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.

Implant wear and osteolysis have been a major cause of failure of total knee implants. In the mid-1990s, manufacturers recognised the impact of oxidation on wear with implants sterilised by gamma irradiation in air and changed their methods of sterilisation. This has resulted in a dramatic reduction in wear. In retrieval studies, non-irradiated polyethylene has not shown the fatigue type of failure associated with oxidation. The percentage of revisions done at the Anderson Clinic for polyethylene wear for osteolysis has dropped from 44% in the late 1990s to 4% in the past decade. With the continued use of polyethylene free of oxidation, we anticipate a further reduction in the need for revision surgery secondary to wear and osteolysis.

Highly cross-linked polyethylene was introduced to further reduce wear with total knee implants. Higher levels of irradiation used increases crosslinking in the polyethylene but the material strength is reduced. Although volumetric wear is reduced, the wear particles are smaller in size and potentially more bio-reactive. The Manufacturer And User Device Experience Database (MAUDE) reports describe early implant breakage and osteolysis of highly cross-linked polyethylene inserts. Implants that were highly crosslinked with quenched free radicals demonstrate increased levels of oxidation after retrieval unlike, never implanted components “off-the-shelf”. Backside wear remains a concern as non-modular implants have better long-term survivorship compared to their modular counterparts. These reports should temper enthusiasm for using highly cross-linked material in knees or modular tibial components until longer term clinical and retrieval studies have been completed.