Journal Club: Effect of running and walking on osteoarthritis and hip replacement risk

The article reviewed is WILLIAMS, P. T. Effects of Running and Walking on Osteoarthritis and Hip Replacement Risk. Med. Sci. Sports Exerc., Vol. 45, No. 7, pp. 1292–1297, 2013

http://www.ncbi.nlm.nih.gov/pubmed/?term=WILLIAMS%2C+P.+T.+Effects+of+Running+and+Walking+on+Osteoarthritis+and+Hip+Replacement+Risk.+Med.+Sci.+Sports+Exerc.%2C+Vol.+45%2C+No.+7%2C+pp.+1292–1297%2C+2013
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Design:

• This well designed article evaluated 74,752 runners and 14,625 walkers from the National Runners' and Walkers' Health Studies.  This is an unusually large number of runners and walkers evaluated, which is often a limiting factor in most studies.
• The runners and walkers were queried as to whether they were ever told by a physician they hip osteoarthritis.  This is an imperfect way of assessing the development of hip osteoarthritis, but as imperfect measures go, it is reasonable.  In some ways, this is a better measure than using a more "objective" standard like criteria based on x-ray or MRI imaging, since the correlation between imaging finding and functional limitations is imperfect, and for most patients, the only reason a physician would tell them they had hip OA is because they went to the doctor regarding a functional issue.  If I had a perfect measure, I'd want some form of functional assessment, but I do think this is a reasonable proxy.
• Another outcome measure was whether they reported having a hip replacement.  This is also a reasonably good measure- I don't know for sure, but I was assume that the correlation between reporting have a hip replacement and actually having a hip replacement is very close to 1.0.  Reporting bias is always a concern, but this is a case where I suspect the effect of reporting bias is negligible.

Results:

• As people age, they are more likely to both develop hip OA and get a hip replacement.  A bit of "no duh" result, but still useful to confirm.
• This effect of age was stronger for women than it was for men.  This confirms some other research (.... I'm thinking specifically of some of the aging/mobility research by Stephanie Studenski, one of my former colleagues from Pitt- http://www.upmc.com/media/experts/pages/stephanie-a-studenski.aspx), which is that people age, men are more frequently limited by medical conditions (like heart disease), and women  are more frequently limited by musculoskeletal conditions.
• Other factors associated with increased risk of either hip OA or hip replacement included: 
• Estrogen + Progesterone usage (notably, estrogen use alone did not, nor did menstrual status)
• Years of eduction (..... I guess a downside of being an MD/PhD)
• Intake of red meat (..... just what I need to hear on the 4th of July)
• Perhaps the most important finding in this study- the risk of hip OA and hip replacement went down the more someone ran.  This is an important finding, since I know many runners are concerned that their mileage is putting them at risk for developing arthritis.  It appears the opposite is true for the hips.
• A similar effect was found for walkers.
• The risk for hip OA and replacement was increased the larger the body size, as measured by body mass index.  Most, but not all, of the benefits of running and walking appeared to be related to the associated decrease in BMI.

Bottom Line: What does this mean for our patients?

• Running is good
• One of the theoretical concerns about running too much is that it may make one more likely to develop osteoarthritis or need a hip replacement.  Per this study, at least, the opposite is true
• Amongst the many benefits of running, it helps maintain a leaner body type, and this is likely one of the mechanisms that explains the protective benefit of running
• The article goes into the biology of cartilage.  In my opinion, much of that is in the realm of speculation and not assessed in this study, so this study does not do anything to alter our knowledge in those domains.  The study is valid regardless.