Anaes · Applied anatomy

Brachial plexus anatomy

Also known as Brachial plexus · Interscalene block · Supraclavicular block · Infraclavicular block · Axillary block · Erb palsy

The brachial plexus supplies the entire upper limb and is the most blocked nerve structure in regional anaesthesia. Its anatomy is taught as a five-stage sequence — roots, trunks, divisions, cords and branches — that maps directly onto the four classic approaches to plexus blockade. The framework rests on six exam-critical ideas. First, the plexus is formed by the ventral rami of C5, C6, C7, C8 and T1 (the roots), which unite into three trunks: the upper trunk (C5-C6), the middle trunk (C7) and the lower trunk (C8-T1). Second, each trunk splits into an anterior and a posterior division; the six divisions regroup into three cords named by their relationship to the axillary artery — the lateral, medial and posterior cords. Third, the cords give rise to five terminal branches: the musculocutaneous nerve (lateral cord, elbow flexors and lateral forearm), the axillary nerve (posterior cord, deltoid and teres minor), the radial nerve (posterior cord, all the extensor compartment of arm and forearm), the median nerve (lateral and medial cords, most of the thenar muscles and lateral palm) and the ulnar nerve (medial cord, the intrinsic hand muscles and medial one and a half digits). Fourth, the plexus runs a recognisable course — between the scalenus anterior and medius (the interscalene groove), over the first rib, behind the clavicle, and into the axilla around the axillary artery — and each location is the site of a named block. Fifth, the four classic ultrasound-guided approaches are interscalene (roots/trunks, shoulder surgery but with a high rate of phrenic-nerve block), supraclavicular (divisions, the whole upper limb, near the pleura), infraclavicular/costoclavicular (cords around the axillary artery, hand and forearm surgery) and axillary (branches, forearm and hand). Sixth, two birth-injury patterns localise damage: Erb's palsy (upper trunk C5-C6, the waiter's-tip posture) and Klumpke's palsy (lower trunk C8-T1, a claw hand and sometimes Horner syndrome). Built on the brachial-plexus MRI pictorial review (van Es 2010), the roots-to-cords variability meta-analysis (Benes 2021), the plexus-injury anatomy review (Pejkova 2021), the birth-injury current-concepts review (Ashworth 2026), the interscalene volume-vs-breathing trial (Riazi 2008), the diaphragm-sparing low-volume interscalene trial (Verbeke 2026), the selective-trunk and supraclavicular block study (Rani 2026), the costoclavicular versus infraclavicular block study (Yazar 2026), the axillary-plexus-blockade study (Solomos 2025), the cord-and-median-loop variation study (Claassen 2016), and two musculocutaneous-nerve-variation reports (Nasrabadi 2017; Lv 2026).