The disease has little to do with ageing or even 'wear and tear'—instead, it's more likely to be caused by environmental factors, such as air pollution.
Cases have doubled in the past hundred years, but this epidemic isn't down to us living longer or even putting on more weight—those are just untested assumptions, say researchers from Harvard University.
They inspected the skeletons of 1,581 people who lived during the 19th century, and who were aged 50 or more, and compared them to those of 819 similar people who lived in the 20th century. After taking into account age and body mass index, cases of knee arthritis had doubled in the later group—which suggests that something other than age and body weight had something to do with the increase.
The big difference between the two centuries has been the rise of industry and pollution, which may well have more of an impact on the disease than the current culprits that medicine believes are responsible, the researchers say.