Doctors of USC

Got a bum knee? You're not alone. More than 6 million people every year go to see a doctor about their knees.

A substantial portion of those doctor's visits are due not to problems with bones or muscles, but with cartilage. Cartilage injuries can be longstanding and painful, according to C. Thomas Vangsness Jr., associate professor of orthopaedic surgery at USC, but there are new alternatives available to possibly help repair the cartilage and relieve the hurt.

So why the trouble? Part of it has to do with the knee's structure and what it needs to do in daily life: twist, rotate and turn. And it bears almost all of the body's weight as it moves.

The knee's complexity also makes it an easy target for injury. The rounded ends of the tibia (the long, bottom bone of the leg) and the femur (the strong top bone of the thigh) are covered with a 3-millimeter-thick layer of articular cartilage to keep the knee moving smoothly. But this tissue can be damaged through an accident or ordinary wear-and-tear.

Damage can range from a slim crack to a craggy fracture, from a rough abraded area to a torn flap. Those with such damage generally suffer from pain, locking, clicking and swelling in the knee. This damaging condition often progresses with increasing pain if left untreated.

Surgeons have used arthroscopic surgery to help such patients for some time. They put an arthroscope, a tiny lens connected to a camera on a thin tube, through a 2-to3-millimeter incision in the skin into the knee to visualize and trim away areas of torn cartilage inside the knee, relieving pain. But the problem is this: cartilage does not grow back on its own, and the area is left vulnerable.

Now surgeons can remove a bit of the patient's own existing localized cartilage and use it to grow millions of new cloned cartilage cells in the laboratory. Then they insert these cells back into the knee. Called Carticel™, the system of articular chondrocyte implantation has proven very effective for patients with localized cartilage damage at the end of the femur.

Surgeons also use another procedure, called an osteochondral autograft, for small cartilage lesions. It works like this: A surgeon bores out a small plug of a patient's own bone and cartilage from one area of the knee, and then transfers and inserts it into the damaged area.

In the future, doctors may be able to introduce substances into the body that get the cartilage to grow back on its own. "Everyone is trying to work on research with growth factors," Vangsness said. "But it's many years away."