Runners and Knee Osteoarthritis
Introduction[edit | edit source]
Running has become an increasingly popular activity, and form of exercise, throughout the world, over the last few decades. Although injuries are possible, there are many health benefits to running. However, there is a large misconception that running may lead to knee osteoarthritis , and it is very uncertain whether running has a detrimental effect on the knees . In fact, there is evidence to prove that the opinion of running causing osteoarthritis is not correct.
As mentioned on the Osteoarthritis page, osteoarthritis is a degenerative condition. It affects the joints, cartilage, bones, tendons, and ligaments. Its main cause its linked to metabolic and systemic conditions, such as hypercholesterolemia, hypertension, and high blood glucose levels, to name a few. Individuals can be asymptomatic, thus would only be diagnosed when they notice symptoms such as joint line tenderness, reduced range of motion, crepitus with movement, joint effusion, and/or joint space deformity, and seek medical attention. 
Benefits of Running[edit | edit source]
Some noted benefits of running, as found from studies of runners and non-runners include, 
- Decreased risk of cardiovascular disease
- Decreased risk of type II diabetes
- Decreased risk of depression
- Decreased prevalence of disability and mortality
- Positively affects bone mineral density, and weight control
The rate of disability and mortality is much lower in runners, compared to non-runners. It was also noted that running can increase longevity, through an increase in muscle strength, cardiovascular reserve, bone mineral density, and glucose tolerance. 
Knee Biomechanics with Running[edit | edit source]
Joint forces[edit | edit source]
The peak joint force on the knee is much higher in running than walking, roughly 3 times as high.  With knee anatomy, it is seen that increased joint loads increase the contact area of the articular surfaces. 
It is interesting to note that the peak knee joint loads exceed the threshold that would lead to osteoarthritis. This threshold is ironically also exceeded in walking, and thus runners would be expected to develop knee osteoarthritis. This expectation or belief is in fact false, for the following reason. 
It would be noted that with running, there is a much shorter contact time with the ground, and most of the time is spent in swing phase. This in turn minimizes the effect of the high peak joint forces experienced at the knee. For this reason, it is seen that the peak joint load, and duration, becomes equivalent to that of walking.  The average cumulative load, which is more significant for the development of osteoarthritis, is quite low in running. 
The peak load on the knee, and the impulse on joint contact force, increases with an increase in running speed. Therefore it is possible that the runner can increase their training speed without increasing their risk of osteoarthritis. 
In another study, compressive loads on the tibial plateau were compared between older adult runners and younger adult runners. With older adults runners, there was an average peak of 4x the bodyweight when running at a slow speed of 1.4-1.7 m/s. In younger adult runners, there was a greater knee joint load at faster speeds, with the range at similar speeds being quite high, 6-13x bodyweight at a speed of 3.5 m/s. 
Cartilage[edit | edit source]
The loading response of articular cartilage depends on the peak load, as well as loading rate and duration. The joint loads from running can be beneficial for preventing knee osteoarthritis, compared to a sedentary lifestyle. 
When considering cartilage, there is a greater compressive stiffness of cartilage in dynamic loading compared to static loading, which also increases with an increasing loading rate. However, an increase in peak joint load, by increasing running speed, doesn't necessarily indicate an increase in cartilage strain. Loading rate variations, duration of loading, and mechanical properties of cartilage need to be considered. The loading difference in cartilage is apparent due to its biphasic composition, which includes a liquid phase, and a porous, viscoelastic solid phase. The strain produced with greater peak loads would be reduced, if paired with greater loading rates, thus would be expected with faster running speeds. 
Factors Associated with Osteoarthritis[edit | edit source]
- Age - Between the ages of 50-75 , there seems to be a non-linear increase in the risk of osteoarthritis, but then there is a relative decrease in the risk after the ages of 75-80. As one ages, it is seen that the repair mechanism of the joints is decreased, which leads to decreased absolute forces overloading the mechanisms of these joints. Age also affects proprioception and the function of the joint capsule, ligaments, and muscles, thus affecting the health of the joint.
