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.