A 30-year-old motorcyclist suffers a forced depression of the right shoulder with lateral neck deviation, resulting in weakness of shoulder abduction, elbow flexion, and external rotation of the arm. Sensation is lost over the lateral arm. Which roots are most likely injured?

• A C8 and T1 (lower trunk) — Klumpke's palsy
• B C5 and C6 (upper trunk) — Erb's palsy ✓
• C C7 alone — middle trunk
• D C6 and C7 — middle and lower trunks

Explanation

Erb's palsy (C5–C6) results from traction injury to the upper brachial plexus: shoulder abduction (deltoid, supraspinatus — axillary/suprascapular nerve from C5), elbow flexion (biceps — musculocutaneous from C5–C6), and external rotation (infraspinatus — suprascapular C5–C6) are all lost. The arm assumes the 'waiter's tip' posture (adducted, internally rotated, elbow extended, forearm pronated). Lateral arm sensation (axillary nerve, C5) is lost. Klumpke's palsy (C8–T1) affects hand intrinsics with claw hand and Horner syndrome.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.