Byte-Sized Summary: Osteoarthritis is a common but debilitating joint disease, commonly of the knee, with unknown causes. A recent study has found that the prevalence of the condition has nearly doubled, and that longevity and BMI alone to not explain the increase.

Researchers at Harvard published their research on the disease in the Proceedings of the National Academy of Sciences (emphasis added):

Overall, knee OA prevalence was found to be 16% among the postindustrial sample but only 6% and 8% among the early industrial and prehistoric samples, respectively. After controlling for age, BMI, and other variables, knee OA prevalence was 2.1-fold higher (95% confidence interval, 1.5–3.1) in the postindustrial sample than in the early industrial sample.

And further (our emphasis):

Our results indicate that increases in longevity and BMI are insufficient to explain the approximate doubling of knee OA prevalence that has occurred in the United States since the mid-20th century. Knee OA is thus more preventable than is commonly assumed, but prevention will require research on additional independent risk factors that either arose or have become amplified in the postindustrial era.

Link to PNAS article here

For online resources on pain management, we refer you to WebMD and materials therein.