As a paleoanthropologist, Dr. Wallace is interested in the evolutionary history of certain diseases, particularly those common today but not as common in the past. Called mismatch diseases, these afflictions common in contemporary culture are attributed to current lifestyles that differ from the conditions under which humans evolved. Diabetes is an example of a mismatch disease.
Recognizing that knee OA may be one of these mismatch diseases, Dr. Wallace and his colleagues undertook the study to examine the long-term trends in knee OA prevalence in the U.S., and to look at how the prevalence has changed from prehistoric times to today.
The researchers looked at cadaver-derived skeletons of people aged 50 years and older from three different time periods: a prehistoric period (i.e., 6,000–300 years ago); the early industrial period (i.e., the 1800s to the early 1900s); and the modern post-industrial period (i.e., the late 1900s to the early 2000s). The 176 skeletons examined from the prehistoric period came from Native American hunter-gatherers and early farmers. The 1,581 skeletons examined from the early industrial period came from individuals who lived in Cleveland, Ohio, and St. Louis, Mo., and the 819 skeletons examined from the modern, post-industrial period came from people who lived in Albuquerque, N.M., and Knoxville, Tenn.
Knee OA was identified in the skeletal samples based on the presence of eburnation (i.e., polish from bone-on-bone contact). The study found the prevalence of knee OA was significantly higher among skeletal samples from the post-industrial period compared with the two earlier periods. After controlling for sex, the prevalence of knee OA found in the post-industrial skeletal samples measured 2.6 times higher than in the early industrial period (i.e., 16% vs. 6%; P<0.001) and two times higher than in the prehistoric period (i.e., 16% vs. 8%; P=0.003).
To examine whether the current knee OA prevalence is attributable to age and BMI, the authors analyzed a subset of skeletal samples for whom age and BMI data were available (which only occurred with the skeletal samples from the early and post-industrial periods). After controlling for age and BMI, the prevalence of knee OA remained 2.1 times higher in the skeletal samples from the postindustrial period compared to skeletal samples for the early industrial period (i.e., 11% vs. 5%; P<0.001).
“The surprising result is that even after you adjust for BMI and age, the increase in prevalence persists,” says David Felson, MD, who works with the Clinical Epidemiology Research & Training Unit at the Boston University School of Medicine.
