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Finite Element Simulations of Biphasic Articular Cartilages With Localized Metal Implants
KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics. (Engineering Mechanics)
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Articular cartilage is a specialized connective soft tissue that resides onthe ends of long-bones, transfers the load smoothly between the bones in diarthrodialjoints by providing almost frictionless, wear resistant sliding surfacesduring joint articulation. Focal chondral or osteochondral defects in articularcartilage are common and show limited capacity for biological repair. Furthermore,changes in the bio-mechanical forces at the defect site may makethe tissue more susceptible to continued degeneration. Alternatively, the contouredfocal resurfacing metal implant can be used to treat such full thicknesscartilage defects. Physiological and biomechanical studies on animal modelswith metal implant have shown good clinical outcomes. However, the mechanicalbehavior of cartilage surrounding the implant is not clearly known withrespect to the joint function after treating such defects with metal implantsand also to improve the implant design. We developed a simple 3-dimensionalfinite element model by approximating one of the condyles of the sheep kneejoint. Parametric study was conducted in the simulations to verify differentprofiles for the implant, positioning of the implant with respect to cartilagesurface, defect size and to show the mechanical sealing effect due to the wedgeshape of the implant. We found the maximal deformations, contact pressuresand stresses which constitute the mechanical behavior of cartilages. We alsoconfirmed that using a metal implant to fill the full thickness chondral defectsis more beneficial than to leave the defect untreated from mechanical point ofview. The implant should be positioned slightly sunk into the cartilage basedon the defect size, in order to avoid damage to the opposing surface. The largerthe defect size, the closer the implant should be to the flush. We also simulatedthe time dependent behavior of the cartilages. In all the simulations, a staticaxial loading was considered. The wedge shape of the implant provided themechanical sealing of the cartilage surrounding the implant. The determineddeformations in the cartilages immediately surrounding the implant are instrumentalin predicting the sticking-up of the implant into the joint cavity whichmay damage opposing soft tissues.

Place, publisher, year, edition, pages
Stockholm: Universitetsservice US-AB , 2010. , viii, 49 p.
Series
Trita-MEK, ISSN 0348-467X ; 2010:10
Keyword [en]
finite element analysis, articular cartilage defects, knee joint, metal implant, poroelastic, biphasic
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-26381OAI: oai:DiVA.org:kth-26381DiVA: diva2:372221
Presentation
2010-12-16, E3, Osquare backe 14, Royal Institute of Technology, Stockholm, 10:15 (English)
Opponent
Supervisors
Note
QC 20101125Available from: 2010-11-25 Created: 2010-11-24 Last updated: 2010-12-03Bibliographically approved
List of papers
1. Finite element simulations of a focal knee resurfacing implant applied to localized cartilage defects in a sheep model
Open this publication in new window or tab >>Finite element simulations of a focal knee resurfacing implant applied to localized cartilage defects in a sheep model
2011 (English)In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 44, no 5, 794-801 p.Article in journal (Refereed) Published
Abstract [en]

Articular resurfacing metal implants have recently been tested in animal models to treat full thickness localized articular cartilage defects, showing promising results. However, the mechanical behavior of cartilage surrounding the metal implant has not been studied yet as it is technically challenging to measure in vivo contact areas, pressures, stresses and deformations from the metal implant. Therefore, we implemented a detailed numerical finite element model by approximating one of the condyles of the sheep tibiofemoral joint and created a defect of specific size to accommodate the implant. Using this model, the mechanical behavior of the surrounding of metal implant was studied. The model showed that the metal implant plays a significant role in the force transmission. Two types of profiles were investigated for metal implant. An implant with a double-curved profile, i.e., a profile fully congruent with the articular surfaces in the knee, gives lower contact pressures and stresses at the rim of the defect than the implant with unicurved spherical profile. The implant should be placed at a certain distance into the cartilage to avoid damage to opposing biological surface. Too deep positions, however, lead to high shear stresses in the cartilage edges around the implant. Mechanical sealing was achieved with a wedge shape of the implant, also useful for biochemical sealing of cartilage edges at the defect.

Keyword
Articular cartilage, Implant, Finite element analysis, Poroelastic, Biphasic, Knee, Sheep
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-26394 (URN)10.1016/j.jbiomech.2010.12.026 (DOI)000288925800002 ()2-s2.0-79952034335 (Scopus ID)
Note

QC 20120328. Updated from submitted to published. Previous title: "Finite element simulation of a focal knee resurfacing implant applied to localized cartilage defects in a sheep model"

Available from: 2010-11-25 Created: 2010-11-25 Last updated: 2013-05-02Bibliographically approved
2. Time-dependent behavior of cartilage surrounding a metal implant for full-thickness cartilage defects of various sizes: a finite element study
Open this publication in new window or tab >>Time-dependent behavior of cartilage surrounding a metal implant for full-thickness cartilage defects of various sizes: a finite element study
2012 (English)In: Biomechanics and Modeling in Mechanobiology, ISSN 1617-7959, E-ISSN 1617-7940, Vol. 11, no 5, 731-742 p.Article in journal (Refereed) Published
Abstract [en]

Recently, physiological and biomechanical studies on animal models with metal implants filling full-thickness cartilage defects have resulted in good clinical outcomes. The knowledge of the time-dependent macroscopic behavior of cartilage surrounding the metal implant is essential for understanding the joint function after treating such defects. We developed a model to investigate the in vivo time-dependent behavior of the tibiofemoral cartilages surrounding the metal implant, when the joint is subjected to an axial load for various defect sizes. Results show that time-dependent effects on cartilage behavior are significant, and can be simulated. These effects should be considered when evaluating the results from an implant. In particular, the depth into the cartilage where an implant is positioned and the mechanical sealing due to solidification of the poroelastic material need a time aspect. We found the maximal deformations, contact pressures and contact forces in the joint with time for the implant positioned in flush and sunk 0.3 mm into the cartilage. The latter position gives the better joint performance. The results after 60 s may be treated as the primary results, reflecting the effect of accumulation in the joint due to repeated short-time loadings. The wedge-shaped implant showed beneficial in providing mechanical sealing of cartilages surrounding the implant with time.

Keyword
Cartilage defects, Finite element modeling, Knee, Metal implant, Poroelastic, Sheep
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-26502 (URN)10.1007/s10237-011-0346-7 (DOI)000303378200012 ()2-s2.0-84861096730 (Scopus ID)
Note
QC 20120628Available from: 2010-11-25 Created: 2010-11-25 Last updated: 2013-05-02Bibliographically approved

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