomosis of the MCN occurs
after the muscular branch to the brachial muscle. Considering that the classifications found in the literature either do not include our example or it fits more than one proposed variation, without our having found another truly similar one, we consider this variation as rare. Conflicts of interest The authors declare no conflicts of interest.
1. Goss CM. Gray anatomia. 29a ed. Rio de Janeiro: Guanabara Koogan; 1977. 2. Rebouc¸as F, Brasil Filho R, Filardis C, Pereira RR, Cardoso AA. Estudo anatômico do trajeto do nervo musculocutâneo em relac¸ão ao processo coracoide. Rev Bras Ortop. 2010;45(4):400–3. 3. Venieratos D, Anagnostopoulou S. Classification of communications between the musculocutaneous and median nerves. Clin Anat. 1998;11(5):327–31. 4. Sachdeva K, Singla RK. Communication between median and musculocutaneous nerve. J Morphol Sci. 2011;28(4):246–9. 5. Radunovic M, Vukasanovic-Bozaric A, Radojevic N, Vukadinovic T. A new anatomical variation of the musculocutaneous and the median nerve anastomosis. Folia Morphol. 2013;72(2):176–9. 6. Maeda S, Kawai K, Koizumi M, Ide J, Tokiyoshi A, Mizuta H, et al. Morphological study, by teasing examination, of the communication from the musculocutaneous to median nerves. Anat Sci Int. 2009;84(1–2):41–6. 7. Guerri-Guttenberg RA, Inglolotti M. Classifying musculocutaneous nerve variations. Clin Anat. 2009;22(6):671–83. 8. Maeda S, Kawai K, Koizumi M, Ide J, Tokiyoshi A, Mizuta H, et al. Morphological study of the communication between the musculocutaneous and median nerves. Anat Sci Int. 2009;84(1–2):34–40. 9. Gujar S, Savita G, Shah GV, Bondre KV. Unilateral variation in musculocutaneous nerve – a case report. IJABMS. 2012;14(18):1–6. 10. Beheiry Eman E. Anatomical variations of the median nerve distribution and communication in the arm. Folia Morphol. 2004;63(3):313–8.
