Brachial Plexus Anatomy
Upper trunk injury (traction with the head pulled away from the shoulder - birth, motorcycle). Loss of abductors/external rotators and elbow flexors → the "waiter's tip" posture (adducted, internally rotated arm, extended elbow, pronated forearm).
Lower trunk injury (traction with the arm pulled overhead). Loss of the intrinsic hand muscles → a claw hand; often associated with Horner's syndrome (ptosis, miosis, anhidrosis) from T1 sympathetic involvement.
Overview
The brachial plexus is the single most-drawn structure in upper-limb vivas, so the goal is to make it automatic: a fixed five-level scaffold (Randy Travis Drinks Cold Beer) onto which you hang the few named branches that actually come off the roots and upper trunk, the posterior-cord ULTRA group, and the five terminal nerves. Once the map is secure, the clinical layer follows naturally — where a lesion sits (supra- versus infraclavicular), which pattern it produces (Erb's, Klumpke's, or whole-plexus), and the one question that changes the operation: is it preganglionic (avulsion) or postganglionic (rupture)? Build the map first, then read every plexus injury off it.
The Five Levels
Roots and Trunks
- Roots: the anterior (ventral) rami of C5-T1, emerging between scalenus anterior and medius. A prefixed plexus has a C4 contribution; a postfixed plexus has a T2 contribution.
- Trunks (in the posterior triangle / supraclavicular fossa):
- Upper trunk = C5 + C6
- Middle trunk = C7
- Lower trunk = C8 + T1
- Branches here: from the roots - dorsal scapular nerve (C5) and long thoracic nerve (C5-C7); from the upper trunk - the suprascapular nerve and the nerve to subclavius.
RTDCB — Randy Travis Drinks Cold BeerThe Five Levels & Posterior Cord
Hook:Randy Travis Drinks Cold Beer (Roots, Trunks, Divisions, Cords, Branches); the posterior cord branches are ULTRA.
Nerve Branches at Each Level
A reliable viva answer names the branches by level, top to bottom.
- Roots: dorsal scapular nerve (C5 - rhomboids, levator scapulae); long thoracic nerve (C5-C7 - serratus anterior).
- Upper trunk: suprascapular nerve (supraspinatus, infraspinatus); nerve to subclavius.
- Lateral cord: lateral pectoral nerve; musculocutaneous nerve; lateral root of median.
- Posterior cord: upper subscapular, lower subscapular, thoracodorsal (latissimus dorsi), axillary (deltoid, teres minor), radial.
- Medial cord: medial pectoral nerve; medial cutaneous nerve of arm; medial cutaneous nerve of forearm; ulnar nerve; medial root of median.
Clinical Correlations
Supraclavicular vs Infraclavicular
- Supraclavicular injuries (roots/trunks) are the most common and include the classic upper (Erb's) and lower (Klumpke's) patterns.
- Infraclavicular injuries (cords/branches) follow shoulder dislocation, humeral fracture, or penetrating trauma and tend to affect specific terminal nerves.
- Preganglionic (root avulsion) vs postganglionic distinction guides reconstruction: avulsion is suggested by Horner's syndrome, winged scapula (long thoracic off the root), and pseudomeningocele on imaging, and is not amenable to direct repair (requires nerve transfer).
ULTRAPosterior cord branches
Hook:All the posterior divisions feed the posterior cord, so its branches are 'ULTRA' — and they run the EXTENSORS plus the subscapularis/lat/teres group.
Localisation, Timing and Reconstruction
The anatomy is only useful if it localises the lesion and times the operation.
Preganglionic (avulsion) versus postganglionic (rupture)
- Preganglionic (root avulsion)
- Proximal to the dorsal root ganglion (rootlets torn from cord)
- Postganglionic (rupture/lesion distal to DRG)
- Distal to the dorsal root ganglion
- Preganglionic (root avulsion)
- Often present (T1 sympathetic) — a red flag for lower-root avulsion
- Postganglionic (rupture/lesion distal to DRG)
- Absent
- Preganglionic (root avulsion)
- Suggests very proximal (root-level) injury of long thoracic/dorsal scapular
- Postganglionic (rupture/lesion distal to DRG)
- Spared
- Preganglionic (root avulsion)
- PRESERVED despite clinical anaesthesia (DRG and peripheral axon intact)
- Postganglionic (rupture/lesion distal to DRG)
- Absent (axon interrupted distal to DRG)
- Preganglionic (root avulsion)
- Pseudomeningocele at the affected level
- Postganglionic (rupture/lesion distal to DRG)
- Often normal or shows a discrete rupture/neuroma
- Preganglionic (root avulsion)
- NOT directly repairable → nerve transfers (neurotisation)
- Postganglionic (rupture/lesion distal to DRG)
- Amenable to nerve grafting (or transfer)
The paradox to quote: in a preganglionic lesion the limb is clinically anaesthetic yet the SNAPs are preserved, because the sensory cell body (in the dorsal root ganglion) and its peripheral axon remain intact even though the central connection is torn.
