The effect of constraint on post damage in total knee arthroplasty: posterior stabilized vs posterior stabilized constrained inserts

Posterior stabilized constrained (PSC) inserts are intended to provide greater varus-valgus and rotational constraint than conventional PS inserts. We determined whether the added constraint resulted in more damage to the post in PSC compared to PS inserts. Retrieved PSC inserts were matched to retrieved PS inserts from the same manufacturer according to patient age, body mass index, and length of implantation. Surface damage was visually assessed, and 3-D surface deviation from pristine was measured. Damage scores for the PSC posts were significantly greater than those of the PS posts. Surface deviation was significantly greater in the posterior and medial post regions of the PSC inserts. Based on short-term follow-up, our results suggest that added constraint is accompanied by greater polyethylene surface damage.