- Gender - Females have a higher risk of developing osteoarthritis in the knees. They are also more likely to be symptomatic, and have a more pronounced radiographic signs. There is a possibility that females may experience osteoarthritis during menopause, or even post-menopause, though estrogen may have a protective effect. Females may also be seen to have a lower cartilage volume, which would be a risk factor.
- Genetics - Genetic factors may account for up to 40% of knee osteoarthritis incidences. Genes are an important contributor to joint health, and it is important to obtain Family History when examining cases related to osteoarthritis.
- Previous injury - Patellofemoral Pain Syndrome (PFPS) has a possibility of leading to a risk of patellofemoral osteoarthritis. It is essential for runners with PFPS to improve running biomechanics to minimize the risk of patellofemoral osteoarthritis. Anterior Cruciate Ligament (ACL) and meniscal injuries also have a strong correlation with the development of knee osteoarthritis. It is possible to experience knee osteoarthritis 1 year after an ACL injury. A meniscal injury following an ACL injury also increases the risk of experiencing knee osteoarthritis. The patellofemoral compartment may be at a higher risk of osteoarthritis after an ACL injury. Meniscal injuries on their own are also a risk for tibiofemoral osteoarthritis.
- Biomechanical factors - Abnormal or unusual knee biomechanics can be factors leading to knee osteoarthritis. A static varus, but not valgus, knee deformity is correlated with tibiofemoral knee osteoarthritis. Individuals who displayed an increased femoral displacement and knee flexion angles at heel strike and midstance showed medial compartment cartilage thinning. Increased knee extension moments and patellofemoral reaction forces in walking or running on inclines are seen to be associated with patellofemoral osteoarthritis.
- Activity level/Sport participation - Soccer and competitive weightlifting seem to have the greatest risk of osteoarthritis. These factors would relate more to the characteristics the sports and their movements and injuries, rather than other metabolic factors.
- Occupational tasks - Occupational workload and environment can be potential risks for developing osteoarthritis. Increased physical demands in occupations such as farming, construction, military, law enforcement, and firefighting are positively correlated with a higher incidence of knee osteoarthritis. Tasks such as kneeling, stair climbing, and repetitive movements can also be contributors.
- Obesity - Obesity is one of the main risk factors for developing osteoarthritis. There is a higher risk for obese or overweight Men to develop osteoarthritis than Women. Weight management solutions, especially through running, is an important consideration to manage or reduce the risk of osteoarthritis.
Sports, such as soccer or football, which involve repetitive, high impact, torsional forces, are more likely to lead to osteoarthritis. Previous injuries to muscles, joints, ligaments, tendons, can also increase the likelihood of osteoarthritis. 
It is seen that an increase in body mass has a direct effect on osteoarthritis. As one's weight increases, the biomechanics of human movement alters, as does the loading surfaces of articular cartilage in weightbearing joints. For instance, with a single-leg stance, an increase in 1lb of bodyweight increases the loading on the knee by about 2-3lbs. 
Radiographic identification of knee osteoarthritis is from structural deterioration, while symptomatic osteoarthritis can be identified by pain during activities of daily living, especially when the joint is loaded. 
Running and Injuries[edit | edit source]
Similar to any activity, running does not come without any risk of injury. Infact, knee and ankle injuries are quite common, which generally occur due to overuse, and can cause injuries such as patellofemoral pain syndrome, iliotibial band syndrome, or achilles tendonitis. 
Dosage and Running[edit | edit source]
Dosage or measurable factors can include many different parameters. This can span from total time running, distance, of a run, speed, cadence, heart rate, perceived exertion, respiration rate, or perspiration rate. these variables can help determine different exposures to running. 
Low Dosage Running[edit | edit source]
It is seen that low dose running alone is not a causative factor for knee osteoarthritis, and in fact it may be a protective factor against osteoarthritis. 
