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Part 1: Review of Knee Cartilage Injury

The end of the femur (thighbone) that helps form the knee joint is covered with a layer of cartilage. This cartilage is referred to as articular cartilage. This is the cartilage that meets with and glides across the surface of the tibia (lower leg bone).

Young active adults, especially athletes, can injure the articular cartilage. If a piece of cartilage is torn away from the bone, it may even take a piece of bone with it. This is called an osteochondral defect. Left untreated, this focal articular cartilage injury can develop into full-blown arthritis.

In this article, Dr. L. P. McCarty, III reviews the basic science of the normal, healthy articular cartilage. It has four separate zones that help make it strong enough to resist deep shear forces. These are the type of forces generated by many sports activities. Changes in the articular cartilage from arthritis decrease its ability to handle various loading conditions.

Tears in the articular cartilage can be graded according to a system developed by the International Cartilage Repair Society. Grade 0 is normal. Grade 1 is nearly normal (small cracks or tears). Grade 2 is a tear through 50 per cent of the cartilage depth.

Grade 3 describes severely abnormal cartilage. The tear goes down to but not through the first layer of bone. Grade 4 is used to describe a severely abnormal cartilage with both full-depth cartilage and subchondral bone tears.

The author outlines an exam method doctors can use to identify cartilage tears. The physical exam includes gait (walking) pattern, swelling, palpation, and range of motion measurements. Tests are done to check the stability of the other soft tissues (ligaments) around the knee.

X-rays can be used but MRI testing is the best method for diagnosing the problem. Specifics of the MRI changes seen with articular tears are discussed. Part two of this review will focus on treatment once the problem is properly diagnosed.

References: L. Pearce McCarty III, MD. Focal Articular Cartilage Injury in the Knee: The Basic Science. In The Journal of Musculoskeletal Medicine. June 2007. Vol. 24. No. 6. Pp. 277-281.

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