Introduction: Revision total hip arthroplasty (THA) can be challenging in patients with severe acetabular bone defects and there is no consensus on the preferred reconstruction technique in this population. The aim of this study is to determine the biomechanical differences between Trabecular Metal Acetabular Revision System (TMARS) and Custom Triflange Acetabular Component (CTAC), in patients with Paprosky grade IIIB acetabular bone defects. Methods: A retrospective study with patients undergoing revision THA surgery TMARS was conducted. For all these patients a virtual CTAC was designed. With this, the TMARS reconstruction could be compared with the virtual CTAC. Assessments of both implants included cortical and cancellous bone contact, center of rotation (COR), inclination, anteversion, and reamed bone volume. Results: The mean bone contact was 5760 mm2 vs 5447 mm2 for TMARS and CTAC respectively. The TMARS showed significantly more cancellous bone contact than the CTAC (4966 mm2 vs 2887 mm2) and less cortical contact (795 mm2 vs 2560 mm2). The TMARS COR was significantly deviated in the medial-lateral direction compared to the CTAC, with a mean difference of 7.4 mm in lateral direction. TMARS showed a significantly greater reamed bone volume with a mean of 15997 mm3 for TMARS and 2292 mm3 for CTAC. Conclusion: A semi-automatic method was designed for the determination of the biomechanical differences between TMARS and CTAC reconstructions. TMARS showed significant more cancellous bone contact, but also significant greater reamed bone volume with respect to CTAC. Furthermore, the TMARS COR was localized significantly more lateral compared to CTAC.

Introduction In recent years, there has been an increasing interest in custom triflange acetabular components (CTAC) for revision and oncological surgery. The aim of this study was to evaluate the surgical accuracy of positioning CTACs in patients receiving either total hip arthroplasty (THA) revision or tumor resection surgery, using a novel 3D analyzing technique. Method This retrospective cohort study included 35 patients (27 tumor and 8 THA revision cases), between February 2017 and March 2021. All patients received a CTAC. The planned and achieved implant position were assessed by means of a developed semi-automatic 3D-CT assessment method. The primary outcomes were the cup angles described as inclination, anteversion and cup rotation, and the translation of center of rotation (COR), pubic flange, ischial flange and ilium flange in three planes. Results The mean deviation, between planned and achieved, in inclination was 0.5° (SD: 3.9°), in anteversion 1.2° (SD: 6.1°) and in cup rotation 0.6° (SD: 3.2°). The mean deviation in COR in the sagittal plane was -0.8 mm (SD: 3.2), in the coronal plane -0.4 mm (SD: 6.3) and in the axial plane 0,6 mm (SD: 6,1). Translation of the ischial flange showed the largest aberration (median absolute value: 7.0 mm), followed by the pubic flange (6.4 mm) and the ilium flange (5.3 mm). Discussion A semi-automatic method to analyze the 3D position of CTAC was presented in this study. The results show good agreement between the planned and achieved implant position in patients receiving THA revision or tumor resection surgery. 89% of the components in this study were accurately positioned according to our criteria.