How do 3D-printed primary uncemented acetabular components compare with established uncemented acetabular cups? The experience of the New Zealand National Joint Registry

Background: 3D-printed or additive manufactured acetabular implants are an exciting new technology being used in hip surgery with increasing frequency especially in complex acetabular reconstructions. However, the performance of acetabular components produced by this method for primary THR is unknown. Methods: 41,272 uncemented cups in primary THR for OA were identified in the NZJR for the purposed of this study. There were 39,080 uncemented cups in the control group (15,798 Pinnacle cups, 12,724 Trident cups and 10,558 RM Pressfit cups) compared to 2192 3D-printed uncemented implants (1397 Delta TT cups, 640 Ti Por and 155 Polymax cups). All-cause revision rates and reasons for revision were examined. Kaplan-Meier survival analysis was performed. Results: 3D-printed cups were inserted into younger, fitter patients with a higher mean BMI compared to those in the control group (p < 0.001). The overall all-cause revision rate for 3D-printed cups was not significantly different to the controls: 0.77/100 cys (95% CI 0.59-1) compared to 0.55/100 cys (95% CI 0.52-0.58) in the control group (p = 0.058, Hazards ratio 1.29, 95% CI 0.992-1.678). There was no difference in aseptic cup loosening or deep infection rates between either group or indeed individual implant designs. Conclusions: 3D-printed uncemented cups provide reliable survivorship and clinical results in primary THR comparable to established designs manufactured by traditional means. The theoretical concerns of increased rates of fatigue failure or deep infection are unsubstantiated.