High Dosage Running[edit | edit source]
Potential Mechanisms for low Osteoarthritis Risk[edit | edit source]
Low Cumulative Load[edit | edit source]
The peak load accumulated per stride (or step) during running may be less important for an osteoarthritis risk compared to the total load accumulated over many strides. Although individual peak knee joint loads are greater in running than in walking, the overall peak load in similar in running and walking due to the shorter ground contact duration and and longer stride length in running. The load accumulated in running may not be as high as the load accumulated in walking the same distance. 
This stress reduction on the knee can have a consequence with running mechanics that have a high amount of knee flexion, which would decrease contact area. Considering the effects on cartilage, it is seen that an individual can accumulate more load by standing for 30 minutes than running for the same duration. 
Running conditions Cartilage[edit | edit source]
It was proposed that cartilage health was regulated by the greatest stress experienced throughout the activities of daily living. As related to running, cartilage in a healthy person can become conditioned to withstand the stresses of running, if it is paired with sufficient stimulus, rest, and nutrition. 
Some indirect evidence for cartilage health can be outlined by the following points, 
- The ankle experiences greater localized joint stress, but has a lower prevalence of osteoarthritis, than knee osteoarthritis.
- Healthy knee cartilage is thicker in weightbearing areas of the joint.
- Knee cartilage glycosaminoglycan content, influencing lubrication and shock absorption, was greater in recreationally active individuals compared to sedentary individuals, and even greater in high-volume runners than recreationally active individuals.
It can be summarized that osteoarthritis doesn't result from an excessive amount of load, but instead from unusual loads. The unusual load would be one that imparts stresses on the joint that it has not adapted to, but will suddenly sustain on a regular basis. 
Running and Osteoarthritis - Evidence[edit | edit source]
Joint Loading[edit | edit source]
It is important to note that running can load the joints as much as three times more than walking. As activity progresses, and muscle capacity decreases due to fatigue, the apparent loading can be even higher. 
This is not to say that joints shouldn't be loaded, and loading is not good, since moderate loading is required for articular cartilage health. 
There is little evidence which demonstrates that running causes osteoarthritis. Despite running being repetitive, with an increase in joint loading, the runner does not experience excessive torsional loads, and a risk of traumatic injuries to joints and ligaments. This is more likely experienced in soccer players, and weightlifters, as there is a higher evidence shown on radiographs, compared to long-distance runners. 
A longitudinal study over 8 years has shown that recreational runners, or runners over 50 years of age, shows that there is no radiographic clinical evidence leading to knee osteoarthritis. 
A study comparing runners and nonrunners which analyzed bone mineral density in the spine, hip osteoarthritis, and knee osteoarthritis, noted that there was higher bone mineral density in runners. Despite this, there were no differences, or presence of, osteoarthritic qualities such as, joint space narrowing, crepitation, or joint instability. 
With these findings, various researchers and authors have concluded that running does not increase the risk of developing osteoarthritis, over the long term. 
The National Runners and Walkers Health Study in 2013, analyzing over 89000 runners, including marathon runners, showed that running does not increase the risk of osteoarthritis. This study also showed that running decreases the risk of osteoarthritis, and hip replacement, due to the lower body mass index (BMI) of the running population. 
Cartilage[edit | edit source]
Changes in cartilage, before and after running, were assessed using magnetic resonance imaging (MRI). Characteristics such as cartilage volume, compression, and thickness, under loads, were assessed using T1- and T2-weighted MRIs. 
- T1 weighted images - these facilitate viewing of the proteoglycan matrix of the cartilage, and acute fluid changes. This would be helpful in determining long-term changes in the cartilage. Signs of early stages of osteoarthritis would be indicated by a decrease in the matrix.
- T2 weighted images - these indicate water and collagen content in the cartilage. This would help determine short-term changes in water content and fluid balance.
Cartilage is seen to have a beneficial effect with moderate exercise, though cannot be confidently extrapolated to high-volume, marathon, runners.
