title: In vivo evaluation of a magnesium-based degradable intramedullary nailing system in a sheep model.
abstract: The biocompatibility and the degradation behavior of the LAE442 magnesium-based intramedullary interlocked nailing system (IM-NS) was assessed in vivo in a comparative study (stainless austenitic steel 1.4441LA) for the first time. IM-NS was implanted into the right tibia (24-week investigation period; nails/screws diameter: 9 mm/3.5 mm, length: 130 mm/15-40 mm) of 10 adult sheep (LAE442, stainless steel, n=5 each group). Clinical and radiographic examinations, in vivo computed tomography (CT), ex vivo micro-computed tomography (μCT), mechanical and histological examinations and element analyses of alloying elements in inner organs were performed. The mechanical examinations (four-point bending) revealed a significant decrease of LAE442 implant stiffness, force at 0.2% offset yield point and maximum force. Periosteal (new bone formation) and endosteal (bone decline) located bone alterations occurred in both groups (LAE442 alloy more pronounced). Moderate gas formation was observed within the LAE442 alloy group. The CT-measured implant volume decreased slightly (not significant). Histologically a predominantly direct bone-to-implant interface existed within the LAE442 alloy group. Formation of a fibrous tissue capsule around the nail occurred in the steel group. Minor inflammatory infiltration was observed in the LAE442 alloy group. Significantly increased quantities of rare earth elements were detected in the LAE442 alloy group. μCT examination showed the beginning of corrosion in dependence of the surrounding tissue. After 24 weeks the local biocompatibility of LAE442 can be considered as suitable for a degradable implant material.
  
  
  CONCLUSIONS
  An application oriented interlocked intramedullary nailing system in a comparative study (degradable magnesium-based LAE442 alloy vs. steel alloy) was examined in a sheep model for the first time. We focused in particular on the examination of implant degradation by means of (μ-)CT, mechanical properties (four-point bending), clinical compatibility, local bone reactions (X-ray and histology) and possible systemic toxicity (histology and element analyses of inner organs). A significant decrease of magnesium (LAE442 alloy) implant stiffness and maximum force occurred. Moderate not clinically relevant gas accumulation was determined. A predominantly direct bone-to-implant contact existed within the magnesium (LAE442 alloy) group compared to an indirect contact in the steel group. Rare earth element accumulation could be observed in inner organs but H&E staining was inconspicuous.
authors.affiliation: Small Animal Clinic, University of Veterinary Medicine Hannover, Bünteweg 9, 30559 Hannover, Germany. Electronic address: christina.roessig@tiho-hannover.de.
authors.forename: Christina
authors.initials: C
authors.lastname: Rössig
authors.affiliation: Small Animal Clinic, University of Veterinary Medicine Hannover, Bünteweg 9, 30559 Hannover, Germany. Electronic address: nina.angrisani@tiho-hannover.de.
authors.forename: Nina
authors.initials: N
authors.lastname: Angrisani
authors.affiliation: Institute of Production Engineering and Machine Tools, Leibniz Universität Hannover, An der Universität 2, 30823 Garbsen, Germany. Electronic address: helmecke@ifw.uni-hannover.de.
authors.forename: Patrick
authors.initials: P
authors.lastname: Helmecke
authors.affiliation: Institute of Continuum Mechanics, Leibniz Universität Hannover, Appelstraße 11, 30167 Hannover, Germany. Electronic address: s.besdo@ikm.uni-hannover.de.
authors.forename: Silke
authors.initials: S
authors.lastname: Besdo
authors.affiliation: Institut für Werkstoffkunde, Leibniz Universität Hannover, An der Universität 2, 30823 Garbsen, Germany; Department of Materials Science and Engineering, Michigan Technological University, 1400 Townsend Dr., Houghton, MI 49931, United States. Electronic address: jseitz@mtu.edu.
authors.forename: Jan-Marten
authors.initials: JM
authors.lastname: Seitz
authors.affiliation: Laboratory for Biomechanics and Biomaterials, Department of Orthopaedic Surgery, Hannover Medical School, Anna-von-Borries-Straße 1-7, 30625 Hannover, Germany. Electronic address: welke.bastian@mh-hannover.de.
authors.forename: Bastian
authors.initials: B
authors.lastname: Welke
authors.affiliation: Department of Pathological Anatomy and Forensic Medicine, SE «Dnipropetrovsk Medical Academy of Health Ministry of Ukraine», Dzerginskogo street 9, Dnipropetrovsk 49044, Ukraine. Electronic address: fedchenko.nick@gmail.com.
authors.forename: Nickolay
authors.initials: N
authors.lastname: Fedchenko
authors.affiliation: Fraunhofer Institute of Toxicology and Experimental Medicine (ITEM), Bio- and Environmental Analytics, Fraunhofer Society for the Promotion of Applied Research, Nikolai-Fuchs-Straße 1, 30625 Hannover, Germany. Electronic address: heiko.kock@item.fraunhofer.de.
authors.forename: Heiko
authors.initials: H
authors.lastname: Kock
authors.affiliation: Small Animal Clinic, University of Veterinary Medicine Hannover, Bünteweg 9, 30559 Hannover, Germany. Electronic address: janin.reifenrath@tiho-hannover.de.
authors.forename: Janin
authors.initials: J
authors.lastname: Reifenrath
mesh_terms: D000497:Alloys / Q000494:pharmacology; D000818:Animals; D004195:Disease Models, Animal; D005260:Female; D005594:Fracture Fixation, Intramedullary; D020007:Implants, Experimental; D008274:Magnesium / Q000494:pharmacology*; D008422:Materials Testing; D012756:Sheep; D013977:Tibia / Q000000981:diagnostic imaging / Q000187:drug effects / Q000473:pathology; D014057:Tomography, X-Ray Computed
chemical_list: D000497:Alloys; D008274:Magnesium
keywords: Biocompatibility; Degradation; In vivo; Intramedullary nailing; Magnesium alloy