Asymmetric Metaphyseal Cones for AORI Type 2 Medial Defects in Tibial Plateau Fractures during Acute TKA

This finite element study evaluated the biomechanical performance of asymmetric metaphyseal cones in large Type 2a/b medial tibial defects simulating medial tibial plateau fractures during acute total knee arthroplasty, to determine thresholds for safe clinical application. A finite element model of a tibia with tibial baseplate, asymmetric metaphyseal cone, and short cemented stem was utilised. Sixteen medial fracture patterns (AORI Type 2a/b defects) were simulated with unsupported surface area ratios from 0% to 60%. Two physiological loading scenarios (walking and stair descending) were applied. Implant stability was evaluated through tangential and normal micromotions at the bone-cone coating interface, with thresholds of 150 μm for osseointegration and 50 μm for long-term stability. Bone mechanical response was quantified through principal strain distributions. Tangential and normal micromotions increased with defect size but remained below critical thresholds, with maximum tangential micromotion of 36 μm during stair descending at a 60% ratio. Micromotions and bone strain demonstrated a threshold effect at approximately 52% ratio, beyond which both parameters increased substantially. At a 60% ratio during stair descending, 0.11% and 0.12% of bone volume exceeded tension and compression thresholds, respectively. Asymmetric metaphyseal cones maintain sufficient stability for managing medial tibial plateau fractures during acute total knee arthroplasty, with interface micromotion below critical thresholds even in severe defects. The recommended maximum unsupported area ratio is 52%, providing a clear quantitative threshold for clinical decision-making.