London, Jan. 30: Thousands of people using BlackBerries, the fashionable hand-held gadget that offers email, text, pager and mobile phone options, are turning up at the doctor with aching digits caused by using the device?s tiny keyboard.

Users of the BlackBerry, dubbed ?crackberries? because they are so addictive, commonly send 500 texts a day, with their thumbs often doing most of the work.

Sean Hughes, the professor of orthopaedic surgery at Imperial College London, said that such frantic use of the thumb would inevitably cause problems.

?The thumb works differently from the other fingers. It?s designed for picking up things. There?s a joint at the bottom of the thumb that allows it to flex and rotate, so when people are bashing away at their mobiles the thumb is moving in different dimensions,? he said.

?But all this movement can cause problems compared with the fingers, which only have to move up and down.?

Professor Hughes said that the reality of ?BlackBerry thumb? was probably rather more prosaic than sufferers realised. ?They could be coming down with what is effectively early osteoarthritis,? he said.

Prosper Benhaim, a hand surgeon and associate professor of orthopaedic and plastic surgery at the University of California, Los Angeles, agreed that overuse of the thumb can create problems.

?Anything that causes repeat motion can predispose someone to injuries of various sorts, whether it is tendinitis or aggravating underlying arthritis,? he said.

?These things can be made worse or even initiated by overuse. But thumb typing is very repetitive, and the keys are so small it makes it difficult to navigate around easily. Because it is so small, people are likely to press harder than they would with a larger keyboard. So the thumb on the BlackBerry does more than you would do with your fingers on a keyboard.

?BlackBerry-users include a significant segment of the population old enough to be developing arthritis ? and this can aggravate it.?