Polished trays reduce backside wear independent of post location in posterior-stabilized TKAs

Abstract

Background: Backside damage of the polyethylene in TKA is a potential source of debris. The location of the tibial post in posterior-stabilized implants may influence micromotion, and thus affect backside damage, as may surface roughness.

Questions: We used implant retrieval analysis to (1) examine if there were differences in backside damage among three modern posterior-stabilized implants attributable to variable surface roughness; (2) determine if the location of damage on the tibial post affected the pattern of backside damage; and (3) determine if demographics influenced backside damage.

Methods: We identified 403 posterior-stabilized tibial retrieved inserts (147 NexGen(®), 152 Optetrak(®), 104 Genesis(®) II). The damage on the surfaces of the tibial posts was previously graded. The backside of the inserts (divided into quadrants) were scored for evidence of damage. The total quadrant damage was compared for each implant group, the relationship between post face damage and location of damage on the backside was determined for each implant group, and total backside damage was compared among the three implant groups.

Results: No correlation was found between the location of damage on the post and location of damage on the backside of the implant for any of the three groups. The Genesis(®) II polyethylene implants, which articulate with a highly polished tibial tray, showed a significantly lower total backside damage score (p < 0.01) when compared with the other two implant groups. The Genesis(®) II and Optetrak(®) showed significantly more damage in the posterior quadrants of the implants (p < 0.01) when compared with the anterior quadrants. A linear regression analysis revealed that lower tibial tray surface roughness was correlated with decreased damage.

Conclusions: An implant design with a highly polished tibial tray was associated with decreased backside damage. However, tibial post design and location did not influence the location of backside damage.

Clinical relevance: Our study showed that a highly polished tibial tray was associated with decreased damage to the backside of polyethylene inserts independent of post design and location. These findings should be taken into consideration when new generations of implants are designed.

Fig. 1

The mean damage scores for the post and backside surfaces of the three groups of posterior stabilized TKA retrieved tibial inserts are shown. The error bars denote SDs. The backside scores for the Genesis^® II inserts were significantly lower (p < 0.01) than those of the other two designs.

Fig. 2

Backside damage scores for the three implant designs varied based on quadrant. The Genesis^® II and Optetrak^® inserts had significantly higher damage (p > 0.05) in the posteromedial quadrant relative to the anteromedial and anterolateral quadrants. Implants from both designs also showed significantly greater damage in the posterolateral quadrant compared with the anterolateral quadrant. In the Genesis^® II group, the anteromedial quadrant also showed significantly greater damage compared with the anterolateral quadrant. There were no significant differences between quadrants in the NexGen^® implant group.