[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/) › Posterior cord [Nervous system](https://durgical.com/en/anatomy/system/nervous-system/) · [Upper limb](https://durgical.com/en/anatomy/region/upper-limb/) # Posterior cord The posterior cord of the brachial plexus lies in the armpit behind the axillary artery; it gives the axillary and radial nerves. Official name: Posterior cord of the brachial plexus [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=upper_limb&select=bp_cord_posterior&side=r) Opens in the Durgical app, no sign-up needed. ## What it is The back bundle of the plexus, behind the axillary artery. ## What it does Gives the axillary and radial nerves. ## Key points - Lies behind the second part of the axillary artery, on subscapularis; formed by all three posterior divisions (C5–T1) - At the lower border of pectoralis minor the radial nerve continues behind the third part of the axillary artery, and the axillary nerve turns back toward the quadrangular space - Crutch pressure in the axilla compresses the posterior cord or the radial nerve high up: unlike Saturday night palsy, the triceps is weak too ## Key facts **Roots** C5–T1 (all posterior divisions) **Moves** Upper and lower subscapular, thoracodorsal, axillary and radial nerves **Feeling from** Via the axillary and radial nerves ## Relations **Course** Formed behind the first part of the [axillary artery](https://durgical.com/en/anatomy/axillary-artery/) by the three posterior divisions, it lies behind the second part, deep to [pectoralis minor](https://durgical.com/en/anatomy/pectoralis-minor-muscle/), and ends at the muscle's lower border by dividing into the [axillary nerve](https://durgical.com/en/anatomy/axillary-nerve/) and the [radial nerve](https://durgical.com/en/anatomy/radial-nerve/) **In front** The axillary artery (second part), with pectoralis minor in front of it **Behind** [Subscapularis](https://durgical.com/en/anatomy/subscapularis/) and the posterior wall of the axilla, down which its subscapular and thoracodorsal branches run ## How to find it In a dissection, lifting the axillary artery forward below the [clavicle](https://durgical.com/en/anatomy/clavicle/) shows the posterior cord directly behind it on subscapularis. On infraclavicular ultrasound it lies just deep to the artery, the usual target for a single injection that spreads to all three cords. ## Examination - Deltoid, [latissimus dorsi](https://durgical.com/en/anatomy/latissimus-dorsi-muscle/) (cough test on the posterior axillary fold), triceps, and wrist and finger extensors: weakness across axillary, thoracodorsal and radial muscles places the lesion at the cord - Triceps reflex (C7) reduced; pinprick over the lower deltoid and the dorsum of the first web space ## On imaging On infraclavicular ultrasound and sagittal MRI it lies behind the second part of the axillary artery, the deepest of the three cords. MRI is the main test after trauma, looking for swelling, discontinuity or scar. With an anterior shoulder dislocation or proximal [humerus](https://durgical.com/en/anatomy/humerus/) fracture, radiographs show the cause and its axillary and radial branches are checked clinically. ## 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](https://durgical.com/en/anatomy/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 - Posterior cord lesions follow anterior shoulder dislocation, proximal humerus fractures and penetrating axillary wounds: deltoid and wrist extensor weakness with a normal biceps - Crutch palsy vs Saturday night palsy: crutch pressure in the axilla hits the radial nerve above its triceps branches; an arm hung over a chair compresses it in the spiral groove and spares the triceps - Posterior cord vs C7 radiculopathy: C7 also weakens wrist flexion and pronation ([flexor carpi radialis](https://durgical.com/en/anatomy/flexor-carpi-radialis/), [pronator teres](https://durgical.com/en/anatomy/pronator-teres/)) and spares the deltoid; a cord lesion does the opposite ## Anatomical variants - Prefixed and postfixed plexuses change its root make-up, and some of its branches (the thoracodorsal or lower subscapular nerve) may arise from the axillary or radial nerve instead of the cord itself ## Development It gathers all the posterior divisions, the nerves of the dorsal (extensor) muscle mass. When the [upper limb](https://durgical.com/en/anatomy/region/upper-limb/) turns outward by about 90° in week 7, that mass ends up facing backward, so every muscle the cord supplies lies on the back of the shoulder, arm or forearm, or in the posterior axillary wall. ## Memory aid Posterior cord branches, 'ULTRA': Upper subscapular, Lower subscapular, Thoracodorsal, Radial, Axillary. ## Related conditions - [Brachial plexus injury](https://durgical.com/en/conditions/brachial-plexus-injury/) - [Axillary nerve injury](https://durgical.com/en/conditions/axillary-nerve-injury/) ## Test yourself Think of the answer, then tap the question to see it. ## How is the posterior cord of the brachial plexus formed, and which branches does it give? By all three posterior divisions (C5–T1); it gives the upper and lower subscapular, thoracodorsal, axillary and radial nerves. ## How does crutch palsy differ from Saturday night palsy? Crutch pressure in the axilla hits the posterior cord or high radial nerve, so the triceps is weak; an arm over a chair compresses the spiral groove and spares the triceps. ## How is a posterior cord lesion told apart from a C7 radiculopathy? C7 also weakens wrist flexion and pronation and spares the deltoid; a posterior cord lesion weakens the deltoid and spares those. [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/anatomy/posterior-cord-of-the-brachial-plexus/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** fasciculus posterior plexus brachialis TA2 6416 **Official Spanish (DeCS)** Fascículo posterior del plexo braquial **English (TA2)** Posterior cord of the brachial plexus ## Related - [Axillary artery](https://durgical.com/en/anatomy/axillary-artery/) 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/); [8.5 Development of the Appendicular Skeleton](https://openstax.org/books/anatomy-and-physiology-2e/pages/8-5-development-of-the-appendicular-skeleton) (OpenStax (Rice University), 2022) · adapted, [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/); Anatomy of the Human Body (20th ed.): The Branchial Region (Lea & Febiger (Gray's Anatomy, 1918), 1918) · adapted, Public domain. ## **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/posterior-cord-of-the-brachial-plexus/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/posterior-cord-of-the-brachial-plexus/