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TECHNICAL PAPERS: Bone/Orthopedic

Effect of Varus/Valgus Malalignment on Bone Strains in the Proximal Tibia After TKR: An Explicit Finite Element Study

[+] Author and Article Information
A. Perillo-Marcone

Bioengineering Sciences Research Group, School of Engineering Sciences, University of Southampton, Southampton, Hampshire 5017 1BJ, UKa̱perillo̱marcone@hotmail.com

M. Taylor

Bioengineering Sciences Research Group, School of Engineering Sciences, University of Southampton, Southampton, Hampshire 5017 1BJ, UK

J Biomech Eng 129(1), 1-11 (Sep 18, 2006) (11 pages) doi:10.1115/1.2401177 History: Received July 29, 2004; Revised September 18, 2006

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 20mm offset. The peak minimum and maximum principal strain values increased as the load was shifted laterally, reaching a maximum magnitude for 20mm 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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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 5

Minimum (compressive) and maximum (tensile) principal strains for models including rigid and deformable tibial components

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Figure 4

(a) AP displacement and (b) IE rotation of the tibial component. Comparison between results produced with deformable and rigid tibial trays and polyethylene component.

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Figure 3

Application point of axial load for different offset values

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Figure 2

Loads and boundary conditions

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Figure 7

Minimum (compressive) and maximum (tensile) principal strains for models with horizontal linear springs

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Figure 8

Kinematics of the tibial component for nine different offset values (model with ligaments): (a) AP displacement; and (b) IE rotation of the tibial component

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Figure 9

Minimum (compressive) and maximum (tensile) principal strains for models with ligaments

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Figure 10

Young’s modulus (GPa) distribution on the resected surface of the tibia

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Figure 6

Kinematics of the tibial component for nine different offset values (model with horizontal linear springs): (a) AP displacement; and (b) IE rotation of the tibial component

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