Accuracy of cup placement in total hip arthroplasty by means of a mechanical positioning device: a comprehensive cadaveric 3d analysis of 16 specimens

Introduction: We tested whether a mechanical device (such as Hipsecure) to pinpoint the anterior pelvic plane (APP) as a guide can improve acetabular cup placement. To assess accuracy we asked: (1) is the APP an effective guide to position acetabular cup placement within acceptable degrees of divergence from the optimal 40 degrees inclination and 15 degrees anteversion; (2) could a mechanical device increase the number of acetabular cup placements within Lewinnek's safe zone (i.e. inclination 30 degrees to 50 degrees; anteversion 5 degrees to 25 degrees)? Methods: 16 cadaveric specimens were used to assess the 3D surgical success of using a mechanical device APP to guide acetabular cup placement along the APP. We used the Hipsecure mechanical device to implant acetabular cups at 40 degrees inclination and 15 degrees anteversion. Subequently, all cadaveric specimens with implants were scanned with a CT and 3D models were created of the pelvis and acetabular cups to assess the outcome in terms of Lewinnek's safe zones. Results: The mean inclination of the 16 implants was 40.6 degrees (95% CI, 37.7-43.4) and the mean anteversion angle was 13.4 degrees (95% CI, 10.7-16.1). All 16 cup placements were within Lewinnek's safe zone for inclination (between 30 degrees and 50 degrees) and all but 2 were within Lewinnek's safe zone for anteversion (between 5 degrees and 25 degrees). Conclusion: In cadaveric specimens, the use of a mechanical device and the APP as a guide for acetabular cup placement resulted in good positioning with respect to both of Lewinnek's safe zones.