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J Biomech. 2016 Oct 3;49(14):3387-3396. doi: 10.1016/j.jbiomech.2016.09.011. Epub 2016 Sep 15.

Spatial variation of fixed charge density in knee joint cartilage from sodium MRI - Implication on knee joint mechanics under static loading.

Author information

1
Department of Applied Physics, University of Eastern Finland, Kuopio, Finland. Electronic address: lasse.rasanen@uef.fi.
2
Department of Applied Physics, University of Eastern Finland, Kuopio, Finland.
3
Department of Diagnostic Radiology, Oulu University Hospital, Oulu, Finland; Research Unit of Medical Imaging, Physics and Technology, University of Oulu, Oulu, Finland.
4
Research Unit of Medical Imaging, Physics and Technology, University of Oulu, Oulu, Finland; High Field MR Center, Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Vienna, Austria.
5
Department of Applied Physics, University of Eastern Finland, Kuopio, Finland; Cancer Center, Kuopio University Hospital, Kuopio, Finland.
6
High Field MR Center, Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Vienna, Austria.
7
Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands.
8
Department of Applied Physics, University of Eastern Finland, Kuopio, Finland; Diagnostic Imaging Center, Kuopio University Hospital, Kuopio, Finland.
9
High Field MR Center, Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Vienna, Austria; CD Laboratory for Clinical Molecular MR Imaging, Vienna, Austria.
10
Department of Diagnostic Radiology, Oulu University Hospital, Oulu, Finland; Research Unit of Medical Imaging, Physics and Technology, University of Oulu, Oulu, Finland; Medical Research Center, University of Oulu and Oulu University Hospital, Oulu, Finland.

Abstract

The effects of fixed charge density (FCD) and cartilage swelling have not been demonstrated on cartilage mechanics on knee joint level before. In this study, we present how the spatial and local variations of FCD affects the mechanical response of the knee joint cartilage during standing (half of the body weight, 13 minutes) using finite element (FE) modeling. The FCD distribution of tibial cartilage of an asymptomatic subject was determined using sodium (23Na) MRI at 7T and implemented into a 3-D FE-model of the knee joint (Subject-specific model, FCD: 0.18±0.08 mEq/ml). Tissue deformation in the Subject-specific model was validated against experimental, in vivo loading of the joint conducted with a MR-compatible compression device. For comparison, models with homogeneous FCD distribution (homogeneous model) and FCD distribution obtained from literature (literature model) were created. Immediately after application of the load (dynamic response), the variations in FCD had minor effects on cartilage stresses and strains. After 13 minutes of standing, the spatial and local variations in FCD had most influence on axial strains. In the superficial tibial cartilage in the Subject-specific model, axial strains were increased up to +13% due to smaller FCD (mean -11%), as compared to the homogeneous model. Compared to the literature model, those were decreased up to -18% due to greater FCD (mean +7%). The findings demonstrate that the spatial and local FCD variations in cartilage modulates strains in knee joint cartilage. Thereby, the results highlight the mechanical importance of site-specific content of proteoglycans in cartilage.

KEYWORDS:

Articular cartilage; Finite element analysis; Fixed charge density; Knee joint; Sodium MRI

PMID:
27667478
DOI:
10.1016/j.jbiomech.2016.09.011
[Indexed for MEDLINE]

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