The effect of polyethylene thickness on revision rates of contemporary cruciate retaining knee replacements. A registry analysis.

BACKGROUND

An attribute that may influence knee replacement survivorship is tibial polyethylene (PE) insert thickness. Previous studies have suggested thin polyethylene made from ultra-high molecular weight polyethylene (UHMWPE) leads to higher rates of revision surgery. This study aimed to determine if modern polyethylene thickness is associated with altered survivorship of primary total knee arthroplasty (TKA) procedures.

METHODS

A retrospective analysis of data from Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) was done on well performing total knee arthroplasty prostheses used in Australia from 1999-2018. Six of the best performing minimally stabilized prostheses were examined and categorized into three PE thickness subgroups: A (≤10 mm), B (11-14 mm) and C (≥15 mm). There were 185,539 TKA procedures, of which 64.3% (n = 119,382) were ≤ 10 mm, 33.5% (n = 62,173) 11-14 mm, and 2.2% (n = 3984) ≥ 15 mm. Differences in revision rates were analysed for all causes, including loosening, wear, and instability.

RESULTS

At 14 years, respective cumulative point revision (CPR) was A: 4.8, B: 4.2 and C: 6.0. The thickest polyethylene group (≥15 mm) had a higher rate of revision for any reason compared to both 11-14 mm and ≤ 10 mm groups. When non-XLPE was analysed the ≤ 10 mm group had higher rates of revision compared to the 11-14 mm group, but this difference was not seen with XLPE.

CONCLUSION

Higher rates of revision were seen overall in the thicker PE group (≥15 mm). This group also had higher rates of revision for loosening, instability, and infection. The use of a thicker insert may be a sign of surgical complexity, but is associated with increased revision.