Fixation Release and the Bone Bandaid: A New Bone Fixation Device Paradigm

Area of Science:

• Biomedical Engineering
• Materials Science
• Orthopedic Surgery

Background:

• Current mandibular reconstruction using Ti-6Al-4V hardware and fibular grafts faces challenges like stress shielding and fixation failure.
• These issues can lead to poor bone integration and necessitate revision surgeries.

Purpose of the Study:

• To develop and evaluate a two-stage fixation device for mandibular segmental defect reconstruction.
• The goal is to ensure proper bone healing and restore natural stress trajectories in the reconstructed mandible.

Main Methods:

• A finite element (FE) model of mandibular reconstruction was developed, simulating healing (locked state) and post-healing (released state) phases.
• Response Surface Methodology (RSM) was used to optimize the geometry and pre-load of a Nitinol (NiTi) wire-frame apparatus.
• FE analysis and experimental testing (compressive and tensile) validated the fixation device's performance and safety.

Main Results:

• The proposed device effectively immobilizes the grafted bone during healing, with minimal surface gaps (21.54 microns).
• FE analysis and experimental studies confirmed the fixation devices' safety, with a safety factor of at least 10.3.
• Optimized NiTi wire parameters (diameters and pre-loads) were determined using RSM, closely matching natural mandibular stress distribution post-release.

Conclusions:

• The two-stage fixation system successfully addresses limitations of current methods by separating immobilization and regenerative phases.
• The NiTi wire-frame apparatus effectively restores natural stress-strain trajectories, promoting graft incorporation and reducing resorption.
• This innovative approach holds significant potential for improving outcomes in mandibular reconstruction surgery.