Computer-aided design and manufacturing technology for identification of optimal Nuss procedure and fabrication of patient-specific Nuss bar for minimally invasive surgery of pectus excavatum

Abstract

The Nuss procedure is one of the most widely used operation techniques for pectus excavatum (PE) patients. It attains the normal shape of the chest wall by lifting the patient's chest wall with the Nuss bar. However, the Nuss bar is for the most part bent by a hand bender according to the patient's chest wall, and this procedure causes various problems such as the failure of the operation and a decreased satisfaction of the surgeon and patient about the operation. To solve this problem, we proposed a method for deriving the optimal operation result by designing patient-specific Nuss bars through computer-aided design (CAD) and computer-aided manufacturing (CAM), and by performing auto bending based on the design. In other words, a three-dimensional chest wall model was generated using the computed tomography (CT) image of a pectus excavatum patient, and an operation scenario was selected considering the Nuss bar insertion point and the post-operative chest wall shape. Then, a design drawing of the Nuss bar that could produce the optimal operation result was derived from the operation scenario. Furthermore, after a computerized numerical control (CNC) bending machine for the Nuss bar bending was constructed, the Nuss bar prototype was manufactured based on the derived design drawing of the Nuss bar. The Nuss bar designed and manufactured with the proposed method has been found to improve the Haller index (HI) of the pectus excavatum patient by approximately 37% (3.14 before to 1.98 after operation). Moreover, the machining error in the manufacturing was within ±5% compared to the design drawing. The method proposed and verified in this study is expected to reduce the failure rate of the Nuss procedure and significantly improve the satisfaction of the surgeon and patient about the operation.