Biomechanical modeling and problematic issues of surgical correction of congenital funnel chest deformity

Congenital funnel chest deformity (CFCD) is noted in 0.6–2.3% of the population and accounts for 90% of all congenital chest deformities. Nuss thoracoplasty is the most common method for treating CFCD, which is considered a minimally invasive technology and provides a quick cosmetic effect. Purpose is to search for models of CFCD and its surgical correction in order to create a technique that is as close to reality as possible, which will make it possible to optimally plan and rationally carry out the forthcoming operation. Analysis of literature sources showed that, on the one hand, the construction of simplified models of the chest allows quick research, but these simplifications do not allow for an objective assessment of the influence and interaction of various elements of the complex biomechanical system «sternum–rib–spine». On the other hand, complex models are more reliable, but hardly available for implementation due to their ultra-high manufacturability and cost. In addition, in studies of stress-strain state on models of the chest, the presence of the spinal column or the interaction of the ribs with the vertebrae has been insufficiently studied. When in the works on modeling road traffic injuries this is justified due to the support of the spine on the seat, then when modeling the correction of chest deformities, the lack of consideration of the mobility of the articular joints and the flexibility of the spinal column can lead to incorrect and false results. It is promising to create a technique for modeling CFCD and its surgical correction in conditions close to reality. This will make it possible to develop a rational modification of thoracoplasty based on the D. Nuss operation under the condition of one–stage full–fledged stable correction and minimal biomechanical loads in the «sternum-rib-spine» system. No conflicts of interest was declared by the authors. Key words: funnel chest deformity, thoracoplasty, biomechanics.

Method of fixing titanium pectus bar in surgical correction of funnel chest and its mathematical modeling

The most common surgery for the correction of congenital funnel chest in the 21st century is the Nuss procedure. This intervention is accompanied by complications related to the actual fixing bar and its size and placement and methods of fixing. The most common of these are bar displacement and chronic postoperative pain. Only one size of corrective bar (thickness, width) is used for this type of operation in all age groups. Purpose – to develop and implement the original modification of the Nuss procedure with individual calculation of the minimum dimensions of the corrective bar; to eliminate the probability of bar displacement; reduce the duration and intensity of postoperative pain. Materials and methods. The original method of the correcting titanium bar fixing as a monolithic metal arched structure with rigidly fixed ends was used in the study, the subperiostal fastening of the bar stabilizers to two ribs on each side was used. This method was used to operate on 34 patients with funnel chest aged from 6 to 17 years. Results. Mathematical modeling of the functioning of the correcting bar as a monolithic metal arched structure with rigidly fixed ends and determination of its strength and rigidity were performed. As an example, when calculating the stiffness of a plate with a width of 12 mm and a thickness of 2.2 mm under the use of a load of 25 kg (250 N) and an arch width of 20 cm, we determine the deflection of the bar 3.57 mm, strength factor 1.8. The loads of 250 N are much higher than those that actually exist. The cases of depression of the thorax (deflection of the bar) and cases of eruption of the bar were non indicated. The analyzis the level of postoperative pain syndrome on the NRSP scale for 4–5 days after surgery in patients with II degree of funnel chest determined an average score of 3.74; with III degree – 4.18; after one month of the operation – 1.0 and 1.63, respectively. Chronic postoperative pain was not noted. Conclusions. Rigid subptriostal fixation of the bat stabilizers to two ribs on each side prevents the plate from shifting. The proposed method of mathematical modeling of plate dimensions allows to individually calculate the dimensions of the correcting bar, providing in the vast majority of cases the correction of deformation bars 10, 11, 12 mm. The intensity and duration of the pain syndrome is much less than in standard technique due to the redistribution of pressure on the fulcrums of the bar and the absence of injury to the intercostal nerves, reducing the size of the plate. The research was carried out in accordance with the principles of the Helsinki declaration. The study protocol was approved by the Zhytomyr Regional Pediatric Clinical Hospital of the Zhytomyr Regional Council, Ukraine. The informed consent of the patient was obtained for conducting the studies. No conflict of interest was declared by the authors. Key words: Nuss procedure, funnel chest, fixing bardimensions, method of fixation.

