gms | German Medical Science

Deutscher Kongress für Orthopädie und Unfallchirurgie (DKOU 2015)

20.10. - 23.10.2015, Berlin

Long-term in vivo degradation behaviour of Mg alloys WZ21 and ZX50 – A micro CT study

Meeting Abstract

  • presenting/speaker Elisabeth Martinelli - Department of Orthopedics, Graz, Austria
  • Johannes Eichler - Department of Orthopedics, Graz, Austria
  • Florian Amerstorfer - Department of Orthopedics, Graz, Austria
  • Tanja Kraus - Department of Pediatric Orthopedics, Graz, Austria
  • Stefan Franz Fischerauer - Department of Orthopedics, Graz, Austria
  • Peter J Uggowitzer - Metal Physics and Technology, Zürich, Switzerland
  • Jörg F Löffler - Metal Physics and Technology, Zürich, Switzerland
  • Annelie-Martina Weinberg - Department of Orthopedics, Graz, Austria

Deutscher Kongress für Orthopädie und Unfallchirurgie (DKOU 2015). Berlin, 20.-23.10.2015. Düsseldorf: German Medical Science GMS Publishing House; 2015. DocPO24-1418

doi: 10.3205/15dkou745, urn:nbn:de:0183-15dkou7459

Veröffentlicht: 5. Oktober 2015

© 2015 Martinelli et al.
Dieser Artikel ist ein Open-Access-Artikel und steht unter den Lizenzbedingungen der Creative Commons Attribution 4.0 License (Namensnennung). Lizenz-Angaben siehe http://creativecommons.org/licenses/by/4.0/.


Gliederung

Text

Objectives: Commonly used permanent materials offer very suitable biomechanical properties for fracture stabilization. In comparison to these commonly, biodegradable magnesium will make a second operation for implant removal unnecessary. Also its elastic modulus similar to human bone promises to support the fracture healing process by the avoidance of stress shielding.

Furthermore, production of hydrogen gas during degradation and the degradation time itself exhibit a strong correlation and need to show a balance between optimal stability during bone healing and moderate gas production. Restitutio ad integrum of bone structure after implant's full degradation should be achieved after 12-15 months. Our group has already investigated the degradation behaviour of two Mg alloys (fast degrading ZX50 and slow degrading WZ21) over a period of 9 months. This follow-up study aims to evaluate the long-term degradation behaviour of these alloys and the response of the bone between month 9 and 24.

Methods: Two different Mg alloys were investigated: ZX50 (Mg-5Zn-0.25Ca-0.15Mn-0Y); WZ21 (Mg-1Zn-0.25Ca-0.15Mn-2Y). For this study cylindrical pins with a diameter of 1.6 mm and a length of 8 mm were used. Eight pins per alloy were implanted through a transcortical drill in both femurs of male Sprague-Dawley® rats. Continuous microCT monitoring of degradation behaviour and histological examinations were performed at time points 9, 12, 15, 18 and 24 months. Volumes and surfaces were quantified using Siemens Inveon Acquisition Workplace Ver. 1.2.2.2.

Results: Implants volume and surface was measured at each timepoint. ZX50 did not show any degradation residuals after 9 months and a completely recovered and remodelled bone was noticed.

Focused on the ongoing degradation of WZ21, changes in pin volume, surface and gas emission were examined in vivo. WZ21 implants showed a production of hydrogen gas until month 12 without any visible interference on bone regeneration. Degradation rate seemed to be delayed in the area of cortical bone compared to the medullar cavity. After 18 months, implant residuals were noticed, but after 24 months WZ21 was degraded without any detectable corrosion products via micro CT or histological examination. The bone was fully remodelled without defects and restitutio ad integrum of the bone structure was achieved. None of the implants showed increase of inflammatory cells.

Discussion and conclusions: MicroCT and histological analysis of ZX50 did not show any noticeable long term defects in treated bone during the study period. The slight degradation rate and moderate gas production and also complete remodelling and restitutio ad integrum of the injured bone after month 24, suggest WZ21 to be a suitable material for orthopaedic application. Nevertheless it is unclear how the included REE Yttrium actually influences physiological reactions in the skeleton.