Two-year outcome of 3D-printed acetabular cup for total hip arthroplasty in Japanese patients: a retrospective study

Three-dimensional (3D)-printed acetabular cups may enhance initial fixation and osseointegration; however, early radiographic findings warrant careful monitoring. This study evaluated short-term radiographic outcomes of an electron beam melting (EBM)–fabricated 3D-printed titanium acetabular component (GS cup) used in primary total hip arthroplasty (THA). This multicenter retrospective cohort study included 236 consecutive primary THAs performed at seven hospitals. Postoperative radiographs at approximately 2 years were analyzed (mean follow-up, 24.6 months; range, 23–31 months). The primary endpoint was the presence of a radiolucent line (RLL) in DeLee and Charnley Zone 2 at 2 years. Secondary endpoints included initial polar gaps (≥ 1 mm), gap filling, RLLs in other zones, osseointegration assessed by Moore criteria, and survivorship with acetabular component revision for any reason as the endpoint. Initial polar gaps occurred in 19/236 hips (8.1%); 14/19 (73.7%) demonstrated gap filling at follow-up. RLLs were present in 48/236 hips (20.3%) (Zone 1, 13.6%; Zone 2, 9.7%; Zone 3, 11.4%). In exploratory univariate analyses, same-diameter reaming showed lower proportions of polar gaps and Zone 2 RLLs compared with 1-mm underreaming; however, no factors remained independently associated with Zone 2 RLLs after multivariable adjustment. At follow-up, 188 cups (79.7%) demonstrated ≥ 3 Moore signs, and no acetabular component revisions occurred by the standardized 2-year assessment. In this multicenter retrospective cohort, the EBM-fabricated 3D-printed titanium acetabular component demonstrated generally favorable early radiographic findings and no acetabular component revisions at approximately 2 years. Given the retrospective design and the limited number of Zone 2 RLL events, the observed associations between surgical factors and radiographic findings should be interpreted cautiously and considered hypothesis-generating. Longer-term follow-up, ideally with comparative designs and clinical outcomes, is warranted.