Does Running Cause Knee Osteoarthritis?
As a physical therapist, I often hear patients say that they used to run, but they stopped in order to protect their knees since “running causes arthritis”. They often ditch running for activities they enjoy less, or that are less effective in building robust health. They stop running to prevent something that may never develop. And this belief that running causes knee arthritis is rampant in our culture.
But what actually causes osteoarthritis (OA)? What role does running play, if any, in the development of knee OA?
Knee OA is caused by a complex interplay of mechanical, inflammatory, metabolic, and genetic factors (1) Notice that this interplay does not lend to a simple definition of “wear and tear”. Humans are biological creatures, and the likening to mechanical wear and tear, like the brakes in our cars, is an oversimplification that fails to account for all the reasons somebody develops knee OA
This is not to say that there is no role for mechanical causes. We know that folks who have sustained an anterior cruciate reconstruction (ACLR) can be 4-6x more likely to develop knee OA vs matched controls (2). So clearly, following some joint damage, there is an increased risk of developing OA. We aren’t exactly sure why this happens, but I have thoughts which I may unpack in a future post.
So, major risk factors for the development of knee OA include (1,3):
Sustaining a previous knee injury (thought to account for ~5% of new cases). This is true for the development of almost any musculoskeletal condition and I will explore this phenomenon in a future post.
Being obese or overweight: This risk factor lends to the idea that there may be contributions from mechanical and metabolic factors
Older age: Older folks are more likely to have sustained previous knee injuries or be metabolically unhealthy
Occupational factors: Some jobs require employers to do years of repetitive lifting. Often these are occupations where the work force is less healthy overall and may not have the physical capacity to perform their job day in and day out.
Knee malalignment and quadricep muscle weakness: Malalignment possibly stems from previous injury. Quad weakness possibly from previous injury which was never fully rehabbed.
Sex: Women appear to be at higher risk of the development of knee. OA.
Running is excluded from this list, and for good reason. A study from 2017 (4) showed that runners had lower prevalence of hip and knee OA (3.5%) compared to both sedentary controls (10.2%) and competitive runners (13.3%).
Meta-analysis and case-control studies have shown that runners have ~50% reduced odds of requiring a total knee replacement (5,6). And even if runners develop knee OA, a 2017 study (7) showed that runners had lower odds of developing symptoms compared to non-runners.
To be fair, not all running is created equal. In the 2017 study by Alentorn-Geli et al (4), it was only recreational runners who seemed to be protected from developing knee OA compared to their non-running and elite running counterparts. The study was not clear what the mileage cutoffs were due to heterogeneity (differences) in studies. One of the research articles included cited >57 miles per week to be the theoretical cut-off. I think this number is almost certainly arbitrary and will leave the world of evidence for a moment, put on my clinical expert hat, and speculate as to why this is.
If we look back to some of the causes of knee OA, we can reason that elite runners, by running more, have more exposures (opportunities) to get injured. As a sports physical therapist who treats his fair share of runners, I think that often times these injuries are not fully rehabbed before the elite runner returns back to sport. Now, that runner is running with the risk factor of sustaining a prior knee injury and potentially running through alignment issues or quad weakness from the incomplete rehab, thus making them more likely to develop further knee pain. As this cascade continues, knee health can deteriorate over time.
I think the evidence is clear enough. Running is extremely healthy for our bodies and our minds. The current research does not point to running as a cause of the development of knee OA. Sure, there are cases when someone should not be running as running will likely make their knee pain worse. These folks should consult with a skilled physical therapist who treats runners regularly to get them safely back into running. For the rest of us, I hope we can stop spreading misinformation around running as a cause of knee OA and embrace it for the health benefits it provides, at any age.
