Influence of varying stem and metaphyseal sleeve size on the primary stability of cementless revision tibial trays used to reconstruct AORI IIA defects. A simulation study.

Traditionally, diaphyseal stems have been utilized to augment the stability of revision total knee replacement (rTKR) implants. More recently metaphyseal augments, such as sleeves, have been introduced to further augment component fixation. The effect of augments such as stems and sleeves have on the primary stability of a rTKR implant is poorly understood, however it has important implications on the complexity, costs and survivorship of the procedure. Finite element analysis was used to investigate the primary stability and strain distribution of various size stems and sleeves used in conjunction with a cementless revision tibial tray. The model was built from computer tomography images of a single healthy tibia obtained from an 81-year-old patient to which an Anderson Orthopaedic Research Institute (AORI) IIA defect was virtually added. The influences of varying body mass index (BMI) and bone modulus were also investigated. Stemless sleeves were found to provided adequate primary implant stability (average implant micro-motion <50 μm) for the studied defect. Addition of a stem did not enhance the primary stability. Furthermore, this study found that varying BMI and bone modulus had a considerable effect on strain distribution but negligible effect on micro-motion in the sleeve area. In conclusion, the addition of diaphyseal stem to a metaphyseal sleeve had little benefit in enhancing the primary stability of tibial trays augmented when simulating reconstructions of AORI IIA tibial defects. Additional studies are required to determine the relative benefit of the diaphyseal stem when using metaphyseal sleeves defects with more extensive bone loss. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1876-1886, 2018.