Perillo-Marcone, A. and Taylor, M.
Effect of varus/valgus malalignment on bone strains in the proximal tibia after TKR: an explicit finite element study
Journal of Biomechanical Engineering, 129, (1), . (doi:10.1115/1.2401177).
Full text not available from this repository.
Malalignment is the main cause of tibial component loosening. Implants that migrate
rapidly in the first two post-operative years are likely to present aseptic loosening. It has
been suggested that cancellous bone stresses can be correlated with tibial component
migration. A recent study has shown that patient-specific finite element (FE) models have
the power to predict the short-term behavior of tibial trays. The stresses generated within
the implanted tibia are dependent on the kinematics of the joint; however, previous
studies have ignored the kinematics and only applied static loads. Using explicit FE, it is
possible to simultaneously predict the kinematics and stresses during a gait cycle. The
aim of this study was to examine the cancellous bone strains during the stance phase of
the gait cycle, for varying degrees of varus/valgus eccentric loading using explicit FE. A
patient-specific model of a proximal tibia was created from CT scan images, including
heterogeneous bone properties. The proximal tibia was implanted with a commercial
total knee replacement (TKR) model. The stance phase of gait was simulated and the
applied loads and boundary conditions were based on those used for the Stanmore knee
simulator. Eccentric loading was simulated. As well as examining the tibial bone strains
(minimum and maximum principal strain), the kinematics of the bone-implant construct
are also reported. The maximum anterior–posterior displacements and internal–external
rotations were produced by the model with 20 mm offset. The peak minimum and maximum
principal strain values increased as the load was shifted laterally, reaching a
maximum magnitude for ?20 mm offset. This suggests that when in varus, the load
transferred to the bone is shifted medially, and as the bone supporting this load is stiffer,
the resulting peak bone strains are lower than when the load is shifted laterally (valgus).
For this particular patient, the TKR design analyzed produced the highest cancellous
bone strains when in valgus. This study has provided an insight in the variations produced
in bone strain distribution when the axial load is applied eccentrically. To the
authors’ knowledge, this is the first time that the bone strain distribution of a proximal
implanted tibia has been examined, also accounting for the kinematics of the tibio–
femoral joint as part of the simulation. This approach gives greater insight into the
overall performance of TKR.
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