Background

An attribute that may influence knee replacement survivorship is the thickness of the tibial polyethylene (PE) insert. Previous studies have observed use of thin polyethylene made from ultra-high molecular weight polyethylene (UHMWPE) leads to a higher rate of revision surgery. The aim of this study was to determine if the thickness of modern polyethylene is associated with altered survivorship of primary total knee arthroplasty (TKA) procedures.

Methods

We used data from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) for knee replacement procedures and compared three groups based on PE thickness (=10mm, 11-14mm and =15mm). The study included the six primary total knee prosthesis combinations with the lowest 10-year cumulative percent revision (CPR) using minimally stabilised (MS) fixed bearings undertaken for osteoarthritis that were recorded by the Registry from September 1999 to December 2018. There were 185,539 TKA procedures of which 64.3% (n=119,382) were =10mm PE thickness, 33.5% (n=62,173) 11-14mm, and 2.2% (n=3984) were =15mm. Rates of revision for all causes, as well as revision for loosening, wear and instability were compared. A sub-analysis for polyethylene type (cross-linked polyethylene (XLPE) and non cross-linked polyethylene (non XLPE)) was also performed.

Results

The group with the thickest polyethylene (=15mm) had a higher rate of revision for any reason compared to both the 11-14mm group and the =10mm group. There were also higher rates of revision in the =15mm group for loosening and particularly instability, but there were too few revisions for wear in this group for analysis. When non-XLPE was analysed the =10mm group had a higher rate of revision compared to the 11-14mm group, but this difference was not seen with XLPE.

Conclusion

Higher rates of revision were seen overall in the thicker PE group (=15mm). The =15mm PE group also had higher rates of revision for loosening and instability. Thin non-XLPE inserts were associated with a higher rate of revision, but not thin XLPE inserts. The use of a thicker insert may be a sign of surgical complexity, but is associated with increased revision.