The knee is the biggest joint in the body, and replacing it is nothing to rush into.

But we're an increasingly active society. Baby boomers are exercising to stay healthy, but that isn't necessarily working out for their knees.

But the couple you're about to meet wasn't going to take bad knees sitting down.

"It's bone on bone and every time you take a step it sends pain up and down the leg and then the swelling immobilizes you where you can't bend," said knee replacement patient Janis Wetherell.

Janis' husband Thomas also had trouble with his knees.  "Anymore I couldn't hardly walk at all," said Thomas Wetherell. "I'd walk to my garage which isn't but about 300 feet and it was just terrible pain to do that."

Thomas and Janis Wetherell spent a lot of time during the last three years sitting. Sitting was at the top of a short list of activities they could do.

No baking cookies for their 10 grandchildren, not as much time visiting on the ham radio.

So they opted to get new knees together.

"An hour after she had her knee done, I had mine," Thomas said.

The Wetherells discovered knee replacement has recently come a long way. Especially for the ladies.

"For decades, the orthopedic surgeons have been reporting back to the implant makers that the implants don't quite fit women," said orthopedic surgeon Sonny Bal.

"It's a known fact of life in my profession that instability in female knees was more of a problem then in men," Bal explained. "And pain is much more common in women with knee replacement surgery than men. And with the newer design, those two problems you can eliminate."

He's talking about gender specific knees. It's a concept that's only been around for about a year.

A knee implant was designed for the average man, not taking into account a woman's narrower knee cap, a thinner end on the thigh bone and the different track the knee follows when she's walking. But now, it does.

"When I woke up, I knew it was wonderful. Janis said, "I would have gotten the one designed for a man and there would have been restrictions. We've talked the friends who've had it and they say they can't kneel, they can't go up steps, I can't climb ladders. Five weeks out I climbed a ladder," Janis said.

It's been nothing short of life changing for the Wetherells.

Thomas said "I was probably down to about 10% ability and now probably 80 or above."

Dr. Bal says today's patients don't tolerate pain or limited activity as an acceptable side effect of surgery and the advances in these gender specific knees make a less-painful life after surgery much more likely.

Dr. Bal says gender specific hips are already in the works and he foresees gender specific medications in the near future too.