This is a combination drawing/photograph I made to illustrate the cross sectional anatomy of the carpal tunnel.
Carpal tunnel cross sectional image
This is looking at your right hand stretched away from you. The hand is in a palm-up position. I’ve colored the tunnel itself WHITE – this is where the problem is. Muscles are colored red.
Nerves in the carpal tunnel cross section image
I’ve colored the two nerves yellow. The one on the right is the median nerve, the main nerve compressed or pinched in carpal tunnel syndrome.
On the left is the ulnar nerve.
The median nerve supplies sensation to the fingers on the thumb (or radial) side of the hand, including thumb, index, middle, and half of the ring finger.
The ulnar nerve is not involved in carpal tunnel syndrome and supplies sensation to the pinky finger (or small finger) and the half of the ring finger on the pinky side.
The flexor tendons in the cross sectional drawing
The small circles around the large median nerve are the nine flexor tendons of the hand. These flex (or bend) the fingers and thumb into a fist.
Each tendon has a lining called a tenosynovium, which can get swollen and compress the median nerve. You can imagine that if all nine were swollen, there wouldn’t be much space left for the nerve! The drawing actually exaggerates how much space there is in the tunnel – it’s very tight in there under normal situations – worse in carpal tunnel syndrome.
Carpal bones – the “floor” of the carpal tunnel in the drawing
The four carpal bones are the large, irregularly shaped objects at the bottom of the drawing.
Transverse carpal ligament – what gets cut in carpal tunnel surgery
I’ve put a star on top of the transverse carpal ligament.
The tissue layer on top of the tendons and the large median nerve is a strong, thick ligament called the transverse carpal ligament (just means the ligament than runs across between carpal bones).
This ligament is what I cut in the carpal tunnel surgery, that relieves pressure on the nerve and lets the compressed nerve heal.