Study of the corrective effect of different fixators on pectus excavatum during Nuss procedure

Abstract

Background. A funnel chest is one of the most common chest deformities, which leads not only to cosmetic problems in adolescents, but also to cardiopulmonary complications. The main method of surgical correction is the Nuss procedure. The issues of the interaction between the fixator and the sternocostal joint depending on the choice of the plate length and the location of the tunnel for the fixator inside the chest to exit it on the opposite side remain undefined. Goal: to study the maximum relative deformities and displacements that occur in the chest model depending on the correction for pectus excavatum. Materials and methods. Four schemes for the correction of a funnel chest were modeled: 1) medial delivery of the fixator, the entry point is parasternal, using one retrosternal plate with transverse stabilizing bars (a short plate); 2) lateral passage of the fixator, the point of entry and exit from the chest is at the level of the anterior axillary line, using one retrosternal plate with transverse stabilizing bars; accordingly, the sternal plate is longer, ends at the level of the midaxillary line (a long plate); 3) a double plate with transverse bars connecting the plates with the help of screws (a short bridge-type fixator) with medial delivery; 4) a double plate with transverse bars connecting the plates with the help of screws (a long bridge-type fixator) with lateral delivery. The models were loaded with a distributed force of 100 N applied to the sternum. Results. When correcting pectus excavatum with a short plate, the cartilages of the fourth ribs turn out to be the most deformed — 3.3 %. In the cartilages of the ribs located above, deformities are in the range from 2.7 to 3.1 %. The use of a long plate decreases the relative deformities of the cartilage on almost all ribs. The scheme of correction using a short bridge-type fixator allows significantly reducing the deformities of all costal cartilages. The maximum is observed in the cartilage of the second and first ribs — 2.0 and 1.8 %, respectively. Replacing a short bridge-type fixator with a long one leads to the fact that the cartilages of the upper ribs remain deformed — 1.8 %, and a deformity gradually decreases to 1.0 % in the cartilages of the fourth ribs. The maximum movements in all schemes for pectus excavatum correction fall on the xiphoid process. The maximum displacement of 6.0 mm in the xiphoid process occurs when using a short plate. Replacing the plate with a long one decreases the displacement of the xiphoid process to 5.0 mm. When using a bridge-type fixator, the displacement of the xiphoid process is determined at the marks of 4 and 3 mm for a short and long fixator, respectively. Conclusions. All the investigated indicators testify to the advantages of a double bridge-type fixator. The medial passage of the fixator (short plates) has greater corrective forces on the anterior chest wall during elevation, which should be considered when choosing a correction technique. However, the lateral application of the fixator distributes the corrective effect by area, which can be important in preventing erosion of the tissues of the inner chest wall, the need for extended elevation of the depression in flat-concave forms of pectus excavatum, and the reduction of pain syndrome in the postoperative period.