A Literature Review done for my Masters in Sports Medicine (MsSpMed), University of Queensland, Australia 2017

• Introduction
• What does running do in the acute setting?
• Does running regularly increase the incidence of OA?
• Discussion
• Methods of detecting OA
• Potential Biases
• Selection Bias
• Confounders
• Limitations
• Exceptions and Advice
• Conclusion
• References

Introduction

It has been established that physical activity is an important aspect of a person’s well being and in the prevention of chronic diseases such as diabetes, hypertension and hyperlipidemia. One of the challenges faced by many physicians is encouraging patients who are well to exercise20. Based on the latest position stand by the American College of Sports Medicine (ACSM)16, it is recommended that healthy adults engage in cardiorespiratory exercise for a total of 150 minutes a week at a moderate-intensity.

To get a well patient to exercise is not an easy task  and to understand why, we need to apply the well accepted biopsychosocial model of behavourial change by Prochaska17. The 5 stages of change as described by Prochaska are Pre-contemplation, Contemplation, Preparation, Action and Maintenance. It is easy to agree  that the spectrum of walking – jogging – running as a form of exercise is  ideal for healthy adults who are currently not engaged in any exercise program as it is cheap, time efficient (cost and time are important factors in the contemplation stage), sustainable (helps in the maintenance stage)  and easy (appealing  in the action stage) – making it appealing for patients at all stages of change.

One of the biggest hurdles at the contemplation stage, however,  is the preconceived notion that too much walking or running even at the prescribed 150 minutes a week can lead to joint pains when people get older. This is especially so in Singapore where I practice where older generations of Chinese believe strongly that running, with its visible pounding on the roads with each step, causes osteoarthritis (OA) of the knee. They in turn influence the younger generation to not pick up such sports which in reality may confer more benefits than harm.

Thus it is key that as physicians, we are well versed in the evidence available regarding this association so that we can bring our patients, both young and old,  through the stages of behavioural change successfully. This topic is also particularly important for family physicians who have great contact with the patients in their community as it is not unheard of that patients are recommended not to walk or jog too much to prevent future osteoarthritis by misinformed physicians.

What does running do in the acute setting?

The key objective of this literature review is to ascertain if running at the recommended amount of 150 minutes a week by the ACSM increases the risk of knee osteoarthritis. However, to understand the impact of a single run on the structure of the knee can be useful when reassuring non runners beginning to pick up this sport.

Several studies have been done on marathoners, using Magnetic Resonance Imaging to scan the subjects’ knees before and after a marathon to determine if marathon running results in acute lesions in the knee. Schueller-Weidekamm et al.12 scanned participants less than 3 hours after finishing a full marathon and found no new cartilage lesions in its 22 subjects and no significant changes in meniscal lesions. Consistency was again seen in the study by Hohmann et al., where pre and post marathon scans did not reveal any marrow edema, periosteal stress reactions or joint effusions in the 7 runners. The study by Krampla et al.19 did the MRI scan 6-8 weeks after the marathon and also found no long term side effects after the marathon.

In a study by Hinterswimmer et al.8, 10 marathon beginners had an MRI of the knee done before and after a 6 months training program followed by running a marathon. Again, no significant changes in cartilage volume and thickness were observed, suggesting that even 6 months of regular running at 25-60km a week (estimated to be 150 – 360 minutes a week) plus running a full marathon of 42.195km does not cause any acute knee abnormalities.

No doubt these studies are limited by their small sample size but they have been consistent in showing that running a marathon that can last anything from 3 to 5 hours, does not cause significant acute changes to the knee structures.

In view of these findings, we can be confident that if a bout of marathon running does not cause acute knee damage, it is unlikely that 30 minutes of moderate intensity jogging can cause any damage to the knee acutely.

Does running regularly increase the incidence of OA?

Does stringing up 150 minutes of jogging a week, every week for many years,  predispose you to chronic knee damage and osteoarthritis? To answer this question, a literature search was done on PubMed to look for studies investigating the association of knee osteoarthritis and running. The results are summarised in Table 1.

Discussion

Most of the studies used distance run per week (kilometre) as a unit of measurement. However, to compare the studies in our context, the running pace of 6minutes per kilometre is used as a rough gauge of the time spent running. Most of the studies above suggest that even when running more than 150 minutes a week for many years does not lead to an increased risk of osteoarthritis. However, there are a few weaknesses in the studies that needs to be addressed.

Methods of detecting OA

One of the the difficulties in interpreting and comparing results from various studies is the use of different methods in detecting osteoarthritis. X-rays was the most commonly used modality as it is easily accessible and economical. In the use of X-rays, 2 main criteria were used – the Ahlback ad Kellgren & Lawrence systems. Both criteria have been shown to have a high level of agreement in the detection of radiographic OA15. A potential weakness in the use of Xrays is that running, as a weight bearing activity, increases bone density, possibly resulting in the effects seen in the study by Lane et al.2 where females (who tend to have a lower bone density than males at baseline21) who ran showed more bony sclerosis and spurs but not in males. As Lane et al.2 has pointed out, it is possible that this increase in bone density can lead to an increased detection of sclerosis and spurs as it increases the contrast seen on the Xray, causing detection bias in the results.

