A motorcyclist falls and sustains a severe traction injury to the upper trunk (C5-C6) of the brachial plexus — an Erb's palsy. Which nerve's autonomous zone will demonstrate reduced pinprick sensation?
- A Medial cutaneous nerve of forearm
- B Ulnar nerve at the little finger
- C Lateral cutaneous nerve of the forearm (regimental badge area of the arm, C5) ✓
- D Median nerve at the thenar eminence
Correct answer: C. Lateral cutaneous nerve of the forearm (regimental badge area of the arm, C5)
Explanation
Erb's palsy (C5-C6 upper trunk) classically involves the axillary nerve (C5) and the musculocutaneous nerve (C5-C6). The autonomous sensory zone for C5 is the 'regimental badge' area (lateral deltoid), and the musculocutaneous nerve's cutaneous branch (lateral cutaneous nerve of forearm) supplies the lateral forearm. The C6 dermatomal area (thumb and lateral forearm) is also affected. Ulnar nerve (C8-T1) and lower trunk territories are spared in Erb's palsy.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.