Biomechanical Test of a New Endoprosthesis for Cylindrical Medullary Canals in Dogs

Abstract

Exo-endoprosthesis is a limb salvage procedure for animals, although only expensive metal devices have been described. Now-a-days, new materials for this type of implant could be considered due to novel and affordable manufacturing techniques. However, a factor of safety (FoS) should be considered. There are kinetic and kinematic studies of canine natural gaits, which can be used to establish an FoS for mechanical tests for new non-metallic devices. Polyetheretherketone (PEEK) is used in different specialties in human medicine. Its mechanical properties (and its close mechanical stiffness to that of bone) make this polymer an alternative to metals in veterinary traumatology. PEEK could also be used in 3D printing. The suitability of a novel inner part of an exo-endoprosthesis manufactured by fuse deposition modeling (FDM) was presented in this study for long canine bones. Mechanical characterization of 3D-printed PEEK material and ex vivo mechanical tests of a customized endoprosthesis were performed to address it. Young's modulus of 3D-printed PEEK suffered a reduction of 30% in relation to bulk PEEK. Customized 3D-printed PEEK endoprostheses had promising outcomes for the tibiae of 20 kg dogs. Pure compression tests of the non-inserted endoprostheses showed a maximum force of 936 ± 199 N. In the bending tests of non-inserted endoprostheses, the PEEK part remained intact. Quasistatic mechanical tests of bone-inserted endoprostheses (compression-bending and pure compression tests) reached a maximum force of 785 ± 101 N and 1,642 ± 447 N, respectively. In fatigue tests, the samples reached 500,000 cycles without failure or detriment to their quasistatic results. These outcomes surpass the natural weight-bearing of dogs, even during a galloping pace. In conclusion, the 3D-printed PEEK part of the endoprosthesis for an exo-endoprosthesis can withstand loading, even during a galloping pace.

Biomechanical Tests on Long-Bone Elliptical Medullary-Canal Endoprostheses for Limb Salvage in Dogs

“…Mechanical properties of the 3D-printed PEEK (Young’s modulus, tensile strength, and bending strength) had already been determined in a previous study [ 20 ]. To determine de Poisson’s ratio of the 3D-printed PEEK, an increasing load was applied with a Universal Testing Machine IBTH/500 (SAE Ibertest, Madrid, Spain) ( Figure 4 ).…”

“…An interesting alternative as a polymer is polyether ether ketone (PEEK) [ 19 ]. It is demonstrated that 3D-printing reduces mechanical properties of polymers, and PEEK is no exception [ 20 ]. Its mechanical properties, even if printed models had 100% infill, were inferior to those of injection-molded PEEK due to the porosity that remains after the 3D-printing process [ 21 ].…”

“…Consequently, instead of just expecting device failure [ 10 , 42 , 43 ], these “natural” values could be considered as a reference for ex vivo mechanical tests of new implants. Hence, the FoS could be readjusted for evaluating new, non-metallic materials as was previously described for canine bones with cylindrical medullary canals in Mendaza et al [ 20 ].…”

“…The aim of this study was an ex vivo assessment of the biomechanical behavior of 3D-printed PEEK for an intraosseous transcutaneous implant for bones with an elliptical medullary canal. Implants were inserted into canine radii which received static (pure compression and torsional loads) and dynamic loads in a vertical fashion, imitating general canine carpus angulation, contrary to what has recently been published for canine tibiae such as bones with a cylindrical medullary canal [ 20 ].…”