Carpal Tunnel? Blame Genes Not Overuse

Long hours surfing the Internet or typing won't wreck your wrists, a new study shows.

Carpal tunnel syndrome, long associated with overuse of the hands and wrists when surfing the Internet or typing, is linked more to genetics than repetitive use, according to the study.

It was presented today at the 74th Annual Meeting of the American Academy of Orthopaedic Surgeons in San Diego.

"The link between carpal tunnel syndrome and hand use is overstated and may be inaccurate," says study researcher David Ring, MD. Ring is an assistant professor of orthopaedic surgery at Harvard Medical School and a hand surgeon at Massachusetts General Hospital, Boston.

"The scientific support for the concept [that carpal tunnel is caused by overuse] is, on average, relatively weak," he says. "The major risk factor for carpal tunnel is genetic."

Exactly what those genetic factors are is not known, he says, but they may be related to the structure of the hand and wrists.

What Is Carpal Tunnel Syndrome?

In carpal tunnel syndrome, the median nerve, running from the arm into the hand, becomes pressed or squeezed at the wrist.

This nerve controls sensations to the thumb's palm side and part of all the fingers except the little finger.

When the median nerve is squeezed, there can be tingling, pain, weakness, or numbness in the wrist and hand that radiates up the arm.

Treatment options include rest, immobilization of the wrist, and surgery to reduce pressure on the nerve.

"A common perception is that carpal tunnel is related to hand use," Ring says.

That perception is more common among consumers, he says, but some doctors also believe it.

Studies on whether carpal tunnel syndrome is associated with hand use have been mixed.

Carpal Tunnel vs. Repetitive Strain Injury

Ring differentiates between carpal tunnel syndrome and repetitive strain injury, which he prefers to call idiopathic (cause unknown) arm pain.

In this condition, he says, there is pain "but no evidence of injury. It doesn't involve the carpal tunnel."

The Study

To clarify the debate, Ring and his colleagues looked at 117 studies on carpal tunnel syndrome published in the medical literature.

They used scientific criteria that determines the strength of a cause-and-effect relationship by giving it a score.

The researchers looked at biological factors -- such as genetics -- and occupational factors -- such as a person's job or the amount of repetitive hand use.

After analyzing the studies, "The quality and strength of evidence supporting genetic or inherent risk factors was felt to be moderate," Ring says.

"The quality and strength of evidence supporting occupational risk factors was felt to be poor," he says.

Average scores for biological factors linked to carpal tunnel syndrome were double those of occupational factors, such as occupation or repetitive hand use, Ring reports.

Implications of the Study

"The link to genetics is strong and believable," Ring says. "If you are diagnosed with carpal tunnel, you are an innocent bystander. You did nothing to cause it."

"This should give reassurance to those who use their hands a lot," he says.

SOURCES: David Ring, MD, assistant professor of orthopaedic surgery, Harvard Medical School; hand and upper extremity surgeon, Massachusetts General Hospital, Boston. 74th Annual Meeting of the American Academy of Orthopaedic Surgeons, San Diego, Feb. 16, 2007.