The mysterious rise in knee osteoarthritis

Robert H. Shmerling, MD

Senior Faculty Editor, Harvard Health Publishing

Follow me on Twitter @RobShmerling

While there are more than 100 types of arthritis, osteoarthritis is by far the most common.

Osteoarthritis is the form of joint disease that’s often called “wear-and-tear” or “age-related,” although it’s more complicated than that. While it tends to affect older adults, it is not a matter of “wearing out” your joints the way tires on your car wear out over time. Your genes, your weight, and other factors contribute to the development of osteoarthritis. Since genes don’t change quickly across populations, the rise in prevalence of osteoarthritis in recent generations suggests an environmental factor, such as activity, diet, or weight.

Osteoarthritis of the knee will affect at least half of people in their lifetime, and is the main reason more than 700,000 people need knee replacements each year in the US.

The obesity-arthritis connection

To explain the rise in the prevalence of osteoarthritis in recent decades, most experts proposed that it was due to people living longer and the “epidemic of obesity,” since excess weight is a known risk factor for osteoarthritis. Studies have shown not only that the risk of joint disease rises with weight, but also that even modest weight loss can lessen joint symptoms and in some cases allow a person to avoid surgery.

But a remarkable new study suggests there is more to the story.

Challenging a common assumption

Researchers publishing in the Proceedings of the National Academy of Sciences examined skeletons from people who had died and donated their bodies to research. Information regarding presence of knee osteoarthritis, age at death, body mass index (BMI), cause of death, and other data were compared for more than 1,500 people who died between 1905 and 1940 (the “early industrial group”) and more than 800 people who died between 1976 and 2015 (the “post-industrial group”).

A third group of skeletons obtained from archeological sites were also assessed for osteoarthritis of the knee. They came from prehistoric hunter-gatherers living hundreds to thousands of years ago, and early farmers living between 900 and 300 BP. BMI could not be determined for these individuals, but gender could be determined and age was estimated based on features of their skeletons.

The findings were intriguing:

  • The prehistoric skeletons and early 1900s cadavers had similar rates of knee osteoarthritis: 6% for the former and 8% for the latter.
  • With a prevalence of 16%, the more recent skeletons had at least double the rate of knee osteoarthritis as those living in centuries past.
  • Even after accounting for age, BMI, and other relevant information, those in the post-industrial group had more than twice the rate of knee osteoarthritis as those in the early industrial group.

Limitations of this study include BMI estimates at the time of death that might not reflect body weight during most of the person’s life, a study population (bodies donated for medical research or from archeological digs) that might not be representative of the population at large, and lack of accurate information regarding diet, activity, and other important factors. Even so, the findings shake some long-held assumptions and make the rise in osteoarthritis in recent years more mysterious than before.

So what?

These findings call into question assumptions about the reasons osteoarthritis is becoming more common. And they suggest that slowing or reversing the dramatic increase in obesity in recent years may not have as much of an impact on knee osteoarthritis as we’d thought. Finally, if longevity and excess weight do not account for the rising rates of knee osteoarthritis, what does? The list of possibilities is long, and as suggested by the authors of this study includes:

  • injury
  • wearing high-heeled shoes (yes, there is at least one study suggesting that the altered forces in the knee among those wearing high-heeled shoes might contribute to the development of osteoarthritis)
  • inactivity
  • walking on hard pavement
  • inflammation (worsened by inactivity, modern diets, and obesity)

The bottom line

As is so often the case in medical research, this new study raises more questions than it answers. We’ll need a better understanding of why and how osteoarthritis develops before we can prevent it or improve its treatment. There are already many dedicated researchers exploring these important questions.


  1. Mr Lee

    I’d put money on it that most of the rise is due to sitting – especially sitting at a desk and that it’s going to get worse as more and more of us work on computers. Desk sitting puts a high level of stress on the patella.

  2. wayne h. alba

    No one has the answer!!!

  3. Toni Umbarger

    After eighteen years on statins, my husband had to have his left knee replaced. He had been taking medication for arthritis for at least five years before that. Since he stopped taking statins, he no longer needs the arthritis prescription. I am convinced that my husband’s arthritis was due to the statin drugs he took. Our experiences with statin adverse effects are outlined in my article:

  4. Tanja will

    I am very surprised that nothing is mentioned about the chance that drugs many of us unfortunately use since years or decades… What about their side effects? I talk about statins…

    I know my osteo-arthritis in both knees derives from statins…. Broke down my muscles and tendons, then the cartilage…. Also osteopenia came with it….

    I am 48 and the next step are artificial knees…. One diagnosis at 42, one at 46…. I had to stop the statin b/c of breaking down my whole body, incl brains….

    Never was obese, healthy diet, sports (esp swimming)… No high heels…. Nothing of that al!…

    Please take my experience serious, and there are many more like me…. Starting with the muscles… Tendons …. Logically, finally also the joints will suffer…. I am not surprised at all about it findings but surprised the link to statins was missing.

    Please give this a thought, a read, a search…. Thank u!

    • holly hansen

      i am trying collagen for many reasons, one is to protect joints have started on whole foods collagen powder with a patented ingredient.

  5. Carolyn Magnus

    I took Simvastatin for 20 years then stopped due to joint side effects in particular sharp pain in my left knee when out. However my right knee is now painful and gives way making walking and going up stairs extremely difficult. I have always been active including swimming and exercise weighing 9.4 most of my life, now weighing 11 stone at 72 years of age female.

  6. david venables

    1/4 of Americans over 45 are on statin drugs. More than half of older people are on them.

    I personally know dozens who developed knee arthritis within a year or two of starting the drug. I myself am one: trekking in the Himalayas at age 68, crippled at age 69. John is another: doing 20-floor stair races at 75, crippled at 77.

