BACKGROUND
Computer-aided design (CAD) has been used in the Nuss procedure to determine the bar length and shape. Despite computer aid, the shape and design remain quite intuitive. We tested a new algorithm to determine the optimal bar shape.
MATERIAL AND METHODS
The normal sterno-vertebral distance was defined on computed tomography (CT) scans of patients without pectus excavatum (PEx) at the same level where the deepest depression was found on CT scans of 97 patients with PEx. Four points were marked on the CT scan of 60 patients with PEx at the deepest deformity: P1: edge of the vertebra; P2: edge of the deformity; P3: the expected contact point of the bar and the rib; and P4: the expected end of the bar. The algorithm generated 3 circles upon these points, and the fusion of the arcs drew the line of the ideal bar. Corrected and normal sterno-vertebral distance values were compared with the Mann-Whitney U test. Ten bars were bent manually guided by a 1: 1 printout of the designed bar and were implanted in 10 adolescents.
RESULTS
The shortest sterno-vertebral distance was 3 cm below the intermammillary line in PEx patients. The normal mean sterno-vertebral distance at this level was 10.16±1.35 cm in non-PEx patients. The mean virtually corrected sterno-vertebral distance was 10.28±1.27 cm. No significant difference was found (P=0.44). The bars were seamless and were successfully implanted. No bar needed adjustment, the operation time was shorter, and the patient satisfaction score was 9.4/10.
CONCLUSIONS
With our new algorithm, an optimal Nuss bar can be designed.

Keywords: Pectus Excavatum; Nuss Procedure; Computer-Aided Design of Custom-Made Nuss Bar; Python Software; Mathematical Model; Thoracic Deformity; Individual Implant; CT-Based Geometric Correction Algorithm