Preserving and protecting knee cartilage

Why are some cartilage injuries of the knee easily repairable while others are not? In order to answer that question, we have to start by understanding what type of cartilage lives in the knee. There are actually two different cartilage structures in the knee. The first is articular cartilage (the joint surface) and the second is the meniscus (the cushion between the bone.)

Articular cartilage is the slippery structure that covers the ends of bones in all the joints in the body, allowing them to move smoothly. And it's good at what it does… in fact, articular cartilage is 100 times more slippery than ice sliding over ice!

The meniscus on the other hand is a C-shaped structure in the knee, which acts as a shock absorber. There are actually two menisci in each knee, one on the inner side of the knee and the other on the outer side. The meniscus is not attached to bone like articular cartilage, but rather it sits in the knee between the thigh bone and the shin bone. Whether walking, running, or jumping, the meniscus absorbs and evenly distributes forces throughout knee.

When we tear the meniscus, it can no longer do its job of protecting the surfaces of the knee, which can eventually lead to arthritis. As orthopedic surgeons, we do everything we can to repair or preserve as much of the meniscus as possible.

There is often confusion with regard to injuries to articular cartilage versus the meniscus. In general, when we hear of an athlete having a "tear" of cartilage in the knee, this refers to the meniscus.  On the other hand, the terms "cartilage defect" or "arthritis" refer to an injury or degeneration of the articular cartilage.

Most knee arthroscopy in athletes involves tears of the meniscus. A tear of the meniscus can be treated surgically in one of two ways: sewing it back together, or removing the torn portion of the meniscus, known as a meniscectomy.

So why not just repair all of them? Menisci have a poor blood supply and often will not heal.  Generally speaking, tears in younger patients in areas with "reasonable" blood supply will heal and can be repaired. Interestingly, repairs require more recovery time than meniscectomies because repairs need time to heal. That is why some athletes undergoing a knee scope for a torn meniscus are back in a few weeks while others are out for months.

I remember receiving a late night call the day prior to a collegiate baseball player's knee arthroscopy whereupon his father (a medical professional) urged me to 'trim' rather than repair the meniscus to get his son back to play quicker. I still see the father and jokingly remind him that I would not have wanted him to be my son's orthopedic surgeon.

Injuries to the articular cartilage are more complicated and difficult to treat because the body does not heal or re-grow this type cartilage on its own. It is different than a fractured bone or a skin laceration. To further complicate matters, there are many athletes who are living with articular cartilage wear and tear and don't even know it. A study of knee MRIs in NBA players in 2005 showed 50 percent of players with joint surface abnormalities. These players had no symptoms!

For those who are symptomatic and unresponsive to medications, therapy and injections, there are surgeries aimed at restoring or replacing the injured and missing cartilage. These include procedures like microfracture, cartilage transfer, and cartilage implantation. These surgeries are for small defects in the articular cartilage and do not work for widespread arthritis. Much work is being done in orthopedics to improve the treatment of these injuries to articular cartilage because, despite our best efforts, these surgeries do not always fix the problem. These injuries can often be debilitating or career ending. (e.g. Jeff Ruland, Greg Oden)

So there you have it… everything you need to know about cartilage in the knee! Just remember, it's like tires on your car—treat them well and don't wear them out.

-By David Rubenstein, M.D., Lankenau Medical Center