A 28-year-old male presents with a motorcycle accident injury causing a traction injury to the right upper limb. On examination, he has loss of abduction and external rotation of the shoulder, with winging of the scapula. Which nerve of the brachial plexus is most commonly injured in such traction injuries?
A. Lower trunk (C8–T1)
B. Middle trunk (C7)
C. Upper trunk (C5–C6)
D. Posterior cord
Explanation
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The upper trunk of the brachial plexus (C5–C6) is the most commonly injured component in traction injuries, accounting for approximately 50–60% of all brachial plexus injuries.
Mechanism of Upper Trunk Injury
Traction injuries occur when:
1.
The shoulder is forcibly depressed (downward)
2.
The head is laterally flexed away from the injured side
3.
This stretches the upper trunk maximally across the transverse cervical artery and anterior scalene muscle
Clinical Presentation of Upper Trunk Injury (Erb's Palsy)
The upper trunk is vulnerable because it is the most superficial and mobile component of the plexus, making it susceptible to stretch injuries.
Why Other Trunks Are Less Commonly Injured
Middle trunk (C7): Protected by its central location; injured in only ~10% of cases
Lower trunk (C8–T1): Injured in ~25% of cases, usually in severe hyperabduction injuries (Klumpke's palsy)
Posterior cord: Rarely injured in isolation; usually part of complete plexus injury
Clinical Pearl
The "waiter's tip" deformity (arm adducted and internally rotated) is pathognomonic for upper trunk injury and is the classic teaching sign in NEET PG.
