Contents · 12 sections
- 1. General scheme
- 2. Roots and Trunks
- 3. Divisions and Cords
- 4. Branches of the Supraclavicular Part
- 5. Branches of the Infraclavicular Part
- 6. Terminal Nerves and Innervation
- 7. Erb-Duchenne Palsy (Upper Type)
- 8. Klumpke Palsy (Lower Type)
- 9. Individual Neuropathies
- 10. Long Thoracic Nerve and Winged Scapula
- 11. Diagnostics and Imaging
- 12. FAQ
In a nutshell. The brachial plexus (plexus brachialis) is the largest nerve plexus of the upper extremity, formed by the anterior rami of C5-T1. Scheme: roots → trunks → divisions → cords → branches. There are 3 trunks (superior C5-C6, middle C7, inferior C8-T1), 2 divisions (anterior and posterior) in each trunk, 3 cords (lateral, medial, posterior), and main terminal nerves (musculocutaneous, axillary, radial, median, ulnar). Clinically: Erb-Duchenne palsy (C5-C6, "waiter's tip hand"), Klumpke palsy (C8-T1, "claw hand"), Horner's syndrome if the sympathetic fibers of T1 are involved. Mnemonic for cords: "Real Texans Drink Cold Beer" (Roots-Trunks-Divisions-Cords-Branches).
1. General scheme
- Origin — anterior rami of spinal nerves C5-T1.
- Emerges through the space between the anterior and middle scalene muscles (interscalene triangle).
- Passes over the 1st rib and subclavian artery, then enters the axilla.
- Consists of 5 levels: roots → trunks → anterior/posterior divisions → cords → terminal branches.
2. Roots and Trunks
| Trunk | Roots |
|---|---|
| Superior trunk (truncus superior) | C5 + C6 |
| Middle trunk (truncus medius) | C7 |
| Inferior trunk (truncus inferior) | C8 + T1 |
3. Divisions and Cords
- Each trunk divides into anterior and posterior divisions.
- Anterior divisions of the superior and middle trunks → lateral cord.
- Anterior division of the inferior trunk → medial cord.
- Posterior divisions of all three trunks → posterior cord.
- The cords are arranged around the axillary artery: lateral — laterally, medial — medially, posterior — posteriorly.
4. Branches of the Supraclavicular Part
- Dorsal scapular nerve (C5) — m. levator scapulae, rhomboids.
- Long thoracic nerve (C5-C7) — m. serratus anterior; its injury leads to a "winged scapula".
- Nerve to subclavius (C5-C6).
- Suprascapular nerve (C5-C6, from the superior trunk) — m. supraspinatus, infraspinatus (rotator cuff).
5. Branches of the Infraclavicular Part
Lateral cord
- Lateral pectoral nerve (C5-C7) — m. pectoralis major.
- Musculocutaneous nerve (C5-C7) — m. biceps brachii, coracobrachialis, brachialis; sensation of the lateral forearm.
- Lateral root of the median nerve.
Medial cord
- Medial pectoral nerve (C8-T1) — m. pectoralis minor + part of pectoralis major.
- Medial brachial cutaneous nerve (T1).
- Medial antebrachial cutaneous nerve (C8-T1).
- Medial root of the median nerve.
- Ulnar nerve (C8-T1).
Posterior cord
- Superior subscapular nerve (C5-C6) — m. subscapularis.
- Thoracodorsal nerve (C6-C8) — m. latissimus dorsi.
- Inferior subscapular nerve (C5-C6) — m. subscapularis + m. teres major.
- Axillary nerve (C5-C6) — m. deltoideus, m. teres minor; sensation over the deltoid muscle.
- Radial nerve (C5-T1) — all extensors of the arm and forearm, part of the sensation on the dorsal hand.
6. Terminal Nerves and Innervation
| Nerve | Segments | Motor function | Sensory function |
|---|---|---|---|
| Musculocutaneous | C5-C7 | Flexors of the arm (biceps, brachialis) | Lateral aspect of the forearm |
| Axillary | C5-C6 | Deltoid, teres minor | Over the deltoid ("shoulder pad" area) |
| Radial | C5-T1 | Triceps, wrist and finger extensors | Posterior shoulder/forearm, dorsum of hand (partially digits I-III) |
| Median | C6-T1 | Most forearm flexors, pronator, thenar | Palmar surface of digits I-III and half of digit IV |
| Ulnar | C8-T1 | Interosseous muscles, hypothenar muscles, part of flexor carpi ulnaris and flexor digitorum profundus | Digit V and half of digit IV, medial border of the hand |
7. Erb-Duchenne palsy (upper type)
- C5-C6 lesion (upper trunk).
