[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 trunks [Nervous system](https://durgical.com/en/anatomy/system/nervous-system/) · [Upper limb](https://durgical.com/en/anatomy/region/upper-limb/) # Plexus trunks The brachial plexus trunks are three nerve bundles (upper, middle, lower) in the base of the neck; they mix the spinal nerve roots on their way to the arm. Official name: Brachial plexus trunks [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=upper_limb&select=bp_trunks&side=r) Opens in the Durgical app, no sign-up needed. ## What it is Three thick bundles formed as the roots join, above the collarbone. ## What it does Mix the roots so each arm nerve gets fibres from several levels. ## Key points - Upper (C5–C6), middle (C7) and lower (C8–T1) trunks cross the posterior triangle of the neck; the lower trunk rests on the first rib, behind the subclavian artery - Upper trunk (Erb) palsy loses deltoid, [supraspinatus](https://durgical.com/en/anatomy/supraspinatus/), [infraspinatus](https://durgical.com/en/anatomy/infraspinatus/), biceps, [brachialis](https://durgical.com/en/anatomy/brachialis/) and [brachioradialis](https://durgical.com/en/anatomy/brachioradialis/): the arm hangs adducted, internally rotated, elbow straight, forearm pronated - Lower trunk (Klumpke) palsy weakens the long finger flexors and all small hand muscles and numbs the medial forearm; Horner syndrome adds a T1 root injury ## Key facts **Roots** Superior C5–C6, middle C7, inferior C8–T1 **Moves** Superior trunk: [suprascapular nerve](https://durgical.com/en/anatomy/suprascapular-nerve/), [nerve to subclavius](https://durgical.com/en/anatomy/subclavian-nerve/) **Feeling from** Via branches (Erb: upper trunk; Klumpke: lower trunk) ## Relations **Course** The roots leave the gap between the anterior and middle scalene muscles and join near the lateral border of the [scalenes](https://durgical.com/en/anatomy/scalenus-anterior-muscle/); the trunks run down and laterally across the posterior triangle of the neck toward the back of the [clavicle](https://durgical.com/en/anatomy/clavicle/), where each splits into divisions **In front** [Platysma](https://durgical.com/en/anatomy/platysma/) and deep [cervical fascia](https://durgical.com/en/anatomy/superficial-investing-cervical-fascia/); crossed by the inferior belly of the [omohyoid](https://durgical.com/en/anatomy/omohyoid-muscle/) and the transverse cervical and suprascapular vessels **Medial** Anterior scalene, with the [phrenic nerve](https://durgical.com/en/anatomy/phrenic-nerve/) on its front; the [subclavian artery](https://durgical.com/en/anatomy/right-subclavian-artery/) lies in front of and below the lower trunk **Behind** Middle scalene **Below** The [first rib](https://durgical.com/en/anatomy/first-rib/), on which the lower trunk lies ## How to find it Above the clavicle, in the angle between the posterior border of the [sternocleidomastoid](https://durgical.com/en/anatomy/sternocleidomastoid-muscle/) and the clavicle, the trunks can sometimes be felt as firm cords that roll under the fingertip, more easily with the head turned to the other side. ## Examination - Adson test: neck extended and turned toward the tested side with a deep breath held; a fading radial pulse with reproduced symptoms suggests thoracic outlet compression, though false positives are common - Elevated arm stress test (Roos): arms in 90° abduction and external rotation while opening and closing the hands for 3 minutes; early heaviness, pain or tingling supports thoracic outlet syndrome - Pattern test: weak shoulder abduction, external rotation and elbow flexion with a lost biceps reflex points to the upper trunk; weak finger flexion and intrinsics with medial forearm numbness points to the lower trunk ## On imaging Ultrasound above the clavicle shows the trunks and divisions as a cluster of dark round bundles ('bunch of grapes') lateral and posterior to the subclavian artery, over the first rib. MRI with fat-suppressed fluid-sensitive sequences shows swelling and signal change after traction or in neuritis. ## 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 - Upper trunk injury comes from forced widening of the neck–shoulder angle: shoulder dystocia at birth, falls onto the shoulder from a motorcycle - Lower trunk injury comes from forced arm abduction (breech delivery with the arm overhead, grabbing to stop a fall): claw hand from loss of the intrinsics - Neurogenic thoracic outlet syndrome usually involves the lower trunk stretched over a cervical rib or fibrous band; long-standing cases waste the thenar eminence most (Gilliatt–Sumner hand) - A Pancoast tumour at the lung apex invades the lower trunk and the sympathetic chain: shoulder and medial arm pain, hand weakness and Horner syndrome - Interscalene and supraclavicular blocks are placed at root and trunk level; the phrenic nerve on the anterior scalene is often blocked as well, paralysing that hemidiaphragm ## Anatomical variants - Prefixed plexus: a large C4 contribution and a small T1; postfixed plexus: a small C5 and a T2 contribution; either shifts the root levels expected from a given lesion - A cervical rib or a fibrous band from C7 can lift and kink the lower trunk ## Development The nerves reach the limb bud while it still sits opposite the lower neck; as the limb comes to lie lower on the trunk the roots slope downward, so the lower trunk arches over the first rib, where a cervical rib (an enlarged C7 costal element) can lift and kink it. ## Memory aid Roots, Trunks, Divisions, Cords, Branches: 'Randy Travis Drinks Cold Beer'. ## Related conditions - [Brachial plexus injury](https://durgical.com/en/conditions/brachial-plexus-injury/) - [Thoracic outlet syndrome](https://durgical.com/en/conditions/thoracic-outlet-syndrome/) ## Test yourself Think of the answer, then tap the question to see it. ## Which roots form the upper, middle and lower trunks of the brachial plexus? Upper C5–C6, middle C7 and lower C8–T1; they cross the posterior triangle of the neck, with the lower trunk on the first rib. ## What arm posture follows an upper trunk (Erb) palsy of the brachial plexus? The arm hangs adducted and internally rotated, elbow straight, forearm pronated: deltoid, supra- and infraspinatus, biceps, brachialis and brachioradialis are lost. ## What does a lower trunk (Klumpke) palsy of the brachial plexus cause, and what does Horner syndrome add? Weak long finger flexors and all small hand muscles (claw hand) with medial forearm numbness; Horner syndrome adds a T1 root injury. ## Which brachial plexus trunk is usually involved in neurogenic thoracic outlet syndrome, and over what? The lower trunk, stretched over a cervical rib or a fibrous band from C7; long-standing cases waste the thenar eminence most (Gilliatt–Sumner hand). ## Why can an interscalene block paralyse a hemidiaphragm? The phrenic nerve lies on the front of the anterior scalene, next to the plexus roots and trunks, and is often blocked as well. [Add to my cards (5)](https://durgical.app/estudiar/?add=/en/anatomy/brachial-plexus-trunks/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** truncus superior plexus brachialis TA2 6398 **Official Spanish (DeCS)** Troncos superior, medio e inferior del plexo braquial **English (TA2)** Brachial plexus trunks **Also called** upper, middle and lower trunks ## Related - [Subclavian artery](https://durgical.com/en/anatomy/right-subclavian-artery/) - [Nerve to subclavius](https://durgical.com/en/anatomy/subclavian-nerve/) 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/); Anatomy of the Human Body (20th ed.): Development of the Muscles (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/brachial-plexus-trunks/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/brachial-plexus-trunks/