Preprint 1 Feasibility of using computer simulation to ...

Preprint

Feasibility of using computer simulation to predict the postoperative outcome of the minimally invasive Nuss procedure: Simulation prediction vs. postoperative clinical observation Kwong Ming Tse1, 2, *, Long Bin Tan1, Shu Jin Lee3, Mohamed Zulfikar Rasheed4, Bien Keem Tan4, Heow Pueh Lee1, * 1

Department of Mechanical Engineering, National University of Singapore 9 Engineering Drive 1, Singapore 117576

2

Department of Mechanical Engineering and Product Design Engineering, Swinburne University of Technology

Level 8, Advanced Technologies Centre, John Street, Hawthorn Campus, Victoria 3122, Australia 3

Mount Elizabeth Medical Centre

#16-13, 3 Mount Elizabeth, Singapore 228510 4

Department of Plastic, Reconstructive and Aesthetic Surgery, Singapore General Hospital 20 College Road, Singapore 169856 *E-mail: [email protected] or [email protected] (Tse, KM); [email protected] (Lee, HP) Phone: +65-65162205

Fax: +65-67791459

1 Tse, K. M.*, Tan, L, B., Lee, S. J., Rasheed, M. Z., Tan, B. K. and Lee, H. P.* (2018). Feasibility of using computer simulation to predict the postoperative outcome of the minimally invasive Nuss procedure: Simulation prediction vs. postoperative clinical observation. Journal of Plastic, Reconstructive & Aesthetic Surgery. doi: 10.1016/j.bjps.2018.05.026

Preprint Abstract The Nuss procedure is the most minimally invasive and commonly used surgical correction for pectus excavatum (PE) by using a pre-bent pectus bar to elevate the deformed chest wall. However, there exist some complications such as postoperative pain as well as surgical uncertainties due to human judgement. It is therefore important to understand the biomechanical effect of the pectus bar on PE thoraces undergoing an operation to alleviate the postoperative pain as well as to improve surgical outcome. The current study incorporated the finite element method (FEM) to simulate the entire Nuss procedure including the flipping process of the pectus bar on a preoperative PE patient-specific thorax model, in conjunction with comparison against the postoperative CT scans. The mid-sagittal sternovertebral elevation was found to be within 5.32 mm while the transverse sternal deviations ranged from 1.59 mm to 3.02 mm. The average discrepancy between the predicted contour and postoperative CT contour was about 3%. On a different note, the stress and strain distributions largely concurred with reported findings. High bilateral stress was seen to occur at the back of ribs near the vertebral column, and particularly over the 2nd to 5th ribs, while the greatest strain was found to be confined to the regions of costal cartilages. It is evident that the FEM is a feasible and robust approach of predicting the mechanical surgical procedure. This contributes to the future development of a predictive tool incorporated in surgical planning to enhance surgical management of pectus excavatum. (244 words) Keywords: Pectus excavatum, finite element, orthopaedic simulation, surgical planner, pectus carinatum, flipping


Preprint 1. Introduction Pectus excavatum (PE) is the most common congenital deformity of the anterior chest wall, in which several ribs and the sternum grow abnormally. The condition occurs in one of every 8001000 live births, with a male predominance 1, 2. Although in most instances PE has a limited impact on the functions of inner organs, the cosmetic appearance of the deformed chest can lead the patients to psychological impairment 3-5. Surgical correction is still considered the standard treatment for PE; and among all, the most feasible and first-choice treatment option is the minimally invasive Nuss procedure 1, 6. The Nuss procedure is basically a biomechanical surgical procedure, which achieves sternal elevation with the aid of a retrosternal metallic curve bar, known as pectus bar 6. Before the procedure, the surgeon prepares the pectus bar using flexible templates and decides on the length and curvature of the pectus bar based on his or her judgement, after identifying the most depressed zone and the most everted costal line on both sides of the sternum 3, 4 . Two skin incisions are then made on both sides of the middle axillary lines and a retrosternal curve pectus bar is inserted with its convex side faces posteriorly. Under thoracoscopy, the pectus bar is turned over with the aid of a bar-flipper, so that the convex side faces anteriorly. Under this lift maneuver, the sternum is pushed in the ventral direction and out of the depressed position, thereby correcting the PE. Despite the almost universal acceptance of the Nuss procedure, various outstanding uncertainties in the surgical parameters such as the placement position, length, and curvature of the pectus bar, pertaining to the procedure remain 7 . A pectus bar that is too tight on the sides will cause painful rib and muscle erosion and an increased likelihood of outgrowing the bar too soon 8 . Modifications and suggestions to improve the procedure have been raised by surgeons in this field of practice, however, these remain largely qualitative. A lack of accurate and reliable tools to quantify these surgical parameters does not only put barriers in surgical planning and communication but also compromises the risk of the surgical outcome as the surgical procedure becomes increasingly subjected to human judgment. In order to improve the surgical outcome of the Nuss procedure, the finite element method (FEM), which offers a cost-effective tool in predicting biomechanical parameters such as stress and strain fields, contact pressure and force between the pectus bar and the rib cage, can be used in surgical planner to eliminate or reduce the uncertainties that may arise from the surgeries solely relied on surgeons’ experience. There were only a few numbers of studies using the FEM to investigate the effect of the pectus bar on the thoracic cage. Nagasao et al. 9 developed adult and child finite element (FE) models of the thoracic cage using beam elements based on computed tomography (CT) scans of 18 patients and analyzed the stress patterns between adult and child patients. They had found that significantly higher stresses occurred in the adult thoracic cage and the stress patterns of the adult thoracic cage were more widely distributed than those in the children. They had also used similar techniques to study the dynamics effects of the Nuss procedure on the spine in the treatment of patients with PE with asymmetric thoraces 10. On the other hand, Chang et al. 11 built three patient-specific FE models of symmetric thoraces to identify the critical region with the greatest strain, i.e. the third through seventh cartilages. Wei et al. 12, 13 3 Tse, K. M.*, Tan, L, B., Lee, S. J., Rasheed, M. Z., Tan, B. K. and Lee, H. P.* (2018). Feasibility of using computer simulation to predict the postoperative outcome of the minimally invasive Nuss procedure: Simulation prediction vs. postoperative clinical observation. Journal of Plastic, Reconstructive & Aesthetic Surgery. doi: 10.1016/j.bjps.2018.05.026

