Joint pain and osteoarthritis affect many different structures within the joint.  But cartilage is the most difficult tissue among these to repair.  That's why it's helpful to know a little about cartilage. It will help you understand what it is, why it wears down, and why the tools we describe to preserve cartilage are important.

1.  Cartilage is mostly water:  About 85 percent of our cartilage is water.  This fades to less than 70 percent in the very old. This loss of water is important to the aging and wearing of cartilage.  Maintaining the cartilage matrix is important to retaining water.  This matrix includes things like collagen, hyaluronic acid, proteoglycans, and other molecules.

2. Cartilage has a poor blood supply: Cartilage is unlike almost any tissue in the body, in that it has a very poor blood supply.  You can picture cartilage as a tissue where the blood vessels only make it to the edges.  Because blood vessels cannot carry nutrients deep into the cartilage, cartilage must get its nutrients and remove its waste by movement of the joint.  Movement of a joint involves a pressing and release action, much like moving the water in and out of a sponge as you press and release it. This process is called imbibition.  It is critical to understand how crticial movment is to maintaining cartilage. Movement keeps the fluids flowing into the joint cartilage, keeping it alive.

3. There are three types of cartilage:  Elastic, fibrous, and hyalin cartilage are the three primary types.  Hyalin cartilage is the kind that covers the knee and the hips, while fibrous cartilage makes up the meniscus in between the joints.  Elastic cartilage is the material in the nose and ear.  We don't need to move our nose and ears to keep the elastic cartilage alive.  But we do need to move our joints to keep the hyalin cartilage alive.

4. Repairing and rebuilding: Joint deterioration appears to be a function of an imbalance between the death and rebuilding of chondrocytes--the cells that make cartilage.  Cartilage is difficult to repair, which is why it is so important to take steps to limit the sources of inflammatory molecules in the body.  This is why attention to diet, nutrition, exercise, movement, stress management, body weight, and other factors that limit inflammation are so important to preserving the cartilage you have.

5. Cartilage repairs slowly: Because of the type of tissue making up cartilage, it is very poor at repair.  This is why it is important to preserve joint cartilage.

6. Shock absorbing: One of main functions of cartilage is to cushion the load on the joint.  It functions as a kind of shock absorber.

7. Smooth gliding:  Cartilage is a smooth surface that generates very little friction with movement.  The fluids that fill the joint, further add to the low friction.  In this way, cartilage helps the bones of the joint glide smoothly with the least amount of resistance, when healthy.  There is now evidence that movement of the joints increases the production of the lubricating fluids, which lowers the forces of friction on joints.

8. Joint fluid bathes the cartilage:  The joint is filled with synovial fluid, a lubricant that keeps the cartilage healthy by reducing friction.  Medical treatments now include injections of hyaluronic acid (a lubricant) into the joint.  Sources of hyaluronic acid are also being used as dietary supplements.

9. Wearing down of cartilage can activate pain fibers: structures within the joint, including cartilage, can erode over time, which can drive inflammation and activate pain fibers.  Pain signals can be amplified, once they reach the spinal cord and feed back into the joint, further worsening an arthritic condition.

10. Damaged cartilage is often associated with damage to the bone beneath the cartilage: This sets up a viscious cycle, where cysts form in the underlying bone.  As cartilage wears away, bone can begin to rub on bone.  Cartilage that has eroded to this point has to be repaired surgically. There is now evidence that blood vessel disorders like atherosclerosis found in heart disease, diabetes, obesity, and hypertension can impair the blood supply to this bone that lies beneath the cartilage.  This can further starve cartilage of its nutrient and oxygen supply. In this way, healthy blood vessels might contribute to healthy joints.