Porous tantalum versus titanium-coated acetabular cups in total hip arthroplasty: Midterm radiological evidence of supralateral bone defect filling without grafting

Purpose Like bone formation, porous tantalum (Ta) for total hip arthroplasty (THA) improves both initial stability and secondary biological fixation compared with porous titanium (Ti). The authors have occasionally observed new bone formation filling the cavity between the acetabular cup and acetabular bone in the supralateral part over time. This study aimed to investigate whether an improvement in bone coverage of the Ta cup was observed over time compared with that of the Ti cup. Methods This study included 223 patients (223 hips) with hip osteoarthritis who underwent primary THA using either a Ta or Ti cup. Host bone coverage of the acetabular cup was examined on radiographs using the cup center-edge (CE) angle and bone coverage index (BCI). Radiologically measured cup inclination (RI) was also measured. Results At 5 years, the mean cup CE angle was 35.3 ​± ​7.5° for Ti and 37.4 ​± ​7.1° for TA ( p ​= ​0.036), and the BCI was 90.8 ​± ​5.4% and 92.6 ​± ​6.6, respectively ( p ​= ​0.033). The improvement rates from 2 years to 5 years and from baseline to 5 years were statistically significantly greater in the Ta group than in the Ti group. In the multiple regression analysis, BCI at baseline ( p ​< ​0.0001), Ta ( p ​= ​0.018), and RI ( p ​= ​0.018) were significant predictors of BCI improvement 2–5 years later. Conclusions Filling the bone deficit in the lateral part of the cup without a bone graft over time had an advantage in the Ta cup over the Ti cup, which may enhance long-term survival. Additionally, RI and BCI were identified as important factors.