I’m learning about the different ways damage to the knee cartilage can be repaired. I think I understand how they work. I’m just not sure how to decide which method to choose. The damage in my knee is too much for the repair process with microfracture. My options are either a transplant of a bone plug or implantation of cartilage cells. Is that right? And how do they decide which one to use?

Microfracture is a repair technique used for small defects in the articular cartilage of the knee. Articular cartilage covers the joint surface and makes it easier for the joint to slide and glide during movement. Osteochondral autologous transplantation (OAT) describes the removal of a plug of full-thickness articular cartilage along with a bit of the underlying bone it is attached to.

Autologous chondrocyte implantation (ACI) is the implantation procedure. The surgeon removes a bit of normal, healthy articular cartilage and sends it to the lab where the cells are expanded and multiplied and then reinjected into the defect. Both of these procedures are considered restoration (rather than repair) procedures.

The decision about which one to choose is usually left up to the surgeon. Sometimes he or she won’t know what approach to take until the area has been debrided (cleaned up and prepared for the repair or restoration). That’s when it’s possible to get a good look at the size, shape, and location of the defect.

There are some guidelines about when to use each technique. For example, small lesions respond well to the microfracture technique. But anything over 2.5 cm2 may require a restorative technique. The osteochondral plug is used for small, but deep lesions. The implantation with chondrocytes harvested from the patient and expanded in the lab may be best for larger but more shallow defects.

Your surgeon will go over the best choice for you and the factors affecting that decision as well as expected outcomes based on current evidence provided by published studies so far. The surgeon will have to take other factors into consideration when selecting the best procedure for you. Younger patients and/or athletes who expect to return to full sports participation seem to respond well to restorative procedures.

There is still a need for future studies to examine durability of these various techniques. For example, how long do the results last? Do some techniques hold up better than others? If so, why? What patient factors or types and sizes of defects affect the final outcomes?