Continuous periprosthetic bone loss around the TOP® cup and inferior survival rate at an 8-year follow-up: a prospective cohort study

Abstract

Abstract Background The trabeculae-oriented pattern (TOP®) cup was designed to minimize acetabular periprosthetic bone loss. In our previous prospective study comprising 30 patients with a two-year follow-up we found a substantial decrease in periprosthetic bone mineral density (pBMD) in the proximal and medial regions of the TOP cup. The present study aims to investigate pBMD changes in the mid-term and how this affects implant survival. Methods We followed the previous cohort and estimated implant survival by Kaplan-Meier analysis, evaluated pBMD with dual-energy X-ray absorptiometry (DXA) and clinical outcome using the Harris Hip Score (HHS). Results Mean follow-up was 8.6 (range 7.8–9.1) years. The eight-year implant survival rate for cup revision for all reasons was 83% (95% confidence interval {CI}: 70–97) and 86% (CI: 74–99) when cup revision due to aseptic loosening was the endpoint. Mean HHS at eight years was 95 (range 77–100). A further 12% (CI: 5–17) loss in pBMD was detected in the proximal Digas zone 1 and 12% (CI: 7–17) loss in Digas zone 2 also between two and eight years after surgery. pBMD continued to decrease up to 30% (CI: 24–36) in Digas zones 1, 2 and 3 compared to pBMD immediately postoperatively. Conclusions The TOP cup shows inferior mid-term survival rates compared to other uncemented cups, as well as a continuous decrease in pBMD. Periprosthetic bone loss cannot be prevented by this uncemented cup. Clinical trial number Not applicable.

Keywords

• Uncemented THA
• Cup
• DXA
• Prospective study
• TOP cup