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Importance of Patient-Specific Collagen Architecture on Knee Joint Stresses and Strains During Walking
Räsänen, LP; Mononen, M; Juvelin, JS; Korhonen, R
University of Eastern Finland, Kuopio, Finland
[email protected]
Introduction: Subject-specific collagen architecture of articular cartilage was recently implemented in a 2D finite element (FE) model
[1]. The effect of the collagen architecture on cartilage stresses was simulated under axial, impact loading. The 2D model could localize
only a single sagittal slice in a knee joint, and included no data on loading during normal human walking. The aim of this study was to
implement subject-specific collagen architecture of cartilage and gait cycle in a 3D FE model. We demonstrated the effect of the
collagen architecture, obtained from clinical MRI, on the distribution of stresses, strains and pore pressures during a subject-specific
gait cycle.
Methods: A 3D geometry of an intact, left knee joint was obtained from 3.0T clinical, magnetic resonance images (PD weighted
VISTA SPAIR - imaging sequence). T2 mapped MR-images (T2 weighted Turbo Spin Echo, six echo times from 13 to 78 ms, in-plane
resolution 0.388mm, Fig. 1a) were also obtained for the same subject (Fig. 1a,d). Cartilages and menisci were segmented by using
Mimics software (v12.3, Materialise, Leuven, Belgium) (Fig 1a,d) and 3D FE model and meshes of the knee joint tissues were created
with Abaqus v6.10 (Dassault Systèmes, Providence, RI, USA) (Fig. 1d). T2 information of the collagen orientation was implemented in
the model using submodeling in chosen lateral and medial locations of the knee joint (Fig. 1d). Submodeling was used in order to
reduce simulation times. It also enabled the increase in the FE mesh density. Three-laminar collagen architectures (i.e. the superficial,
middle and deep zones) were determined for the submodels from the dept-wise T2 profiles (Fig. 1b, model I) [1]. For comparison, we
created an alternative model in which the collagen architectures were obtained from the literature (model II, zone thickness of 11 and
32% in the superficial and middle zones) [2]. The superficial zones were implemented with the collagen fibrils oriented parallel to the
cartilage surface, the middle zones with collagen fibrils oriented in a 45 degrees angle and the deep zones with perpendicularly oriented
collagen fibrils (Fig. 1c). Split line patterns were also included in cartilage [3]. Cartilage tissues were modeled as fibril reinforced
poroviscoelastic materials [4, 5], whereas the menisci were modeled as transversely isotropic materials [6]. The global knee joint model
was simulated with the experimentally measured, patient-specific gait cycle (duration of 0.6s). The obtained nodal displacements in the
cartilage surface of the global model were then used as loading inputs for the simulations of the submodels.
Results: Compared to model II, the fibril strains were increased in all layers in model I (patient-specific), especially in the middle layer
of cartilage (up to +60 % at time fraction of 0.82 in medial tibial plateau and up to +50% at time fraction of 0.30 in lateral tibial
plateau). Correspondingly, von Mises stresses were increased especially in the middle layer of cartilage (up to +54 % at time fraction of
0.57 (medial tibia, Fig. 2b) and up to +30% at time fraction of 0.30 (lateral tibia, Fig. 2e)). In medial tibial cartilage, pore pressures
were increased in model I in the superficial (up to +43 % at time fraction of 0.86) and middle layers (up to +91% at time fraction of
0.96), but decreased significantly in the superficial region at the end of the cycle (-111 %). In lateral tibial cartilage, pore pressures first
decreased in the superficial and middle layers (up to -40% at time fraction of 0.13), but then increased at all depths at time fractions of
0.82-0.84 (up to +21% in deep layer).
Discussion: For the first time, patient-specific collagen fibril architecture of cartilage, as obtained from clinical MRI, and gait cycle of
the same patient were implemented in a 3D computational model. The patient-specific collagen architecture modulated cartilage
stresses and strains in medial and lateral tibial plateau primarily during the terminal stance of the gait cycle (approximately at time
fractions of 0.7-0.9) and the loading response of the gait cycle (at time fractions of 0.2-0.4), respectively. This behavior corresponded
well with the varus-valgus rotation within the knee joint [7,8]. Compared to the model with the collagen architecture from the literature
(model II), the patient specific model (model I) experienced larger fibril strains which led to increased stresses especially in the
superficial and middle layers of cartilage [1]. This was due to increased tensile stiffness of cartilage in the patient-specific model caused
greater amount of tangentially oriented collagen fibrils in the superficial tissue (model I) [1, 4]. In our current study, we implemented
patient-specific collagen architectures, as obtained from clinical MRI, in the contact area of medial and lateral tibial cartilages.
However, it should be noted that the used method can be adapted to evaluate the effect of patient-specific collagen architecture in any
locations of the knee joint (in 3D). Therefore, we believe that the evaluation and implementation of the collagen architecture of cartilage
will improve the estimation of cartilage mechanics in a patient-specific manner.
Significance: By taking into account the patient-specificity of the cartilage structure one will obtain more realistic evaluation of the
knee joint mechanics. Especially, implementation of the patient-specific joint geometry with true collagen architecture of cartilage in
3D as well as the realistic, patient-specific joint loading during walking may provide a more accurate tool for evaluating the possible
failure points in knee joints.
Acknowledgements: European Research Council, Academy of Finland, Kuopio University Hospital (EVO).
References: [1] Räsänen, J Orthop Res, 2012, DOI: DOI 10.1002/jor.22175; [2] Kurkijarvi, Magn Reson Imaging 26:602-607, 2008;
[3] Mononen, J Biomech 45:579-587, 2012; [4] Mononen, Biomech Model Mechanobiol 10:357-369, 2011; [5] Wilson, J Biomech
37:357- 66, 2004; [6] Zielinska, J Biomed Eng 128:115-123, 2006; [7] Yang, J Orthop Res 28:1539-1547, 2010; [8] Mononen, Trans
Orth Res Soc 37:1881, 2012;
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Figure 1: (a) The original MR-images with T2 mapped tibia. (b) Close-up from the contact region of tibia indicated by a white
rectangle in (a), the corresponding, depth-wise T2 profile and the half-maximum limit (red line). (c) The obtained collagen orientations
of the area indicated in (a) and (b) in the patient-specific model (model I). (d) The global knee joint model (above) and submodels in the
medial and lateral tibia (red).
Figure 2: The Von Mises stresses during the gait cycle in the contact area of (a-c) medial and (d-f) lateral tibial cartilages for both
models (areas in Fig 1). The superficial, middle and deep cartilage layers correspond to those in model I (Fig. 1c).
ORS 2013 Annual Meeting
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Poster No: 1678
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