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Research Papers

Effect of the Strain Rate on the Twisting of Trabecular Bone from Women with Hip Fracture

[+] Author and Article Information
Ana C. Vale

e-mail: ana_cvale@hotmail.com

Jennifer Faustino

Instituto de Ciência e Engenharia
de Materiais e Superfícies,
Instituto Superior Técnico,
Universidade de Lisboa, Avenue Rovisco Pais,
Lisbon P-1049-001, Portugal;
Rheumatology Research Unit,
Instituto de Medicina Molecular,
Faculdade de Medicina da
Universidade de Lisboa,
Lisbon P-1649-028, Portugal

Luís Reis

Instituto de Ciência e Engenharia
de Materiais e Superfícies,
Instituto Superior Técnico,
Universidade de Lisboa, Avenue Rovisco Pais,
Lisbon P-1049-001, Portugal;
Departamento de Engenharia Mecânica,
Instituto Superior Técnico,
Avenue Rovisco Pais,
Lisbon P-1049-001, Portugal

Bruno Vidal

Rheumatology Research Unit,
Instituto de Medicina Molecular,
Faculdade de Medicina da
Universidade de Lisboa
Lisbon P-1649-028, Portugal

Jacinto Monteiro

Serviço de Ortopedia,
Hospital de Santa Maria,
Lisbon P-1649-028, Portugal

Helena Canhão

Rheumatology Research Unit,
Instituto de Medicina Molecular,
Faculdade de Medicina da
Universidade de Lisboa,
Lisbon P-1649-028, Portugal;
Serviço de Reumatologia e
Doenças Ósseas Metabólicas, HSM,
Lisbon P-1649-028, Portugal

Maria F. Vaz

Instituto de Ciência e Engenharia
de Materiais e Superfícies,
Instituto Superior Técnico, T.U.,
Lisbon, Avenue Rovisco Pais, Portugal;
Departamento de Engenharia Mecânica,
Instituto Superior Técnico,
Avenue Rovisco Pais,
Lisbon 1049-001, Portugal

1Corresponding author.

Contributed by the Bioengineering Division of ASME for publication in the Journal of Biomechanical Engineering. Manuscript received June 25, 2012; final manuscript received August 19, 2013; accepted manuscript posted September 6, 2013; published online October 10, 2013. Assoc. Editor: Yener N. Yeni.

J Biomech Eng 135(12), 121005 (Oct 10, 2013) (9 pages) Paper No: BIO-12-1244; doi: 10.1115/1.4025322 History: Received June 25, 2012; Revised August 19, 2013; Accepted September 06, 2013

As one of the major functions of bone is to provide structural support for the musculoskeletal system, it is important to evaluate its mechanical strength. Bones may be subjected to multiaxial stresses due to bone pathologies, accidental loads which may lead to hip, wrist fracture, or to a prosthetic joint replacement. Twist loading may lead to fractures, especially involving long bones from lower limbs. The aim of this work was to study the effect of the strain rate on the shear properties of trabecular bone samples from women with hip fracture (from 65 to 100 years). Cylindrical samples were core drilled from human femoral heads along the primary trabecular direction. The cylinder's ends were polished and embedded in blocks of polymeric material which fit the grips of the testing device. Deformation rates of 0.005, 0.01, 0.015, and 0.05 s−1 were applied. Twisting tests were conducted with or without an applied axial load of 500 N. From the torque-angular displacement curves, the shear stress–strain curves were obtained. The maximum shear strength and the shear modulus (i.e. the slope of the linear region) were determined. A large scatter of the results of the shear strength and the shear modulus was found, which is probably related to the heterogeneity of nonhealthy human bone samples. There is no significant effect of the strain rate on the maximum shear stress and the shear modulus, either in tests undertaken with or without the application of an axial load. The effect of strain rate on nonhealthy bone trabecular twisting properties did not follow the trend observed on the effect of strain rate in healthy bone, where an increase is detected.

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References

Figures

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Fig. 1

Photograph of a twisting test setup

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Fig. 2

Twisting curves: (a) experimental torque T versus angular deformation θ curve; (b) calculated shear stress τ as a function of the shear strain γ

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Fig. 3

(a) Bone sample after pure twisting test and (b) another sample after twisting with axial compressive load

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Fig. 4

Experimental values of: maximum shear stress as a function of age (a) in pure twisting and (b) in twisting with an axial compressive load; shear modulus as a function of age (c) in pure twisting and (d) in twisting with an axial compressive load

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Fig. 5

Experimental values of: (a) and (b) maximum shear stress and (c) and (d) shear modulus as a function of strain rate; in pure twisting (a) and (c), and in twisting with axial compressive load (c) and (d)

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Fig. 6

Scanning electron microscopy photographs, obtained with backscattered electrons of the trabecular bone: (a) surface of failure; (b) and (d) arrangement of the lamellae in a trabeculae prior to twisting test; (c) and (e) breakage of the lamellae in a trabeculae after the twisting test (black arrows indicate the lamellae)

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Fig. 7

Shear modulus as a function of the maximum shear stress for all samples tested (a) in pure twisting and (b) twisting with axial load, with the linear trendline represented

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Fig. 8

(a) Maximum shear stress and (b) shear modulus as a function of strain rate. Experimental values are dots, while the lines are the plots of Eqs. (6) and (7) in Fig. 8(a), and Eqs. (8) and (9) in Fig. 8(b).

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Fig. 9

(a) Shear stress and (b) shear modulus as a function of the apparent density measured by the Archimedes' method: straight lines are plots of Eqs. (1) and (2) for the strain rates of 0.005 s–1, 0.015 s–1, and 0.05 s–1

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