The carpal tunnel is a narrow, tunnel-like structure in the wrist. The bottom and sides of this tunnel are formed by wrist (carpal) bones. The top of the tunnel is covered by a strong band of connective tissue called the transverse carpal ligament. The median nerve travels from the forearm into the hand through this tunnel in the wrist. The median nerve controls feeling in the palm side of the thumb, index finger, and long fingers. The nerve also controls the muscles around the base of the thumb. The tendons that bend the fingers and thumb also travel through the carpal tunnel. These tendons are called flexor tendons. The carpal tunnel protects the median nerve and flexor tendons that bend the fingers and thumb.
Carpal tunnel syndrome occurs when the tissues surrounding the flexor tendons in the wrist swell and put pressure on the median nerve. These tissues are called the synovium. The synovium lubricates the tendons and makes it easier to move the fingers. This swelling of the synovium narrows the confined space of the carpal tunnel, and over time, crowds the nerve. Carpal tunnel syndrome is caused by pressure on the median nerve traveling through the carpal tunnel. Many things contribute to the development of carpal tunnel syndrome:
- Heredity factors are the most important contributors – carpal tunnels are smaller in some people, and this trait can run in families.
- Hand use over time can play a role.
- Hormonal changes related to pregnancy can play a role.
- Age — carpal tunnel syndrome occurs more frequently in older people.
- Medical conditions, including diabetes, rheumatoid arthritis, and thyroid gland imbalance can play a role.