The Magnet-Actuated Craniofacial (MAC) Distraction System: Magnetic Coupling Modeling

Craniofacial distraction osteogenesis (DO) has proven clinical effectiveness in the management of syndromic craniosynostosis and other complex craniofacial abnormalities. However, current craniofacial distraction systems rely on external activation ports which, in turn, increase the risk of infection, mechanical failure, premature removal of the distraction system and significant sociopsychological burden. To address these problems, we developed the Magnet-Actuated Craniofacial (MAC) distraction system, a fully-internalized distraction system to eliminate the need for external activation ports.

We conducted a comprehensive three-dimensional magnetostatic finite element modeling (FEM) framework to optimize the magnetic coupling efficiency of the MAC distraction system. Magnetic coupling configurations included a traditional coaxial dipole coupling and a redesigned U-shaped, flux-guided magnetic circuit incorporating high-energy neodymium magnets and a ferromagnetic shunt plate. Parametric analyses quantified torque-angle behavior, torsional stiffness, and axial forces over variable air domains (separation distances) up to 11.5 mm.

The coaxial dipole configuration exhibited steep torque and force decay with increasing air domain, limiting reliable actuation and torque transmission across variable, clinically relevant soft-tissue thicknesses. In contrast, the U-shaped, flux-guided architecture enforced a dominant magnetic return path, yielding up to a six-fold increase in peak torque and over a five-fold improvement in torsional stiffness at small air domains, while maintaining clinically relevant transmissible torque and attractive forces even at larger air domains.

Magnetic actuation limitations are not intrinsic but design-dependent. Flux-guided magnetic circuit engineering enabled robust, precise, predictable, and anatomy-tolerant transdermal torque transmission, supporting the feasibility of a fully-internalized, magnetically-actuated craniofacial distraction.