Customized implants for acetabular Paprosky III defects may be positioned with high accuracy in revision hip arthroplasty

Purpose In revision hip arthroplasty, custom-made implants are one option in patients with acetabular Paprosky III defects. Methods In a retrospective analysis, we identified 11 patients undergoing cup revision using a custom-made implant. The accuracy of the intended position of the implant was assessed on post-operative 3D CT and compared to the pre-operative 3D planning in terms of inclination, anteversion, and centre of rotation. In addition, the accuracy of post-operative plain radiographs for measuring implant position was evaluated in relation to the 3D CT standard. Results We found a mean deviation between the planned and the final position of the custom-made acetabular implant on 3D CT of 3.6 degrees +/- 2.8 degrees for inclination and of -1.2 degrees +/- 7.0 degrees for anteversion, respectively. Restoration of center of rotation succeeded with an accuracy of 0.3 mm +/- 3.9 mm in the mediolateral (x) direction, -1.1 mm +/- 3.8 mm in the anteroposterior (y) direction, and 0.4 mm +/- 3.2 mm in the craniocaudal (z) direction. The accuracy of the post-operative plain radiographs in measuring the position of the custom-made implant in relation to 3D CT was 1.1 degrees +/- 1.7 degrees for implant inclination, -2.6 degrees +/- 1.3 degrees for anteversion and 1.3 mm +/- 3.5 mm in the x-direction, and -0.9 mm +/- 3.8 mm in the z-direction for centre of rotation. Conclusion Custom-made acetabular implants can be positioned with good accuracy in Paprosky III defects according to the preoperative planning. Plain radiographs are adequate for assessing implant position in routine follow-up.