Marathons and Knee Cartilage

Here we go again!  For my regular readers, as you know, I ran a marathon way back in November on not nearly enough training.  The race itself was great, but my knees tended to disagree with the decision for about 6 weeks after the race.

From that point on, I have been curious about the actual impact (pun intended) running has on knee cartilage.  Obviously some damage takes place over the course of 3+ hours of running, but is this damage irreversible?

Arthritis and Running

While studying at chiropractic school, it was made very clear to us that moderate levels of running are not associated with an increased incidence of knee arthritis.  Factors such as genetics, trauma, and BMI are much more strongly correlated with developing osteoarthritis of the knee.

However, the studies we reviewed in school were typically epidemiological in nature (they often looked retrospectively at these various risk factors in large populations, and then looked at the incidence and severity of knee arthritis in the same population).  These studies are great, but they fail to look prospectively at how a knee responds to a strenuous bout of running.

Because of this, I was still curious about how ONE marathon could impact the cartilage within a knee.  That's when I came across this study published in 2010 in the American Journal of Sports Medicine.  I should mention that I was exposed to the study via Research Review Service which is a great resource for all manual therapists.

The Study:

Past studies have looked at the acute impact of long distance running on knee cartilage using an MRI- some show no changes, others show some transient changes.

This 2010 article is so great because it used new methods of quantifying the cartilaginous changes that happen- the researchers were able to assign specific numbers to rate the changes that took place during the marathon.

Design:

10 runners were followed during this study.  They were selected based on a number of factors, two of which included the fact that they had never run a marathon before, and were active 30 minutes or less per day.  These subjects were not runners!

Without getting into the details, the two outcome measures used in this study included:

•  T1ρ- measures damage to the collagen-proteoglycan matrix (i.e. the protein and carbohydrates that link together and make up the structure of the cartilage)
• T2- collagen orientation and water content (i.e. is the protein in the right position, and is there enough water in the cartilage?)

The runners were tested before the marathon, 48 hours after, and then during a 3 month follow up.


Results:

• The T1ρ values (looking at damage to the protein and carbohydrates):
• Significant changes beneath the knee cap AND throughout the middle aspect of the knee
• These changes were seen at both the 48 hour and 3 month mark

• The T2 values (looking at collagen orientation and water content):
•  Significant changes beneath the knee cap AND throughout the middle aspect of the knee
• These changes were seen at the 48 hour mark
• The changes were seen to a much lesser degree at the 3 month follow up

The control group (i.e. same tests, no marathon run), showed absolutely no change in their T1ρ or T2 values throughout the study.

Explanation:

So what does this show?  Essentially, if you aren't trained, and you have never run a marathon before, you can expect to see some lasting damage to the cartilage in your knee.  This damage comes in the form of loss of water content as well as having a negative impact on the protein and carbohydrate structure of the cartilage.

This study also shows that while the damage to the proteins and carbohydrates persist 3 months later, the water content within the cartilage seems to return to baseline levels.

Limitations:

While very interesting, as with most research, there are limitations to this study.  It is important to keep in mind that these were untrained runners who ran a marathon, and then preceded to not train after the race.  Would the same degradation have taken place if they had trained properly beforehand?  Would the rate of recovery improve if they had continued to train after the race?  Would we still see the same changes 6 months or 1 year down the road?  These are all questions that this study fails to address.

That being said, it is a great preliminary round of research on the impact of marathons on knee cartilage.  It generates a plethora of questions that hopefully can be addressed in future, more comprehensive studies.

Take Home:

Running a marathon (and the training for it) definitely causes acute degradation of the articular cartilage in the knee.  This study also shows that there is a possibility that these changes persist long term.

Nevertheless, the health benefits of running for the general population (with no underlying conditions or risk factors) undoubtedly exceed the risks.  This study should not discourage you from running.  If anything at all,  this study should encourage you to incorporate a diversity of cross training to complement your running regime.