- Cause: birth trauma (downward traction on the newborn's head), motorcycle accident (shoulder pulled up, head forced to the side).
- Deficits: shoulder abduction (deltoid), external rotation (supraspinatus, infraspinatus), forearm flexion (biceps, brachialis), supination.
- «Waiter's tip» posture: shoulder adducted and internally rotated, forearm extended and pronated.
- Sensation — impaired on the lateral surface of the arm and forearm.
8. Klumpke palsy (lower type)
- C8-T1 lesion (lower trunk).
- Cause: birth trauma (upward traction on the upper limb), compression by Pancoast tumor (lung apex), cervical rib.
- Deficits: intrinsic muscles of the hand (interossei, thenar, hypothenar), long finger flexors.
- «Claw hand» posture (combination of ulnar and partial median nerve palsy).
- Sensation — impaired on the medial surface of the forearm and hand.
- When T1 sympathetic fibers are involved — Horner's syndrome (miosis, ptosis, anhidrosis, enophthalmos).
9. Specific neuropathies
- Radial nerve — «Saturday night palsy» (compression in the spiral groove of the humerus): «wrist drop», inability to extend the wrist and fingers.
- Median nerve — carpal tunnel syndrome: numbness and pain in digits I-III, nocturnal awakenings, positive Phalen's and Tinel's tests; thenar atrophy.
- Ulnar nerve — cubital tunnel syndrome (in the ulnar groove): numbness of digit V and half of digit IV, «claw hand», weakness of thumb adduction (Froment's sign).
- Musculocutaneous nerve — rarely isolated; weakness of forearm flexion, ↓ biceps reflex.
- Axillary nerve — associated with shoulder dislocation or surgical neck fracture of the humerus; abduction weakness, anesthesia over the deltoid.
10. Long thoracic nerve and winged scapula
- Injury — during mastectomy with axillary dissection, heavy exertion, trauma.
- Weakness of m. serratus anterior → scapula protrudes from the chest wall when pushing against a wall with the hand.
- Additionally — weakness in raising the arm above the horizontal plane.
- Often recovers within 6–12 months.
11. Diagnostics and imaging
- Clinical examination — assessment of muscle strength (MRC 0-5), sensation, reflexes.
- NCS + needle EMG — localization of the lesion, differentiation between pre- and postganglionic injuries (crucial for surgical management).
- MRI of the brachial plexus — most informative; CT myelography if root evaluation is necessary.
- Chest X-ray — cervical rib, Pancoast tumor.
- Ultrasound — evaluation of superficial structures and compression.
12. FAQ
Why is it called «waiter's tip» hand in Erb-Duchenne palsy?
Abductor and external rotator muscles (deltoid, supraspinatus, infraspinatus) are paralyzed, along with forearm flexors (biceps) and supinators. The antagonists — adductors, internal rotators, and pronators — remain intact, causing the arm to hang in a characteristic posture.
What is the difference between preganglionic and postganglionic injury?
Preganglionic — root avulsion from the spinal cord; regeneration is impossible, neurotization using a donor nerve is required. Postganglionic — injury to the trunk/cord distal to the ganglion; regeneration or primary repair is possible.
Why does Horner's syndrome develop in Pancoast tumor?
A tumor of the lung apex compresses the lower trunk of the brachial plexus (C8-T1) and adjacent sympathetic fibers traveling to the superior cervical ganglion. Horner's triad — miosis, ptosis, anhidrosis.
How to easily remember the cords and their positions?
Mnemonic: «Real Texans Drink Cold Beer» — Roots, Trunks, Divisions, Cords, Branches. The cords surrounding the axillary artery — lateral, medial, posterior (according to their anatomical position relative to the artery).
What is the treatment for traumatic plexopathy?
Conservative: physical therapy, bracing, neuroprotection (B vitamins). Surgical: neurolysis, nerve repair, nerve grafting, neurotization (Oberlin procedure — ulnar nerve fascicle transfer to musculocutaneous nerve to restore elbow flexion), and muscle transfers in delayed cases.
See also: Muscles of the upper limb · Carpal tunnel syndrome · Horner's syndrome · Pancoast tumor · Anatomy catalog