What Is the Relationship Between Bad Cartilage and Knee Pain?

Everyone who knows my story of recovery knows this part:

I finally surmised, based on the evidence, that cartilage damage was causing my knee pain. I then set about trying to heal and strengthen the tissue through a long, slow program of high-repetition movement -- easy at first, then progressively harder. Happily, I succeeded.

When I share with others this cartilage-centric view of the origins of knee pain, I sometimes get a response like this:

How can you say cartilage problems necessarily cause knee pain? People with significant defects can have no pain, while others who have cartilage that looks normal have lots of pain. That shows that cartilage isn’t the problem!

I thought it would be good to address this line of thought, head on. After all, even Scott F. Dye, whose “envelope of function” perspective I much admire, noted (in support of the anti-cartilage viewpoint) that he has “documented grade III chondromalacia” (one level from grade IV, or worn to the bone) that is “totally asymptomatic.”

True, cartilage probably isn’t a factor in all chronic knee pain. However, I think it often is, and the argument above (in italics) misses several critical points.

(1) The correlation between the apparent condition of someone’s knee cartilage and pain in that same joint isn’t perfect, but it undeniably exists.

Quick test of common sense: You have 100 people who have thin knee cartilage that’s pockmarked with lesions. You have another 100 people who have normal-looking knee cartilage. Which group do you expect to have more cases of knee pain?

Okay, that answer is glaringly obvious. Even so, why isn’t the correlation between the presence of lesions and the incidence of pain closer to 1? I think there are several reasons, such as #4 (below).

(2) Bad cartilage is so consistently found in osteoarthritic knees that on the MDGuidelines website it says “loss or damage of articular cartilage is an early finding in osteoarthritis.”

Still, is all chronic knee pain osteoarthritis, or a precursor to osteoarthritis? Not necessarily. However, listen to a description of why chondromalacia causes pain:

The source of chondromalacia pain is not the articular cartilage itself, but the thinning of it, which transfers loads onto the underlying subchondral bone, which is pain-sensitive. (UCSF School of Medicine, Physical Therapy and Rehabilitation, on patellofemoral pain)

Got that? So the problem isn’t the cartilage, but the bone. But the bone is a problem because the cartilage is too thin. So the problem actually is the cartilage.

(3) Sometimes quality matters more than quantity.

This may answer the question: How could someone with cartilage that appears normal have knee pain that’s caused by bad cartilage? Two things to note here:

First, I bet that the normal-looking tissue isn’t being directly inspected, but rather viewed indirectly such as by an MRI. MRIs are good, though imperfect -- so they may not detect some early-stage defects.

Second -- the big point -- a test such as an MRI (at least a traditional MRI) will not give you very good feedback about the stiffness of that cartilage or its other qualities. Why that matters: An athlete may have asymptomatic lesions because the rest of his cartilage is pretty stiff (I use “stiff” to mean in a good way), while someone with lesser defects may have problems because the tissue is too soft and beginning to flake apart, or is poorly mediating the forces being transferred into the joint.

(4) Cartilage has no nerves!!!

This greatly complicates the effort to draw lines between cause and effect. Example: I stab you in the arm with a needle; you cry “Ouch!” I stab your articular cartilage with a needle; you feel nothing.

So it’s not the existence of a hole in the cartilage that causes problems, it’s the impact of the existence of that hole (and what’s going on in the tissue around the hole) on nearby structures that causes problems. And that is more difficult to suss out.

All the reasons above, I think, provide good support for the position that cartilage damage often does contribute to long-term knee pain. And even a skeptic has to admit that cartilage plays a critically important role in a knee joint. So keeping it in good health -- and knowing how to (slowly) make it stronger -- matters a lot.