Measurement accuracy in acetabular cup migration. A comparison of four radiologic methods versus roentgen stereophotogrammetric analysis.

Four different methods of radiologic evaluation of the acetabular component migration following total hip arthroplasty have been compared with roentgen stereophotogrammetry, a proven highly accurate method for studying early migration. In the Sutherland and Wetherell method the implant's position is measured with a pencil and a ruler from an ordinary pelvis radiograph. New reference lines of the Wetherell method are thought to be more accurate. The Sulzer and EBRA methods are computerized. In the Sulzer method prominent bone markers are digitized and used as reference points. In the EBRA method a system of tangents on prominent pelvis structure is digitized and used to detect radiographs with similar projection. The implant's position is calculated as the mean position of similar radiographs. The Sutherland, Wetherell, and Sulzer methods had almost the same accuracy, whereas the EBRA method was more accurate and could be used for pro- and retrospective studies in a large number of patients.