No "shock absorber": If the protective cartilage is not sufficiently replicated, the bones rub against one another, causing considerable pain
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Osteoarthritis is the most common chronic joint disease worldwide. Consider Germany, where a nationwide study commissioned by the Federal Ministry of Health shows that one in four people between the ages of 18 and 79 have at least one joint region affected by osteoarthritis. And one in two over-60s have joint damage visible on an X-ray. In the period to middle age, it is predominantly men who suffer from this disease; in later life, mainly women.
According to the German Federal Statistics Office, the costs incurred as a result of diseases of the musculoskeletal system totaled EUR 28.5 billion in 2008. That is equivalent to the value of a mid-size car every minute. A major portion of these costs of this goes toward treating osteoarthritis. Given the continuing rise in life expectancy, this is only the beginning of a massive cost explosion. At present there is no treatment that gets to the root cause of this disease. The current therapy options are either painkillers or joint replacement.
Accidents: a possible cause of osteoarthritis
Why doesn’t damaged cartilage heal by itself, instead of resulting, sooner or later, in osteoarthritis? The answer to this question lies in the structure of articular cartilage. Essentially, articular cartilage is made up of a “cartilage matrix” consisting of fibers of connective tissue woven together with proteins with long sugar chains. But only five percent of total cartilage mass actually consists of the cartilage cells that produce this matrix. Moreover, cartilage itself does not contain any blood vessels.
Instead, its cells are supplied with nutrients via the articular capsule. As a result, cartilage tissue is chronically undernourished, and this in turn means that it can only replace damaged cells at a very slow rate. In normal circumstances, growth and breakdown of cartilage matrix functions without any problems. In the event of osteoarthritis, however, this equilibrium shifts in the direction of cartilage breakdown. In other words, more matrix is lost than is replaced by the cells. The causes of this failure on the part of the cells are still not fully understood.
On the other hand, several of the risk factors are well known: advanced age, injuries to joints, genetic predisposition, obesity, and adverse stress on joints. In the case of osteoarthritis in the knee joint, sport injuries and traffic accidents are a significant cause of this condition in later life. Were it possible to heal acute injuries through the formation of new, healthy hyaline cartilage, this would represent a major step toward prevention of later joint degeneration. But the body is incapable of replacing lost cartilage. Instead, it merely produces repair cartilage, which is of an inferior quality to genuine articular cartilage and doesn’t have the same biomechanical properties. Today there is no therapy that stimulates the formation of healthy cartilage.
A knee joint affected by various stages of osteoarthritis from healthy (left) to Stage 3 (right). Osteoarthritis is a degenerative joint disease that is mostly caused by strong or wrong strain. It is known as a "form-function" problem. The cartilage gradually frays and abrades until it is completely worn away. The worn off pieces of cartilage cause pain in the knee joint