Magnetic Mini Mover
The Problem
At present, pectus excavatum, or sunken chest disorder (one of the most common chest wall deformities), can be repaired only by a large and brutal operation requiring 3-7 days in the hospital. There are over 4,000 patients worldwide who undergo this operation every year.
The current surgery places a bar in the chest and uses extreme force applied during the operation to move the chest back to a normal position. There is serious post-operative pain associated with the procedure, and the patient may have to remain in the hospital for up to four days. The bar remains in place for up to two years before removal. Many people prefer to live with pectus excavatum rather than undergo this surgery due to the pain and prolonged discomfort.
The Solution
The Magnetic Mini Mover Procedure (3MP) uses two rare earth magnets to slowly reconfigure the child’s chest, similar in concept to orthodontics. By adjusting the external magnet (Magnatrac), the internal magnet (Magnimplant) can slowly reconfigure the chest.
In a 30 minute surgical procedure, one magnet, encased in titanium, is attached to sternum. Surgeons close the small incision, and the patient usually leaves the hospital on the same day. The patient continues to wear an orthotic brace that contains another embedded magnet.
As the magnets are slowly drawn together, the chest wall reforms to its normal position within a two year period. The device also has a means to monitor usage and pressure, a measurement of the procedure’s success. The device is currently in a clinical trial funded by the FDA, and the results are very promising.
We have incorporated a high-density steel focusing cup which optimizes the configuration of the external neodymium magnet. This focusing cup increases the magnetic force (applied by the external magnet) toward the internal magnet by shielding the force facing away from the brace. To assess this relationship, we tested various external magnet configurations coupled to an implant in an Instron mechanical testing machine and generated force-versus-displacement profiles for each setup. These data values allowed us to determine the configuration that generates adequate levels for force and reduces the weight and profile of the brace. The addition of the focusing cup increased the force between 6-8%.
We incorporated the following into the development of the Magnatract
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We have designed a small, robust device that will accurately measure force and temperature data over extended periods of time that can be easily downloaded from a micro SD card in the data logger.
Force (blue) and temperature (red) data for one month period. Data shows periods of brace wear.
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The can evolved to a completely self-contained and sealed unit, but with a micro SD card in the data logger that when removed and plugged into a computer via USB allows the doctor to download the data. The design specifications for the device are presented in the figure below.
Design specifications for Magnatract can with FSRs and data logger
For more information about 3MP and ongoing trials, please visit the UCSF Pediatric Surgery website.
There is an ongoing trial at UCSF for enrolled patients; it is currently closed to new patients. The status of the upcoming multicenter trial for children ages 8 to 14 years is still pending at this time. Please monitor the 3MP website for updates about when the status of the multicenter trial changes and new patient enrollments.
Links
Multicenter Trial of Magnetic Mini-Mover for Pectus Excavatum
Magnetic Mini-Mover Procedure - UCSF Benioff Children's Hospital
