Abstract
Over the last decade, demand has increased for developing new, alternative materials in pediatric trauma care to overcome the disadvantages associated with conventional implant materials. Magnesium (Mg)-based alloys seem to adequately fulfill the vision of a homogeneously resorbable, biocompatible, load-bearing and functionally supportive implant. The aim of the present study is to introduce the high-strength, lean alloy Mg‒0.45Zn‒0.45Ca, in wt% (ZX00), and for the first time investigate the clinical applicability of screw osteosynthesis using this alloy that contains no rare-earth elements. The alloy was applied in a growing sheep model with osteotomized bone (simulating a fracture) and compared to a non-osteotomy control group regarding degradation behavior and fracture healing. The alloy exhibits an ultimate tensile strength of 285.7 ± 3.1 MPa, an elongation at fracture of 18.2 ± 2.1%, and a reduced in vitro degradation rate compared to alloys containing higher amounts of Zn. In vivo, no significant difference between the osteotomized bone and the control group was found regarding the change in screw volume over implantation time. Therefore, it can be concluded that the fracture healing process, including its effects on the surrounding area, has no significant influence on degradation behavior. There was also no negative influence from hydrogen-gas formation on fracture healing. Despite the proximal and distal screws showing chronologically different gas release, the osteotomy showed complete consolidation. Statement of SignificanceConventional implants involve several disadvantages in pediatric trauma care. Magnesium-based alloys seem to overcome these issues as discussed in the recent literature. This study evaluates the clinical applicability of high-strength lean Mg‒0.45Zn‒0.45Ca (ZX00) screws in a growing-sheep model. Two groups, one including a simulated fracture and one group without fracture, underwent implantation of the alloy and were compared to each other. No significant difference regarding screw volume was observed between the groups. There was no negative influence of hydrogen-gas formation on fracture healing and a complete fracture consolidation was found after 12 weeks for all animals investigated.
Highlights
Osteosynthesis has become the procedure of choice for unstable and displaced bones in fracture treatment in the field of pediatric orthopedics
We investigated screws made of ZX00 in vivo for their applicability in fracture stabilization and their degradation during bone healing in a growing animal
The alloy composition was determined by inductively coupled plasma optical emission spectrometry (ICP-OES) and trace elements were quantified by glow discharge mass spectrometry (GDMS), which entails a relative error of 20%
Summary
Osteosynthesis has become the procedure of choice for unstable and displaced bones in fracture treatment in the field of pediatric orthopedics. Rigid internal fixation is a limitation, especially in childhood trauma Most of these implants must be removed in a second surgery, to avoid impeding longitudinal bone growth or growth disturbances, if inserted near or in the physis [4]. These implants appear to be too rigid and exceed their purpose of stabilization and deprive the bone of its task as a load carrier. This can cause "stress shielding", which leads to reduced bone remodeling due to the implant, with subsequently higher rates of re-fractures [5,6,7]
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