Some animals — like lizards and lobsters — can regrow tails or arms or legs.

Humans can't.

But they can regrow cartilage. Or, more accurately, ask medical professionals to regrow it for them.

Matrix-induced autologous chondrocyte implantation (MACI) is a knee procedure that implants expanded versions of a patient's cells to replace damaged cartilage.

“We have to remove that cartilage because it's not normal,” said Dr. Joshua Szabo, an orthopedic surgeon with Tri Rivers Musculoskeletal Centers. “Cartilage is more involved than what we would expect.”

Szabo, who is also a U.S. ski and snowboard physician at the UPMC Lemieux Sports Complex in Cranberry Township, works in partnership with UPMC and Butler Health System. He said he followed MACI's success in Europe for many years before it was approved by the FDA in 2016. Once it was approved, Szabo was able to bring the procedure to Butler County.

“I think it's fantastic,” said Stephanie Heusey, a Butler resident who had MACI surgery in 2018.

Heusey is a student at Edinboro University and one of Szabo's patients who needed knee surgery following general joint deterioration.

“I never had a specific thing happen,” Heusey said. “Just overall wear-and-tear.”

There are six steps in the MACI process, according to the biopharmaceutical company Vericel.

First, a biopsy of healthy cartilage is taken. Then, the biopsy is processed to isolate cartilage cells. Cartilage cells are regrown in four to six weeks and placed on collagen membrane.

The membrane is delivered to the patient's surgeon, who then implants it in the patient's knee. The patient goes through rehab to regain normal joint activity.

The ideal patient is an adult with symptomatic cartilage damage between the ages of 18 and 55.

“In general, it's a pretty hard cutoff,” Szabo said.

According to Szabo, MACI is effective because patients are using their own genes to heal.

“They're your own cells,” Szabo said. “They're the best ones to ... do this.”

“You get these injuries, (and) it just really hurts,” Heusey said. “I like knowing that I can go around without feeling pain.”

Szabo said keeping knee joints healthy is a matter of being proactive. The earlier any issue with the knee joint is identified, the better the chance of a successful surgical outcome.

In the meantime, Szabo advises people to participate in daily physical activity such as walking. He said it's important to keep cartilage healthy.

“If you rest, you rust,” Szabo said.

It may take MACI patients six months to a year to experience the full benefits of the procedure.

“There's no perfect procedure,” Szabo said. “(But) this is the best one we have.”