[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Upper limb](https://durgical.com/en/anatomy/region/upper-limb/) › Plexus divisions [Nervous system](https://durgical.com/en/anatomy/system/nervous-system/) · [Upper limb](https://durgical.com/en/anatomy/region/upper-limb/) # Plexus divisions The brachial plexus divisions lie behind the collarbone; they split the nerve fibres into those for the front and those for the back of the arm. Official name: Brachial plexus divisions [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=upper_limb&select=bp_divisions&side=r) Opens in the Durgical app, no sign-up needed. ## What it is Each trunk splits into a front and a back division behind the collarbone. ## What it does Separate the fibres for the front (bending) and back (straightening) muscles. ## Key points - Six divisions, three anterior and three posterior, lie behind the middle third of the clavicle; the divisions give off no named branches - All three posterior divisions join to form the [posterior cord](https://durgical.com/en/anatomy/posterior-cord-of-the-brachial-plexus/), which is why it supplies every extensor muscle of the limb - Retroclavicular level: a displaced clavicle fracture, its callus or a narrow costoclavicular space can compress them, often together with the subclavian vessels ## Key facts **Roots** Each trunk -> anterior and posterior division **Moves** Anterior divisions -> flexors (lateral, medial cords); posterior -> extensors (posterior cord) **Feeling from** No direct [skin](https://durgical.com/en/anatomy/skin/) branches ## Relations **Course** Each trunk splits near the lateral border of the [first rib](https://durgical.com/en/anatomy/first-rib/), behind the [clavicle](https://durgical.com/en/anatomy/clavicle/); the divisions pass down through the apex of the axilla (between the clavicle, the first rib and the upper border of the [scapula](https://durgical.com/en/anatomy/scapula/)) and regroup as cords **In front** The clavicle and the [subclavius](https://durgical.com/en/anatomy/subclavius/) muscle; the [subclavian vein](https://durgical.com/en/anatomy/subclavian-veins/) lies further forward and medial **Medial** The third part of the [subclavian artery](https://durgical.com/en/anatomy/right-subclavian-artery/), in front of and medial to the bundle as both cross the first rib **Below** The first rib and, below it, the dome of the [pleura](https://durgical.com/en/anatomy/pleura/) ## How to find it Not palpable: they are hidden behind the middle third of the clavicle. On ultrasound they are found by following the trunks down beside the subclavian artery to where the bundles pass under the clavicle; in surgery they are reached by retracting or dividing the clavicle and subclavius. ## Examination - Costoclavicular (military brace) maneuver: shoulders pulled back and down narrow the space between the clavicle and the first rib; reproduced symptoms or a fading radial pulse suggest compression there ## On imaging MRI is the main test for the plexus. Above the clavicle, ultrasound shows trunks and divisions as a cluster of dark circles lateral to the subclavian artery ('bunch of grapes'), but not behind the clavicle. In trauma MRI looks for swelling, discontinuity or scar; root avulsion is better seen on CT or MR myelography. Radiographs show a clavicle fracture or cervical rib. ## Common problems - Stretch injuries from motorcycle crashes or falls that force the head and shoulder apart. - Birth injury (Erb's palsy) affecting the upper trunk: the arm hangs turned inward ('waiter's tip'). - Compression at the thoracic outlet between the collarbone and the first rib. ## How it is diagnosed A detailed exam of strength and feeling in each nerve's area. MRI, EMG and nerve conduction studies show the level and severity. ## Treatment - Physical therapy and watching for recovery; many stretch injuries improve. - Nerve repair, graft or nerve transfer surgery for injuries that do not recover, ideally within months. ## Clinical notes - Clavicle fractures rarely injure the divisions at the time of injury, but a displaced fragment or abundant callus of a middle-third fracture can compress them later - The supraclavicular block is placed at the trunk–division level, where the plexus is most compact; the pleura just below explains the classic risk of pneumothorax - Isolated division lesions are rare; most injuries at this level are part of a combined supraclavicular and infraclavicular plexus injury ## Development Limb muscles form from a ventral (future flexor) and a dorsal (future extensor) mass; anterior divisions grow into the ventral mass and posterior divisions into the dorsal mass, which explains the flexor/extensor split of the cords. ## Related conditions - [Brachial plexus injury](https://durgical.com/en/conditions/brachial-plexus-injury/) ## Test yourself Think of the answer, then tap the question to see it. ## How many divisions does the brachial plexus have, and where do they lie? Six, three anterior and three posterior, behind the middle third of the clavicle; they give off no named branches. ## Why does the posterior cord supply every extensor muscle of the upper limb? Because all three posterior divisions of the brachial plexus join to form it; anterior divisions go to the flexors. ## How can a middle-third clavicle fracture affect the brachial plexus divisions? Rarely at the time of injury, but a displaced fragment or abundant callus can compress them later, often with the subclavian vessels. [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/anatomy/brachial-plexus-divisions/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** divisio anterior trunci superioris plexus brachialis TA2 6399 **Official Spanish (DeCS)** Divisiones anteriores y posteriores de los troncos del plexo braquial **English (TA2)** Brachial plexus divisions Sources: Terminologia Anatomica (TA2); [Anatomy, Shoulder and Upper Limb, Brachial Plexus](https://www.ncbi.nlm.nih.gov/books/NBK500016/); [Anatomy, Head and Neck: Brachial Plexus](https://www.ncbi.nlm.nih.gov/books/NBK531473/). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/anatomy/brachial-plexus-divisions/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/brachial-plexus-divisions/