Carpal tunnel syndrome is caused by compression of which nerve?

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

Answer: (C)

Carpal tunnel syndrome results from compression of the median nerve as it travels through the carpal tunnel at the wrist. The carpal tunnel is a narrow passage under the flexor retinaculum that houses the median nerve and several flexor tendons. When the median nerve is compressed, you get numbness, tingling, and sometimes weakness in the thumb, index finger, middle finger, and the radial side of the ring finger, along with possible thenar muscle weakness that affects thumb opposition. Symptoms often worsen at night, and provocative maneuvers like Phalen’s or Tinel’s sign can reproduce them. The other nerves listed don’t run through this tunnel—ulnar nerve travels toward the hand but through Guyon’s canal, radial nerve supplies the dorsum of the hand and posterior forearm, and axillary nerve supplies the shoulder—so they aren’t the ones typically compressed in carpal tunnel syndrome.