Causes
The median nerve carries messages between the thumb, index finger, and middle
finger and the brain. Pain, touch, and sensation are transmitted one way.
Instructions to move muscles are sent in the opposite direction.
The transverse ligament runs across the inside of the wrist like a watch
strap. The carpal tunnel is the space between this and the bones on the outside
of the wrist. The tendons, the muscles of the fingers, blood vessels, and nerves
pass through it. The median nerve lies on top of them on the inside of the wrist.
There is just enough room for it between the tendons and the transverse ligament.
The tendons are lubricated to prevent rubbing. If something goes wrong with
the lubrication, they get inflamed. They swell up, pushing the median nerve
against the transverse ligament. Eventually the nerve gets so compressed that it starts
to malfunction. Some medical conditions are associated with problem tendons
and therefore with carpal tunnel syndrome, including:
- rheumatoid arthritis
- diabetes
- pregnancy
- hypothyroidism (an underactive thyroid gland)
- previous broken wrist
Carpal tunnel syndrome can result from repeated physical stress on the hands
and wrists. It is sometimes work related and tends to affect people who:
- repeatedly make the same motions with their wrists
- are frequently exposed to vibrations in their hands (e.g., heavy-machinery
operators)
- keep their hands in the same positions for long periods of time (typists,
for instance)
Many people have carpal tunnel syndrome for no obvious reason.