An obsession with the mobile game app Candy Crush put a California man in the hospital where he underwent surgery to repair a ruptured tendon in his thumb.

The unnamed San Diego resident told doctors he had been playing the game on his smartphone almost all day long for six to eight weeks, using only his left hand—and thumb—while leaving his right hand free for all other tasks.

"Playing was a kind of secondary thing, but it was constantly on," the man told doctors.

He had reportedly just left the Navy and was playing Candy Crush regularly while waiting to begin a new civilian job.

The repetitive tapping on various locations on the screen eventually caused the tendon of the man's thumb to rupture—not at its thinnest point, where such injuries are common, but at the tendon's thickest point, doctors reported in the JAMA Internal Medicine journal.

Torn ligament injuries are usually painful from the moment they occur, but the 29-year-old patient told doctors he had not noticed any pain while playing and only felt it later as a chronic ache that prompted the visit to the hospital's emergency room and the subsequent surgery.

Playing video games obsessively can possibly numb people's pain threshold—similar to a "runner's high"—and could be a contributing factor to video game addiction, said Dr. Andrew Doan, co-author of the case report.

"We need to be aware that certain video games can act like digital painkillers," said Doan, head of addictions research at the Naval Medical Center San Diego. "We have to be very cognizant that that can be abused."

Studies have shown that playing video games can release chemicals in the brain linked to excitement and pleasure, but those chemicals can also act as painkillers, possibly masking an injury, the doctors said in the published case study.

"The potential for video games to reduce pain perception raises clinical and social considerations about excessive use, abuse, and addiction," they wrote.

Such addictions, in addition to risking injury, can also create problems in people's relationships, work and finances, Doan said.

The injury potential of smartphones has long been known. There's even a phrase, "BlackBerry thumb," inspired by the repetitive strain injuries risked by overuse of thumbs when operating the buttons on mobile devices.

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