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Research Papers

An Effective Approach for Optimization of a Composite Intramedullary Nail for Treating Femoral Shaft Fractures

[+] Author and Article Information
Saeid Samiezadeh

Department of Mechanical
and Industrial Engineering,
Ryerson University,
350 Victoria Street,
Toronto, ON M5B 2K3, Canada
e-mail: saeid.samiezadeh@ryerson.ca

Pouria Tavakkoli Avval

Department of Mechanical and
Industrial Engineering,
Ryerson University,
350 Victoria Street,
Toronto, ON M5B 2K3, Canada
e-mail: ptavakko@ryerson.ca

Zouheir Fawaz

Department of Aerospace Engineering,
Ryerson University,
350 Victoria Street,
Toronto, ON M5B 2K3, Canada
e-mail: zfawaz@ryerson.ca

Habiba Bougherara

Department of Mechanical and
Industrial Engineering,
Ryerson University,
350 Victoria Street,
Toronto, ON M5B 2K3, Canada
e-mail: habiba.bougherara@ryerson.ca

1Corresponding author.

Manuscript received April 14, 2015; final manuscript received September 19, 2015; published online October 20, 2015. Assoc. Editor: David Corr.

J Biomech Eng 137(12), 121001 (Oct 20, 2015) (9 pages) Paper No: BIO-15-1178; doi: 10.1115/1.4031766 History: Received April 14, 2015; Revised September 19, 2015

The high stiffness of conventional intramedullary (IM) nails may result in stress shielding and subsequent bone loss following healing in long bone fractures. It can also delay union by reducing compressive loads at the fracture site, thereby inhibiting secondary bone healing. This paper introduces a new approach for the optimization of a fiber-reinforced composite nail made of carbon fiber (CF)/epoxy based on a combination of the classical laminate theory, beam theory, finite-element (FE) method, and bone remodeling model using irreversible thermodynamics. The optimization began by altering the composite stacking sequence and thickness to minimize axial stiffness, while maximizing torsional stiffness for a given range of bending stiffnesses. The selected candidates for the seven intervals of bending stiffness were then examined in an experimentally validated FE model to evaluate their mechanical performance in transverse and oblique femoral shaft fractures. It was found that the composite nail having an axial stiffness of 3.70 MN and bending and torsional stiffnesses of 70.3 and 70.9 Nm2, respectively, showed an overall superiority compared to the other configurations. It increased compression at the fracture site by 344.9 N (31%) on average, while maintaining fracture stability through an average increase of only 0.6 mm (49%) in fracture shear movement in transverse and oblique fractures when compared to a conventional titanium-alloy nail. The long-term results obtained from the bone remodeling model suggest that the proposed composite IM nail reduces bone loss in the femoral shaft from 7.9% to 3.5% when compared to a conventional titanium-alloy nail. This study proposes a number of practical guidelines for the design of composite IM nails.

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References

Figures

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Fig. 1

Finite-element models of a femur with a transverse (a), PMDL oblique (b), and PLDM oblique (c) fracture, which was fixed with an IM nail

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Fig. 2

Fracture opening (a) and shear movement (b) at the fracture site for transverse, PMDL oblique, and PLDM oblique midshaft fractures with the use of composite (C1–C7) and conventional metallic (C8) IM nails

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Fig. 3

Nail ISF for composite IM nail candidates (C1–C7) and the metallic IM nail (C8) in transverse, PMDL oblique, and PLDM oblique midshaft fractures

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Fig. 4

Compressive normal force at fracture (a) and average nodal stress in the bone at the vicinity of the fracture (b) for composite IM nail candidates (C1–C7) and the metallic IM nail (C8) in transverse, PMDL oblique, and PLDM oblique midshaft fractures

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Fig. 5

Long-term average bone loss in the femoral shaft fixed with the composite IM nail candidates (C1–C7) and metallic IM nail (C8) (a). Percent change in femoral density in response to a typical IM nail candidate (b) as well as the metallic IM nail (c).

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