Heterotopic bone formation after hip replacement. The influence of the type of osteoarthritis.

The relationship between heterotopic bone formation and the morphological type of osteoarthritis was examined after 43 hip replacements. Of the 43 hips studied, nine were atrophic, 19 were normotrophic, and 15 were hypertrophic. The incidence of heterotopic bone formation in the atrophic type was 11%, in the normotrophic type 32%, and in the hypertrophic type 87%. The difference between each type was statistically significant (p less than 0.001).