There are two different types of cartilage found in joints such as the knee and shoulder. The first is articular cartilage, also referred to as hyaline cartilage, which covers the joint surfaces. The second is fibrocartilage, making up the knee meniscus and shoulder labrum. Fibrocartilage is also responsible for replacing damaged articular cartilage. During sports, articular cartilage acts as a protective surface for the joint allowing it to withstand significant load.
HOW IS ARTICULAR CARTILAGE INJURED? Articular cartilage injuries can occur as a result of a minor twisting injury (like skiing) or more significant trauma (like a motocross accident). With injury, an articular cartilage fragment can break loose from the underlying bone, which can float in the joint interfering with normal joint motion. Unfortunately, articular cartilage has no direct blood supply, and little capacity to repair itself.
HOW IS AN ARTICULAR CARTILAGE DEFECT (INJURY) DIAGNOSED? Patients will often present with knee swelling and vague pain. If a loose fragment is present, ‘locking’ or ‘catching’ might occur. Articular cartilage injuries are difficult to diagnose with physical exam alone, and evaluation with a MRI or arthroscopy may be necessary.
WHEN IS SURGERY NECESSARY? Painful lesions and ones that cause mechanical locking or catching are generally treated with surgery. Defects smaller than 2 cm have the best prognosis and treatment options. Surgical options include arthroscopic surgery using techniques to remove damaged cartilage and increase blood flow from the underlying bone (e.g. drilling or microfracture). This produces a blood clot that turns into fibrocartilage to cover the exposed bone.
For larger defects, it may be necessary to transplant cartilage from a cadaver donor (OATS procedure). In this procedure a piece of fresh cadaver cartilage with a sliver of bone is fashioned to fit the cartilage defect and ‘press-fit’ into position much like a wood dowel. Because cartilage does not produce an immune response, it is a safe transplant tissue without the fear of rejection. Results of cartilage transplantation provide significant improvements in pain and function.