Discussion
Cement mantle thickness, aseptic loosening, cement-bone interlock, TKA
STILL
The present study showed no difference in mean MTPM between the cementless 3D-printed and cemented tibial implants at 5 years postoperatively, despite higher initial migration of the 3D-printed implant. While the cemented implant had less migration in the early postoperative period, it showed progression of migration beyond 1 year, whereas the cementless implant remained stable. Moreover, only 1 cementless implant was continuously migrating beyond 2 years versus 4 cemented implants. This was probably related to a strong implant-bone interlock in the cementless design and a less favorable cement-bone interlock in the cemented implant.Previous studies have reported excellent clinical outcomes of the 3D-printed implant at short-term and midterm follow-up, which was confirmed by our resultsTwo RSA studies with at least 5 years of follow-up using the same cemented TKA design have been performed in the same hospital as the present study (Hässleholm Hospital)Significant progression in MTPM does not directly imply a clinically relevant increase in the rate of aseptic loosening. Still, the migration of the cemented implant beyond 2 years was unexpected and warrants further research. Cement mantle thickness and proper penetration of cement into bone have been suggested to influence implant stabilityA strength of this study was the use of RSA for a highly accurate measurement of implant migration. Besides the comparison of 2 TKA designs, RSA allows for analysis of implant migration over time within 1 group. However, some limitations should be noted. The effect of the 3D-printed cementless design cannot be separated from that of the 4 additional pegs on the undersurface of the tibial plateauIn conclusion, there was no progression in MTPM for the cementless 3D-printed tibial components between 2 and 5 years, whereas the cemented components showed progression in migration. The early postoperative migration of the cementless 3D-printed TKA components occurred mainly during the first 3 months and can probably be considered physiological as part of the implant settling phase.