Flexion angles of the knee in different resting positions and their relation to the prevalence of osteoarthritis.

The effect of different resting postures on the loading profile of the knee in 1,155 subjects was studied. The recent change to chair sitting has radically modified this profile, resulting in an increase in midflexion loading and virtual disuse of full flexion of knee and hip. Domestic activities do not compensate for this underutilization. There is consistent evidence from 7 communities that the prevalence of osteoarthritis of the hip is substantially lower in communities that do not habitually chair-sit. No other adequate explanation for this difference has been identified. These findings suggest a need to reexamine the incomplete use hypothesis.