KNOXVILLE, Tenn. — For her 71st birthday, Nan Scott threw herself a party and got some new knees.

"And we all drank a margarita to stem cells," said Scott.

Instead of a traditional knee replacement surgery, she chose to try stem cell injections.

"I don't want to be taking drugs," said Scott. "I don't want to have a lot of contraptions in my body. I want my own body to repair itself."

Optimal Health in Turkey Creek specializes in regenerative medicine.

They're one of a handful of places in Knoxville using stem cell therapy to heal joint issues in places like knees, hips and shoulders.

 "Stem cells are the body's master cells," said Dr. Charlotte MacDonald. "They are found in various tissues and they have the ability to take on the properties of other cells."

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MacDonald administers the stem cell injections.

That clinic uses umbilical stem cells donated at hospitals from live c-section births.

"We de-thaw the stem cells, and then we perform the joint injection," said MacDonald.

The injection process only takes a few minutes and doesn't look much different from getting a vaccine.

"Needles and doctors are like kryptonite and Superman to me, I just get so scared and nervous over that," said Brad Bentley.

But the needles scared Bentley less than the idea of a full hip replacement.

Nine weeks after he had two stem cell hip injections, he said he's walking better than he has in a long time.

"I'm up and I'm at the swimming pool doing my therapy at like 7:30 every morning," said Bentley. "I'm losing weight. I've had more energy than I have in the last three years."

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The day of his injections, he walked out of the office and drove home to Gatlinburg with no pain.

"It's been a godsend for me," said Bentley.

Stem cell therapy is not FDA approved and has only been available in the Knoxville area for a few years.

"I just think it's exciting that we're at the forefront of medicine and I think in 10 years this is going to be a very popular treatment done by a lot of offices," said MacDonald.

Umbilical stem cells are legal to use in the U.S.

Doctors said these stem cell injections can last from two to 10 years.

Insurance does not cover the procedure, but it's often a fraction of the cost of a knee or hip replacement.