Article
Effect of different thin, degradable ceramic coatings on the biomechanical stability of femoral implants
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Authors
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Philip Przybilla
- G.E.R.N., Dept. of Orthopedics Freiburg University, Freiburg, Germany
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Anke Bernstein
- G.E.R.N., Dept. of Orthopedics Freiburg University, Freiburg, Germany
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Michael Seidenstücker
- G.E.R.N., Dept. of Orthopedics Freiburg University, Freiburg, Germany
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Karola Müller
- G.E.R.N., Dept. of Orthopedics Freiburg University, Freiburg, Germany
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Sergio Latorre
- G.E.R.N., Dept. of Orthopedics Freiburg University, Freiburg, Germany
| Published: | October 22, 2019 |
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Outline
Text
Objectives: Modern implant coatings may increase osteointegration of orthopedic implants thereby achieving earlier secondary stability and reducing implant loosening. The most effective materials and optimal characteristics are currently unknown. This study aims to assess the effect of thin coatings consisting of ß-tricalcium phosphate (ß-TCP), Ca2KNa(PO4)2 (GB14), hydroxyapatite (HA) and Bioglass on shear strength of femoral implants at different points of time after implantation.
Methods: In this study, we surgically placed 146 titanium bone implants with 20 µm thick coatings of ß-TCP, GB14, HA or Bioglass bilaterally into the distal femoral metaphysis of 73 New Zealand White rabbits under general anesthesia with the standardized drill hole method. Implants were coated with high-velocity suspension flame spraying (HVSFS) to achieve coatings with a thickness of only 20 µm. After implantation, the rabbits were allowed full, unrestricted weight bearing by the legs. The femora were harvested 2, 4, 6, 12 or 24 weeks after implantation. Each metaphysis was cut into three discs of 2 mm each. Capacity to withstand shear forces at each harvest time was assessed through push-out testing with the Universalprüfmaschine Zwick Z020 under visual control. Afterwards, microscopy was performed to determine structural integrity of the coating. In parallel, histological examination and histomorphometry were carried out to evaluate coating degradation and osteointegration over the study period.
Results: Implants coated with HA achieved average shear strength of 1.92, 2.42, 2.39, 3.44 and 2.84 Megapascal (MPa) after 2, 4, 6, 12 and 24 weeks, respectively. Those with a ß-TCP coating reached 3.27, 3.87, 3.24, 3.91 and 3.30 MPa. GB14-coated implants arrived at 0.94, 3.11, 3.62, 3.66 and 5.47 MPa. Implants coated with Bioglass achieved 0.35, 0.17, 0.29, 1.04 and 2.26 MPa. At 2, 4 and 12 weeks, the ß-TCP-coated implants reached the greatest shear strength compared with the other implants and achieved maximum shear strength at 12 weeks. GB14-coated implants saw continuous increases in shear strength and reached the highest overall shear strength. Implants with HA coatings performed similar to GB14-coated implants except for the 24-week mark at which HA coatings lead to significantly lower shear strength than GB14 coatings. Implants coated with Bioglass reached the lowest shear strength at all harvesting times which corresponds to a demineralizing effect noted on histology. The generally high shear strengths observed correspond well with large areas of implant-bone-contact as noted on histological examination and histomorphometry.
Conclusion: The greatest average shear strength in the earlier stages between 2 and 12 weeks was achieved by implants coated with ß-TCP. At the final 24 week mark GB14-coated implants reached the highest shear strength of all implants. Our findings suggest that thin coatings of GB14, ß-TCP and HA may enhance the stability of bone implants.
