Safe Parameters for Utilizing Magnetic Growth Rods in Patient With a Vagal Nerve Stimulator and Case Report

Magnetic growing rods are being utilized more frequently in children with early-onset scoliosis. Many of these children have multiple medical problems and additional medical devices implanted that utilize similar magnetic technology, including vagal nerve stimulator (VNS) devices. There is some concern that the external remote controller (ERC) used to control the magnetic growth rod will interact with these devices during lengthening procedures. We believe there are safe parameters which allow the magnetic growth rod ERC to be utilized in patients with an implanted VNS.

A VNS device was tested in a simulation with the magnetic growth rods ERC to determine if it would activate/inactivate the device during a lengthening procedure. This study consists of 2 simulations. Simulation 1 evaluates placing the VNS adjacent to the ERC in the same coronal plane. Simulation 2 elevates the ERC placement above the device to simulate the thickness of a torso while increasing the distance of the VNS from the ERC in the coronal plane.

The time of exposure of the VNS device to the magnetic field had no correlation with activation. Distance had an effect on device activation. In the coronal plane of the device, activation occurred 43% of the time at 0 cm, 71% at 4 cm, and 5% activation at 8 cm. Greater than 10 cm had no activation. In the sagittal plane with the ERC 8 cm above the device, activation occurred 71% at 0 cm distance, 38% at 2 cm, and no activation occurred at a distance of >4 cm.

Utilization of the magnetic growth rod ERC can be carried out safely in patients with a VNS. Simulations show that an actuator implanted 4 cm from the VNS device in the coronal plane in a child with >8 cm chest wall thickness will not activate the VNS device. When choosing a rod configuration for implantation, the child's chest wall thickness and the ERC placement should be considered.