A 12- to 18-year radiographic follow-up study of Charnley low-friction arthroplasty : the role of the center of rotation

In a 12- to 18-year radiographic follow-up study of 95 Charnley low-friction total hip arthroplasties (THA), there was a statistically significant correlation between location of the center of rotation of the total hip prosthesis (notably the element horizontal distance cup to tear-drop) and long-term, unfavorable, radiographic signs, such as acetabular and stem demarcation, cup wear, cup migration, subsidence of the stem, and calcar resorption. Small differences, as little as 2 mm, in the placement of the cup in relation to anatomic landmarks were responsible for these findings. A logistical regression analysis showed that the horizontal distance cup to teardrop was the most significant parameter influencing long-term unfavorable radiographic signs of a THA in comparison with the parameters of age, gender, diagnosis, and body-weight.