Does the modelling of the pectus bar affect its stability? Rationale for using a short flat bar

OBJECTIVES Although the Nuss procedure for pectus excavatum is still associated with a non-negligible risk of postoperative bar displacement, the potential effects of the length and shape of the bar on its corrective ability and stability have not been sufficiently studied. The aim of this study was to determine how the modelling of the pectus bar affects its stability and whether an alternative configuration of the implant can improve clinical success. METHODS Simulated implantation of bars with different shapes and sizes in a computational model was carried out. A 250 N sternal force was applied to the bars, and the resulting forces and moments on the fixation points were identified. Afterwards, a clinical trial was carried out in a group of patients with pectus excavatum, some of whom received long inverted U-shaped bars and some of whom received implants designed from the computational results. RESULTS When U-shaped bars were tested, the sternal force generated unbalanced horizontal reaction forces (16 vs 61 N) and large reaction moments at the ends of the bar, conferring the tendency to slide and to rotate, respectively. No lateral or rotational destabilizing forces occurred in the case of a flat bar. Cosmetic outcomes, postoperative times and hospital stays were similar in both clinical groups. However, 2 cases (2/15) of bar flipping occurred in patients who received the conventional bar. CONCLUSIONS The shape of the bar is a determinant of its stability. A flat, shorter pectus bar provides adequate correction of the deformity with less tendency for bar displacement in the repair of pectus excavatum.