Nuss surgery: ways to reduce the frequency of postoperative complications, severity and duration of postoperative pain

Funnel chest deformity is the most common malformation of the anterior chest wall, which in many cases leads to cardiorespiratory disorders and psychological problems. The undisputed progress in her treatment is the Nuss procedure, which is the «gold standard». However, this surgical operation and its modifications carry potential risks of severe postoperative and intraoperati. The aim is analyzation the existing variants of Nuss procedure and developing our own modification of this kind of surgery to eliminate intraoperative risks, reduce the level of postoperative complications, minimize postoperative pain. Materials and methods. In 2018–2019, the authors operated on 34 patients with funnel chest (Nuss operation in its own modification) with II and III degrees of deformity. The analysis of postoperative complications, the level of postoperative pain on the NRSP scale up to 3 months after surgery; duration of interventions, volume of intraoperative bleeding are made. Features of the proposed modification of the operation are: 1) Using of a monolithic T-shaped titanium bar with a removable stabilizer; 2) Formation of the tunnel is strictly under the muscles; 3) Rigid subperiostal fixation of bar stabilizers to two ribs on each side; 4) Using bars of different width for different age categories; 5) As a device for gradual dosed intraoperative lifting of the sternum used a turnbuckle; 6) The working port is entered through the right main access and through the right subpectoral tunnel; 7) Correction of asymmetric forms of deformation is carried out due to asymmetric rigid fixation of stabilizers and traction of the sternum by several ligaturesve complications. Results. The proposed modification of the Nuss operation reduces intra- and postoperative risks: only one postoperative complication was registered (2.9%); the method fixation of bar avoids the risks of eruption, displacement and reversal of the bar (no case has been registered), significantly reduces postoperative pain and prevents its chronicity. In all cases of correction of asymmetric forms of deformation it was possible to achieve good aesthetic results with the installation of one fixing bar. Conclusions. Gradual traction of the sternum to the position of moderate hypercorrection eliminates the risk of manipulation in the retrosternal space; subperiostal fixation of the bar to two ribs on each side guarantees reliable fixation of the plate without the risk of its displacement and reversal. Smaller bar thickness and width; fixing it as an arched structure reduces injuries of intercostal vascular nerve bundles and ribs and reduces postoperative pain. Placing the working port at the point of exit of the bar from the right pleural cavity facilitates and ensures manipulation in the mediastinum, providing sufficient elevation of the sternum. When using the proposed modification in most cases, it is sufficient to install one correction bar. The research was carried out in accordance with the principles of the Helsinki Declaration. The study protocol was approved by the Local Ethics Committee of these Institutes. The informed consent of the patient was obtained for conducting the studies. The authors declare no conflicts of interests. Key words: Nuss procedure, funnel chest, postoperative complications, postoperative pain syndrome, intraoperative lifting of sternum, turn-buckle, fixation of bar, thoracoscopy.

Morphological Features in the Tissues of the Sternal-rib Complex in Children with Funnel Chest Deformation

Objective: to evaluate the reactive changes in chondrocytes of the cartilage of the sterno-costal complex with its morphological characteristics of the components of the sterno-costal complex in children with funnel chest deformity. Methods. This article presents the material of morphological studies of the biopsy material of the costal-cartilage part, taken from 66 children (3-18 years old). For histological examination, intraoperatively removed tissue pieces from the anatomically modified cartilaginous elements of the sternum-costal complex of the anterior chest wall during thoracoplasty, were fixed in an aldehyde-osmium solution, and were placed in aralditis. A quantitative study of reactive changes in chondrocyte cartilage was carried out. Results. The quantitative studies of changes in the chondrocytes of the cartilage of the sterno-costal complex indicate pronounced changes in the chondrocytes of the surface zone with a decrease in the nuclear-cytoplasmic index with a more significant increase in the volume fraction of cytoplasm. The obtained results indicate a rather high degree of severity of compensatory reactions of the cartilage tissue of the sterno-costal complex in children. Conclusions. Morphological studies show that properly selected preoperative administration of patients with funnel chest deformity leads to a significant prevention of residual effects of connective tissue dysplasia, which also reduces the likelihood of the formation of gross morphological changes in the structures of the sterno-costal complex.

Pectus updates and special considerations in Marfan syndrome

Congenital chest wall or pectus deformities including pectus excavatum (funnel chest) and pectus carinatum (pigeon chest) affect a significant proportion of the general population and up to 70% of patients with Marfan syndrome. Patients often experience significant morbidity and psychological distress, which can worsen with age. Here we discuss new techniques for both operative and non-operative treatment of pectus deformity, the importance of a welltimed intervention and special considerations in patients with Marfan syndrome.