Timing and nerve transfers
- Timing: explore sharp/penetrating lacerations early (primary repair); explore closed traction injuries that show no clinical/electrical recovery by about 3 months, and ideally operate before 6–9 months while the target muscle can still be reinnervated.
- Common nerve transfers (neurotisation): spinal accessory → suprascapular (shoulder external rotation/abduction), Oberlin (ulnar fascicle → biceps branch of musculocutaneous) and a median fascicle → brachialis branch (elbow flexion), and triceps branch (radial) → axillary (deltoid). Late salvage uses tendon/free-functioning-muscle transfers or arthrodesis.
- Related lower-plexus pathology: the lower trunk (C8–T1) is also the target of thoracic outlet syndrome and of a Pancoast (superior sulcus) tumour — both can present with intrinsic hand wasting and, in the latter, Horner's syndrome.
The intraplexal transfers above (spinal accessory, Oberlin ulnar fascicle, triceps branch) need a healthy donor root/nerve. In a pan-plexus injury with multiple root avulsions there may be none, so the examiner expects the extraplexal donors:
- Intercostal nerves (typically three, T3–T6) — to the musculocutaneous nerve for elbow flexion (or to a free muscle).
- Phrenic nerve — a powerful donor but at the cost of diaphragmatic/respiratory function (used cautiously, avoided in children/respiratory compromise).
- Contralateral C7 — for total avulsion, routed across (often through a vascularised ulnar nerve graft) to the median or musculocutaneous nerve.
- Spinal accessory remains the workhorse extraplexal donor to the suprascapular nerve.
And the reconstruction priority when you cannot restore everything: (1) elbow flexion first, then (2) shoulder stability/abduction & external rotation, then (3) hand sensation (protective) and wrist/finger function — intrinsic hand recovery is rarely achieved in the adult, which is why hand function is prioritised lowest and salvaged by transfers/fusions.
Beyond the SNAP paradox and the pseudomeningocele, three timing/test points are examinable:
- Delay EMG/nerve conduction studies ~3–4 weeks. Wallerian degeneration must occur before denervation changes (fibrillations, positive sharp waves) appear; a study done too early is falsely reassuring. SNAPs (for the pre- vs postganglionic distinction) are also most reliable after this interval, then repeated serially to track reinnervation (nascent motor units).
- Intraoperative nerve action potential (NAP) recording across a neuroma-in-continuity decides the operation: a present NAP means axons have crossed → neurolysis alone; an absent NAP means no useful regeneration → resect and graft.
- Histamine triple-response (axon-flare) test: intradermal histamine normally gives a wheal-and-flare; the flare is an axon reflex needing an intact peripheral sensory axon from the dorsal root ganglion, so — like preserved SNAPs — it is PRESERVED in a preganglionic avulsion (intact DRG/peripheral axon) despite clinical anaesthesia and lost in a postganglionic lesion.
Guidelines, Registries & Global Practice
Global Practice Picture
Brachial plexus anatomy is universal core knowledge and the framework for diagnosing and reconstructing plexus injuries worldwide. The consistent principles are: classify the lesion by level (supra- vs infraclavicular, pre- vs postganglionic), recognise the Erb's and Klumpke's patterns, and use detailed terminal-branch anatomy to plan nerve transfers.
Side-by-Side Synthesis
- Key structures / branches
- Dorsal scapular (C5), long thoracic (C5-7)
- Key structures / branches
- Suprascapular + n. to subclavius (upper trunk)
- Key structures / branches
- Anterior + posterior; behind clavicle; no named branches
- Key structures / branches
- Named by axillary artery; posterior cord = ULTRA
- Key structures / branches
- Musculocutaneous, axillary, radial, median, ulnar
Evidence Base
Both references (checked against PubMed) are reviews/anatomical series, not outcome trials — appropriate for a structural topic. Pejkova anchors the five-level scaffold, the five terminal branches and the injury-pattern classification that drive reconstruction. Bhardwaj's nerve-transfer series shows why the fine terminal-branch anatomy is not academic: variation is common and must be confirmed intra-operatively during neurotisation. For a viva the reproducible map, the branch-at-each-level list, the Erb/Klumpke patterns and the pre- versus postganglionic distinction matter more than any single citation.
Brachial Plexus Injuries - Review of the Anatomy and the Treatment Options
- Reviews the five anatomical sections of the brachial plexus: roots, trunks, divisions, cords and terminal branches
- The plexus ends in five terminal branches: musculocutaneous, median, axillary, radial and ulnar nerves
- Injury patterns classified as upper trunk, extended upper trunk, lower trunk, or whole-plexus ('swinging hand')
- Reconstruction (neurolysis, grafting, neurotisation, tendon/free-muscle transfer, arthrodesis) is chosen by injury type and deficit
Anatomic Variations of the Musculocutaneous Nerve and Clinical Implications for Restoration of Elbow Flexion
- Prospective study of 150 brachial plexus injury patients undergoing nerve transfer for elbow flexion
- Detailed the branching of the musculocutaneous nerve (a terminal branch of the lateral cord)
- Anatomic variation in plexus terminal branches is common and must be anticipated intra-operatively
- Knowledge of the branching pattern is key to safe, effective neurotisation