title: Biomechanical characteristics of bioabsorbable magnesium-based (MgYREZr-alloy) interference screws with different threads.
abstract: OBJECTIVE
  Degradable magnesium implants have received increasing interest in recent years. In anterior cruciate ligament reconstruction surgery, the well-known osteoconductive effects of biodegradable magnesium alloys may be useful. The aim of this study was to examine whether interference screws made of MgYREZr have comparable biomechanical properties to commonly used biodegradable screws and whether a different thread on the magnesium screw has an influence on the fixation strength.
  
  
  METHODS
  Five magnesium (MgYREZr-alloy) screws were tested per group. Three different groups with variable thread designs (Designs 1, 2, and 3) were produced and compared with the commercially available bioabsorbable Bioacryl rapid polylactic-co-glycolic acid screw Milagro®. In vitro testing was performed in synthetic bone using artificial ligament fixed by an interference screw. The constructs were pretensioned with a constant load of 60 N for 30 s followed by 500 cycles between 60 N and 250 N at 1 Hz. Construct displacements between the 1st and 20th and the 21st and 500th cycles were recorded. After a 30 s break, a maximum load to failure test was performed at 1 mm/s measuring the maximum pull-out force.
  
  
  RESULTS
  The maximum loads to failure of all three types of magnesium interference screws (Design 1: 1,092 ± 133.7 N; Design 2: 1,014 ± 103.3 N; Design 3: 1,001 ± 124 N) were significantly larger than that of the bioabsorbable Milagro®interference screw (786.8 ± 62.5 N) (p < 0.05). However, the greatest maximum load was found with magnesium screw Design 1. Except for a significant difference between Designs 1 and 2, there were no further significant differences among the four groups in displacement after the 20th cycle.
  
  
  CONCLUSIONS
  Biomechanical testing showed higher pull-out forces for magnesium compared with a commercial polymer screw. Hence, they suggest better stability and are a potential alternative. The thread geometry does not significantly influence the stability provided by the magnesium implants. This study shows the first promising results of a degradable material, which may be a clinical alternative in the future.
authors.affiliation: Department of Orthopedic Surgery, Hannover Medical School, Anna-von-Borries-Straße 1-7, 30625, Hannover, Germany. marco.ezechieli@ddh-gruppe.de.
authors.forename: Marco
authors.initials: M
authors.lastname: Ezechieli
authors.affiliation: Department of Orthopedic Surgery, Hannover Medical School, Anna-von-Borries-Straße 1-7, 30625, Hannover, Germany.
authors.forename: Max
authors.initials: M
authors.lastname: Ettinger
authors.affiliation: Department of Orthopedic Surgery, Hannover Medical School, Anna-von-Borries-Straße 1-7, 30625, Hannover, Germany.
authors.forename: Carolin
authors.initials: C
authors.lastname: König
authors.affiliation: Department of Orthopedic Surgery, Hannover Medical School, Anna-von-Borries-Straße 1-7, 30625, Hannover, Germany.|CrossBIT, Center for Biocompatibility and Implant-Immunology, Department of Orthopedic Surgery, Hannover Medical School, Feodor-Lynen-Straße 31, 30625, Hannover, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Weizbauer
authors.affiliation: Institute of Production Engineering and Machine Tools (IFW), Leibniz Universität Hannover, Lise-Meitner-Straße 1, 30823, Garbsen, Germany.
authors.forename: Patrick
authors.initials: P
authors.lastname: Helmecke
authors.affiliation: Syntellix AG, Schiffgraben 11, 30159, Hannover, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Schavan
authors.affiliation: Syntellix AG, Schiffgraben 11, 30159, Hannover, Germany.
authors.forename: Arne
authors.initials: A
authors.lastname: Lucas
authors.affiliation: Department of Orthopedic Surgery, Hannover Medical School, Anna-von-Borries-Straße 1-7, 30625, Hannover, Germany.
authors.forename: Henning
authors.initials: H
authors.lastname: Windhagen
authors.affiliation: Department of Orthopedic Surgery, Hannover Medical School, Anna-von-Borries-Straße 1-7, 30625, Hannover, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Becher
mesh_terms: D020341:Absorbable Implants; D000497:Alloys; D016118:Anterior Cruciate Ligament / Q000601:surgery; D059549:Anterior Cruciate Ligament Reconstruction / Q000295:instrumentation; D001696:Biomechanical Phenomena; D001863:Bone Screws; D006801:Humans; D019344:Lactic Acid; D008274:Magnesium; D011100:Polyglycolic Acid; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer
chemical_list: D000497:Alloys; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; D019344:Lactic Acid; D008274:Magnesium
keywords: Anterior cruciate ligament; Biomechanics; Interference screw; Magnesium