Brachial Plexus — Viva Pearls and KUHS PYQs
Essential Mnemonics
| Mnemonic | What it Represents |
|---|---|
| ”Really Tired Drink Coffee Now” | R=Roots, T=Trunks, D=Divisions, C=Cords, N=Nerves |
| ”My Aunt Ragged My Uncle” | Terminal nerves lateral→medial in axilla: Musculocutaneous, Axillary, Radial, Median, Ulnar |
| ”ULTRA” | Posterior cord branches: Upper subscapular, Thoracodorsal, Lower subscapular, Axillary, Radial |
| ”LOAF” | Median nerve hand muscles: Lumbricals (1+2), Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis |
| ”C5C6 upper, C7 middle, C8T1 lower” | Trunk formation |
| ”Lateral loves 2, Medial has 1, Posterior gets all 3” | Cord formation from divisions |
High-Yield One-Liners
| Question / Stem | Answer |
|---|---|
| Brachial plexus formed by | Anterior primary rami of C5, C6, C7, C8, T1 |
| Number of roots / trunks / divisions / cords | 5 roots → 3 trunks → 6 divisions → 3 cords |
| Upper trunk formed by | C5 + C6 |
| Middle trunk formed by | C7 alone |
| Lower trunk formed by | C8 + T1 |
| Lateral cord formed by | Anterior divisions of upper + middle trunks |
| Medial cord formed by | Anterior division of lower trunk |
| Posterior cord formed by | Posterior divisions of all three trunks |
| Cords named in relation to | 2nd part of the axillary artery |
| Only trunk that gives branches | Upper trunk (suprascapular + nerve to subclavius) |
| Middle trunk branches | None |
| Lower trunk branches | None |
| Erb’s point — how many nerves meet? | Six nerves |
| Only nerve arising from two cords | Median nerve (lateral + medial cords) |
| Largest nerve of brachial plexus | Radial Nerve |
| Nerve of the thenar eminence | Median nerve |
| Nerve piercing coracobrachialis | Musculocutaneous nerve |
| Nerve winding around surgical neck of humerus | Axillary nerve |
| Nerve in the spiral groove of humerus | Radial nerve (with profunda brachii artery) |
| Nerve behind medial epicondyle | Ulnar nerve |
| Injury to long thoracic nerve → | Winging of scapula |
| Injury to axillary nerve → | Deltoid paralysis + flattening of shoulder |
| Erb’s paralysis → deformity | Policeman’s / Waiter’s tip hand |
| Klumpke’s paralysis → deformity | Claw hand (all fingers) |
| Horner’s syndrome in which plexus injury | Klumpke’s (T1 proximal injury) |
| Features of Horner’s syndrome | Ptosis + miosis + anhydrosis + enophthalmos |
| Saturday night palsy → nerve and site | Radial nerve in spiral groove |
| Saturday night palsy → triceps | Spared (nerve to triceps arises proximal to groove) |
| Crutch palsy → nerve and site | Radial nerve in axilla |
| Crutch palsy → triceps | Paralyzed |
| Wrist drop without triceps paralysis | Spiral groove injury (Saturday night palsy) |
| Wrist drop with triceps paralysis | Axillary injury (crutch palsy) |
| Carpal tunnel → nerve | Median nerve |
| Carpal tunnel → sensation spared | Thenar eminence (palmar cutaneous branch above retinaculum) |
| Carpal tunnel → deformity if untreated | Ape thumb (Simian hand) |
| Most common entrapment neuropathy | Carpal tunnel syndrome |
| LOAF muscles supplied by | Median nerve |
| Ulnar nerve supplies intrinsics except | LOAF (which are median nerve) |
| Froment’s sign positive means | Adductor pollicis paralysis (ulnar nerve) |
| Ulnar claw involves which fingers | Ring and little fingers (partial claw) |
| Complete (true) claw hand | Combined median + ulnar nerve injury |
| Segmental supply of small muscles of hand | T1 |
| Segmental supply of flexors of elbow | C5, C6 |
| Segmental supply of extensors of elbow | C6, C7 |
| Axillary sheath derived from | Prevertebral fascia |
| Autonomous sensory area of median nerve | Pulp of index finger |
| Autonomous sensory area of ulnar nerve | Pulp of little finger |
| Autonomous sensory area of radial nerve | First web space on dorsum of hand |
KUHS PYQ-Style Questions and Model Answers
Q1. Describe the brachial plexus. Add a note on Erb’s palsy.
