Inter-patient evaluation of stresses in proximal implanted tibiae
Inter-patient evaluation of stresses in proximal implanted tibiae
In biomechanics finite element analysis (FEA) is still only a comparative tool. To the authors' knowledge, no study has examined multiple tibiae or included patient specific data. Only by constructing finite element models taking into account these parameters in combination with prospective clinical studies can the predictive power of FEA be assessed. The purpose of this study was to evaluate the differences in the predicted stresses and risk ratios observed on the resected surface of models of proximal implanted tibiae created from patient specific data.
Finite element models of four proximal implanted tibiae were analysed. The models were created from quantitative computed tomography (QCT) data. The immediate post-operative situation was modelled by assuming frictionless contact between the tibia and the tibial plateau. Post-operative alignment of the implants were considered in the study. The loads used in the models were equivalent to three times the weight of each patient. A bi-condylar load case was used, in which 60% of the total force was applied on the medial side and 40% on the lateral side. The forces were applied directly on the tibial plateau.
A program called Bonemat, was used to assign the material properties on an element-by-element basis, based on the correlation between QCT data and the material properties of the bone (i.e. apparent density and stiffness). Meshes of linear tetrahedral elements were created in I-DEAS for both bone and implant. Risk ratio values (defined as the Von Mises stress divided by the ultimate compressive strength) on the resected surface of each tibia were examined and compared between all four models. All the analyses were carried out using MARC K7.3.2.
In all four models, a similar overall risk ratio distribution on the surface of interest was observed, with peak values of 319%, 315%, 322% and 327% for patients 1,2,3 and 4, respectively. In all the models, the peak values were found in the portion of cancellous bone supporting the posterior side of the tibial plateau.
For all four tibiae there were areas of bone, particularly around the posterior cruciate cut-out, where the localised risk of failure was high. However, in general, the risk of failure was below 100% over the majority of the resected surface. RSA studies of tibial plateaus have shown that during the first six months after surgery, there is a period of rapid migration. This is widely thought to be due to the implant "bedding in". The findings of this study support this view, as some regions presented considerably high risk ratios. In these regions, the cancellous bone will be crushed and the load redistributed on the resected surface until an equilibrium position is reached. This study has shown that patient specific FE model do demonstrate subtle differences in the predicted stress and risk ratio distributions. This emphasises the importance of moving away from the traditional generic modelling approach to patient specific modelling.
382
Perillo-Marcone, A.
14bf1408-6e29-46e1-9376-ecd9ae748814
Ryd, L.
4b08bb72-7753-4cfa-a79e-8756fd4b79f3
Taylor, M.
e368bda3-6ca5-4178-80e9-41a689badeeb
2001
Perillo-Marcone, A.
14bf1408-6e29-46e1-9376-ecd9ae748814
Ryd, L.
4b08bb72-7753-4cfa-a79e-8756fd4b79f3
Taylor, M.
e368bda3-6ca5-4178-80e9-41a689badeeb
Perillo-Marcone, A., Ryd, L. and Taylor, M.
(2001)
Inter-patient evaluation of stresses in proximal implanted tibiae.
International Society of Biomechanics XVIIIth Congress, Zurich, Switzerland.
07 - 12 Jul 2001.
.
Record type:
Conference or Workshop Item
(Paper)
Abstract
In biomechanics finite element analysis (FEA) is still only a comparative tool. To the authors' knowledge, no study has examined multiple tibiae or included patient specific data. Only by constructing finite element models taking into account these parameters in combination with prospective clinical studies can the predictive power of FEA be assessed. The purpose of this study was to evaluate the differences in the predicted stresses and risk ratios observed on the resected surface of models of proximal implanted tibiae created from patient specific data.
Finite element models of four proximal implanted tibiae were analysed. The models were created from quantitative computed tomography (QCT) data. The immediate post-operative situation was modelled by assuming frictionless contact between the tibia and the tibial plateau. Post-operative alignment of the implants were considered in the study. The loads used in the models were equivalent to three times the weight of each patient. A bi-condylar load case was used, in which 60% of the total force was applied on the medial side and 40% on the lateral side. The forces were applied directly on the tibial plateau.
A program called Bonemat, was used to assign the material properties on an element-by-element basis, based on the correlation between QCT data and the material properties of the bone (i.e. apparent density and stiffness). Meshes of linear tetrahedral elements were created in I-DEAS for both bone and implant. Risk ratio values (defined as the Von Mises stress divided by the ultimate compressive strength) on the resected surface of each tibia were examined and compared between all four models. All the analyses were carried out using MARC K7.3.2.
In all four models, a similar overall risk ratio distribution on the surface of interest was observed, with peak values of 319%, 315%, 322% and 327% for patients 1,2,3 and 4, respectively. In all the models, the peak values were found in the portion of cancellous bone supporting the posterior side of the tibial plateau.
For all four tibiae there were areas of bone, particularly around the posterior cruciate cut-out, where the localised risk of failure was high. However, in general, the risk of failure was below 100% over the majority of the resected surface. RSA studies of tibial plateaus have shown that during the first six months after surgery, there is a period of rapid migration. This is widely thought to be due to the implant "bedding in". The findings of this study support this view, as some regions presented considerably high risk ratios. In these regions, the cancellous bone will be crushed and the load redistributed on the resected surface until an equilibrium position is reached. This study has shown that patient specific FE model do demonstrate subtle differences in the predicted stress and risk ratio distributions. This emphasises the importance of moving away from the traditional generic modelling approach to patient specific modelling.
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Published date: 2001
Venue - Dates:
International Society of Biomechanics XVIIIth Congress, Zurich, Switzerland, 2001-07-07 - 2001-07-12
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Local EPrints ID: 21813
URI: http://eprints.soton.ac.uk/id/eprint/21813
PURE UUID: c122f5bc-8374-4ea6-85a8-b5f73c8837eb
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Date deposited: 22 Feb 2007
Last modified: 11 Dec 2021 14:33
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Author:
A. Perillo-Marcone
Author:
L. Ryd
Author:
M. Taylor
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