Biomechanical characteristics of bioabsorbable magnesium-based (MgYREZr-alloy) interference screws with different threads
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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.
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.
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.
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.
KeywordsAnterior cruciate ligament Magnesium Interference screw Biomechanics
We thank our project partner Syntellix for providing us with the magnesium alloy MgYREZr (MAGNEZIX™), and the Institute of Production Engineering and Machine Tools in Hannover for producing the screws. We are also grateful for the support of the German Research Foundation (DFG) in promoting this research within the collaborative research Project SFB 599.
Conflict of interest
The company Syntellix AG, Hannover, employs Mr. Robert Schavan and Mr. Arne Lucas; they have not influenced the collection of data or its interpretation. The other authors have no competing interests. The other authors, their immediate family, and any research foundation with which they are affiliated did not receive any other benefits from any commercial entity related to the subject of this article.
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