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Technical Briefs

A Preliminary Biomechanical Study of Cyclic Preconditioning Effects on Canine Cadaveric Whole Femurs

[+] Author and Article Information
Rad Zdero1

Martin Orthopaedic Biomechanics Lab, St. Michael’s Hospital, Li Ka Shing Building (West Basement, Room B116), 38 Shuter Street, Toronto, ON, Canada, M5B-1W8; Department of Mechanical and Industrial Engineering,  Ryerson University, Toronto, ON, Canada, M5B-2K3zderor@smh.ca

Chris H. Gallimore, Michael D. McKee, Emil H. Schemitsch

Department of Surgery, Faculty of Medicine,  University of Toronto, Toronto, ON, Canada, M5S-1A8

Alison J. McConnell

 Medtronic of Canada, Brampton, ON, Canada, L6Y-0R3

Harshita Patel, Golam Morshed, Habiba Bougherara

Department of Mechanical and Industrial Engineering,  Ryerson University, Toronto, ON, Canada, M5B-2K3

Rosane Nisenbaum

 Centre for Research on Inner City Health, Applied Health Research Centre, St Michael’s Hospital, Toronto, ON, Canada, M5B-1W8

Henry Koo

 Collingwood General and Marine Hospital, Collingwood, ON, Canada, L9Y-1W9

1

Corresponding author.

J Biomech Eng 134(9), 094502 (Aug 27, 2012) (7 pages) doi:10.1115/1.4007249 History: Received March 29, 2012; Revised July 15, 2012; Posted July 27, 2012; Published August 27, 2012; Online August 27, 2012

Biomechanical preconditioning of biological specimens by cyclic loading is routinely done presumably to stabilize properties prior to the main phase of a study. However, no prior studies have actually measured these effects for whole bone of any kind. The aim of this study, therefore, was to quantify these effects for whole bones. Fourteen matched pairs of fresh-frozen intact cadaveric canine femurs were sinusoidally loaded in 4-point bending from 50 N to 300 N at 1 Hz for 25 cycles. All femurs were tested in both anteroposterior (AP) and mediolateral (ML) bending planes. Bending stiffness (i.e., slope of the force-vs-displacement curve) and linearity R2 (i.e., coefficient of determination) of each loading cycle were measured and compared statistically to determine the effect of limb side, cycle number, and bending plane. Stiffnesses rose from 809.7 to 867.7 N/mm (AP, left), 847.3 to 915.6 N/mm (AP, right), 829.2 to 892.5 N/mm (AP, combined), 538.7 to 580.4 N/mm (ML, left), 568.9 to 613.8 N/mm (ML, right), and 553.8 to 597.1 N/mm (ML, combined). Linearity R2 rose from 0.96 to 0.99 (AP, left), 0.97 to 0.99 (AP, right), 0.96 to 0.99 (AP, combined), 0.95 to 0.98 (ML, left), 0.94 to 0.98 (ML, right), and 0.95 to 0.98 (ML, combined). Stiffness and linearity R2 versus cycle number were well-described by exponential curves whose values leveled off, respectively, starting at 12 and 5 cycles. For stiffness, there were no statistical differences for left versus right femurs (p = 0.166), but there were effects due to cycle number (p < 0.0001) and AP versus ML bending plane (p < 0.0001). Similarly, for linearity, no statistical differences were noted due to limb side (p = 0.533), but there were effects due to cycle number (p < 0.0001) and AP versus ML bending plane (p = 0.006). A minimum of 12 preconditioning cycles was needed to fully stabilize both the stiffness and linearity of the canine femurs. This is the first study to measure the effects of mechanical preconditioning on whole bones, having some practical implications on research practices.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

Grahic Jump Location
Figure 1

Experimental setup for AP (anteroposterior) and ML (mediolateral) 4-point bending tests, showing femurs, swivel joints, clamps, pins, and base plates. The force is applied vertically from the top in the downward direction.

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Figure 2

Typical raw force-vs-displacement results for a particular canine’s left femur undergoing 4-point AP (anteroposterior) bending showing (a) experimental data (•) from cycle 12 with a straight line of best fit and (b) the entire preconditioning regime of 25 cycles of minimum-to-maximum-to-minimum loads. The 0 mm displacement corresponds to the unloaded femur prior to the application of the 50 N preload just before cycle 1; thus, cyclic loading actually begins at a nonzero displacement, such as 0.05 mm for this particular femur.

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Figure 3

Stiffness results for the (a) AP (anteroposterior) bending plane and (b) ML (mediolateral) bending plane, showing data for a combined average of left and right femurs. Exponential lines of best fit described the experimental data well with an average fit of R2  = 0.99. Standard errors of the mean (SEM) bars are shown. Overall, there was no statistical effect on stiffness due to limb side (p = 0.166), but there was an effect caused by cycle number (p < 0.0001) and AP versus ML bending plane (p < 0.0001).

Grahic Jump Location
Figure 4

Linearity R2 results for the (a) AP (anteroposterior) bending plane and (b) ML (mediolateral) bending plane, showing data for a combined average of left and right femurs. Exponential lines of best fit described the experimental data well with an average fit of R2  = 0.98. Standard errors of the mean (SEM) bars are shown. Overall, there was no statistical effect on linearity due to limb side (p = 0.533), but there was an effect caused by cycle number (p < 0.0001) and AP versus ML bending plane (p = 0.006).

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