I recently attended a presentation on osteoarthritis (OA), at which an experienced physiotherapist was speaking to a rather large audience consisting of patients and healthcare professionals. The speaker described knee OA as a degenerative disease characteristic of “wear-and-tear”. When speaking of the importance of exercise in the conservative management of knee OA, the speaker stated that running and other high-impact exercises and activities were not appropriate. These activities were said to be dangerous because of their potential to “create more damage” at the knee and consequently, further progress the disease. Afterward, the speaker advised that all exercise in patients with knee osteoarthritis was to be pain-free, as this was key to not “creating more damage” or “making knee OA worse”.
The most important treatment we provide is patient education. Every word that comes out of our mouths has a tremendous impact on our patients. Our patients look to us for guidance and education. If we build a strong therapeutic alliance, our patients will heed our advice. We need to be careful when providing recommendations. We need to ensure that our education does not induce unncessary fear, as this may have important repercussions.
For the longest time, we have been told that we should fear high-impact activities such as running. We have been told that running damages the knees and leads to osteoarthritis. Our understanding of knee osteoarthritis and the capacity for cartilage to adapt has evolved significantly over the years. We now know that knee osteoarthritis is more than just a consequence of aging (i.e. “wear-and-tear”). It is a complex and multi-factorial disease. The experience of pain does not necessarily signify tissue damage, especially in a chronic degenerative disease such as knee OA. Therefore, it should guide exercises but not limit them (i.e. mild pain tolerable during exercises, stop if pain reaches a level that is no longer tolerable). We also need no longer vilify running. Current evidence suggests that not only does running not cause knee OA, but it seems to have a protective effect as well!
Running Does Not Cause Knee OA!
Let’s review some of the evidence:
- A nested cohort study of 1251 participants published in 2015 concluded that running was not associated with worsening knee pain or radiographically defined structural progression over a 4 year observation period. It is important to note that this study had certain limitations, seeing as it was observational and the runners were self-selected.
- A prospective study examined 45 long-distance runners and 53 controls with a mean age of 58 (range 50–72) years from 1984 to 2002 with serial knee radiographs. In 1984, the prevalence of knee OA in long-distance runners was 6.7% in runners compared to 0% in controls. In, 2002 the prevalence of knee OA in long-distance runners was 20% in runners, compared to 32% in controls. According to their regression models, higher initial BMI, initial radiographic damage, and greater time from initial radiograph were found to be associated with worse radiographic OA at the final assessment. There were no significant associations seen with gender, education, previous knee injury, or mean exercise time.
- Results from a recent systematic review and meta-analysis of 15 studies suggested a protective effect of running against surgery due to osteoarthritis. However, evidence regarding symptomatic outcomes was limited.
- Another systematic review published in 2017 examined 22 studies with over 100 000 pooled participants. The prevalence of hip and knee OA was 10% in controls/non-runners, 3.5% in recreational runners, and 13% in elite runners. I would like to specify that runners were regarded as being part of the elite/competitive group if the authors specifically reported that the runners were professional, elite, or ex-elite athletes, or in any case in which runners represented their countries in International competitions. The take-home message here is that recreational runners actually had a decreased prevalence of hip and knee OA.
Why Do Runners Not Have An Increased Risk For Knee OA?
Peak knee joint contact forces in running are much higher than they are in walking (ref 1, ref 2). In addition, high peak knee joint loads (contact force between the articulating tibiofemoral surfaces) at baseline have been associated with knee OA progression (ref 1, ref 2). However, runners do not seem to have an elevated risk of osteoarthritis compared with non-runners. Why is that? How can we explain these results?
Peak Joint Loads Vs. Per-Unit-Distance Loads
A study published in 2014 by Miller et al. compared peak and per-unit-distance (PUD) knee joint loads between human walking and running. Fourteen healthy adults (yes I know, it’s a small sample size) walked and ran at self-selected speeds. Ground reaction force and motion capture data were measured and combined with inverse dynamics and musculoskeletal modeling to estimate the peak knee joint loads. Their results were the following: peak load was three times higher in running, but the PUD load did not differ between running and walking. The peak load increased with increasing running speed, whereas the PUD load decreased with increasing speed.
Therefore, the authors concluded that compared with walking, the relatively short duration of ground contact and relatively long length of strides in running appeared to blunt the effect of high peak joint loads. This was evidenced by that fact that the PUD loads were no higher than when compared to walking.
The Body Can Adapt!
Another potential reason for why runners do not necessarily have an increased risk for developing knee OA is that running may actually condition the cartilage and increase its capacity to tolerate load (ref). Simply put, if you run, the tibio-femoral cartilage will progressively adapt to withstand the mechanical stresses of running as long as the loads applied are within the capacity of the cartilage to adapt. So don’t worry, even a degenerative knee has the capacity to adapt to load!
In general, our patients should not be discouraged from running. There will always be exceptions. That being said, there is a certain amount of clinical reasoning that must go into this decision. Like any condition it is important to monitor signs and symptoms. For instance ,there should not be any worsening of symptoms with running (i.e. increase in pain, morning stiffness, and/or swelling observed during and after running). If this is the case, the training volume can be adjusted accordingly. If this is still not sufficient, then perhaps the patient can try other less symptom-provoking activities to increase load tolerance prior to attempting to run again.
In addition, if a non-runner with knee OA would like to begin running, it is up to the treating physiotherapist to determine whether or not this is a realistic objective given the patient’s subjective and objective clinical examination. If they increase their training volume progressively, this will increase their tolerance to load (otherwise known as the quantification of mechanical stress), and they will adapt to running.
It is important to highlight that the research examining the effects of running as an intervention in patients with knee OA is currently quite limited. Promoting running in those with pre-existing knee OA who have never run before may have unknown consequences. Running appears to have a protective effect on knee osteoarthritis but we can’t say for sure how a non-runner with pre-existing knee OA would respond in the short or long term. Are there certain sub-sets of patients with knee OA who would respond more to running? Are there certain sub-sets of patients with knee OA who would respond poorly to running? We don’t know. There are plenty of questions we still need answers to. Another question that has been often asked is can and should patients with total knee arthroplasties run? Would it be ill-advised? Why or why not?
To conclude, knee OA is a complex and multi-factorial disease. It’s not as simple as we’d like it to be. However, the current evidence would suggest that running does not cause knee OA and as a result, running should not be discouraged in these patients unless otherwise indicated.
Anthony Teoli MScPT
Registered Physiotherapist & Founder of InfoPhysiotherapy