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Magnetic Mini-Mover Procedure for pectus excavatum: I. Development, design, and simulations for feasibility and
Michael R Harrison1, Denise Estefan-Ventura, Richard Fechter
1Division of Pediatric Surgery, Department of Surgery, University of California, San Francisco, CA 94143-0570, USA. harrisonm@surgery.ucsf.edu
Background/Purpose:
Correction of pectus excavatum (PE) results in measurable improvement in lung capacity and cardiac performance as well as improved appearance and self-image. The Nuss and modified Ravitch approaches attempt to correct the chest wall deformity by forcing the sternum forward in 1 step and holding it in place using a metal strut. The initial operation requires extensive manipulation under general anesthesia and results in postoperative pain, requiring hospitalization and regional anesthesia. Pain and disability may last for weeks. Both procedures are expensive. A better principle would be a gradual bit-by-bit repair via small increments of pressure applied over many months. We developed the Magnetic Mini-Mover Procedure and applied this strategy to correct PE.
Methods:
The Magnetic Mini-Mover Procedure uses magnetic force to pull the sternum forward. An internal magnet implanted on the sternum and an external magnet in a nonobtrusive custom-fitted anterior chest wall orthosis produce an adjustable outward force on the sternum. Outward force is maintained until the abnormal costal cartilages are remodeled and the pectus deformity is corrected.
Results:
We implanted a magnet in human skeletons and measured the force applied to the sternum when the distance between the internal and external magnets was varied in increments. With the 2 magnets 1 cm apart, the outward force was adequate to move the sternum at least 1 cm. We also mapped the magnetic field in the two-magnet configuration and found that maximum field strengths at the surface of the heart and at the outer surface of the orthosis were at safe levels.
Conclusions:
The Magnetic Mini-Mover Procedure allows correction of PE by applying magnetic force over a period of months. Crucial questions raised during our design, redesign, and simulation testing have been satisfactorily answered, and we have received a Food and Drug Administration Investigation Device Exemption (G050196/A002) to proceed with a phase I to II clinical trial.
