On its way, the nerve travels through a tunnel. The floor of the tunnel is made up by the wrist (or carpal) bones, and the roof is made up of a thick band of sinewy connective tissue. The median nerve shares the carpal tunnel with nine tendons that transmit force generated by muscles in the forearm to make the fingers and the thumb grip. Because the tunnel floor is hard bone, and the roof is tough sinew, swelling inside the tunnel has nowhere to expand into, and instead presses on the very sensitive median nerve. There are a lot of things that can cause swelling inside the tunnel, one of the most common being chronic, repetitive movements. Other factors that probably contribute to compression include genetics and diseases like diabetes.
Compression of the median nerve in the carpal tunnel causes the group of symptoms called carpal tunnel syndrome
. These symptoms include numbness or tingling
of the thumb, index, and middle finger (other fingers are usually involved depending on the individual's anatomy); loss of dexterity; pain that can radiate into the wrist or arm; and weakness and muscle damage in the hand. The symptoms often start out worse at night, and people with carpal tunnel syndrome often feel a bit better if they "shake out" their hands.
Numbness and weakness in the hand can have other causes, including compression of the median nerve elsewhere in the arm, and compression of nerves in the neck. When you go to the doctor (preferably a neurologist with training in neuromuscular disorders
), the doctor will examine your limb to help locate the problem. The doctor should also discuss additional tests like an EMG nerve conduction study (see my health guide), or ultrasound.
There are a lot of ways to treat carpal tunnel syndrome. These range from wrist splints and physical therapy
, to injections, to surgery. There are two kinds of surgery: open, and endoscopic. Endoscopic surgery uses an endoscope. An endoscope is a camera at the end of a flexible tube that is used to look at the inside of the tunnel to guide surgical instruments. In endoscopic carpal tunnel surgery
, one or two small incisions are made at one end of the carpal tunnel (usually the wrist), or both (the wrist and the palm). Using the endoscope, the surgeon will guide the surgical tools to cut part of the sinewy roof of the tunnel called the transverse carpal ligament, creating more room in the tunnel. He would also look around for anything else that might be causing compression. The cutting goes on inside the tunnel and doesn't go all the way through to the surface of the skin. At the end of the surgery, the surgeon will place a couple of stitches to close the hole (or holes) that he made.
By comparison, open carpal tunnel surgery creates an incision between 2 and 4 inches long from the palm to the wrist. This incision cuts all the way through the roof of the tunnel, including the transverse carpal ligament and something called the palmar aponeurosis (the other sinewy stuff). After open carpal tunnel surgery, the incision is usually closed by stitches and surgical staples.
Because endoscopic carpal tunnel surgery makes smaller incisions and disrupts less tissue, recovery is usually faster. There are cases, however, where open carpal tunnel surgery might be preferable.