Abstract
Nickel-titanium shape memory alloy (NiTi-SMA) implants might allow modulating fracture healing, changing their stiffness through alteration of both elastic modulus and cross-sectional shape by employing the shape memory effect (SME). Hypotheses: a novel NiTi-SMA plate stabilizes tibia osteotomies in rabbits. After noninvasive electromagnetic induction heating the alloy exhibits the SME and the plate changes towards higher stiffness (inverse dynamization) resulting in increased fixation stiffness and equal or better bony healing. In 14 rabbits, 1.0 mm tibia osteotomies were fixed with our experimental plate. Animals were randomised for control or induction heating at three weeks postoperatively. Repetitive X-ray imaging and in vivo measurements of bending stiffness were performed. After sacrifice at 8 weeks, macroscopic evaluation, µCT, and post mortem bending tests of the tibiae were carried out. One death and one early implant dislocation occurred. Following electromagnetic induction heating, radiographic and macroscopic changes of the implant proved successful SME activation. All osteotomies healed. In the treatment group, bending stiffness increased over time. Differences between groups were not significant. In conclusion, we demonstrated successful healing of rabbit tibia osteotomies using our novel NiTi-SMA plate. We demonstrated shape-changing SME in-vivo through transcutaneous electromagnetic induction heating. Thus, future orthopaedic implants could be modified without additional surgery.
Highlights
Besides biological factors, such as blood supply, cellular immune response, and availability of osteoinductive cytokines, fracture healing strongly depends on adequate biomechanical stimuli [1,2,3]
After noninvasive electromagnetic induction heating the alloy exhibits the shape memory effect (SME) and the plate changes towards higher stiffness resulting in increased fixation stiffness and equal or better bony healing
We demonstrated shape-changing SME in-vivo through transcutaneous electromagnetic induction heating
Summary
Besides biological factors, such as blood supply, cellular immune response, and availability of osteoinductive cytokines, fracture healing strongly depends on adequate biomechanical stimuli [1,2,3]. While articular fractures require anatomic reduction and heal via direct (primary) bone healing without callus formation, this concept of absolute stability has occasionally led to nonunions, delayed healing, or implant failure in shaft fractures. More mechanically flexible devices for fixation, such as bridging plates or intramedullary nails, have been introduced, which allow for indirect (secondary) fracture healing via callus formation [4, 5]. It was further postulated that optimal strain would range between the minimum required for the induction of callus and the maximum that allowed bony bridging [4]. Others referred to interfragmentary movements to describe local mechanical conditions needed for adequate bony healing [6, 7]
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