Acetabular Component Positioning Using Anatomic Landmarks of the Acetabulum

Background The acetabular cup should be properly oriented to prevent dislocation and to reduce wear. However, achieving proper cup placement is challenging with potentially large variations of cup position. We propose a new technique to position the acetabular cup. Questions/Purposes We used this technique, then determined actual cup position and subsequent dislocation rate. Methods We measured acetabular abduction (alpha degrees) and anteversion (beta degrees) on preoperative CT scans in 46 patients 50 hips) scheduled for THA. During the operation, we identified the transverse acetabular notch (TAN) and anterior acetabular notch (AAN), a notch at the anterior acetabular margin. We then marked two reference points for 40 degrees abduction at the acetabular rim: the superior point, which is opposite the TAN, and the inferior point at |alpha - 40| mm inside (when alpha was > 40 degrees) or outside the TAN (when alpha was < 40 degrees). We also marked two reference points for 15 degrees anteversion: the posterior point opposite the AAN and the anterior point at |beta - 15| mm inside (when beta was < 15 degrees) or outside the AAN (when beta was > 15 degrees). During cup insertion, we aligned cup abduction to the line between the superior and inferior points and cup anteversion to the line between the anterior and posterior points. We measured cup abduction and anteversion and evaluated the dislocation rate. One patient was lost to followup before 60 months; the minimum followup for the other 45 patients was 60 months (mean, 62.8 months; range, 60-65 months). Results The mean cup abduction was 40 degrees (range, 32 degrees-47 degrees) and the mean cup anteversion was 17 degrees (range, 8 degrees-25 degrees). No dislocation occurred postoperatively in 49 hips (45 patients) for a minimum of 5 years followup. Conclusions We obtained adequate cup position with our method and none of 45 patients (49 hips) had dislocation. Level of Evidence Level IV, therapeutic study. See Guidelines for Authors for a complete description of level of evidence.