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Is Knee Cartilage Repair Right for Me?

In part one, we explained how cartilage injuries are like potholes. In part two, we’ll explore the treatment options available for knee cartilage repair.

James L. Carey, MD, MPH
James L. Carey, MD, MPH

You probably take for granted how well your knees work. Our joints allow us to move effortlessly.

But in the process, they endure a lot of wear and tear—particularly in the knees. This is why as you get older, you start experiencing pain.

When the smooth surface called cartilage that coats our bones has a defect, treatment is required.

James L. Carey, MD, MPH, Director of the Penn Cartilage Center, explains what treatment options are available for knee cartilage repair.

Size Matters

A patient’s treatment options depend on the size and location of the defect. Generally speaking, Small defects in specific locations may be treated using an osteochondral autograft transfer or a microfracture, which can be performed with smaller incisions.

Osteochondral autograft transfer

This procedure involves borrowing a little piece of cartilage and bone from a less critical part of the knee and putting it in a more critical part.

“As you can imagine, most of our cartilage is pretty critical or it wouldn’t be there,” Dr. Carey says. “So, there are limits to how much we can borrow. That’s why this can only be used for small defects, usually less than two square centimeters.”


During microfracture, “little holes are drilled in the bone to allow the marrow to leak out,” Dr. Carey explains.

Frank, a patient at the Penn Musculoskeletal CenterThis is because “marrow cells are special cells. They can go down many pathways. One pathway is cartilage, which is what we want. It fills the defect and patches it,” he says.

Larger defects may be treated using autologous chondrocyte implantation (ACI) or osteochondral allograft transplantation, both of which require open incisions.

Autologous chondrocyte implantation (ACI)

ACI is a two stage treatment. The first stage is done arthroscopically. This means only two small incisions are made.

“A little biopsy of cartilage—about the size of a Tic Tac—is harvested and sent to a laboratory, where they grow millions and millions of the patient’s own cells,” explains Dr. Carey.

“Then, about three to five weeks later, they send back vials of the patient’s own cells—about 12 million cells per vial,” he adds.

The second stage is an open procedure with an incision long enough for access to the injury site.

During this procedure, a collagen membrane is sewn around the surrounding cartilage, Dr. Carey says. “The cells are then injected underneath the membrane and sealed watertight, so that the cells don’t leak out.”

The cells mature over time—as long as 18 months—and become cartilage, he adds.

Osteochondral Allograft Transplantation

“This procedure is like a heart or lung transplant, but for cartilage and bone,” says Dr. Carey.

During the procedure, the damaged cartilage or bone is replaced with the donor tissue.

Dr. Carey adds that you don’t have to worry about matching donors based on blood type like you do with organ donation. Instead, bone and cartilage are generally matched based on size.

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