Brachial plexus:
- Formed by anterior primary rami of C5–T1
- 5 Roots → 3 Trunks (upper: C5+C6, middle: C7, lower: C8+T1) → 6 Divisions → 3 Cords (lateral, medial, posterior relative to 2nd part of axillary artery) → Branches
- Supraclavicular branches: long thoracic, dorsal scapular (from roots); suprascapular, nerve to subclavius (from upper trunk)
- Infraclavicular branches: from three cords
Erb’s palsy:
- Upper trunk injury (C5, C6) at Erb’s point
- Cause: widening of head-shoulder angle (birth injury, fall)
- Muscles: deltoid, biceps, brachialis, brachioradialis, supraspinatus, infraspinatus, supinator paralyzed
- Deformity: policeman’s tip — arm adducted + medially rotated; elbow extended + forearm pronated
- Sensory loss: lateral aspect of arm
- Autonomic: absent (T1 unaffected)
Q2. Write short notes on Klumpke’s paralysis.
- Lower trunk injury (C8, T1)
- Cause: hyperabduction of arm (clutching during fall, birth injury in breech)
- Muscles: all intrinsic hand muscles (T1) + FCU and medial FDP (C8) paralyzed
- Deformity: claw hand — hyperextension at MCP joints, flexion at IP joints, all fingers
- Sensory loss: medial border of forearm and hand
- Horner’s syndrome if T1 injured proximal to white ramus — ptosis, miosis, anhydrosis, enophthalmos
Q3. Describe the formation of the cords of brachial plexus.
- Lateral cord: anterior divisions of upper (C5, C6) and middle (C7) trunks
- Medial cord: anterior division of lower trunk (C8, T1)
- Posterior cord: posterior divisions of all three trunks (C5–T1)
- Named by their relation to the 2nd part of the axillary artery
- Lateral cord gives: lateral pectoral, musculocutaneous, lateral root of median
- Medial cord gives: medial pectoral, MC arm, MC forearm, medial root of median, ulnar
- Posterior cord gives: ULTRA (upper subscapular, thoracodorsal, lower subscapular, axillary, radial)
Q4. What is Saturday night palsy? What are its features?
Saturday night palsy is injury to the radial nerve in the spiral groove, caused by the arm being draped over the back of a chair while sleeping (in an intoxicated individual). The nerve is compressed against the humerus.
Features:
- Wrist drop (loss of wrist extension)
- Loss of extension of fingers
- Loss of supination with elbow extended
- Triceps spared (nerves to long and lateral heads of triceps arise proximal to the groove)
- Sensory loss: small area on dorsum of hand (1st web space)
Also caused by: midshaft fracture of humerus; wrong intramuscular injection.
Q5. Write short notes on carpal tunnel syndrome.
Carpal tunnel syndrome = entrapment of the median nerve under the flexor retinaculum in the carpal tunnel.
Features:
- Burning pain, tingling in lateral 3½ digits — worst at night
- Thenar eminence sensation spared (palmar cutaneous branch passes above retinaculum)
- Weakness of thenar muscles (APB, OP, FPB)
- Ape thumb deformity if untreated — thumb adducted, in plane of palm, unable to oppose
- Positive Tinel’s sign + Phalen’s test
Treatment: Decompression by longitudinal incision through flexor retinaculum.
Q6. What is Erb’s point? Name the nerves that meet at it.
Erb’s point = the region of the upper trunk of the brachial plexus where six nerves meet:
- C5 root (ventral ramus)
- C6 root (ventral ramus)
- Suprascapular nerve (branch of upper trunk)
- Nerve to subclavius (branch of upper trunk)
- Anterior division of upper trunk
- Posterior division of upper trunk
Segmental Innervation of Upper Limb Muscles
| Segment | Key Muscles / Movements |
|---|---|
| C5 | Deltoid, supraspinatus, infraspinatus, teres minor, coracobrachialis, biceps brachii, brachioradialis, supinator → abductors + lateral rotators of shoulder; flexors + supinators of forearm |
| C6 | Pectoralis major/minor, subscapularis, latissimus dorsi, teres major, serratus anterior, triceps, pronator teres + quadratus → adductors + medial rotators of shoulder; extensors + pronators of forearm |
| C7 | Extensors and flexors of the wrist |
| C8 | Long flexors and extensors of the fingers |
| T1 | Small (intrinsic) muscles of the hand |
Quick Classification of Common Deformities
| Deformity | Nerve / Injury |
|---|---|
| Wrist drop | Radial nerve (axilla or spiral groove) |
| Policeman’s / Waiter’s tip hand | Erb’s palsy (C5, C6 — upper trunk) |
| Claw hand (all fingers) | Klumpke’s palsy OR combined median + ulnar |
| Ulnar claw hand (ring + little fingers) | Ulnar nerve at medial epicondyle |
| Ape thumb / Simian hand | Median nerve (carpal tunnel — thenar muscles) |
| Benediction hand | High median nerve injury (above elbow) |
| Winging of scapula | Long thoracic nerve |
| Flattening of shoulder | Axillary nerve (surgical neck fracture) |