Knee Cartilage Replacement
Last Updated on October 22, 2023 by The SportsMD Editors
John Klimkiewicz slices into both sides of Shannon McMillan’s right leg and pulls back her kneecap. “It’s a boy,” jokes the Georgetown University Hospital surgeon as he pops opens the knee, revealing bone and cartilage. The slippery connective tissue that covers the ends of McMillan’s bones and acts as a shock absorber has worn down in three places, leaving lesions, or holes. Without that thin layer of cartilage that allows for smooth movement of the joint, bone-on-bone action leads to pain and arthritis.
This surgery is a long shot at stopping that process. Sitting on a table nearby are two vials of cartilage cells that McMillan, 39, believes offer the best hope for avoiding a full knee replacement. The hopes of legions of weekend athletes for a long, active future may ride on the procedure.
Klimkiewicz removes all remaining cartilage within the holes. Next, he carves out three patches of membrane from McMillan’s left shinbone and sutures them over the lesions in her right knee. He’ll use this membrane as a patch to hold the new cartilage cells in place. He injects the cells into a tiny opening in the three patches, closes the holes and glues the edges into place. Finally, he moves her kneecap into a position where it doesn’t rub against the new cartilage, drills screws into McMillan’s bone to secure it and — three hours after making the first cut — sews up her knee.
One Approach to Knee Cartilage Replacement
Each year, hundreds of thousands of Americans undergo surgery to repair torn knee cartilage. “Repair” usually means shaving damaged cartilage. But some younger, healthier patients are trying cartilage replacement, a more experimental therapy. One replacement method involves growing new cartilage cells from those in the patient’s body and transplanting them into the knee.
Techniques for Repairing Knee Cartilage
In the past 20 years, researchers and surgeons have made advances in repairing and restoring knee cartilage, but no foolproof method exists. Options for cartilage repair include:
Shaving or Debridement: One of the most common treatments for cartilage defects that have not worn to the bone. Using a pencil-thin instrument called an arthroscope inserted into the knee through a small incision, a surgeon shaves and smooths shredded or frayed cartilage. Debridement is often used in combination with the other treatments. Because the technique doesn’t fix underlying causes of injury, symptoms may return.
Success rate*: 75 percent
Microfracture or Abrasion: Common for patients with cartilage damage all the way to the bone. Surgeons use arthroscopic tools to scrape the damaged area and create bleeding of the bone. Small holes are then picked into the defect, allowing blood vessels and bone marrow cells to come in contact with the injury. Bone marrow fills the defect, which eventually matures into scar cartilage. Often used as a first-line technique.
Advantages: Surgery is performed arthroscopically. Relatively fast recovery (six to nine months) and cost-effective.
Disadvantages: According to Kai Mithoefer, clinical instructor of orthopedics at Harvard Medical School and author of several landmark studies on cartilage repair, 40 to 70 percent of patients have decreasing knee function after an initial increase, and the surgery has unpredictable results for larger defects.
Success rate: 65 to 80 percent.
Autologous Chondrocyte Implantation (ACI): Cartilage cells are arthoscopically removed from the injured knee and grown outside the body in a tissue culture. After about four weeks, the cells are implanted into the defect. Over time, the cells grow to fill the defect with a new cartilage surface. Generally recommended for defects over 200 millimeters when there is no cartilage wear around the defect.
Advantages: Many researchers say the technique produces normal hyaline cartilage. It’s often used after other techniques have failed and has good durability.
Disadvantages: Requires large incisions, a two-stage technique, has a slow recovery (12 to 18 months) and is expensive.
Success rate: 70 to 90 percent.
Osteochondral Autograft Transfer (OATS): Surgeons take a plug of the patient’s cartilage from a part of the knee that does not bear weight during walking and transplant it into the injured part of the knee.
Advantages: Normal hyaline cartilage is used, with a relatively short recovery (four to eight months). Relatively cost-effective, and long-term durability is good.
Disadvantages: The surgery is best for fixing smaller defects (less than 4 centimeters). Norman Marcus, a Springfield orthopedic surgeon who performs several types of cartilage repair surgeries, describes this as “robbing Peter to pay Paul.”
Success rate: 75 to 95 percent up to 10 years.
Autologous Chondrocyte Implantation (ACI): Cartilage cells are arthoscopically removed from the injured knee and grown outside the body in a tissue culture. After about four weeks, the cells are implanted into the defect. Over time, the cells grow to fill the defect with a new cartilage surface. Generally recommended for defects over 200 millimeters when there is no cartilage wear around the defect.
Advantages: Many researchers say the technique produces normal hyaline cartilage. It’s often used after other techniques have failed and has good durability.
