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How does cartilage damage impact the knee joint?

22nd September 2017

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Osteoarthritis always starts with damage to the articular (joint) cartilage, which plays a central role in the healthy joint. It is as a protective layer covering the bone ends meeting each other in the joint. It cushions the joints and helps them move smoothly and easily (allowing them to glide over each other when in motion). It also protects the bone from abrasion and damage.

What is the anatomical structure of cartilage?

Its smoothness and durability come from its specific anatomical structure. It consists of only approximately one percent out of living cartilage cells, so-called chondrocytes. They are responsible for the formation of the cartilage substance, the extracellular matrix. Long-chain protein sugar compounds (proteoglycans), which have an extremely high water binding capacity and make sure that the cartilage ultimately consists of 60-70 percent water, which is the main component of this matrix. This water is buffering the main load of the joint, and is also supported by collagen fibers.

Knee diagram

What are the weaknesses of cartilage?

As stable and resilient the articular cartilage may be, it has one weakness: it has no blood supply and it must get all the important nutrients from the synovial fluid.

The synovia fluid fills the joint space between the cartilage and soaks and nourishes the cartilage tissue and ensures the removal of waste substances. The most important part of the synovial fluid besides water is hyaluronic acid, a substance that ascertains its viscosity and lubrication properties. The special kind of supply makes the cartilage on the one hand particularly resilient, but on the other hand not as effective as the blood circulation. Meaning that damaged cartilage is difficult to regenerate and does considerably worse than other tissue.

With age, the damages to the cartilage often accumulate, its water binding abilities worsen and the quality and concentration of hyaluronic acid in the synovial fluid can be reduced. The result is often osteoarthritis, of first the cartilage, later also the bones are subjected to increasing wear.

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