EVALUATION OF MATERIAL LOSS IN FIXED-BEARING UNICOMPARTMENTAL KNEE ARTHROPLASTY POLYETHYLENE INSERTS

Objectives Unicompartmental knee replacement (UKR) is a conservative option for degenerative disease, with mobile (Oxford UKR) and fixed bearing (Physica ZUK) the most commonly used devices. The primary reasons for revising UKRs include disease progression (36.9%), loosening (31.7%), and pain (7.5%). Loosening typically occurs due to osteolysis caused by wear particles from the polyethylene (PE) inserts. There is limited published literature which has quantified volumetric material loss from the PE inserts of cemented fixed-bearing UKRs. This study aimed to quantify bearing wear and backside deformation of these PE components. Design and Methods At our national retrieval centre, we measured changes volumetric bearing wear and backside deformation of 31 explanted fixed-bearing Physica ZUK UKR PE inserts using a peer-reviewed methodology based on coordinate measuring machine analysis. These explants had been revised for any indication [Females (19) and Males (12)]. The location of the wear scars was identified and mapped. We compared the volumetric wear from the bearing surface with contemporary total knee replacement (TKR) inserts. Results The median (IQR) total volumetric wear of the UKR PEs [96(50-152) mm 3 ] was significantly higher (p<0.001) than contemporary TKR PEs [40 (24-83) mm 3 ]. The median (IQR) total volumetric wear of the PEs in males [148(122-200) mm 3 ] was significantly higher(p=0.016) than in females [56(61-119) mm 3 ]. The wear scars were situated in the anterior third in 61% of cases, with 26% located posteriorly. Examination of the PE backside surfaces exhibited damage in the area directly inferior to the bearing surface wear scar in the majority of cases. Conclusion In conclusion, this study highlights significant PE wear of Physica ZUK UKR inserts, with higher wear rates compared to contemporary TKR inserts, particularly in males.