Disadvantages: Requires large incisions, a two-stage technique, has a slow recovery (12 to 18 months) and is expensive.
Success rate: 70 to 90 percent.
Osteochondral Autograft Transfer (OATS): Surgeons take a plug of the patient’s cartilage from a part of the knee that does not bear weight during walking and transplant it into the injured part of the knee.
Advantages: Normal hyaline cartilage is used, with a relatively short recovery (four to eight months). Relatively cost-effective, and long-term durability is good.
Disadvantages: The surgery is best for fixing smaller defects (less than 4 centimeters). Norman Marcus, a Springfield orthopedic surgeon who performs several types of cartilage repair surgeries, describes this as “robbing Peter to pay Paul.”
Success rate: 75 to 95 percent up to 10 years.
Osteochondral Allograft Transplantation: Surgeons take a plug of cartilage from a cadaver.
Advantages: Preferred for deep, large defects.
Disadvantages: Large incision necessary, potential for disease transmission from cadaver tissue, cartilage cells must be transferred quickly from cadavers, long waiting times for tissue, high cost, declining success rate over time and slow recovery (more than 12 months).
Success rate: 95 percent after five years, 71 percent after 10 years, 66 percent after 20 years.
* Surgical success rates generally reflect improvement in pain and activity levels.
Back to Shannon McMillan. Two days later, her knee swathed in bandages, McMillan wears the clenched-jaw look of someone in pain. But she’s optimistic there will be a payoff for the arduous recovery ahead.
“I’ll do whatever it takes,” says the Prince William County Public Schools bus driver and mother of four. “I’ll feel so relieved the first morning I wake up and don’t feel pain in my knee. It will be like the first time your kids sleep through the night.”
In the past two decades, surgeons have developed once-inconceivable ways to replace cartilage worn by age, overuse or trauma: cultivating healthy cells from patients and cadavers, plugging them back into the knee and stimulating them to grow in place. But although the field is advancing rapidly, scientists haven’t yet found a way to give lab-grown cartilage the durability and elasticity of the original material. And sometimes the new cells don’t bind to the bone or adhere to the cartilage that’s already there.
That has made cartilage replacement an option, so far, for only a relative handful of patients: those who have limited damage, are young enough (usually younger than 50) not to have widespread arthritis, and have tried other remedies first. But if researchers can solve the technological problems, doctors could be virtually sure of having plenty of knees to work with.
Each year hundreds of thousands of Americans undergo surgery because of torn or damaged knee cartilage: For 150,000 to 200,000 of them, the surgery is a form of cartilage repair. But “repair” — most often, the shaving of rough edges — leaves less cartilage and the likelihood that pain will eventually return. About 500,000 need total knee replacements. A last-resort option, replacement can relieve pain, but an artificial joint generally won’t last more than 20 years and often can’t match the flexibility or range of motion of the original. About 21 million Americans have osteoarthritis. For now, they’re not candidates for cartilage implantation — joint inflammation limits cartilage regeneration, and cells don’t grow as well after age 50 — but researchers say that that could change within the next decade. Cartilage implantation won’t eliminate the need for knee replacements, but it could buy arthritic patients more time.
A Contested Field
One method gaining ground is McMillan’s surgery, autologous chondrocyte implantation, or ACI, first developed in Sweden in the early ’90s. Technicians use a few cells from a patient’s injured knee to grow millions of new cells in the lab. After about four weeks of growth, the cells are ready to be implanted into the knee, where they react with the bone and membrane to begin to fill in the damaged area. In the United States, Genzyme is the only company authorized to grow the cells, creating a product they call Carticel. About 13,000 U.S. patients have had Carticel implants. Success rates range from 70 to 90 percent, according to Genzyme. About 15 percent of patients have overgrowth of the implanted cells, which can cause knee pain or discomfort. The remedy is a second surgery — requiring only a tiny incision this time — to shave away extra cartilage. About 16 percent of patients experience knee stiffness or catching, according to the company.
But the $35,000 Carticel procedure is controversial and not always covered by insurance. Some surgeons and researchers say less-costly, less-invasive procedures work just as well. But research in the area is conflicting and the quality of studies generally poor, experts say.
McMillan’s knee saga began in January: When she bent down, her knee would lock and she couldn’t get back up. In February, she had surgery to realign her kneecap; that made matters worse, she says. She saw three orthopedic surgeons before opting for a cartilage transplant.
“My only other option,” McMillan says, “was a knee replacement. I had everything to gain and nothing to lose.”
Klimkiewicz, who performs about 15 ACI surgeries a year and has been paid by Genzyme to lecture on the procedure, said it’s important for surgeons to pick the right patients and to fix knee alignment problems or tears of the meniscus — rubbery cushioning on either side of the joint — at the same time. But for the right patient, he says, he has seen good results.
