Pectus Excavatum (PE) is a common deformity of the thoracic wall, characterized by a depression of the sternum. In the current golden standard for surgical correction of PE, the deformity is instantaneously corrected, causing severe and prolonged post-operative pain. The goal of this study is to design and validate a novel implant to slowly correct PE over time and minimize post-operative pain. A
new procedure was developed called SCARPE: spring-loaded continuously actuated repair of pectus excavation. During the SCARPE procedure, an implant continuously applies a small force on the posterior surface of the sternum. The continuous force is just large enough to stimulate cartilage remodeling and correct the deformity in two years. The SCARPE implant uses two symmetrically
located tape springs as force generator. A tape spring is a thin sheet of metal with a constant cross sectional radius. When subjected to sufficient bending, a tape springs starts to buckle and applies a constant bending moment. The resultant force can be controlled by adjusting the fold location of the buckled tape spring. Adjustments are non-invasively actuated by an external drive mechanism that creates a rotating magnetic field.
A proof-of-concept experiment was performed to investigate the force displacement relationship (FDR) of a tape spring mechanism in various conditions. It was found that the elevation force increased with spring size, number of layers and thickness. Furthermore, the FDR of the tape spring mechanism showed a unique curve for each fold distance, but was equal for the number of spring layers. Only three layered tape springs, with layers fixed together, applied an average elevation force large enough to correct the PE deformity in two years. None of the tape spring configurations, however, could adhere to all requirements simultaneously.
Although the tape springs could achieve a constant force within the force boundaries, some challenges arose. Mainly, the small margin towards the lower force boundary, delamination and anatomical constraints pose a problem. In its current form, the SCARPE implant is not yet suited for clinical application, but is to be considered as a novel approach towards PE repair. Several recommendations are presented for optimization, as well as alternative design proposals for future research.