Lateral cord !
The lateral cord of the brachial plexus lies in the armpit beside the axillary artery; it gives the musculocutaneous nerve and part of the median nerve.
Official name: Lateral cord of the brachial plexus
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What it is
The outer bundle of the plexus beside the axillary artery.
What it does
Gives the musculocutaneous nerve and part of the median nerve.
Key facts
- Roots
- C5–C7 (anterior divisions of the superior and middle trunks)
- Moves
- Lateral pectoral nerve, musculocutaneous nerve, lateral root of the median nerve
- Feeling from
- Via the musculocutaneous and median nerves
Relations
- Course
- Formed in the apex of the axilla by the anterior divisions of the upper and middle trunks, it descends lateral to the axillary artery behind pectoralis minor and divides at the muscle's lower border into the musculocutaneous nerve and the lateral root of the median nerve
- In front
- Pectoralis minor and the clavipectoral fascia, which its lateral pectoral branch pierces with the thoracoacromial artery
- Medial
- The axillary artery (second part), with the medial cord on the artery's other side
- Lateral
- The coracoid process and coracobrachialis, which its musculocutaneous branch enters
- Behind
- The posterior cord, behind the artery, and subscapularis on the posterior wall of the axilla
How to find it
Below the clavicle, medial to the coracoid process, the cords lie deep to pectoralis major and pectoralis minor around the axillary artery. On ultrasound for an infraclavicular block they appear as bright ovals; the lateral cord is the one above and lateral to the artery.
Examination
- Resisted elbow flexion with the forearm supinated and the biceps reflex (C5–C6): weakness and a reduced reflex point to the musculocutaneous fibres
- Resisted pronation with the elbow straight and resisted wrist flexion: weakness as well places the lesion above the split into musculocutaneous and median fibres
- Pinprick on the lateral forearm: loss in the lateral antebrachial cutaneous territory
On imaging
Cords are named by their position around the second part of the axillary artery, the landmark on infraclavicular ultrasound (used for blocks) and sagittal MRI; the lateral cord lies on its lateral, upper side. After trauma MRI looks for swelling, discontinuity or scar. In shoulder dislocation or proximal humerus fracture, radiographs show the cause.
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
- Infraclavicular blocks target the three cords around the second part of the axillary artery
- Isolated cord injuries are uncommon; infraclavicular lesions follow shoulder dislocation, proximal humerus fractures and stab or gunshot wounds, often with axillary artery injury
- Lateral cord lesion vs C6 radiculopathy: both weaken elbow flexion and pronation; normal paraspinal muscles on EMG and no neck pain favour the cord
Anatomical variants
- The lateral root of the median nerve can be doubled or join low, so the median nerve forms in the arm; some median fibres may travel in the musculocutaneous nerve and cross over lower down
- A small branch from the lateral cord (C7) to the ulnar nerve, the so-called lateral root of the ulnar nerve, is present in some people
Development
Built only from anterior divisions (C5–C7), it supplies muscles that grew from the ventral (flexor) mass of the limb bud; its C5–C6 fibres belong to the preaxial border, which becomes the radial side of the flexor compartment and the lateral forearm skin.
Memory aid
The 'M' across the front of the axillary artery, lateral to medial: musculocutaneous nerve, lateral root, median nerve, medial root, ulnar nerve.
Related conditions
Test yourself
Think of the answer, then tap the question to see it.
How is the lateral cord of the brachial plexus named, and which branches does it give?
By its position lateral to the second part of the axillary artery; it gives the lateral pectoral nerve, the musculocutaneous nerve and the lateral root of the median nerve.
What is the «M» landmark of the brachial plexus in front of the axillary artery?
Lateral to medial: musculocutaneous nerve, lateral root, median nerve, medial root, ulnar nerve; it is used to find the plexus in dissection.
Which deficits suggest a lateral cord lesion of the brachial plexus?
Weak elbow flexion plus weak pronation and wrist flexion (pronator teres, flexor carpi radialis), with lateral forearm numbness.
Educational information, not medical advice. For any symptom, see a health professional.
Its names
- Official Latin (TA2)
- fasciculus lateralis plexus brachialis TA2 6415
- Official Spanish (DeCS)
- Fascículo lateral del plexo braquial
- English (TA2)
- Lateral cord of the brachial plexus
Related
Sources: Terminologia Anatomica (TA2); Anatomy, Shoulder and Upper Limb, Brachial Plexus; Anatomy, Head and Neck: Brachial Plexus; Anatomy of the Human Body (20th ed.): The Branchial Region (Lea & Febiger (Gray's Anatomy, 1918), 1918) · adapted, Public domain.
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Representative model, for educational purposes only.
