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.

Figure 1

Photographs of composite bone models during biomechanical testing. A, A four-point bending apparatus is used to test the flexural rigidity of a fourth-generation composite femur, with the lateral surface in tension. B, Torsional stiffness is tested by the application of a rotational force to this fourth-generation composite femur bedded in preformed molds crafted from an aluminum-filled epoxy resin. C, Appearance of a fourth-generation composite femur resting in shaped recesses proximally and distally during axial stiffness testing. A compressive load was applied through the formed interface to simulate a single-leg stance. (Panel A reproduced with permission from Heiner AD, Brown TD: Structural properties of a new design of composite replicate femurs and tibias. J Biomech 2001;34[6]:773-781. Panels B and C reproduced with permission from Gardner MP, Chong AC, Pollock AG, Wooley PH: Mechanical evaluation of large-size fourth-generation composite femur and tibia models. Ann Biomed Eng 2010;38[3]:613-620.)

Figure 2

Photographs of normal-density (A) and low-density osteoporotic (B) bone models. A, The normal-density fourth-generation composite bone model has a rigid urethane foam core that mimics cancellous bone found in cadaver specimens. B, Fourth-generation low-density model with open cell urethane foam and reduced thickness of the cortical short glass fiber reinforced material, which replicates osteoporotic changes. Low-density bone models have not yet been validated against cadaver specimens. (Reproduced with permission from Pacific Research Laboratories, Vashon, Washington.)