What does the research say about running after a knee replacement?

From Sports Injury Physio, Feb 15, Maryke Louw 

Will I be able to run after a knee replacement? 

Yes, there are people who go back to running and appear to do so without any issues. 

A study of ultra marathon runners who took part in at least one of the five Ultra-Trail du Mont Blanc races in France from 2015 to 2017 (ranging from 55 km to 300 km) found that three of the four runners who ran with a knee replacement completed their race. This drop-out rate of 25% (admittedly from a tiny sample) compares favourably with the overall drop-out rate of 19.6% among the 3,171 surveyed runners who started a race. 

None of the four runners with a knee replacement reported adverse symptoms relating to the knee before, during, or after the race, whereas some of the runners who had had hip replacements did report such symptoms. 

Marco Konings and colleagues did a review of 19 research studies on a total of 4,074 knee replacement patients. They found that 23 out of a total of 131 runners in these studies had returned to running post-op. 

The above shows that it is possible to run after a knee replacement, for ultra runners and for mere mortals. 

However, in practice, not all runners who have had a knee replacement do go back to running, as is clear from the results of the Konings study. Several studies have found that the percentage of people who return to high-impact activities, such as running, after a knee replacement was much lower than that of people returning to lower-impact activities, such as cycling or swimming. 

It is not clear from any of these studies whether people who didn’t return to running were physically unable to run after their knee replacement and/or whether they were afraid of damaging or wearing out their new knee. This brings us to the next question. 

Will running wear out my knee replacement? 

We’re not sure. Expert opinion is that high-impact activities may wear out your replaced joint more quickly, but there is actually no strong research to back this up. There’s very little research that investigated the effect of physical activity on prosthesis wear. 

What about high-intensity exercise? 

In a similar review of the research, Elena Zaballa and colleagues found only one paper that assessed post-operative “leisure time physical activity” (i.e. also sport) in relation to the risk of damage to your replaced knee. It showed no increased risk in participants doing “high-intensity” leisure activities. Unfortunately, they didn’t specify whether these high-intensity activities were “high-impact”, such as running, or low-impact, e.g. interval cycling. 

So, these results can’t produce a definitive answer. All it tells us is that you can likely do high-intensity exercise without increasing your risk of having to go for knee surgery once again but not what type of exercise is best. 

What about high-impact activities (like running)? 

We could not find any studies with empirical findings about the risk of damaging a replaced knee by running or doing other high-impact activities. 

A research review conducted earlier this year on hip replacements showed that the degree of wear and tear depended not only on the amount of physical activity but also on the mechanical loading of the joint. This in turn depended on body weight, type of physical activity, and technique (whether you are an experienced or a newbie athlete), where high-impact activity and poor motor control increased the risk. 

These results suggest that high-impact activities may increase the risk of damaging a hip replacement, but it was one of many factors. Research for knee replacements is still lacking. 

A recent survey of knee replacement experts showed that the majority say that patients can safely go back to jogging and running after knee replacements. Thaler et al. questioned 120 knee surgeons from 31 countries, and 68% agreed that patients could go back to jogging after six months, 60% said they could jog on the road, 54% said that patients could run on a treadmill, and 51% said any type of running. 

They didn’t explain how they defined the difference between jogging and running, but I assume jogging would be easy running and running would be harder sessions. 

For some context, these experts agreed overwhelmingly that people who have had a knee replaced should never play squash again. 

What’s the verdict? 

A lack of research showing that running will wear out or damage your knee replacement should not be seen as evidence that running with a replaced knee is safe. It might increase your risk, but most experts these days feel that patients can resume jogging and running after six months.