Patient specific cup anteversion in total hip arthroplasty: a computed tomography study investigating the use of the transverse acetabular ligament to control cup placement

Background Ensuring optimal position of the acetabular component during total hip arthroplasty is a complex problem. Although computer assisted techniques have been developed to achieve this, these systems may result in improper cup alignment caused by errors in registration of the anterior pelvic plane. Furthermore, set goals for cup placement do not reflect the variation in acetabular morphology. Aneed exists to developamethodfor cuppositioning that is patient specific and eliminates the need to register the anterior pelvic plane. It is our hypothesis that the transverse acetabular ligament can be used to do this. The objective of this study was to define the version of acetabular components placed using this technique. Methods In this series of 40 consecutive primary hip replacements, the transverse acetabular ligament was used as the sole method to define cup version. Postoperative CT scans of the pelvis were analyzed tomeasure the anteversion of the acetabular component. Results At a minimum follow-up of 12 months (range 12-18 months), none of the hips dislocated. Using the transverse acetabular ligament as the sole method to control the version of the acetabular component resulted in an average radiographic anteversion of 19.78 +/- 8.18 (mean +/- standard deviation) which equates to an operative anteversion of 28.18 +/- 11.38 (mean +/- standard deviation). Conclusions This paper highlights the variation in cup version when the transverse acetabular ligament is used to establish and control cup placement. This questions the one-size-fits-all philosophy of a set goal for cup positioning.