FEMORAL AND TIBIAL COMPONENT MISMATCH DOES NOT INCREASE RISK OF REVISION WHEN THE INSERT MATCHES THE FEMUR IN PRIMARY FIXED BEARING TOTAL KNEE ARTHROPLASTY: AN AOANJRR ANALYSIS

Background Femoral and tibial components in primary total knee arthroplasty (TKA) are sized independently to satisfy the goal of bone coverage whilst optimising flexion extension space balancing and patellofemoral tracking. Two highly used prostheses, with excellent survivorship, have reported increased revision risk when femoral tibial mismatch occurs, even within the manufacturers size compatibility recommendations. The aim of this study was to compare the risk of revision with femoral and tibial component size mismatching with a TKA design where the insert always matches the femoral component. Methods We analysed 17,510 primary, cruciate-retaining, fixed-bearing Attune TKA procedures recorded by the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) from February 2013 to October 2025 to investigate all-cause revision risk for matched and mismatched component combinations. Data used in this abstract were validated and cleaned on the Annual Report level up to 31/12/2024; data for procedures after this date were cleaned and matched with the revision procedures but are not matched against mortality data. Standard AOANJRR methods were utilised for analyses. Results Mismatched component combinations were present in 58.2% of procedures. Compared with matched component combinations, mismatched combinations had a similar CPR at 10 years (Size Matching − 3.6% (3.1, 4.2), Size Mismatch − 3.5% (3.1, 4.0)) and were not associated with an increased risk of all-cause revision (Size Match versus Size Mismatch-HR 1.07; 95% CI 0.89 to 1.30; P = 0.461). No statistically significant differences in the risk of revision for loosening or instability were observed between the matched and mismatched groups. In subgroup analyses, neither femoral size greater than tibial size nor femoral size less than tibial size demonstrated a statistically significant increased risk of revision. Conclusion In this AOANJRR analysis of a cemented fixed-bearing cruciate-retaining TKA, where the insert matches the femoral component size, mismatched femoral and tibial component size was not associated with an increased risk of all-cause revision, loosening or instability. These findings differ from previous reports in systems where mismatch occurs at the femoral-polyethylene articulation, suggesting that the clinical implications of size mismatch may depend on prosthesis specific articular design.