MIAMI (CBS4) _ Karen Farriera is all about being active. But not so long ago, she was anything but.

“I was wearing a brace all day, living on pain killers and I could barely walk my dogs around the block,” explained Farriera of her knee predicament.

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Her doctor tried physical therapy and cortisone shots. But ultimately, she needed a new knee.

“I thought he was pretty much crazy. I was 46 at the time. It just didn’t seem possible,” said Farriera.

But it was. The number of knee surgeries has doubled in the last decade and more women than men are ending up in the operating room.

Currently, four-and-a-half million Americans live with one knee replacement. It’s the fact that the people getting them are younger and younger, decades younger, that is so baffling.

Dr. Maury Harwood explained that the reason for this trend is threefold:

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1. Baby Boomers are more physically active.

2. Today’s “NEED IT NOW” mentality.

3. And improved technology.

“The main advancement in knee replacement technology is we’re moving toward custom implants. Nowadays, what we ‘re doing is we’re using MRI and CT scans and we’re actually building three-dimensional models of people’s knees and making implants that fit them specifically,” Dr. Harwood explained.

Karen Farriera had a partial knee replacement. “I’m back to walking my five, six miles. I ride my bike. I can do all the activities I love.”

The custom fit makes it easier than ever to get back to normal. Right now, Karen has only one regret.

“I should never have waited as long as I did,” she said.

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There are concerns. Studies show if you are very, very active after the surgery, you could loosen the replacement causing you to need surgery and another knee replacement again. Experts say avoiding certain pounding exercises could help the replacement, as well as your real knees, last longer.