Hip Resurfacing Implant Orientation Analysis: A Comparison of a Computer-Added Design Technique and Computed Tomography.

BACKGROUND: Accurate acetabular component orientation in hip resurfacing is mandatory. The aim of this study is to analyze if interpretation of pelvic radiographs with computer-added design (CAD) software is comparable to computed tomography (CT) in measurement of acetabular anteversion and inclination of a Birmingham Hip Resurfacing (BHR) hip. METHODS: A consecutive series of 49 patients (50 hips) who underwent hip resurfacing arthroplasty between 2005 and 2007 with the BHR system were retrospectively included. The surgical procedure was performed by 1 orthopedic surgeon in the beginning of his learning curve. Computer-added design software was used to measure acetabular component orientation on an anteroposterior pelvic radiograph. These measurements were compared with CT measurements. We calculated the correlation between the CAD software and CT analysis. The degree of underestimation or overestimation was determined, and a Bland-Altman plot was created to visualize the agreement between CAD software and CT results. RESULTS: We analyzed 50 BHR hips with mean inclination of 54.6° and 55.6° and mean anteversion of 24.8° and 13.3° measured by CT and CAD, respectively. Pearson correlation coefficient for inclination was 0.69 (P < .001) and for anteversion 0.81 (P < .001). Computer-added design showed a mean underestimated anteversion of 11.6° (P < .001). There was no significant underestimation or overestimation of inclination with CAD analysis compared to CT measurements. CONCLUSION: The CAD software is useful to assess acetabular inclination in hip resurfacing but underestimates anteversion.