Abstract
A modular tibial insert exchange is a seemingly attractive benign and simple surgical alternative when compared to full knee revision. Unfortunately, the results have been less than satisfactory with modular insert exchange for polyethylene wear and knee instability. Babis et al reported the results of 56 isolated insert exchanges performed for wear or instability. The re-revision rate was 25% at a mean follow-up of 3-years and the cumulative survival rate was only 63.5% at 5.5 years. In another study, 27% (6/22) insert exchanges for wear required re-revision within 5 years. Bert et al reported scoring and damage in 89% of 55 retained components considered candidates for isolated insert exchange. Such damage could account for accelerated wear of a new insert.
These studies are misleading. The new insert must be polyethylene not prone to oxidation and accelerated wear. In a recent study of 177 revisions for wear and osteolysis, the survivorship of insert exchange using non-irradiated poly was 100%. Insert exchange does not correct the problem of a poor tibial locking mechanism. Whiteside and Katerberg reported 3 failures in 49 insert exchanges, fabrication of the tibial locking mechanism was used to address this problem. With revision for instability, insert exchange must provide full stability in both flexion and extension.
Tibial insert exchange must correct the underlying cause of failure that led to the revision surgery. Full knee revision is a complex procedure that brings with it increased risks of perioperative complications such as infection and should be reserved only for cases that will not do well with simple insert exchange.
