The discrete nature of trabecular bone microarchitecture affects implant stability

Wirth, Andreas; Müller, Ralph; Lenthe, G. Harry van

doi:10.1016/j.jbiomech.2011.12.024

Cited by 48 publications

(36 citation statements)

References 17 publications

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“…Huiskes and Chao [16] completed an excellent review of the beginnings and early applications of the FE method, while recent exponents [17,18] have developed a systematic approach to its use. The heterogeneous architecture of cancellous bone means that it can vary significantly.…”

Section: Introductionmentioning

confidence: 99%

“…The outcome is a continuum model with variable mechanical stiffness but no geometric peculiarities. Melchels et al [22] evaluated various mathematically defined architectures for the FE lattice modeling including cube, diamond, gyroid, and an irregular salt-leached structure, and demonstrated that for the same porosity a cubic structure will have a higher stiffness than a gyroid structure, while Wirth et al [18] compared CT-based models and continuum models for application with screws. In both high and low density structures they found a significant difference in bone-implant stiffness between models in which the bone/anchor interface is assumed to be contiguously connected, and concluded that continuum models are of limited use for peri-implant analyses.…”

Section: Introductionmentioning

confidence: 99%

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Bone Anchors—A Preliminary Finite Element Study of Some Factors Affecting Pullout

Hughes

Bordush

Robioneck

et al. 2014

Journal of Medical Devices

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Bone anchors (or suture anchors) are used to provide attachment points for sutures to connect tissue such as tendons or ligaments to bone, and work by engaging a threaded portion-sometimes tapered-to the cancellous and/or cortical bone. Such repair is often needed after trauma, or as part of reconstructive surgery. This paper uses the finite element method to compare the pullout characteristics of one common type of bone anchor in different cancellous bone structures. Finite element models are created by using computed tomography (CT) scans of cancellous bone and building computer-aided design (CAD) models to define the cancellous bone geometry. Orthopedic surgeons will sometimes remove parts of the cortical shell and this paper also examines the mechanical effects of decortication. Furthermore, the importance of the connection between anchor and cortical layer is examined. One of the key outcomes from the model is that the coefficient of friction between bone and anchor determines potential mechanisms of pullout. The stiffness of anchors and the effect of the cortical layer are presented for different pullout angles to obtain the theoretical response. The results show the detailed modeling that includes the micro-architecture of the cancellous bone is necessary to capture the large variations that can exist.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Bone Anchors—A Preliminary Finite Element Study of Some Factors Affecting Pullout

Hughes

Bordush

Robioneck

et al. 2014

Journal of Medical Devices

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show abstract

“…Thus, pullout strength should be strongly determined by bone quality, and results normalised for density should show good correlation. However, cancellous bone structures are cellular matrices (Gibson and Ashby, 1999) with quite distinct characteristics and, even in models, cannot be simplified to continua (Wirth et al, 2011). Gausepohl et al (2001) have shown the effect of having small threads to produce better holding power in cancellous bone.…”

Section: Discussionmentioning

confidence: 99%

“…The use of an axisymmetric (2-D) model is a simplification that represents the cancellous bone as a series of regularly-spaced interconnected thin-walled annular tubes (Brown et al, 2013). Nevertheless, this gives a better approximation to cancellous bone structure than the alternative use of a continuum (Wirth et al, 2011), as it defines the connectivity between screw threads and the surrounding medium. The position of the screw relative to the bone surface can be moved both radially and along the axis of the screw.…”

Section: Finite Element Modelmentioning

confidence: 99%

Variability of the pullout strength of cancellous bone screws with cement augmentation

Procter

Bennani

Brown

et al. 2015

Clinical Biomechanics

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Background: Orthopaedic surgeons often face clinical situations where improved screw holding power in cancellous bone is needed. Injectable calcium phosphate cements are one option to enhance fixation. Methods: Paired screw pullout tests were undertaken in which human cadaver bone was augmented with calcium phosphate cement. A finite element model was used to investigate sensitivity to screw positional placement. Findings: Statistical analysis of the data concluded that the pullout strength was generally increased by cement augmentation in the in vitro human cadaver tests. However, when comparing the individual paired samples there were surprising results with lower strength than anticipated after augmentation, in apparent contradiction to the generally expected conclusion. Investigation using the finite element model showed that these strength reductions could be accounted for by small screw positional changes. A change of 0.5 mm might result in predicted pullout force changes of up to 28%. Interpretation: Small changes in screw position might lead to significant changes in pullout strength sufficient to explain the lower than expected individual pullout values in augmented cancellous bone. Consequently whilst the addition of cement at a position of low strength would increase the pullout strength at that point, it might not reach the pullout strength of the un-augmented paired test site. However, the overall effect of cement augmentation produces a significant improvement at whatever point in the bone the screw is placed. The use of polymeric bone-substitute materials for tests may not reveal the natural variation encountered in tests using real bone structures.

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“…The heterogeneous and complex microstructure leads to complex mechanical interactions between the screw and the bone, and previous studies on this topic have shown that models considering the trabecular bone as a continuum fail to predict the strain field and more generally the mechanical behaviour of a screw implant (Wirth et al. 2012a). …”

Section: Introductionmentioning

confidence: 99%

Trabecular deformations during screw pull-out: a micro-CT study of lapine bone

Joffre

Isaksson

Procter

et al. 2017

Biomech Model Mechanobiol

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The mechanical fixation of endosseous implants, such as screws, in trabecular bone is challenging because of the complex porous microstructure. Development of new screw designs to improve fracture fixation, especially in high-porosity osteoporotic bone, requires a profound understanding of how the structural system implant/trabeculae interacts when it is subjected to mechanical load. In this study, pull-out tests of screw implants were performed. Screws were first inserted into the trabecular bone of rabbit femurs and then pulled out from the bone inside a computational tomography scanner. The tests were interrupted at certain load steps to acquire 3D images. The images were then analysed with a digital volume correlation technique to estimate deformation and strain fields inside the bone during the tests. The results indicate that the highest shear strains are concentrated between the inner and outer thread diameter, whereas compressive strains are found at larger distances from the screw. Tensile strains were somewhat smaller. Strain concentrations and the location of trabecular failures provide experimental information that could be used in the development of new screw designs and/or to validate numerical simulations.Electronic supplementary materialThe online version of this article (doi:10.1007/s10237-017-0891-9) contains supplementary material, which is available to authorized users.

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The discrete nature of trabecular bone microarchitecture affects implant stability

Cited by 48 publications

References 17 publications

Bone Anchors—A Preliminary Finite Element Study of Some Factors Affecting Pullout

Bone Anchors—A Preliminary Finite Element Study of Some Factors Affecting Pullout

Variability of the pullout strength of cancellous bone screws with cement augmentation

Trabecular deformations during screw pull-out: a micro-CT study of lapine bone

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