Custom-made acetabular implants for revision total hip arthroplasty: postoperative evaluation of the accuracy of implant positioning

BACKGROUND: The increasing need for revision total hip arthroplasty due to complications such as bone defects following implant loosening has - among others - led to the development of custom-made acetabular implants. This study evaluated the accuracy of implant positioning measured on AP radiographs and the respective clinical outcomes. METHODS: A retrospective analysis of 31 cases involving severe acetabular bone loss (Paprosky type IIIa/ IIIb) was conducted. Preoperative planning was based on CT scans, and postoperative evaluation was performed via AP radiographs, focusing on Lewinnek's safe zone for anteversion (AV) and inclination (INCL). RESULTS: Results showed that 87.1% of the implants were positioned within or on the border of Lewinnek's safe zone for AV and INCL. Mean AV (SD) was 13.9° (8.7°), mean INCL (SD) 46.9° (6.1°). Mean deviations between planning and postoperative results were 7.4° for AV (SD) (5.5°; p = 0.704) and 3.7° for INCL (SD) (5.2°; p = 0.068). Implant survival was 96.7% over a median follow-up (IQR) of 43.0 months (65.0). CONCLUSIONS: Correct positioning of customized acetabular implants could be achieved via assessment on plain AP radiographs using a superimposition method. The results were further emphasized by the low rate of mechanical complications and high implant survival. Lewinnek's safe zone is a good guideline for proper cup positioning but should not be prioritized over primary stability of the implant. Accurate planning is key to achieving both a satisfying position and sufficient osseous integration. Further research involving higher case numbers through a multi-center approach is needed to draw definitive conclusions.