However, another study showed that runners, having run three marathons or less in their lifetime, may experience negative long term biomechanical changes to articular cartilage. This was seen with long term changes in the T1 imaging, while T2 imaging returned to normal subsequent to three months. An MRI was taken immediately post-marathon. Changes were noticed in T1 and T2 imaging upon MRI, but the T1 imaging remained altered subsequent to three months. 
Another study showed that there were no changes in bone marrow edema, joint effusion, or periosteal reactions, between pre-marathon and post-marathon MRIs. It was concluded that long-distance running does not lead to internal stresses on bones and joints. 
From a study conducted examining the radiographic images of recreational runners compared to nonrunners, of mid-to older-age adults, it was concluded that there was no evidence to suggest that general runners in the community have an increased risk of knee osteoarthritis, compared to nonrunners. When analyzing running activity at different life stages, leisurely running did not pose a risk to prevalence of knee pain, radiographic osteoarthritis, or symptomatic osteoarthritis. The study even found that runners experienced less knee pain than nonrunners.  However, another study claims that runners are not at a greater or lower risk of knee osteoarthritis, compared to nonrunners. 
Knee pain and symptomatic osteoarthritis were least observed in current runners, and is most common in those who do not run at all. 
The Bottom Line for Running and the likelihood of Knee OA[edit | edit source]
Considering various studies on knee articular cartilage, and analyzing the gait cycle of running and walking, it is seen that the peak force applied on the knee while running may in fact be less than that applied during walking the same distance, thus leaving running with a lower risk of knee osteoarthritis. 
Video Resources[edit | edit source]
Here are some interesting videos - one is a general health nd fitness discuss with research evidence, and the other two are tips from Physiotherapists. Each subsequent video is longer than the preceding video.
References[edit | edit source]
- Plack Leigh-Ann. Can Running Cause Osteoarthritis? ACSM's Health & Fitness Journal 19(1):23-28.
- Lo Grace H, Driban Jeffrey B, Kriska Andrea M, McAlindon Timothy E, Souza Richard B, Petersen Nancy J, Storti Kristi L, Eaton Charles B, Hochberg Marc C, Jackson Rebecca D, Kwoh C. Kent, Nevitt Michael C, Suarez-Almazor Maria E. Is There an Association Between a History of Running and Symptomatic Knee Osteoarthritis? A Cross-Sectional Study From the Osteoarthritis Initiative. Arthritis Care & Research. 2017:69(2):183-191.
- Miller Ross H, Edwards W. Brent, Brandon Scott C. E, Morton Amy M, Deluzio Kevin J. Why Don’t Most Runners Get Knee Osteoarthritis? A Case for Per-Unit-Distance Loads. Medicine & Science in Sport & Exercise. 2014:572-579.
- Miller Ross H. Joint Loading in Runners Does Not Initiate Knee Osteoarthritis. Exercise and Sport Science Reviews. 2017:45(2):87-95.
- Kenyon C.D, Gessel T.P, Harrast M.A. Osteoarthritis and Running. In: Harrast M.A editor. Clinical Care of the Runner - Assessment, Biomechanical Principles, and Injury Management. Seattle, USA. Elseir Inc. 2020. p169-180.
- Michael Braccio. Does Running Cause Knee Osteoarthritis? Episode 28. Available from: https://www.youtube.com/watch?v=wriHPGF99Q4&ab_channel=MichaelBraccio (accessed 29 September 2022).
- Age Fit with Tess. Running With Osteoarthritis // Physiotherapist Top 5 Tips. Available from: https://www.youtube.com/watch?v=-rGebJhZof8&ab_channel=AgeFitwithTess (accessed 29 September 2022).
- Sports Injury Physio. Tips for Running With Arthritis in your Knees. Available from: https://www.youtube.com/watch?v=HGmbqtDYyvo&ab_channel=SportsInjuryPhysio (accessed 29 September 2022).