Composite bone models in orthopaedic surgery research and education.
ABSTRACT Composite bone models are increasingly used in orthopaedic biomechanics research and surgical education-applications that traditionally relied on cadavers. Cadaver bones are suboptimal for many reasons, including issues of cost, availability, preservation, and inconsistency between specimens. Further, cadaver samples disproportionately represent the elderly, whose bone quality may not be representative of the greater orthopaedic population. The current fourth-generation composite bone models provide an accurate reproduction of the biomechanical properties of human bone when placed under bending, axial, and torsional loads. The combination of glass fiber and epoxy resin components into a single phase has enabled manufacturing by injection molding. The high level of anatomic fidelity of the cadaver-based molds and negligible shrinkage properties of the epoxy resin results in a process that allows for excellent definition of anatomic detail in the cortical wall and optimized consistency of features between models. Recent biomechanical studies of composites have validated their use as a suitable substitute for cadaver specimens.
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ABSTRACT: 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 dynamic cyclic conditions, experiments were done using 6 artificial femurs cyclically loaded through the femoral head in axial compression for 4 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 traditional metal plate (Zimmer, Warsaw, IN, USA) (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 commercially-used metal bone plates.Journal of Biomechanical Engineering 05/2014; · 1.75 Impact Factor