Cartilage, more specifically hyaline cartilage lines the ends of long bones in joints, protecting them from abrasion during movement and weight bearing.   It is also found in the nose, ribs and ear.

Unlike muscle, organ and skin which is mostly comprised of cells, cartilage itself is mostly comprised of a matrix secreted by cells called chondrocytes.   The chondrocytes secrete and “live” in this matrix, called the extracellular matrix or ECM.

Electron micrograph of chondrocytes in hyaline cartilage.

ECM is comprised mostly of collagen, a type of protein that has elastic properties, and proteogylcans which are molecules containing a protein attached to a glycosaminoglycan; basically a sugar molecule bound with an amino acid.

Glycosaminoglycans are highly polar and attract and bind with water.  They are therefore useful as a lubricant or as a shock absorber; hence their role in joints.

Healthy cartilage is very smooth and sturdy.  In fact, if you ever cooked soup bones, which are usually sections of beef hip and knee joints you probably noticed that it’s not easy to hold onto them because they are so slippery; almost frictionless.

Because of cartilage’s water content, it can absorb pressure (bear significant weight and repeated impact forces).  Remember from physics that water is non-compressible and is therefore great for redistributing forces.   Hydraulic pistons are able to move heavy things thanks to this property of water.

But even with this wonderful design, joint wear and tear is inevitable especially if you aren’t careful or if you are unlucky and injure a joint.

Take your knees, for example.

Knee osteoarthritis is the result of progressive cartilage deterioration in the knee, which is very common in people over 50.  It is so common that osteoarthritis is viewed as a normal part of aging.  In fact, about 4.5 million Americans have at least one total knee replacement (TKR).  Over 650,000 TKR surgeries were performed in 2009, and there was an 87% increase in TKR surgeries from 1997 to 2009 (

But, don’t resign yourself to thinking that osteoarthritis is normal and that you will get it in a matter of time.  I believe that you can avoid knee osteoarthritis by being mindful of your health and following a certain preventive routine.  You don’t have to go down the “osteoarthritis path” as you age.  More on this to follow.

How Osteoarthritis Gets Going

One of the affects of aging is that the hypothalamus secretes less human growth hormone (HGH), the “youth” hormone.   And one of the functions of HGH, true to its nickname is to maintain muscle mass, and cartilage in the knees and elsewhere.  This is why kids are able to run and jump off rooftops and keep going with no problem.  Doing this is not such a good idea if you’re over 40.

With lower levels of HGH, the cartilage starts to thin and lose elasticity, probably because of less water content and degraded collagen strands from oxidative stress.

The pounding from walking forms tiny cracks to appear, which develop into pits that can gradually expand in size.   If you are overweight, it compounds the problem.  Small fragments of cartilage break off the bone and deposit inside the knee, interfering with movement and generating an inflammatory reaction.   Bare bone is exposed and walking becomes painful.  This is the typical sequence of events that lead to knee replacement surgery.

What Limits Cartilage Healing

Cartilage doesn’t have a direct blood supply, which makes injury healing sluggish.  The same goes for ligaments and tendons.   When you have a direct blood supply to tissues, nutrients and reparative cells like fibroblasts can get there fast.  With no blood supply, the injured tissue has to rely on absorption or other means to get nutrients in.

This is why joints, whose main structures are cartilage, ligaments and tendons, take so long to heal when injured and often require surgery.  Once you hurt it, it can take months, even years before it fully heals, if it does at all.  ACL tears of the knee; meniscal tears, rotator cuff tears, and tendonitis are known for their stubbornness in healing and their tendency to become chronic.

But, do you really need a direct blood supply in order for chondrocytes to make cartilage?  That’s the assumption.

Let’s talk about where these chondrocytes originate.

The Origins of Cartilage

Chondrocytes– the cells that make cartilage– start out as mesenchymal stem cells, or MSCs.  These are cells that originated from the mesoderm, one of several embryonic (fetal) tissue types that together eventually form the human body.  The mesoderm transforms into cells that make up bone, connective tissue and blood.

Mesenchymal stem cell

Mesenchymal stem cells are still present in adulthood and still have the ability to transform (differentiate) into bone, tendons, ligaments, cartilage and blood, a trait called pluripotential.  Certain genes (specifically BMP4 and FGF2) are known to increase differentiation of MSCs into chondroblasts.  Cell signaling and environmental factors probably play a role in MSC differentiation as well.

In adults, MSCs are found in small amounts in the bone marrow.   The ones that are destined to transform into chondrocytes start by transforming into so called chondrogenic cells at the location of chrondrification; in this case, the ends of the long bones.  Then, they transform in to chondroblasts and start making extracellular matrix, forming cartilage.

The chondroblast matures into a chondrocyte and rests inside the ECM in an inactive state, but can still make or degrade cartilage tissue depending on the conditions.

Mesenchymal stem cells can transform into different types of cells.

Formed Cartilage May Not Have a Direct Blood Supply, But Chondrocytes Do

So, given that chondroblasts are formed from mesenchymal stem cells in the bone marrow, which has a blood supply and is therefore able to get nutrients for tissue repair, it makes sense that these cells can make new cartilage where it is needed— those small cracks and pits in the cartilage that line the weight bearing long bones; i.e. your knees and hips.  Even though the final cartilage tissue/ extracellular matrix does not have a direct blood supply, the tiny cells that create it do have access to a blood supply when they live in the bone.

My point is that, even though the reality is that the body cannot grow back the large areas of cartilage damage in advanced osteoarthritis, there is still that potential for cells to grow cartilage, since MSCs still exist in bone marrow and they still are able to transform into cartilage-making cells.

But when you are older and the number of MSCs are few (about .01% of bone marrow cells)  it is understandable that the potential for your body to grow back damaged cartilage is not very strong.   But that possibility is there, nevertheless.

As it stands,

The best treatment available for severe cartilage damage is surgery to replace the damaged joint with an artificial one. Because MSCs can differentiate into cartilage cells called chondrocytes, scientists hope MSCs could be injected into patients to repair and maintain the cartilage in their joints. Researchers are also investigating the possibility that transplanted MSCs may release substances that will tell the patient’s own cells to repair the damage.

~ Euro Stem Cell

That being said, I believe a better approach, if you are in the early stages of osteoarthritis, is to attack the problem nutritionally:  do things that get those chondrocytes busy making cartilage.  They will be slow, but slow and steady wins the race.

  • Increase green plants and vegetables in your diet; half of them raw
  • Consume bone broth soup regularly, which contains lots of collagen and other cartilage constituents
  • Avoid excessive trauma to your knees and hips; strengthen your muscles instead using closed kinetic chain exercises like squats.

For a comprehensive, online self-study course on rehabilitating chronic knee pain, see my Teachable course on Self-Rehabilitating Chronic Knee Pain Due to Early Osteoarthritis.  It contains specific steps including my “secret” therapies to accelerate knee joint repair.

Lastly, if you have chronic knee pain and are concerned that knee replacement surgery is a few years down the road, here’s an inspiring article.  It’s a story from a guy who actually experienced natural cartilage regeneration:

Knee Cartilage Repair: How One Patient Proved His Doctors Wrong

The Bottom Line:  First and foremost, to avoid a future of osteoarthritis of the knees or hips and all the limitations it causes, think prevention — diet and lifestyle modification.  Natural cartilage repair and regeneration is still possible, but it is extremely slow and only works if the damage is minimal.   Intervene early, not later.  Go heavy on nutrition that supports cartilage growth because, as this blog post asserts, the cells that make cartilage are still alive and active.  They just need some help.


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