    No one reports the adverse effects of any drugs–no system for that, which seems medical madness.

    But wouldn’t it be a cheap study to simply ask everyone who has knee arthritis whether or not they’re on statins? Ah, but who would fund such a thing?

  7. Bob Herman

    It was twenty years ago when I was diagnosed with OA in my neck and wrists. I’ve always been proactive with my health and spent the next year looking for answers, When I came across the combination of Glucosamine and Condroitin I began taking those products, which incidentally were recent to the market. Within three months my arthritis disappeared ….. pain and all. I was excited and told everyone that I knew about who were having OA issues. To my surprise no one experienced the same results. Delving into reading about OA, I came across article related to OA and joint oxidation. It was then I realized that another product I was taking, Grape Seed Extact, was the third leg in my therapy. I still take these supplements to this day and no OA. I’m 76, cycle 80 miles per week and am enjoying a pain free life.

  8. mike p

    Its a scientific mystery, I guess, as the evidence isnt available yet.

    But from this list, its no mystery to me:-

    wearing high-heeled shoes (yes, there is at least one study suggesting that the altered forces in the knee among those wearing high-heeled shoes might contribute to the development of osteoarthritis)
    walking on hard pavement
    inflammation (worsened by inactivity, modern diets, and obesity)

  9. James M. Raver

    As a farm origin person who became a doctor, my surmise is that we have much broader exposure to infectious agents, viral, insect borne , bacteria and fungi by virtue of travel, population density and occupation than ever before.

  10. Mario Ribadeneira

    I have been told that platelet en-riched blood (PRP) I had one treatment
    done. Felt (or thought) relief. One week later I was back to square one.
    Stem cell treatments (with cells harvested from ones own fat, are supposed to be successful.
    I wonder whether that holds true for those of us that have lost virtually all knee cartilage. I have read that stem cell treatment is succesful for recovery of soft tissues – not the case for cartilage.

    What is your experience?

    • Karen Colbourn

      RE: Stem Cell Therapy for Osteoarthritis of the Knee
      My osteopedic surgeon advised against it. His rationale was that, while stem cells successfully regenerate many kinds of body cells, human joints are not the best candidates for treatment. Stem cells regenerate better when there is a vascular supply. Most joints are supplied by synovial fluid, and therefore, would not benefit from stem cell injections.

  11. susan sargent

    So many of us have played sports in the last 50 years! Exercise has been stressed as being very important to good health and many us have heeded the call and enjoyed it. Women have been playing many more sports in the past 40 years than in the past –tennis, paddle tennis, running etc etc.

  12. Maurice Peugh

    From what I have read and tried, Chondroitin Sulfate is the one supplement shown to regrow cartilage. My knee pain went away after using it. Now, I need something to do the same for hip arthritis.

  13. Pam

    Increased height is not considered as a potential risk factor for osteoarthritis in this article. Might the several inches that better nutrition has added to the human frame put more wear and tear on the joints?

  14. Phyllis Kahn

    I have been told that buying chondroitin at a veterinary supply place is more cheaper. Same product

  15. Anne

    No Chondroitin is not worth the money. Try MSM instead, the sulfur in it is more likely to help you.

    • Maurice Peugh

      MSM does nothing for me. Chondroitin Sulfate cured my arthritis in my knees good enough to start karate again. It has been shown to help regrow cartilage. Pain Free is a book that was more helpful than any supplement if you have the time by Pete Egoscue.

  16. Heather bruce

    No word of food choices?

  17. Ron

    I would think that inactivity would be the most probable cause of the increase in OA. Jobs are becoming increasingly sedentary along with our off time where electronics cause us to sit more. Without the activity, joints (which do not have blood circulation) have no way of stirring nutrients in and pulling out waste in the synovial fluid. Doug Kelsey’s “The 90 Day Knee Arthritis Remedy” seems to have some references going back to the 70’s that show that joint movement can save knees.

  18. Jac Radoff

    Here is an exercise that will help your knees:
    1- Stand up straight with your feet not more than 2″ apart.
    2- Cup your hands over your kneecaps, knuckles pointing toward your toes, weight evenly distributed.
    Now slowly make 12 VERY SMALL counterclockwise circles, never allowing your knees to extend out beyond your toes or the outside margins of your feet.
    Stop. Wait at least 3 seconds.
    3- Now reverse and make 12 very small slow clockwise circles, also taking care these circles do NOT extend beyond your toes or the outside margins of your feet.
    4- Stop. Finished. Do this exercise once a day, everyday. Remember to go slowly and keep the circular motions small.

    • LP

      These instructions are unclear. First you say to stand up straight. Then you say to cup your hands over your knee caps which requires one to bend over. It’s also totally unclear what part of the body is making circles. Are you rotating at the hips to move the legs in a circular fashion? Or massaging the knees in circles?

  19. Emma Stamas

    What about running on pavement?
    What about being a weekend warrior?
    What about previous injuries causing faster wear and tear?
    I know lots of others that have had knee replacements and these reasons existed for those who were not obese.
    You could learn lots of info by just asking all candidates for knee replacement to answer a series of questions about this.

  20. James Martin

    I am 75 with knee problems from years of running. A year ago I switched to walking barefoot as much as possible and wearing “barefoot” shoes outside. Most, if not all of my knee pain has gone away. I blame my knee problems on high-tech running shoes which prevent the foot from doing it’s proper job of impedance matching the leg to the walking surface.

  21. john h davis

    since it is from irritation I suggest extra weight and poor standing posture are the main causes of this

  22. Rick

    Spending a lot of money for Chondroitin – is this worthwhile to prevent knee pain, osteoarthritis?

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