Numerical simulation of the post-surgical result in patients with pectus excavatum M Couto1, J Gomes Fonseca1, ACM Pinho2, J Fonseca3, J Correia-Pinto1, JL Vilaça1,4 1
ICVS/3B’s - PT Government Associate Laboratory, Braga/Guimarães, Portugal; 2 Mechanical Engineering Department, University of Minho, Guimarães, Portugal; 3 Industrial Electronics Department, University of Minho, Guimarães, Portugal; 4 DIGARC, Polytechnic Institute of Cávado and Ave, Barcelos, Portugal (
[email protected])
Introduction
Results
Pectus excavatum (PE) is a very common deformity characterized by the depression of the sternum and adjacent costal cartilage, which occurs in 1:400 births. Currently, the most performed surgical correction procedure is the minimally invasive Nuss technique, which consists on the substernal placement of a prosthetic bar, promoting the elevation of the chest wall.
For the analysis of the post-surgical chest surface variation, a sectional study was conducted in order to evaluate the correction area displacement: axial plane (nipple line) and sagittal plane (sternum line).
Fig.1 – Pectus excavatum chest. Diagram of the minimally invasive Nuss technique procedure.
Fig.3 – Representation of the anatomic planes considered to measure the mesh surface progression.
Objectives
30
• An accurate simulation of the surgery is able to provide, before the procedure, a 3D visualization of the thoracic cage final outcome. Therefore, considering the implications of the result, the surgeon is able to improve the bar application technique.
Mesh FEM Mesh Scan
25 (mm)
• The main goal of this work was to study the post-surgical result of patients with PE through numerical simulation of the Nuss procedure.
Mesh Surface in Axial Plane
20 15 10 5 0 30
Methods
Mesh Surface in Sagittal Plane Mesh FEM Mesh Scan
25 (mm)
Bar insertion surgery (Nuss technique)
Pectus excavatum patient
20 15 10
Thoracic CT
5
Chest Scan
0
Fig.4 – Lines of the mesh surface shape in axial and sagittal planes of the thorax sections.
3 Anatomic structures segmentation
FEM Numerical simulation of the post surgical result
3D volumetric mesh reconstruction
Comparison of the numerical simulation results with the chest surface scan performed after the bar insertion
A mesh overlap technique was used to provide a displacement magnitude map between CT pre-surgical model and the post-surgical FEM simulation. The results showed a variation of ~20mm on the correction area. Similarly, the same procedure was performed between the simulated FEM surface and the post-surgical scan. The results revealed a variation of ~10mm.
4
1
2
Fig.2 – Data processing for pectus excavatum patients flowchart.
1) Based on information provided by Computed Tomography, the internal and external morphological features of the deformed thoracic cage of a 16 year old male-patient with PE, were reproduced in a tridimensional model. 2) Taking into account the deformation asymmetry and depth, a patientspecific corrective bar was modeled and implemented in the ABAQUS simulation environment. 3) A 3D laser scanning of the chest wall (using Polhemus Fastscan System) was performed after the surgical procedure, characterizing the real thoracic surface features after the insertion of the prosthesis. 4) The results obtained were compared to the numerical simulation of the thoracic surface in order to validate the finite element analysis.
A
B
Fig.5 – Mapping of the displacement magnitude between the following mesh surfaces: A) CT data VS FEM simulation, and B) FEM simulation VS FastScan .
Conclusion Being the main purpose of the PE surgery the cosmetic result, the introduction of virtual simulation tools to predict and improve the overall curvature of the prosthetic bar, as well as the functional and visual outcome, has become the main reason to enhance patients quality of life. As so, it is expected that this novel method to predict the patient surgical outcome will help patients to accept the correction surgery and decrease the post-surgical corrections. Although this methodology have shown promising results for this PE case, a vast set of new patients is needed to prove the effectiveness of this approach. Also the different modeling steps and the FEM model achievement must be further improved and tested.
PTDC/SAU-BEB/103368/2008
FCOMP-01-0124-FEDER-010934
