Which nerve is affected in carpal tunnel syndrome?

• A. Ulnar nerve
• B. Median nerve
• C. Radial nerve
• D. Axillary nerve

Answer: (B)

Carpal tunnel syndrome occurs when the median nerve is compressed as it passes through the carpal tunnel under the flexor retinaculum. This nerve provides sensation to the palmar aspect of the thumb, index, middle, and half of the ring finger, and it innervates the thenar muscles that move the thumb. Compression here leads to numbness, tingling, and sometimes weakness in thumb opposition, with possible thenar wasting in advanced cases.

The other nerves don’t fit because they don’t travel through the carpal tunnel. The ulnar nerve is mainly affected in lesions near Guyon’s canal at the wrist and would cause sensory changes in the little finger and half of the ring finger and affect most intrinsic hand muscles. The radial nerve supplies the dorsum of the hand and extensor compartments and does not pass through the carpal tunnel. The axillary nerve serves the shoulder region and is unrelated to the wrist.