articular cartilage replacement

Articular Cartilage Restoration

Articular Cartilage

There are two types of cartilage in the knee. The first is the meniscus which is made of fibrocartilage. The second is the articular cartilage, which is a smooth, white covering over the bone surfaces. The meniscus functions as a cushion in the knee. The function of articular cartilage is to provide a smooth, low-friction, weight-bearing surface that also acts to protect the underlying bone.

Articular cartilage is made of chondrocytes which live in a matrix of water, collagen and proteoglycan molecules. Proteoglycans are large molecules that bind water in the cartilage. Primarily Type II collagen is another part of the matrix. The chondrocytes make up only a small portion of the cartilage but have a very important function by providing the metabolic activity that is necessary to maintain the cartilage. All of the above combine to form an articular cartilage that can resist compressive loads. This complex and specialized structure functions well but has no blood supply. Once damaged, there is a very poor healing response.

Most articular cartilage damage is due to chronic or repetitive use of the joint that comes with aging. Restoration of normal cartilage in this situation is very difficult. More acute injuries may be repaired using articular cartilage restoration procedures. Patients with knee injuries or pain can be evaluated for repair. The goal of these procedures is to restore a normal, functioning articular cartilage that will hold up for a long period of time. Following an evaluation options for repair are discussed.

Articular Cartilage Repair

1. Microfracture: This is an arthroscopic procedure in which holes are placed in the bone beneath the articular cartilage defect. Typically, a fibrocartilage repair tissue forms in the defect. This is not a normal hyaline cartilage but does cover the previously exposed bone. The long term wear characteristics of fibrocartilage are not as predictable as normal, hyaline articular cartilage
2. Arthroscopic Debridement: This arthroscopic technique simply removes unstable articular cartilage from injured surfaces and usually provides short-term to medium-term relief. If the area injured is small, a good long-term result can occur.
3. Osteochondral Autograft: Typically, this procedure is performed arthroscopically. It is most often used when the articular cartilage defect is less than 2 centimeters in size. A round plug of bone and normal overlying cartilage is transferred from one part of the knee into the injured area. This allows a normal cartilage to overly the previous injured area.
4. Autologous Chondrocyte Implantation: This procedure may be recommended when the articular cartilage defect is larger than two centimeters. Two procedures are required. The first involves an arthroscopic evaluation of the defect. If appropriate criteria are met, small samples of normal articular cartilage are harvested from the knee. These samples are then used to grow millions of the patients own chondrocytes in a lab. After the cells have been grown, they are implanted into the defect during a second, open procedure. This technique produces a more normal articular cartilage. For more information, go to: Genzyme.com
5. Osteochondral Allograft: This is typically an open procedure. Bone and cartilage from a cadaver are taken and fit accurately into the articular defect. This can be very effective but the viability of the chondrocytes can vary. It is a technique that may be offered in certain situations.

There are many factors that are utilized to determine the best procedure. Age, activity level, alignment of the leg, size of the articular defect and other criteria are used. The appropriate procedure is recommended following an evaluation involving a history of the injury, examination of the knee, and a review of the imaging studies.