“For the biggest lesions, for the ones that are the worst, Carticel is the best,” Klimkiewicz says.
Research doesn’t always support that claim. In 2004, a team of Norwegian researchers published a study in which they found no significant difference in outcomes after two years between ACI patients and those who underwent microfracture, a cheaper, less-invasive and more common procedure in which surgeons create tiny fractures in the bone to encourage the development of new cartilage.
Lars Engebretsen, a professor of orthopedics at the University of Oslo and one of the study’s authors, says five-year follow-up results, published in October, are consistent with earlier findings.
“There is still no difference between the two techniques, from any angle,” Engebretsen says.
Another Contender
The microfracture procedure was developed by Richard Steadman in the late 1980s in Colorado. Today, a team of surgeons at the Steadman-Hawkins clinic in Vail are famous for patching up the knees of professional skiers and other athletes. (Professional basketball player Greg Oden of the Portland Trail Blazers had a microfracture procedure Sept. 13; Steadman consulted.) Overall surgical success rates range from 65 to 70 percent, depending on the study, although Steadman claims 80 to 90 percent success.
The procedure is much more common than ACI, with an estimated 60,000 performed each year in the United States.
“In the microfracture, the cartilage that’s formed is the body’s recipe for repair,” Steadman says. “It is a natural process. It seems that this cartilage does hold up over time.”
Steadman, who has performed more than 3,000 microfractures, says the procedure has a shorter recovery time than ACI.
One contentious issue is what type of cartilage grows back after each procedure: hyaline cartilage, like that before the injury, or fibrocartilage, which may not have the same durability or strength. Some studies show that both procedures produce a hybrid. Others show that microfracture produces fibrocartilage, and ACI a more hyaline-like cartilage.
One thing researchers appear to agree on: If microfracture fails, ACI is still an option.
Bill Conkey of Alexandria was glad to learn that. The 35-year-old architect’s knee problems began when he tore his anterior cruciate ligament (ACL) and meniscus while playing soccer 10 years ago.
After surgeries to repair his torn meniscus and reconstruct his ACL, he returned to soccer and snowboarding, but every few years his knee would catch and orthopedic surgeon Vincent Desiderio would trim off loose cartilage.
Desiderio performed microfracture surgery in 2003 and warned Conkey that if he kept up the same level of activity he would need a knee replacement in 10 years. When the pain returned a few years later, Conkey wanted to know what he needed to do to keep his knee.
“I have a 5-year-old daughter,” Conkey says. “I want to be able to play soccer and snowboard with her.” Desiderio referred him to Klimkiewicz, who told him he was a perfect candidate for ACI.
Inserting a thin surgical instrument through a small incision, Klimkiewicz had taken a piece of cartilage from Conkey’s bad knee in December to grow the cells. Conkey’s insurer balked at first but eventually covered the surgery. Conkey had the ACI and a kneecap realignment in June.
After a painful first two weeks that included up to eight hours of rehab a day and five more weeks with crutches and a cane, Conkey says his recovery is proceeding smoothly. He says he has just gone back to kicking the soccer ball around with his daughter, and for the first time his knee feels better than it did before the surgery.
“My doctor tells me that by next spring I should be almost pain-free,” he says. “It will be the first time in 10 years.”
Making Refinements
Doctors in Europe and Australia are performing some cartilage regeneration surgeries arthroscopically, and several companies are competing to improve the type of cell grown for cartilage repair.
Researchers are also experimenting with growing cartilage cells on tiny pieces of scaffolding; they hope it will let surgeons implant a substance more like actual cartilage, potentially saving months of recovery time, says Kai Mithoefer, an orthopedic surgeon with Harvard Vanguard Medical Associates in Boston and clinical instructor of orthopedics at Harvard Medical School.
“It’s a very exciting and encouraging evolution,” he said. Three months after her surgery, McMillan sounds like a different woman. “I’m doing better than expected,” she says. “I had three days of misery, but now my knee hasn’t felt so good since before it started hurting.”
After months on Percocet, she says she feels like she’s getting her life back. “My husband and the children who live at home have taken the brunt of it,” she says, her voice catching. “I don’t think I realized the psychological impact until now. I was staying in my bedroom all the time. I can’t go back to all my activities yet, but I’m going on the porch and playing cards with the kids. My children told me they’re glad to have me back.”
She’s hoping to get back to hiking in West Virginia and swimming in the Greenbrier River next spring.
Most important, she returned to driving the school bus Nov. 7. It’s sometimes uncomfortable, she says, but she’s glad to be back at work; the family has been stretching its dollars for months to live on her husband’s salary alone. “I’m starting to feel at least that I can breathe,” she says.
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