The average American today is twice as likely to be diagnosed with knee osteoarthritis as in the years before World War II, Harvard scientists say. And the reasons are less clear than you might think.
Based on a study of more than 2,000 skeletons from cadaveric and archaeological collections across the United States, the Harvard report is the first to definitively show that knee osteoarthritis prevalence has dramatically increased in recent decades.
The findings, published in the Proceedings of the National Academy of Sciences, also upend the belief that the disease is a wear-and-tear condition widespread today because people live longer and are more likely to be obese.
“Before this study, it was assumed without having been tested that the prevalence of knee osteoarthritis has changed over time,” said first author Ian Wallace, a postdoctoral fellow in the lab of Daniel Lieberman, the Edwin M. Lerner II Professor of Biological Sciences and senior author of the study.
“We were able to show, for the first time, that this pervasive cause of pain is actually twice as common today than even in the recent past. But the even bigger surprise is that it’s not just because people are living longer or getting fatter, but for other reasons likely related to our modern environments.”
Osteoarthritis affects an estimated one-third of Americans over age 60, and is implicated in more disability than almost any other musculoskeletal disorder.
“Understanding the origins of knee osteoarthritis is an urgent challenge because the disease is almost entirely untreatable apart from joint replacement, and once someone has knee osteoarthritis, it creates a vicious circle,” Lieberman said. “People become less active, which can lead to a host of other problems, and their health ends up declining at a more rapid rate.”
Wallace and Lieberman think that their study has the potential to change the popular perception of knee osteoarthritis as an inevitable consequence of aging, creating momentum behind efforts to prevent the disease—much like we now do with heart disease.
“There are a lot of well-understood risk factors for heart disease, so doctors can advise their patients to do certain things to decrease their chances of getting it,” Lieberman said. “We think knee osteoarthritis belongs in the same category because it’s evidently more preventable than commonly assumed. But to prevent the disease more work needs to be done to figure out its causes.”
The researchers’ initial goal was to determine how old the disease actually is, and whether it is really on the rise. “There are famous examples in the fossil record of individuals, even Neanderthals, with osteoarthritis,” Lieberman said, but no one had looked at the data in a comprehensive way before.
Wallace crisscrossed the country to examine skeletons spanning more than 6,000 years to search for a telltale sign of osteoarthritis called eburnation, caused when two bones that comprise a joint come into direct contact and rub against each other. The data Wallace collected was combined with analyses from other researchers, creating a large pool of older individuals from three broad time periods—prehistoric times, early industrial times (mainly the 1800s), and the modern post-industrial era.
After correcting for a number of important covariates, they concluded that people born after World War II have approximately twice the likelihood of getting knee osteoarthritis at a given age or BMI than those born earlier. Wallace and Lieberman are now working to identify what factors may be behind the increase.
Source: Harvard University; August 14, 2017.