Acetabular Component Positioning Using Anatomic Landmarks of the Acetabulum

Abstract

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 (a°) and anteversion (b°) 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°abduction at the acetabular rim: the superior point, which is opposite the TAN, and the inferior point at |a À 40| mm inside (when a was [ 40°) or outside the TAN (when a was \ 40°). We also marked two reference points for 15°anteversion: the posterior point opposite the AAN and the anterior point at |b À 15| mm inside (when b was \ 15°) or outside the AAN (when b was [ 15°). 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°(range, 32°-47°) and the mean cup anteversion was 17°(range, 8°-25°). No dislocation occurred postoperatively in 49 hips (45 patients) for a minimum of 5 years followup.

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“…We set the goal of cup position at 40° abduction and 15° anteversion as suggested by Lewinnek et al 13) The acetabular cup was positioned according to the method described by Ha et al 12) Before implantation of the final prosthesis, trial prostheses were implanted and we tested their stability. In case of instability, abduction and anteversion of the acetabular component were adjusted to a more stable position.…”