➤ Primary osteoarthritis of the hip is a separate phenotype that occurs at a rate of 3% to 6% in the populations of the world with European ancestry.
➤ In all non-European populations, there is a consistent rarity of primary osteoarthritis that suggests a different etiology for these few patients.
➤ Family, sibling, and twin studies prove primary osteoarthritis to be a genetic disease with a 50% heritability caused by European genetic variants.
➤ The genetic basis is reinforced by the lower rate of primary osteoarthritis in American minorities consistent with their degree of European gene admixture.
➤ Whether the mechanism of degeneration of primary osteoarthritis may be secondary through a morphologic deformity, such as femoroacetabular impingement, remains unknown.
➤ The virtual absence of the disease in non-Europeans indicates that the European gene component is necessary for the expression of this separate phenotype of osteoarthritis.