By Stephanie Stahl

PHILADELPHIA (CBS) — Doctors are freezing away the pain to make knee replacement surgery easier, and it doesn’t involve opioids or other medications. It’s a big new field — drug-free pain relief. One approach being used by a growing number of orthopedic surgeons is cold therapy before surgery.

Cindy McCoy’s knees were worn out.

“I was falling constantly,” McCoy said.

But now, after two knee replacements, she’s moving pain-free. She credits injections she had before the operations.

“It would cut down on the pain, cut down on how long you would do the pain medication and the recovery time,” McCoy said.

It’s a new kind of cold therapy where tiny, compressed cartridges of nitrous oxide — or laughing gas — cools the nerves to minus-80 degrees.

“We inject the nitrous oxide in the area around where the nerves run. It freezes the outside of those nerves,” Forbes Hospital Dr. Brian Moore said. “It causes them to have to regenerate, which can take two to three months. And while they’re regenerating, theoretically, they shouldn’t be able to transmit as much nerve pain.”

The injections, called iovera, are given two weeks before surgery.

“When I saw the three prongs coming up, I’m like, ‘Oh that’s going to hurt going in there,'” McCoy said. “All you really felt was pressure. You don’t feel any pain and all that.”

It’s FDA-approved and covered by insurance.

“The biggest downside is it may not work,” Moore said. “I would rate our effectiveness over 90%. The patients are usually pretty happy.”

McCoy says she’s now exceeding expectations in rehab.

“I’m so glad that I did it,” McCoy said.

Doctors say the therapy does not treat the underlying cause of the pain and the effect on the nerve is temporary, providing pain relief until the nerve regenerates and function is restored.

For more information on the new kind of cold therapy, click here.

Stephanie Stahl