The carpal tunnel is a narrow passageway on the palm side of your wrist, about the width of your thumb. It’s formed by small wrist bones on three sides and a tough band of tissue (the transverse carpal ligament) stretched across the top like a roof. Through this tight space run nine flexor tendons, which bend your fingers, and the median nerve, which provides feeling and movement to parts of your hand. Most people hear the term only when something goes wrong with it, but the tunnel itself is a normal part of your anatomy that exists in every human wrist.
What’s Inside the Carpal Tunnel
The median nerve is the most important structure passing through the tunnel. It provides sensation to the palm side of your thumb, index finger, middle finger, and part of your ring finger. It also controls some of the small muscles at the base of your thumb that let you pinch and grip. Alongside the nerve, nine tendons slide back and forth every time you curl or straighten your fingers. Each tendon is wrapped in a slippery lining that reduces friction during movement.
In a healthy wrist, the pressure inside the carpal tunnel is very low, roughly 2 to 10 mmHg. That’s barely above zero. The nerve, tendons, and their protective linings all fit together with just enough room to function. But because the tunnel’s walls are rigid (bone on three sides, ligament on top), there’s almost no capacity for swelling. Any increase in the contents or decrease in space raises pressure quickly, and the median nerve is the first structure to suffer.
How Carpal Tunnel Syndrome Develops
Carpal tunnel syndrome happens when sustained pressure compresses the median nerve inside the tunnel. The most common cause isn’t a single injury. Instead, the tendon linings gradually swell over time, crowding the nerve. Repetitive hand and wrist motions, especially with the wrist bent, can contribute to this swelling. So can fluid retention, which is why the condition often appears during pregnancy or in people with kidney failure.
Several health conditions raise your risk. Diabetes increases vulnerability to nerve damage in general, making the median nerve more sensitive to even mild compression. Inflammatory conditions like rheumatoid arthritis and gout cause swelling in the tendon linings, directly reducing tunnel space. Thyroid disorders, particularly an underactive thyroid, are linked to tissue swelling throughout the body, including the wrist. Women develop carpal tunnel syndrome roughly three times more often than men, partly because their tunnels tend to be anatomically smaller.
What the Symptoms Feel Like
The earliest sign is usually tingling or numbness in the thumb, index finger, middle finger, and the thumb side of the ring finger. The little finger is unaffected because it’s served by a different nerve. Many people first notice symptoms at night, waking up with a numb or “pins and needles” feeling that improves after shaking the hand. This happens because most people sleep with their wrists bent, which narrows the tunnel further.
As compression worsens, numbness can become constant during the day, especially during activities that involve gripping or bending the wrist: driving, holding a phone, typing. Over months or years, the muscles at the base of the thumb can weaken and visibly shrink, making it harder to pinch objects or open jars. At that stage, nerve damage may be partially irreversible, which is why catching the condition early matters.
How It’s Diagnosed
Doctors often start with simple physical tests in the office. One common test involves holding both wrists fully bent (backs of the hands pressed together) for one minute. If this reproduces tingling in the median nerve’s territory, it’s considered positive. This test catches the condition about 68% of the time. Another involves tapping repeatedly over the ligament on the palm side of the wrist for up to 60 seconds, looking for an electric shock sensation into the fingers. That one is positive about 50% of the time.
Because these physical tests miss a fair number of cases, nerve conduction studies are the standard confirmation. A technician places small electrodes on the hand and forearm and measures how fast electrical signals travel through the median nerve. Slowed conduction across the wrist confirms compression. Ultrasound is sometimes used as well, measuring the cross-sectional area of the median nerve at the wrist. A nerve swollen beyond about 11 square millimeters at wrist level is a common threshold suggesting compression.
Nonsurgical Treatment Options
Mild to moderate cases often improve without surgery. A wrist splint worn at night keeps the wrist in a neutral position, preventing the bending that increases tunnel pressure while you sleep. Many people notice significant relief within a few weeks of consistent nighttime splinting. Avoiding or modifying the repetitive motions that aggravate symptoms also helps. If you work at a keyboard, adjusting wrist position so your hands stay level rather than angled upward can reduce pressure inside the tunnel.
Corticosteroid injections into the carpal tunnel can reduce swelling around the tendons and provide relief lasting weeks to months. They work well as a bridge, buying time to see whether lifestyle changes or splinting will be enough. For people whose symptoms are driven by an underlying condition like hypothyroidism or rheumatoid arthritis, treating that condition can sometimes resolve the wrist symptoms on its own.
What Surgery Involves and Recovery
When symptoms are severe, constant, or involve muscle wasting, surgery becomes the most reliable option. The procedure is called carpal tunnel release, and its goal is simple: cut the transverse carpal ligament to permanently open the roof of the tunnel and relieve pressure on the nerve. It can be done through a small incision in the palm (open release) or through one or two tiny incisions using a camera (endoscopic release). Both approaches have clinical success rates above 95%.
Recovery varies. Your wrist will typically be bandaged or splinted for one to two weeks after surgery, and you may use a brace intermittently for about a month. Grip strength and fine motor control return gradually over weeks to months. Numbness and tingling usually improve quickly, sometimes within days, though nerves that were severely compressed can take longer to fully recover. Some soreness at the incision site in the palm is normal and fades over time.
The ligament does eventually heal back together, but with a gap that leaves more room than before. The tunnel is permanently wider, which is why recurrence after surgery is uncommon.