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  • Study: Prevalence of Knee OA Today Twice What It Was 75 Years Ago

    Knee osteoarthritis (OA) has more than doubled among Americans since 1940, say researchers, and the increase can't be explained by longer lifespans or a higher prevalence of obesity and overweight in recent decades. Instead, the real culprit could be physical inactivity, which authors describe as "epidemic in the postindustrial era."

    The study, appearing in the Proceedings of the National Academy of Sciences, compared knee joints of 2,756 skeletons from 3 groups of individuals: those who lived in the 1800s and early 1900s ("early industrial," N=1,581), those who lived during the late 1900s through the early 2000s ("postindustrial," N=819), and prehistoric hunter-gatherers who lived between 6,000 and 300 BCE (“prehistoric,” N=176). Researchers were looking for knee joint eburnation—the ivory-like result of bone-on-bone contact that occurs after cartilage erodes—as the indicator for moderate to severe OA.

    Here's what they found:

    • The prevalence of knee OA in the postindustrial skeletons was about 16%, a rate 2.6 times higher than the early industrial group, which had a 6% incidence rate. Knee OA prevalence among the prehistoric sample was 8%.
    • After controlling for body mass index (BMI) and age when that information was available (1,859 of the 2,756 skeletons), researchers were unable to establish a correlation between these factors and prevalence of knee OA—instead, rates remained 2 times higher for the postindustrial group even when compared with early industrial skeletons with similar ages and BMIs. BMI for the prehistoric sample could not be estimated.
    • In the postindustrial individuals with knee OA, 42% had the disease in both knees. Bilateral occurrence was 30% among the early industrial samples with knee OA, and 17% among the prehistoric group.

    "Although knee OA prevalence has increased over time, today's high level of the disease is not, as commonly assumed, simply an inevitable consequence of people living longer and more often having a high BMI," authors write. "Instead, our analyses indicate the presence of additional independent risk factors that seem to be either unique to or amplified in the postindustrial era."

    The researchers believe that risk factor could have to do with "environmental changes"—namely, the reduced levels of physical activity associated with the postindustrial era, despite the human body's need for regular exercise. It's a phenomenon known as a "mismatch disease," when the human body can't easily or rapidly adapt to changes in the lived environment.

    "Although altered loads generated by walking more frequently on hard pavement … or with certain forms of footwear … might be factors, another possibility that merits more study is physical inactivity, which has become epidemic during the postindustrial era," authors write. "Less physically active individuals who load their joints less develop thinner cartilage with lower proteoglycan content … as well as weaker muscles responsible for protecting joints by stabilizing them and limiting joint reaction forces."

    The good news, according to the researchers, is that their findings point to the possibility that knee OA is a largely preventable condition—providing there's a widespread "reappraisal of potential risk factors that have emerged or intensified only very recently."

    "As with other mismatch diseases, it is likely that any effective prevention strategy will involve adjusting physical activity patterns and diets to approximate more closely the lifestyle conditions under which our species evolved," authors write.

    Research-related stories featured in PT in Motion News are intended to highlight a topic of interest only and do not constitute an endorsement by APTA. For synthesized research and evidence-based practice information, visit the association's PTNow website.


    • Along with (or caused by) lack of activity, sleeping glutes, flexed posture, stiff pelvis, and poor abdominal control can shift too much work to the knees and/or low back. By viewing the body as a musculoskeletal SYSTEM, one can conclude that poor function in one area can shift work to another area. The area doing the extra work is where you see breakdown. As movement specialists PTs can identify musculoskeletal deficits and correct them. Think of arthritis as a symptom, then treat the problem.

      Posted by Brian Lambert, PT on 8/17/2017 10:09 AM

    • I have wondered, for quite some time now, about the effects of the passing of Title IX on women with OA and the need for joint replacements. Title IX opened the door to increased opportunity and acceptance of women in competitive sports. The population of young women at that time are now in their 60's and 70's. Could this be one cause for an increase in joint replacements?

      Posted by Kathleen Rafferty PT on 8/18/2017 5:41 AM

    • Agree with above comment by Brian. Lifestyle changes such as inactivity, lack of frequent squatting and rising from the floor etc.. have made me ponder over this several times when I worked in the US for almost 2 decades. Severe OA and consequent TKR are an urban phenomenon in a country like India, where the lifestyle is starkly different between cities and villages. In rural areas, people frequently sit on the floor or on lower surfaces. Consequently, frequent rising from the floor entails exercise for the hips, pelvis, abs, and gluts. Therefore less likelihood of obesity and OA knees?

      Posted by Ushma Goradia PT on 9/10/2017 11:10 PM

    • Inactivity may be one cause among many. It is simplistic to search for a single cause. OA affects those with high activity levels as well as those with low. Since it is an inflammatory condition I wonder how much dietary changes during the time span noted have influenced prevalence of OA. The standard American diet (plentiful industrial oils, sugar, processed foods, and lacking whole fruits and vegetables) is a new phenomenon and has changed in the same time span as the observed increase in OA. Diet could be part of the problem.

      Posted by Michelle Slaughter DPT, GCS on 9/13/2017 12:25 PM

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