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LAS VEGAS -- Intensity of distance running had no bearing on the prevalence of hip and knee osteoarthritis among participants in recent editions of the Chicago Marathon, researchers reported here.

Rather, the risk factors for pain and arthritis were merely those seen in the general population: age, overweight/obesity, and family history of these conditions, reported Matthew Hartwell, MD, now at the University of California San Francisco, and colleagues at Northwestern University's Feinberg School of Medicine in Chicago.

In all, 7.3% of 3,804 marathon participants who completed a survey had hip or knee osteoarthritis, and 36.4% reported musculoskeletal pain, the group said at the American Academy of Orthopaedic Surgeons (AAOS) annual meeting.

Despite the notable prevalence of pain, 94% of the runners said they intended to keep on with marathons, and one-quarter of all participants said their doctors had urged them to cut back or stop altogether.

"Healthcare providers should consider these findings when discussing the risks and benefits of running," Hartwell's group concluded. They indicated that theirs is the largest survey-based study on the topic to date.

Whether marathons and other forms of distance running increase the risk for hip and knee osteoarthritis has been debated for many years. A large found that "competitive" runners had vastly higher prevalence of arthritis compared with "recreational" runners (13.3% vs 3.5%), but the authors noted that causation could not be established. Meanwhile, a found a lower prevalence compared with the general U.S. population, and the risk factors were the usual ones (age, family history, surgical history).

The new study by Hartwell and colleagues bolsters those latter findings.

"Our multivariate analysis showed that the factors that increase a person's risk for arthritis are the same for anyone with joint degeneration -- whether or not they're a runner," Hartwell said in an AAOS press release.

His group distributed surveys to more than 37,000 runners who entered the Chicago Marathon in 2019 and 2021, with a response rate just over 10%. Their mean age was 44 (SD 11), and 52% were men.

Most had significant prior marathon experience. Respondents had run an average of 9.5 marathons, although that was skewed by immense numbers completed by a few individuals (51 respondents had run 51-100 previous marathons, and one person had completed an astonishing 664). Nearly two-thirds of the sample had done five or fewer.

Respondents had an average of 15 years' running history and, currently, 28 miles of running per week at a mean of 8.5 minutes per mile.

Prevalence of pain was inversely related to age and their marathon history -- that is, younger individuals and those with the fewest previous marathons had the highest rates of reported pain. (That makes sense, insofar as people running marathons by the dozen would probably not be those in constant pain.)

But for arthritis, there was no hint that running intensity -- number of past marathons, years of running, weekly mileage, and pace (in minutes per mile) -- was a risk factor. In comparing runners with and without arthritis, odds ratios were all close to 1.0.

On the other hand, these standard risk factors were significantly associated with arthritis:

• Age: OR 1.08 per year (95% CI 1.06-1.10)
• Family history of hip/knee arthritis: OR 3.47 (95% CI 2.52-4.79)
• Body mass index: OR 1.10 per kg/m² (95% CI 1.05-1.15)

There was, however, one potentially running-related parameter that did predict arthritis: a history of lower-limb injury that prevented running (OR 5.04, 95% CI 3.45-7.34). Along those lines, a personal history of hip/knee surgery was also a significant risk factor (OR 5.85, 95% CI 4.33-7.92).

Limitations to the study included reliance on respondents' self-report for all data and the low response rate, as well as the possibility that Chicago Marathon participants aren't representative of those elsewhere (most according to age and sex, or else have successfully completed five previous editions in the past 10 years).

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