Parametric Optimization of a Permanent Magnet Driver for Implantable Intramedullary Nail

An intramedullary lengthening nail avoids complications frequently found in the external fixator and shows remarkable clinical results. The magnetic drive is the mainstream actuation method for intramedullary lengthening nails which shows good results, but clinicians claim insufficient distraction torque of the intramedullary lengthening nail will occur occasionally. In this paper, we investigate the optimal parameters for magnetic drive intramedullary lengthening nail based on parametric modeling to ensure the rotor magnet is rotated synchronously and the distraction torque is sufficient for bone lengthening. The driver-rotor magnet model is established, and parametric optimization of the angular position of the driver magnet local coordinate system, the angular velocity of the driver magnet, the number of driver magnets, and the number of pole pairs of the driver magnet to determine optimal values. Optimal parameters are selected and verified by experiments. The results show that a pair of single-pole pairs of the driver magnet rotating with an angular speed of 50 rpm can meet the minimal distraction torque of 1.5 N mm, which is around 5.6 N mm.