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Research Papers

An Analytical Approach to Study the Intraoperative Fractures of Femoral Shaft During Total Hip Arthroplasty

[+] Author and Article Information
Leila Malekmotiei

Department of Civil Engineering,
Sharif University of Technology,
P.O. Box 11155-9313,
Tehran, Iran
e-mail: leila.malekmotiee@gmail.com

Farzam Farahmand

School of Mechanical Engineering,
Sharif University of Technology,
P.O. Box 11155-9567,
Tehran, Iran
e-mail: farahmand@sharif.edu

Hossein M. Shodja

Department of Civil Engineering,
Sharif University of Technology,
P.O. Box 11155-9313,
Tehran, Iran;
Institute for Nanoscience and Nanotechnology,
Sharif University of Technology,
P.O. Box 11155-9161,
Tehran, Iran
e-mail: shodja@sharif.edu

Aref Samadi-Dooki

Department of Civil Engineering,
Sharif University of Technology,
P.O. Box 11155-9313,
Tehran, Iran
e-mail: arefsamadi@gmail.com

1Corresponding author.

Contributed by the Bioengineering Division of ASME for publication in the Journal of Biomechanical Engineering. Manuscript received July 31, 2012; final manuscript received February 3, 2013; accepted manuscript posted February 19, 2013; published online April 2, 2013. Assoc. Editor: Pasquale Vena.

J Biomech Eng 135(4), 041004 (Apr 02, 2013) (8 pages) Paper No: BIO-12-1334; doi: 10.1115/1.4023699 History: Received July 31, 2012; Revised February 03, 2013; Accepted February 19, 2013

An analytical approach which is popular in micromechanical studies has been extended to the solution for the interference fit problem of the femoral stem in cementless total hip arthroplasty (THA). The multiple inhomogeneity problem of THA in transverse plane, including an elliptical stem, a cortical wall, and a cancellous layer interface, was formulated using the equivalent inclusion method (EIM) to obtain the induced interference elastic fields. Results indicated a maximum interference fit of about 210 μm before bone fracture, predicted based on the Drucker–Prager criterion for a partially reamed section. The cancellous layer had a significant effect on reducing the hoop stresses in the cortical wall; the maximum press fit increased to as high as 480 μm for a 2 mm thick cancellous. The increase of the thickness and the mechanical quality, i.e., stiffness and strength, of the cortical wall also increased the maximum interference fit before fracture significantly. No considerable effect was found for the implant material on the maximum allowable interference fit. It was concluded that while larger interference fits could be adapted for younger patients, care must be taken when dealing with the elderly and those suffering from osteoporosis. A conservative reaming procedure is beneficial for such patients; however, in order to ensure sufficient primary stability without risking bone fracture, a preoperative analysis might be necessary.

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References

Figures

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Fig. 1

Cross-section of the femoral shaft with inserted stem and multilayer cancellous bone

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Fig. 2

An elliptical multi-inhomogeneous inclusion

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Fig. 3

A multi-inhomogeneous inclusion (left) has been replaced by an equivalent multi-inclusion (right)

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Fig. 4

Decomposition of an equivalent multi-inclusion

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Fig. 5

Geometry of the basic model including the stem (at the center), cortical wall (in the peripheral) and cancellous layer (at the interface). Dimensions are in mm.

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Fig. 6

Distribution of the interference induced stresses (top) and strains (bottom) along the short and long radii of the elliptical cortical wall. “d” denotes the distance from the origin of the stem along the short and long axes of the elliptical cortical wall

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Fig. 7

Effects of the cancellous layer thickness and the stem material on the maximum interference fit before bone fracture

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Fig. 8

Effects of the cortical wall thickness and mechanical properties on the maximum interference fit before bone fracture

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