BOSTON -- Video games are not just for entertainment anymore.

One interactive game system has become the latest tool in weight loss. It is now being used for therapy.

A massive house fire in Brookline last April injured several firefighters. Lt. Owen Thompson, of Billerica, Mass, was one of them.

"I had an entire ceiling fall down on top of me," Thompson said. "My left knee got injured. I have some hard cartilage damage in my knee."

After surgery to repair the damage, Thompson has been undergoing physical therapy at the New England Rehabilitation Hospital Outpatient Clinic in Billerica. And it's here that a virtual reality game has come to his rescue.

"With the Wii, it's been able to show me how well my knee is or is not coming along," Thompson said.

"It really flows well to what we're doing with traditional therapy," said Joann Ingram, a physical therapist.

The clinic started using Nintendo's Wii Fit four months ago. Ingram said it offers a distraction from the tedious and often difficult physical therapy exercises. Thompson said being on the videogram gets his mind off the therapy.

"What he needs to do is work on his balance to get the balls in the holes," said Heidi Brincklow, Thompson's physical therapist.

The Wii offers a variety of exercises, from balance activities to yoga poses.

"As you look at his foot, you see how hard his muscles have to work and how much his knee is struggling," Brincklow said.

As Thompson practices, he improves his strength, flexibility and balance. And the computer gives him feedback.

"So they self-correct as they learn how to do it," Ingram said.

"As the points are scored, 36 is a good indication that his balance on his injured involved leg is still not as good as his uninvolved leg," said Brincklow. "At this point in time, for him to return to work he would be at risk for injuring his leg."

It's a risk Thompson is not willing to take, for himself, his fellow firefighters or the people he has dedicated his life to saving.