In more recent studies5, Magnetic Resonance Imaging (MRI) was used to detect lesions in the ligaments, cartilages, meniscus and bone marrow. The use of MRI offers a higher sensitivity to soft tissue lesions than that offered by the conventional Xray. However, the downside of its sensitivity is that many MRI findings may not necessarily translate into clinical symptoms23.

One of the studies done by Lane et al.10 did not utilise imaging in the comparison between groups. Instead, they argued that because clinical osteoarthritis is more applicable for the patient, it is more practical to compare the extent of disability that they face from joint pains10. In addition, it was logistically difficult to carry out imaging on big population studies. In this study, the Disability-30 questionnaire10 was used.

Cheng et al.4 on the other hand,  used self-reported physician diagnosed osteoarthritis. This method is likely to be the least accurate and can be easily influenced by recall bias. In addition,  physicians who are not well versed in Sports Medicine may also wrongly diagnose patients with knee pain as knee osteoarthritis when it may be other conditions such as patellofemoral pain syndrome. This makes this method of detection highly unreliable.

As it has been shown that Xray or MRI findings and clinical symptoms do not always relate23, it may  yield the most accurate results when both are studied together, which was done in the study by Timothy et al9. In his study, knees were classified as incident symptomatic OA when patients develop new pain in a pain questionnaire as well as having new findings on Xray imaging.

Potential Biases

Selection Bias

Possible selection bias can occur in the large scale studies such as that by Cheng et al.4. For example, It is possible that non runners that are selected as controls were actually runners who became non-runners because of the onset of knee pain which may have resulted secondary to OA of the knee. This may bias the results, making runners and non runners more similar than they are in terms of incidence of OA. Thus, this is very important to elicit this during patient selection via careful history taking which may be difficult in large scale studies.

Some studies had poor methodology in classifying activities, making it difficult, if not impossible, to interpret results. In the study by Timothy et al.9 which utilized the Framingham Heart Study participants in its cohort, classified activities engaged by subjects as light, moderate or heavy. Due to poor definitions, activities such as swimming which is non weight bearing and has little loading of the knees are classified as ‘Heavy’, mixing with other ‘Heavy’ , activities like shovelling, digging and carrying objects greater than 5 pounds. Activities like carrying heavy objects as part of an occupation or exercise has been linked to an increase risk of OA knee3, and to place them in the same group as competitive swimming leads to significant bias. Similarly, to have competitive running placed in the same group with activities which are known risk factors of OA will affect the interpretation of the results.

Confounders

Confounders are sources of bias in any study. One of the biggest confounders recognised is body weight as runners who engage in regular physical activity will end up having a smaller body mass which reduces their risk of OA. In all of the studies, weight is being matched to controls, effectively removing its confounding effects. Another potential source of bias is the subject’s daily occupation as jobs that are more physical and involve carrying heavy loads inevitably places more forces on the knee. In the study by Kujala et al.3, subjects whose work involve kneeling or squatting leads to an increased incidence of OA knee. None of the other studies took this into consideration in the analysis of the results.

Limitations

One limitation of the above studies is that it is difficult to determine if someone who had started running from young as compared to someone who started running when they are much older have any difference in the risk of osteoarthritis. As mentioned in the study by Kujala et al.3, which studied elite olympic runners, their subjects were runners who trained since young. Thus the results may not be able to be generalised to adults who start running when they are older as it is well accepted that joint cartilage adapts to progressive loading and it is unsure if a sudden increase in running can lead to cartilage breakdown. This will have implications on how gradual and progressive a running program has to be to allow body adaptations.

With regards to running pace and risk of OA, Only one study5 attempted to analyse the difference between runners with different training speeds and found  no correlation between training speeds and OA-like lesions in the knee. This is supported in kinematics studies which shows that work done at the knee joint is not affected by increasing running speed22.

Exceptions and Advice

However, like all sports, not everyone may be suitable to pick up running. Patients with an increased BMI3,4 and who had previous knee injuries3 are at risk of osteoarthritis and should not be encouraged to engage in this weight bearing activity but should start off with low impact exercise such as swimming or cycling. In addition, due to the inability of generalising study findings to novice runners who start running at a later age, any exercise prescription should also be gradual and progressive to allow the patient’s body to adapt to the new activity. This process can be made simple and safe  by gradually increasing the duration of exercise from 30minutes a week to 150minutes a week over a period of 1 to 2 months.

Conclusion

Walking or running within the ACSM’s guidelines of 150 minutes a week does not seem to increase the risk of knee osteoarthritis based on this literature review. Patients should be reassured on the low risk of knee osteoarthritis when embarking on this new exercise regime.

References

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2. Lane NE. Long-Distance Running, Bone Density, and Osteoarthritis. JAMA: The Journal of the American Medical Association. 1986;255(9):1147. doi:10.1001/jama.1986.03370090069022.
3. Kujala UM, Kettunen J, Paananen H, et al. Knee osteoarthritis in former runners, soccer players, weight lifters, and shooters. Arthritis & Rheumatism. 1995;38(4):539-546. doi:10.1002/art.1780380413.
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