Cartilage injuries can occur as a result of many different causes. These injuries are often the result of sports-related injuries, trauma, inflammation and arthritis, or can occur from osteoarthritis as people age (Figure 1).
Cartilage is the tough but flexible connective tissue that gives shape, support and provides cushion between bones in the joints. Unlike other connective tissue, cartilage does not have its own blood supply. Instead, it is composed primarily of water, chondrocytes, collagen and proteoglycans which produce and maintain a structural matrix giving cartilage tissue its form and function (Figure 2).
Proteoglycans are composed of numerous glycosaminoglycans attached to a core protein. The predominant glycosaminoglycans in cartilage are chondroitin sulfate and keratin sulfate (Figure 3). Within the cartilage matrix there are numerous proteoglycan monomers attached by linked protein to a molecule of hyaluronic acid. This is all woven with collagen to form an elastic and compressible structure.
Normal articular cartilage, also known as hyaline cartilage, provides a smooth crystal clear gliding surface to aid in the motion of the joints. The structure of hyaline cartilage is divided into four layers: the superficial, middle, deep, and calcified layer, with the calcified layer representing a transition from articular cartilage to bone (Figure 4). This cartilage is designed to achieve and maintain proper function over the majority of a person’s life. If the cartilage is subjective to excessive weight, overuse, improper alignment, or injury it begins to wear away leaving bone to rub on bone.
Articular cartilage does not have the ability to heal itself, however there are several treatment options available to aid in the repair of injured cartilage. The knee is the most common joint in the body with cartilage injury issues. The knee joint is composed of a femur, tibia and a patella (Figure 5). There are two types of cartilage in the knee joint: the articular cartilage and the meniscus, which is a shock absorbent cartilage. There are also important ligaments within the knee joint. The anterior cruciate ligament and the posterior cruciate ligament.
The goal of treating injured cartilage is to reduce pain and improve the function of the affected area. Anti-inflammatory medications are commonly used to combat injured cartilage, but they can potentially cause cardiovascular, renal, or gastrointestinal toxicity. Damaged cartilage can also be treated with a series of injections. Steroid injections such as cortisone are powerful anti-inflammatory drugs used in the treatment of osteoarthritis (Figure 6).
Hyaluronic acid is a substance produced naturally in the body and is present within cartilage. When isolated, hyaluronic acid is a thick viscous solution that can be added to the natural hyaluronic acid of the knee joint. This solution used purified hyaluronic acid derived from either rooster combs or genetically engineered cells.
Glucosamine is another option for treatment that can be injected directly into the joint. Glucosamine is a modified sugar that is formed by the human body and is used to form larger molecules involved in the formation and repair of cartilage.
Other methods such a gene therapy, platelet rich plasma (Figure 7). Growth factors and stem cells are in the experimental stage and are not proven as an effective therapeutic modality. Drilling and debridement of cartilage may help with injured cartilage. Occasionally, the cartilage is replaced, regrown, and implanted.
When the cartilage is damaged and arthritis is severe, the choice is often simple, as the patient will need a total knee replacement (Figure 8). Many different types of designs and materials are currently used in total knee replacement surgery. Nearly all consist of three components: a patella component which consists of durable plastic, a tibial component made of a durable plastic cushion often held within a metal platform, and the femoral component which is usually made of highly polished metal.
Total knee replacement is the most predictable option to treat severe arthritis of the knee joint (Figure 9). When the arthritis is minimal, almost all treatment methods will work. However, when the extent of arthritis is moderate there are many different treatment options presented to the physician but none of them are predictable.
It is logical to pursue and recognize the efficacy of biological treatment such as platelets and stem cells in cartilage regeneration (Figure 10). Simply, because it is better for the patient to be able to regenerate their own cartilage, than for is to be replaced with an artificial joint. However, the effectiveness of these treatment modalities is not proven. prospective randomized clinical trials are needed to judge the efficacy of the treatment modalities. What has been proven to work for arthritis is physical therapy, weight loss, nonsteroidal anti-inflammatory drugs (NSAIDs), and possible injections (steroids or hyaluronic acid).
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