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Femoro-Tibial Size Mismatch Does Not Increase Polyethylene Wear in Fixed-Bearing Total Knee Arthroplasty: A Retrieval
Fabio Mancino1, Nikhil Sabharwal2, Matthew Greenaway2
1Department of Orthopaedics, Fremantle Hospital, Fremantle, Western Australia; The Orthopaedic Research Foundation of Western Australia (ORFWA), Bethesda Hospital, Claremont, Western Australia; School of Medicine, The University of Western Australia (UWA), Perth, Western Australia.
Background:
This study aimed to determine whether femoro-tibial component size mismatch in a fixed-bearing total knee arthroplasty (TKA) design is associated with increased polyethylene (PE) wear. We hypothesized that mismatched knees, particularly those with a femur greater than the tibia, would demonstrate higher PE wear.
Methods:
A retrospective retrieval analysis was performed on a fixed-bearing design revised between 2008 and 2024. Implants were categorized as matched (femur = tibia), femur (F) greater than tibia (T), or femur less than tibia. A total of 105 implants were included. The PE inserts were graded using the modified Hood scoring system. Mixed-effects models evaluated associations between mismatch and wear severity across regions and surfaces, and Cox regression analyzed time in situ.
Results:
Total PE wear did not differ between groups (mean matched 47.6 ± 23.6; F greater than T, 46.1 ± 22.6; F less than, T 51.3 ± 19.4; P = 0.81; Cohen's d < 0.20). In multilevel modeling, mismatch was not associated with overall wear (Wald Chi-square 0.42; P = 0.81). A significant surface × mismatch interaction was identified (P < 0.001): F greater than T knees exhibited greater backside wear compared with matched (P = 0.021; d approximately 0.37), but there was no increase in bearing-surface wear (P = 0.24). Time in situ (P < 0.001) and older age (P = 0.014) were the only independent predictors of wear. Burnishing, scratching, and pitting were the dominant wear mechanisms. Mismatch did not affect implant survival, with no difference in time in situ (Cox P = 0.456).
Conclusions:
Femoro-tibial size mismatch did not result in greater total or bearing-surface PE wear. The modest increase in backside wear observed in F greater than T did not translate into reduced survivorship. These findings suggest that the higher revision risk reported in mismatched TKAs may involve mechanisms beyond PE wear alone.