Three finned press-fit cup: Does its initial fixation strength provide an adequate stability? Clinical midterm results of 685 implants

Introduction: One of the major causes of loosening of cementless acetabular cup implants is insufficient initial stability. A technical proposal to decrease the risk of suboptimal first stability is a circumferential finned design of the cup. This design aims to improve periacetabular bone contact and prevent rotational micromotion of the cup when optimal press-fit cannot be obtained. Materials and Methods: We retrospectively reviewed a group of 712 consecutive patients who underwent total hip arthroplasty from June 2006 to June 2014. In all patients, a titanium cup, characterized by three anti-rotational circumferential fins at the superior pole, was implanted. Results: Five hundred and ninety-two patients, for a total of 685 hips, were evaluated at a mean follow-up of 58 months (range 12-96 months). At 1-year follow-up, the average score increased to 82.90 (range 100-70) and at the final follow-up (58 months, range 12-96 months), it was 80.12 (range 100-66). In 22 cases (3%), screws to obtain a secure primary stability of the cup were used. Nineteen complications (2.6%) needing revision surgery were observed. Survivorship at 10 years was 98.7% (95% confidence interval [CI], 98.7-99.7%) with revision for aseptic cup loosening as an endpoint and 96.7% (95% CI, 98.3-95.1%) with revision for all causes of revision as the second endpoint. Discussion: In our group of patients, we did not observe the cases of very early cup loosening. The only two-cup revision, do to loosening of osteolysis, was observed 26 and 32 months before surgery. Conclusion: Our very low rate of additional screws represents an indirect sign of finned cup first stability. Three-finned cup design clinically confirmed to improve initial cup stability.