Biomechanical study of using patient-specific diaphyseal femoral cone in revision total knee arthroplasty (rTKA)

Background: The primary objective of revision total knee surgery is to achieve solid bone fixation. Generally, this could be accomplished using sleeves and long stems, which require substantial remaining bone stock and may increase the risk of stem tip pain. An alternative approach involves the use of customized diaphyseal cones, which can preserve the integrity of the bone canal. This study evaluates the impact of employing femoral diaphyseal cones with various stem lengths on stress distribution and relative motion. Methods: CT scan data from five patients were used to generate the 3D model of the femur, cement, customized stems, and cones, along with assigning patient-specific material for each candidate's femur. Three different stem lengths, both with and without the customized cone, were assessed under three gait loading conditions to compare the resulting Von Mises stress distribution and relative motion. Results: Analysis indicated that the use of customized femoral cones moderately increases stress distribution values up to 30 % while significantly reducing relative motion at the femoral canal-cone interface by nearly 60 %. The presence of the cone did not significantly alter relative motion with varying stem lengths, although stem length variation without a cone substantially affected these values. Conclusion: Incorporating cones alongside stems enhances metaphyseal fixation, reduces stress shielding, potentially allowing for the use of shorter stems. Furthermore, cones promote osseointegration by minimizing relative motion, ultimately improving prosthetic stability.