Is a shorter bar an effective solution to avoid bar dislocation in a nuss procedure?

BACKGROUND: A variety of expedients to minimize bar dislocation in the Nuss procedure has been reported. The aims of this study were to create a mathematical model to define mechanical stresses acting on bars of different lengths in the Nuss procedure, and to apply this model to clinical scenarios. METHODS: Finite element model analyses were used to outline the mechanical stresses and to mathematically define different cases. Data from a group of patients with procedures carried out using standard Nuss criteria (NC group; bars half an inch shorter than the distance between the mid-axillary lines) were compared with data from a second group treated by applying model-based suggestions (MS group; bars approximately 3 inches shorter than the distance between the mid-axillary lines). RESULTS: Mean patient age in the NC group (48 cases) was 16.4 years old (84% males). The mean operating time was 57 minutes, and the mean bar length was 14.19 inches. There were 5 cases (10.4%) of bar dislocation. Mean patient age in the MS group (88 cases) was 16.2 years old (87% males). The mean operating time was 43 minutes and the mean bar length was 11.67 inches. There was only 1 bar dislocation, a reduction from 10.4% (NC) to 1.1% (MS) odds ratio 0.0989 (confidence interval 0.0112 to 0.8727), p = 0.0373. CONCLUSIONS: A shorter Nuss bar reduces tension on the sutures applied at bar extremities. This leads to enhanced bar stability and a reduced risk that the bar will flip. The use of a shorter Nuss bar may reduce the incidence of bar dislocation