Stiffness reduction of the rib cage to perform a minimally invasive pectus excavatum repair: biomechanical evaluation

OBJECTIVES

To study the influence of sternal transection and costal chondrotomies on the stiffness and stresses in the rib cage of adult patients undergoing Nuss pectus excavatum procedure.

METHODS

Four pectus excavatum models with different Haller indexes were created by parameterizing a 3D model of a rib cage obtained based on a computed tomography scan of a patient with no pectus deformity. Using the finite element method, insertion of intrathoracic bars into all models was simulated in 3 conditions, namely, non-intervened, transverse sternal section and costal chondrotomies. Stiffness, stress distribution and maximum stresses for each case were obtained and compared.

RESULTS

Transverse sternotomy provided a reduction of 44% to 54% in the stiffness of the rib cage, depending on the Haller index analysed, while chondrotomies promoted a stiffness reduction of 70%. Stress distribution in the rib cage followed similar pattern for all the tested Haller index, but the maximum stress decreased by 36% when performing a transverse sternotomy, whereas when performing costal chondrotomies, it decreased by 47%.

CONCLUSIONS

Computational results report that transverse sternotomy reduces appreciably the stiffness of the rib cage, while costal chondrotomies promote even a higher stiffness reduction. Thus, these surgical procedures could improve the clinical outcomes of adult patients undergoing a pectus excavatum repair.

Customized Two-Dimensional Computed Tomography-Guided Preoperative Pectus Bar Shaping

INTRODUCTION

Successful minimally invasive repair of pectus excavatum relies on a pectus bar that closely conforms to the desired shape of the sternum and ribs to produce optimal elevation and remodeling. However, the present method of empirical intraoperative bar shaping is tedious and risks trauma to surrounding structures. To overcome this, we devised a technique using a life-sized computed tomography (CT) printout of the patient's chest wall to guide preoperative bar bending.

METHODS

A 5-cm-wide polymethylmethacrylate block placed on the sternum as the patient underwent chest CT was used as a marker to guide scaling of an axial screenshot of the patient's chest to life-size. This life-size image was printed and the planned correction of the patient's chest wall was traced onto it. The pectus bar was bent according to this template. Patient demographics, Haller index, surgical indications, operative technique, complications, aesthetic and functional improvements, and overall satisfaction were assessed.

RESULTS

Thirty patients (4 women) underwent primary minimally invasive repair of pectus excavatum with a single pectus bar shaped preoperatively over an 8-year period. The average age and Haller index was 20.6 years and 5.4, respectively. The mean operative time was 66.4 minutes. Satisfactory sternal elevation was attained with a single attempt at bar insertion in all cases. Two patients had pneumothoraxes that resolved without intervention. The mean follow-up period was 50.1 months. There were no cases of bar migration or recurrence of deformity after bar removal. On a 5-point Likert scale, all patients indicated an improvement in aesthetic appearance (4.6), and patients with physical symptoms (10) reported an improvement in function (4.4). The overall satisfaction score was 4.7.

CONCLUSIONS

This technique of CT-guided preoperative pectus bar shaping is straightforward, eliminates the need for intraoperative revisions to bar shape, and achieves effective correction of the pectus excavatum deformity. All patients were satisfied with the aesthetic, functional, and overall outcomes.

Analysis of chest wall elevation after the Nuss procedure using 3D body scanning technique in patients with pectus excavatum

PURPOSE

For the evaluation of the chest wall deformity, we adopted a non-invasive 3D body scanning system. The objective of this study is to evaluate surgical effect on the whole thorax using 3D scanning technique before and after Nuss procedure.

METHODS

We performed 3D body scanning using Structure Sensor (Occipital Inc, USA) in 11 symmetric patients (average age 13 ± 3.2) under general anesthesia before and after Nuss procedure. Using the scanned data, the improved chest wall was analyzed using 3D-Rugle (Medic Engineering, Japan) imaging software. Preoperative and postoperative 3D data were super-imposed and a thoracic elevating distance in the line of the axial and sagittal section through the deepest point was calculated. Pre- and postoperative external sternal angle (ESA) were calculated from the scanned data.

RESULTS

Mean thoracic elevation distance at the deepest point was 38.6 ± 6.1 mm and it was 28.4 ± 5.1 mm and 19.4 ± 4.9 mm at 4 cm and 8 cm cranial side, respectively. Average ESA improved from 3.9 ± 1.6 degrees to 15.0 ± 1.1 degrees after the operation.

CONCLUSION

Chest depression was effectively elevated 39 mm at the deepest point after Nuss procedure. An indirect elevation effect by pectus bars was found on the wide area of the anterior chest.