Enhancing Torque Output for a Magnetic Actuation System for Robotic Spinal Distraction

Area of Science:

• Biomedical Engineering
• Medical Devices
• Orthopedic Surgery

Background:

• Magnetically controlled growing rods are used for early-onset scoliosis (EOS) treatment.
• Current limitations include insufficient distraction force and inability to monitor implant output in vivo.
• Optimizing rotor torque and defining a continuous rotation domain are crucial for safety and efficacy.

Purpose of the Study:

• To optimize the maximum torque and continuous rotation domain of magnetically controlled growing rods.
• To enhance the distraction force and in vivo monitoring capabilities of these implants.
• To address the clinical limitations of current EOS treatment devices.

Main Methods:

• Established a transient finite element magnetic field simulation model using ANSYS Maxwell.
• Analyzed the effects of clamp angle, pole pairs, rotor diameter, and rotational speed on rotor torque.
• Validated simulation results with experimental torque measurements and tested distraction force on a spinal growing rod platform.

Main Results:

• Optimized parameters (120° clamp angle, 1 pole pair, 8 mm rotor diameter) increased maximum torque by 201% in simulations.
• Experimental validation showed a threefold increase in maximum torque (30 N·mm to 90 N·mm).
• The optimized growing rod achieved a peak distraction force of 413 N, nearly double the commercial MAGEC system (208 N).

Conclusions:

• The study successfully optimized the performance of magnetically controlled growing rods, significantly enhancing distraction force.
• The established simulation and experimental methodologies provide a pathway for in vivo performance prediction and monitoring.
• This advancement addresses critical needs for safer and more effective smart implantable technologies in EOS treatment.