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Research Papers

Biomechanical Analysis of a New Carbon Fiber/Flax/Epoxy Bone Fracture Plate Shows Less Stress Shielding Compared to a Standard Clinical Metal Plate

[+] Author and Article Information
Zahra S. Bagheri, Pouria Tavakkoli Avval

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

Habiba Bougherara

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

Mina S. R. Aziz

Institute of Medical Science,
University of Toronto,
Toronto, ON M5S-1A8, Canada

Emil H. Schemitsch

Institute of Medical Science,
University of Toronto,
Toronto, ON M5S-1A8, Canada
Faculty of Medicine,
University of Toronto,
Toronto, ON M5S-1A8, Canada
Martin Orthopaedic Biomechanics Lab,
St. Michael's Hospital,
Toronto, ON M5B-1W8, Canada

Radovan Zdero

Department of Mechanical
and Industrial Engineering,
Ryerson University,
Toronto, ON M5B-2K3, Canada
Martin Orthopaedic Biomechanics Lab,
St. Michael's Hospital,
Toronto, ON M5B-1W8, Canada

1Corresponding author.

Manuscript received January 23, 2014; final manuscript received May 9, 2014; accepted manuscript posted May 14, 2014; published online June 26, 2014. Assoc. Editor: Joel D. Stitzel.

J Biomech Eng 136(9), 091002 (Jun 26, 2014) (10 pages) Paper No: BIO-14-1045; doi: 10.1115/1.4027669 History: Received January 23, 2014; Revised May 09, 2014; Accepted May 14, 2014

Femur fracture at the tip of a total hip replacement (THR), commonly known as Vancouver B1 fracture, is mainly treated using rigid metallic bone plates which may result in “stress shielding” leading to bone resorption and implant loosening. To minimize stress shielding, a new carbon fiber (CF)/Flax/Epoxy composite plate has been developed and biomechanically compared to a standard clinical metal plate. For fatigue tests, experiments were done using six artificial femurs cyclically loaded through the femoral head in axial compression for four stages: Stage 1 (intact), stage 2 (after THR insertion), stage 3 (after plate fixation of a simulated Vancouver B1 femoral midshaft fracture gap), and stage 4 (after fracture gap healing). For fracture fixation, one group was fitted with the new CF/Flax/Epoxy plate (n = 3), whereas another group was repaired with a standard clinical metal plate (Zimmer, Warsaw, IN) (n = 3). In addition to axial stiffness measurements, infrared thermography technique was used to capture the femur and plate surface stresses during the testing. Moreover, finite element analysis (FEA) was performed to evaluate the composite plate's axial stiffness and surface stress field. Experimental results showed that the CF/Flax/Epoxy plated femur had comparable axial stiffness (fractured = 645 ± 67 N/mm; healed = 1731 ± 109 N/mm) to the metal-plated femur (fractured = 658 ± 69 N/mm; healed = 1751 ± 39 N/mm) (p = 1.00). However, the bone beneath the CF/Flax/Epoxy plate was the only area that had a significantly higher average surface stress (fractured = 2.10 ± 0.66 MPa; healed = 1.89 ± 0.39 MPa) compared to bone beneath the metal plate (fractured = 1.18 ± 0.93 MPa; healed = 0.71 ± 0.24 MPa) (p < 0.05). FEA bone surface stresses yielded peak of 13 MPa at distal epiphysis (stage 1), 16 MPa at distal epiphysis (stage 2), 85 MPa for composite and 129 MPa for metal-plated femurs at the vicinity of nearest screw just proximal to fracture (stage 3), 21 MPa for composite and 24 MPa for metal-plated femurs at the vicinity of screw farthest away distally from fracture (stage 4). These results confirm that the new CF/Flax/Epoxy material could be a potential candidate for bone fracture plate applications as it can simultaneously provide similar mechanical stiffness and lower stress shielding (i.e., higher bone stress) compared to a standard clinical metal bone plate.

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Figures

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Fig. 1

Fracture fixation plates used presently. (a) Composite plate fixed on lateral femur surface with four proximal unicortical screws and four distal bicortical screws, (b) metal plate fixed on lateral femur surface with four proximal unicortical screws and four distal bicortical screws, (c) diagram of CF/Flax/Epoxy composite plate cross-section, and (d) photo of CF/Flax/Epoxy composite plate cross-section.

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Fig. 2

The experimental set up for the anterior view during cyclic loading tests for femurs in 15 deg of adduction

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Fig. 3

Photograph of experimental setup used for infrared thermographic imaging

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Fig. 4

Stiffness values obtained from experiments. Symbols (*, **, #) indicate pairwise comparisons that were statistically different (p < 0.05), whereas all other comparisons were not different (p ≥ 0.05).

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Fig. 5

Thermographic stress maps for the synthetic femurs. (a) Stage 1, (b) stage 2, (c) stage 3, and (d) stage 4. The anterior view is shown. M = metal plate and C = composite plate.

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Fig. 6

Thermographic stress values for femurs and plates above the fracture gap for (a) anterior femur, (b) medial femur, (c) lateral femur, and (d) lateral plate data. White circles (○) shown on the schematic of the femurs were the locations where the stress values were extracted. Thermal image stresses were extracted at specific distances from the top of the fracture gap, as follows: anterior femur view (along the lateral edge at 10, 50, 90, 125, and 160 mm), medial femur view (along midline at 10, 35, 60, 85, and 115 mm), lateral femur view (along midline starting at 120, 140, and 160 mm), and lateral plate view (along midline at 15, 45, 75, and 105 mm).Symbols (&, $, ∼, #, @, *, %, =, +, −) indicate pairwise comparisons that were statistically different (p < 0.05), whereas all other comparisons were not different (p ≥ 0.05). Numerical values are the sum of the principle stresses.

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Fig. 7

FEA stress maps for the synthetic femurs showing (a) stage 1, (b) stage 2, (c) stage 3, and (d) stage 4. The anterior view is shown. M = metal plate and C = composite plate.

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Fig. 8

FEA stress values for femurs and plates for (a) anterior femur, (b) medial femur, (c) lateral femur, and (d) lateral plate data. The locations from where the stress values were extracted are illustrated by white circles (○) on the schematic of the femurs. FE stresses were extracted at specific distances from the top bone surface of the fracture gap, as follows: anterior femur view (along the lateral edge at 10, 50, 90, 125, and 160 mm), medial femur view (along midline at 10, 35, 60, 85, and 115 mm), lateral femur view (along midline starting at 120, 140, and 160 mm), and lateral plate view (along midline at 15, 45, 75, and 105 mm). Numerical values are the sum of the principle stresses.

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