Today we’re following up on a recent article on Osteoarthritis of the knee with some additional insight from faculty member Jamie McGaha, OTR, CHT, CEAS, OTD, COMT. We originally posted on this article in the “What we’re reading” section of a recent newsletter with commentary from our directory of education, Dr. Bob Niklewicz. You can find the original article here: Study: Prevalence of Knee OA Today Twice What It Was 75 Years Ago and here’s what Dr. Bob had to say:

OA is a complicated problem and prevention is the best treatment. Ergo breaks and proper ergonomic education to avoid end of range lifting stressors to the knees can be improved by good ergonomics in many cases. – Dr. Bob Niklewicz.

Jamie McGaha is an occupational therapist with a self described “passion for the subject of arthritis” and had some comments of her own on the article which you can read below:

OA is a multifactorial disease, we are finding more and more that genetics plays a large role in development in addition to external factors such as prior injury, activity level, types of activity possibly, occupation etc. As they mention in the discussion it likely not 1 thing that is leading to an increase in knee OA prevalence; we live longer, we do have less physically demanding and active occupations, overall more sedentary lifestyles. A key thing in my opinion is the change in active lifestyles and occupations. Not only does movement maintain mobility in joints, it is critical for the exchange of synovial fluid and blood profusion for joint nutrition. Additionally, as a joint becomes less responsive to daily compression and distraction through activity and less fluid exchange occurs in the joint, mechanoreceptors becomes less adept in relaying information from the musculoskeletal system to the nervous system. This causes muscles to have compensatory effects in harnessing their neuromuscular reflexes designed for controlling load and essentially cushioning our joints as we load/use them. This is why we see compensatory gait changes, muscle weakness, and lack of strength in the knee musculature. We can also see muscle weakness and atrophy from lack of use, which may be due to pain or stiffness, which can then lead increase in OA symptoms (becomes a cycle quickly).

– Occupation was only reported for 23% of the skeletons used, so I wonder what the changes in preindustrial to postindustrial jobs would tell us anything. BMI was only available for 1,859 of the 2,756 skeletons, I don’t know if we would see differences with around 900 more subjects added into analysis, possibly as that is a large number. Their analysis results support the increase in prevalence of knee OA in postindustrial skeletons, compared to all the others, which I think many of us agree is certainly the case, more now than there was before, but they want to know if BMI is the “why” predictor. After controlling for BMI and age in their model, they did still find both had a relationship on the prevalence of OA, but OA was still higher in postindustrial cohort “Age and BMI were positively associated with knee OA prevalence (P < 0.001 for both variables) (Fig. 1D<http://www.pnas.org/content/114/35/9332#F1>), but at all ages, knee OA prevalence was at least twice as high in the postindustrial sample than in the early industrial sample, even after controlling for BMI (Fig. 2<http://www.pnas.org/content/114/35/9332#F2>)”

I don’t think this tells us the “why” there is more OA now or that BMI truly “predicts”  any development of OA, but we do know there is a positive association between age and BMI to knee OA prevelance.

I also think this is a broad statement as we know OA is not caused by just 1 thing, but BMI may increase someones OA symptoms, we see it often in therapy.
“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,”

Other current studies have slightly different results on BMI and OA:

1. Grotle, Margreth, Hagen, Kare B. Natvig, Bard Dahl, Fredrik A and Kvien, Tore K.”,
Obesity and osteoarthritis in knee, hip and/or hand: An epidemiological study in the general population with 10 years follow-up. “BMC Musculoskeletal Disorders”,2008”,9(1),p 132doi=”10.1186/1471-2474-9-132”
2. Holmberg S1, Thelin A, Thelin N. J Rheumatol. 2005;34(1):59-64. Knee osteoarthritis and body mass index: a population-based case-control study.
3. Zheng, H., & Chen, C. (2015). Body mass index and risk of knee osteoarthritis: systematic review and meta-analysis of prospective studies. BMJ Open, 5(12), e007568. http://doi.org/10.1136/bmjopen-2014-007568

However some have found:
1. Effect of recreational physical activities on the development of knee osteoarthritis in older adults of different weights: The Framingham Study.
“In conclusion, walking for exercise and other recreational activities in older persons without knee OA do not affect these individuals’ risk of developing OA, even if they are overweight. Although dynamic loading may have a trophic effect on cartilage, there is no measurable protective effect of recommended weight‐bearing exercise on OA. Physical activity can be done safely without concerns that persons will develop knee OA as a consequence.”

So yes, we may have more knee OA than before, but I don’t think BMI is the sole predictor nor do I believe that BMI has 0 effect on OA. We have to remember the complex nature of the human system and body. Many intrinsic factors that we cannot control (age, sex, genetics, injury) and many extrinsic factors that we can control (activity, BMI, lifestyle, jobs,) are all interrelated and can impact OA development and progression. You could always argue chicken or egg as well- what was first, OA or obesity? You can say the same of exercises- those who exercise too much can injure cartilage, some may do too little impacting cartilage health, some may get OA no matter what they have done, why do we sometimes see OA in only 1 knee and not always bilateral?

Cool study, we definitely must take a holistic approach in understanding and treating OA with the growing knowledge of the patho-phsyiology of the disease and ever evolving lifestyles. – Jamie McGaha