Tibial revision knee arthroplasty: influence of modular stems on implant fixation and bone flexibility in AORI Type T2a defects.

BACKGROUND: Due to the varying bone defects presented to surgeons during revision total knee arthroplasty, modular implant systems are preferred over standard implant designs. However, every implant combination (sleeves, stems and augments) can affect the fixation in different ways and thus influence the long-term outcome. We therefore aimed to analyze the effect of large metaphyseal sleeves with and without short modular stems on implant fixation and bone flexibility of a modular tibial revision knee system.

METHODS: A new tibial revision implant (Attune RP Revision; DePuy Synthes) with a sleeve was compared to a sleeve/stem combination implanted in synthetic bones with Anderson Orthopaedic Research Institute (AORI) Type T2a defects and also compared to an intact bone. Implant-bone-interface micromotions and bone deformations during standardized load application were measured using a digital image correlation system.

RESULTS: The lowest relative micromotions were measured more distally for stemmed implants, and more proximally for the stemless group. When compared to an intact bone, there is increased proximal bone deformation in the stemless group.

CONCLUSIONS: Using a short stem in addition to a tibial revision implant with a metaphyseal sleeve in a moderate bone defect provides for more natural bone deformation. Although the main fixation area was shifted distally, relative micromotions were reduced. Based on this biomechanical study, the use of diaphyseal short stems with metaphyseal sleeves seems to be beneficial in terms of the initial implant fixation and for its flexibility, which is similar to that of intact bones in the case of AORI T2a defects.