The carpal tunnel is a narrow, fibrous passage in the wrist that protects the median nerve, which runs down the length of arm and through the wrist into the hand. It controls some hand movement, and sensation in the thumb, index and middle fingers, and half of the ring finger. Irritation or compression of the median nerve within the carpal tunnel can cause tingling and numbness in the fingers, as well as pain in the arm, a condition known as carpal tunnel syndrome (CTS).
CTS is linked to, among other conditions, wrist injuries and diabetes, and inflammatory diseases such as rheumatoid arthritis. And although no link has conclusively been shown to exist, certain repetitive motion activities seem to cause CTS.
An effective treatment for CTS is corticosteroid injection, which reduces the swelling of tendons, easing pressure on the median nerve. Injected directly into the inflamed area, the corticosteroid works by minimizing the body's reaction to inflammation. Pain, numbness, weakness and tingling typically subside within a few days of the patient's being injected. The relief provided by the injections lasts for a few weeks to a few months.