Anatomic Variations in Relation to the Origin of the Musculocutaneous Nerve: Absence and Non-Perforation of the Coracobrachialis Muscle. Anatomical Study and Clinical Significance/Variaciones Anatómicas en Relación al Origen del Nervio Musculocutaneo: Ausencia y no Perforación del Musculo Coracobraquial: Estudio Anatómico y Significado Clínico

The most frequent anatomic variations of the musculocutaneous nerve could be divided in two main groups: communicating branches with the median nerve and variations in relation to the origin, which in turn can be subdivided into absence of the nerve and non-perforation of the coracobrachialis muscle. Unusual clinical symptoms and/or unusual physical examination in patients with motor disorders, could be explained by anatomic variations of the musculocutaneous nerve.A total of 106 arms were evaluated, corresponding to 53 fresh male cadavers who were undergoing necropsy. The presence or absence of the musculocutaneous nerve was evaluated and whether it pierced the coracobrachialis muscle or not. The lengths of the motor branches and the distances from its origins to the coracoid process were measured. In 10 cases (9.5 %) an unusual origin pattern was observed, of which six (5.7 %) correspond to non-perforation of the coracobrachialis muscle and four (3.8 %) correspond to absence of the nerve. The length of the branch for the brachialis muscle was 37.7 [+ or -] 15.4 mm and for the short and long heads of the biceps 27.6 [+ or -] 11.7 mm and 33.2 [+ or -] 10.1 mm respectively. The study showed that our population has similar prevalence of absence of the musculocutaneous nerve and non-perforation of the coracobrachialis muscle compared to previous reports in different populations. Moreover, there was no statistical correlation between the sides and the evaluated variables. KEY WORDS: Anatomic variation; Musculocutaneous nerve; Median nerve; Brachial plexus; Arm injuries. Las variaciones anatomicas mas frecuentes del nervio musculocutaneo se pueden dividir en dos grupos principales: Ramas comunicantes con el nervio mediano y variaciones en relacion al origen, que a su vez se pueden subdividir en la ausencia del nervio y la no perforacion del musculo coracobraquial. Los sintomas clinicos inusuales y / o el examen fisico inusual en pacientes con trastornos motores podrian explicarse por variaciones anatomicas del nervio musculocutaneo. Se evaluaron un total de 106 brazos, que corresponden a 53 cadaveres de machos frescos sometidos a necropsia. Se evaluo la presencia o ausencia del nervio musculocutaneo y si atraveso o no el musculo coracobraquial. Se midieron las longitudes de las ramas motoras y las distancias desde sus origenes hasta el proceso coracoides. En 10 casos (9,5 %) se observo un patron de origen inusual, de los cuales seis (5,7 %) corresponden a la no