Anatomical study of prefixed versus postfixed brachial plexuses in adult human cadaver

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The brachial plexus is usually formed by the fusion of anterior primary rami of C5–C8 and T1 (fifth to eighth cervical and first thoracic) spinal nerves. It is formed of three trunks. The upper trunk (UT) is formed by the fusion of C5 and C6 spinal nerves; on the other hand, the middle and lower trunks (MT and LT) are formed by the C7 spinal nerves and the union of C8 and T1 spinal nerves, respectively. Soon after the formation of the mentioned trunks, each of them bifurcates into anterior and posterior divisions. The fusion of two anterior divisions of the UT and MT leads to the formation of lateral cord (LC). The anterior division of the LT continues as the medial cord (MC). However, the posterior divisions of the three trunks form the posterior cord (PC). Later, the cords give rise to terminal nerve branches supplying mainly the different parts of the upper limbs. Anterior divisions of the trunks supply anterior (flexor) compartments of the upper limb; however, the posterior divisions of the trunks supply posterior (extensor) compartments.
As it is clearly demonstrated so far, the brachial plexus is a complex structure which may be accompanied with variations in the formation of roots, trunks, divisions and cords.1 For instance, the possibility of the formation of root of brachial plexus is made with the small contributions of the anterior rami of C4 or T2. As the origin of the superiormost root of the plexus is C4 and the inferiormost root is C8 or T1, it is termed as prefixed brachial plexus. Conversely, as the origin of the superior and inferior roots is C5/C6 and T2, respectively, it is a postfixed brachial plexus. In the case of postfixed brachia plexus scenario, the inferior trunk of the plexus may presumably compressed by the first rib and may induce certain neurovascular symptoms in the upper limb.2 Generally, anatomical variation was reported by different scholars in different part of the globe.
Studies conducted in Brazil, Turkey, Korea and Slovakia reported the dominancy of normal brachial plexus formation scheme as compared with either prefixed or postfixed brachial plexuses. Besides, these studies demonstrated the incidence of prefixed brachial plexuses in the cadaver of the respective countries with the proportion of 24%, 30.77%, 21.7% and 48%.5 On the other hand, findings from Brazil and Slovakia reported 5% and 2% postfixed brachial plexuses, respectively.6 Turkey and Korea cadaver‐based study, however, hardly demonstrated the occurrence of postfixed brachial plexuses.5 In general, the variation of brachial plexuses in not only on the sense of origin (prefixed or postfixed) but also on the difference of arrangement on the right and left sides.
Study conducted in Nigeria with 90 cadavers showed anomalous patterns of formation of the plexus; these include an additional fourth trunk formed by C5 in 20 cadavers and anticlockwise displacement of the cords around the axillary artery in 12 cadavers.9
Anatomical variations have clinical significance to surgeons, radiologists who interpret plain and computerized imaging. Besides, it is worthy important for anaesthesiologists who are applying needle to administer anaesthetic blocks. Therefore, the aim of this study is to assess anatomical variation of brachial plexus formation.
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