Comparative analysis of the stress-deformed state of the chest during the correction of the funnel-shaped deformity with the use of two plates: a comparison of the parallel and crossed methods of placing the fixators

Abstract

Minimally invasive correction of funnel-shaped chest deformity by the Nuss is an effective and cosmetic method of surgical correction of this deformity. Some authors have proposed the use of two plates with a crossed technique for correction. Purpose - to study the changes that occur in the stressed-deformed state of the chest model in comparison of the parallel crossed arrangement of the fixators during the minimally invasive correction of funnel-shaped chest deformity according to Nuss. Materials and methods. 2 schemes for the correction of the funnel-shaped deformation of the sternum were modeled: with a parallel arrangement of plates (parallel method), with a cross-shaped arrangement of plates (crossed method). The models were loaded with a distributed force of 100 N applied to the sternum. They studied the stress values in the bone elements, the relative deformations of costal cartilage, as the softest and, as a result, the most favorable to deformation element of the models. The magnitudes of the maximum movements of the sternum and corrective plates were also studied as an indicator of the preservation of the achieved correction. Results. The crossed method of positioning the corrective plates ensures a slightly lower level of stress in almost all bone elements. An exception can be considered the seventh ribs, where the stress, in this case, reaches 9.0 MPa, which is close to the lower limit of the indicators of the strength limit of the ribs. From the point of view of preserving deformation correction, the crossed method of arranging the correcting plates has a slight advantage of 1.0 mm. But the parallel scheme provides a smaller relative deformation of the costal cartilages. Taking into account all of the above, it can be concluded that none of the studied schemes has an unequivocal advantage over the other according to the criteria of mechanical indicators. Therefore, when choosing one or another scheme for the correction of a funnel-shaped sternum deformity, additional information should be taken into account, such as the shape of the sternum deformity and the rib, the convenience of carrying out the plates, the age of the patient, etc. Conclusions. None of the studied schemes has an unequivocal advantage over the other according to the criteria of mechanical indicators. From the point of view of preserving deformation correction, the crossed method of arranging the correcting plates has a slight advantage of 1.0 mm. The parallel scheme ensures a smaller relative deformation of the costal cartilages. According to the criterion of stress distribution in the bone elements of the model, the crossed method of arranging the corrective plates provides a slightly lower level in almost all bone elements, but the maximum stress value of 9.0 MPa on the seventh rib with the cross-shaped arrangement of the corrective plates approaches the lower limit of the index of the strength limit of the ribs which, in some cases, can cause its fracture. Additional information should be taken into account when choosing one or another scheme for the correction of the funnel-shaped deformity of the sternum. No conflict of interests was declared by the authors.