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Research Papers

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

[+] Author and Article Information
C. M. Hughes

School of Engineering and Design,
Brunel University,
Uxbridge UB8 3PH, UK
e-mail: chris.hughes@brunel.ac.uk

A. Bordush

Stryker Osteosynthesis,
Schönkirchen 24232, Germany
e-mail: Astrid.Bordush@gmail.com

B. Robioneck

Stryker Osteosynthesis,
Schönkirchen 24232, Germany
e-mail: Bernd.Robioneck@stryker.com

P. Procter

Stryker Osteosynthesis,
Schönkirchen 24232, Germany
e-mail: philip.procter@stryker.com

C. J. Brown

School of Engineering and Design,
Brunel University,
Uxbridge UB8 3PH, UK
e-mail: chris.brown@brunel.ac.uk

1Corresponding author.

Manuscript received October 21, 2013; final manuscript received February 12, 2014; published online xx xx, xxxx. Assoc. Editor: Rita M. Patterson.

J. Med. Devices 8(4), 041006 (Aug 19, 2014) (9 pages) Paper No: MED-13-1262; doi: 10.1115/1.4026901 History: Received October 21, 2013; Revised February 12, 2014

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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Copyright © 2014 by ASME
Topics: Bone , Density
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References

Figures

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Fig. 1

(a) Image of low BV/TV. (b) Image of higher BV/TV.

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Fig. 2

Clockwise from top left: isometric view of piece of bone, with anchor inserted, contact area shown on anchor, the final construct

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Fig. 3

Anchor with dimensions

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Fig. 4

(a) Contact region in higher apparent density bone. (b) Contact region in lower apparent density bone.

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Fig. 5

Variation of peak reaction force with friction coefficient

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Fig. 6

Upper surface of anchor at increasing load. Left: low friction coefficient. Right: higher friction coefficient.

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Fig. 7

Variation of reaction force with cortical thickness for two apparent densities, with engaged and nonengaged anchors (a) vertical load, (b) load at 45 deg, (c) load at 72.5 deg, and (d) load horizontal

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Fig. 8

Slice showing deformation under (a) vertical load and (b) horizontal load

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Fig. 9

Elements in contact with increasing displacement for vertical and horizontal loads

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Fig. 10

(a) Variation of reaction force (N) with angle for low apparent density bone. (b) Variation of reaction force (N) with angle for higher apparent density bone.

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