Abstract
Questions/purposes:
What factors influence tibial tray-cement interface bond strength? We developed a laboratory model to investigate this issue with the goal of providing technical recommendations to mitigate the risk of tibial tray-cement loosening.
Methods:
Forty-eight size 4 Triathlon® tibial trays were cemented into an acrylic holder using two different cements: Simplex® and Palacos®; three different cementing times: early (low viscosity), per manufacturer (normal, medium viscosity), and late (high viscosity); two different cementation techniques: cementing tibial plateau only and cementing tibial plateau and keel; and two different fat (marrow) contamination conditions: metal/cement interface and cement/cement interface. A push-out test was applied at a velocity of 0.05 mm/s, and the load recorded continuously throughout the test at a rate of 10 Hz. The test was stopped when the plate debonded from the cement (i.e. the tray visibly separated from the acrylic support and the load dropped substantially). Statistical analysis was performed using Welch's t-tests and Cohen's d tests.
Results:
Compared to cementing under manufacturer-recommended conditions (normal), late cementing reduced the interface strength of Simplex™ by 47%. Early cementing increased interface strength of Simplex by 48% and Palacos by 139%. Cementing the keel increased the bond strength of Simplex™ 153% and Palacos™ 243% and over the respective normal cementing of the plateau only. Fat contamination of the metal-cement interface reduced the interface strength to practically zero (−99% Simplex and −91% Palacos), but by adding cement to the underside of the tibial tray prior to an insertion resulting in fat contamination, this was reduced to −65% in Simplex (the difference in strength between normal and fat contamination with the underside cemented was not statistically significant in Palacos).
Conclusions:
Under laboratory conditions, a clean tibial tray-cement interface is strong, but much stronger when the keel is cemented. Earlier application of the cement to metal increases bond strength while later application reduces bond strength. Fat contamination of the tibial tray-cement interface reduces bond strength, but application of cement to the underside of the tibial tray prior to insertion substantially mitigates this.
Clinical relevance: To maximize tibial tray-cement bond strength, 1) apply cement to the component soon after mixing, 2) thoroughly dry the entire tibial interface (plateau and keel), and 3) cement the keel as well as the plateau. These results suggest that clinical loosening at the tibial tray-cement interface can result from too late application of cement to the tray, and/or interface contamination by marrow or other fluid (blood or saline). The surgeon should consider applying cement to the undersurface of the component soon after mixing (while tacky). Cement placed into the keel region may also reduce the potential for marrow or other fluid contamination of the interface.
