Q: I have a full-thickness tear in the cartilage covering my knee joint. The surgeon says they can can do an operation and take some of my healthy cartilage and patch it up nearly as good as new. Will my repair just wear away as I continue to use that knee?

A: Defects or lesions of the articular cartilage that lines the surface of your knee joint are called full-thickness when the cartilage pulls away with a piece of the underlying bone still attached. Damage like that often causes painful swelling, locking of the knee joint, and instability.

Surgery to repair the problem can be done in a variety of different ways. One is called microfracture. The surgeon goes down to the bone level and drills tiny holes into the bone marrow. Blood from the bone marrow rises up through the holes and initiates a healing response. This technique works well for small defects.

But large, full-thickness lesions have better results when the cartilage implantation is done. Just as the surgeon told you, healthy chondrocytes (cartilage cells) are harvested from a non weight-bearing area of the knee joint and taken to a lab where they are treated to grow more cells. When there are enough intact and healthy chondrocytes to patch up the hole, surgery is done to implant them in and around the lesion.

Results are very good and long-term studies confirm that healing is successful. In fact, testing done anywhere from nine to 18 years after the original autologous chondrocyte implantation (ACI) has been done. Good quality of repair tissue (very similar to the surrounding normal cartilage) has been demonstrated.

Sometimes osteophytes (bone spurs), bone cysts, and bone edema (fluid) develop in, under, or around the repair tissue. These new lesions don't seem to bother the patients or affect knee function.

So although the analogy of a pothole is a good one in terms of explaining deep damage to the knee joint cartilage and using the chondrocyte implantation repair to fill in the defect, that's where the similarities end. Your "pothole" will be more than just patched -- it will be repaired with good healing at the cellular level.

Reference: Haris S. Vasiliadis, MD, PhD, et al. Autologous Chondrocyte Implantation in Cartilage Lesions of the Knee. In The American Journal of Sports Medicine. May 2010. Vol. 38. No. 5. Pp. 943-949.