Preprint reconstructed a preoperative patient-specific FE thoracic model of a child with PE and applied anterior displacement to lift a pectus bar that was deliberately placed with its convex side faces anteriorly. It was found that the predicted deformed shape of the thoracic cage was similar to that obtained from the postoperative CT scan. Despite the valuable information, these preliminary FE studies have some underlying limitations which can be improved further before the development of a FEM-based surgical planner for the Nuss procedure. Firstly, the existing studies did not simulate the turning over of the pectus bar during the actual Nuss procedure, and this would have a significant effect on the prediction of biomechanical parameters. Moreover, none of the studies showed any quantitative validation with postoperative measurement. The Nuss procedure, as described earlier, is a biomechanical procedure, in which the deformed thorax is forcibly corrected by insertion of the pre-bent pectus bar which generates stress on the chest wall. In our study, the entire Nuss procedure is replicated on a preoperative patient-specific FE model of a PE thorax in multiple steps of translational and rotational displacements. It is also the interest of this study to validate the feasibility of using the FEM in surgical planning by quantitatively comparing the mid-sagittal and transverse sternovertebral elevation between the FE simulation and postoperative measurement from CT scans. The validity of this study provides a basis for the future development of a non-invasive and reliable surgical planner to enhance surgical management of PE. 2. Methods and Materials 2.1 The FE Thoracic Model In this study, geometrical information of the thorax of an 18-year-old male patient (with height of 167 cm and weight of 50.7 kg) who suffered from PE (with preoperative Haller index of 2.83) was obtained from preoperative CT axial images with an in-plane resolution of 512 by 512 pixels with a pixel size of 0.592 mm and slice thickness of 5.0 mm. These medical images were imported into Mimics v15.01 (Materialise, Leuven, Belgium) for segmentation and reconstruction of a preoperative 3D patient-specific model of the PE thoracic cage (Figure 1). The patient-specific thoracic model comprised of the thoracic spine, ribs, costal cartilages and sternum (Figure 1A). The rib cortical bone was assumed to be of 0.75 mm thick 14 and was modelled as shell elements, whilst the trabecular bone was meshed with tetrahedral elements, conforming to the meshes of the cortical bone. The preoperative pre-bent pectus bar was modelled based on the dimensions obtained from the postoperative CT scans as well as from the BIOMET medical manufacturer’s product manual 15. A semi-automatic meshing technique was employed in HyperMesh v11.0 (Altair HyperWorks, Troy, MI, USA) to optimize between computational efficiency and element quality, resulting in 995,017 linear tetrahedral elements and shell elements in total. The entire thorax, comprised of the thoracic spine, ribs, costal cartilages and sternum costal cartilages, as well as the stainless steel pectus bar were modeled with linear elastic, isotropic material properties, shown in Table 1. 4 Tse, K. M.*, Tan, L, B., Lee, S. J., Rasheed, M. Z., Tan, B. K. and Lee, H. P.* (2018). Feasibility of using computer simulation to predict the postoperative outcome of the minimally invasive Nuss procedure: Simulation prediction vs. postoperative clinical observation. Journal of Plastic, Reconstructive & Aesthetic Surgery. doi: 10.1016/j.bjps.2018.05.026

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Table 1: Material properties of the skeleton components of thorax FE model in the Nuss procedure. Components

Young's Modulus (MPa)

Ref.

Poisson's ratio

Ref.

Density (kg/m3)

Ref.

Cortical Bone

17500

9

0.3

16

2000

16

Trabecular Bone

1800

9

0.45

16

1000

16

Costal Cartilage

12

11

0.4

17

1000

17

Pectus Bar

200000

0.3

7800

2.2 Finite Element Simulation As aforementioned, the entire Nuss procedure with the turning progress of the pectus bar was replicated in this study. The pectus bar was initially positioned with its convexity facing posteriorly, replicating the condition before the turning process (Figure 1A & 1B). In order to accurately reproduce the turning process executed by the surgeon with the bar-flipper, the motion of the pectus bar was described by the surgeon based on experience and a sequence of 22 microsteps, which comprised of rotational motion in all the 3 axes and translational motion only in the posterior-anterior direction (Figure 2). Only the two ends of the vertebral column were assumed to be fixed (Figure 2), with the assumption that the shape of the vertebral column remains changed during the procedure 11. All the thoracic cage components were tied to one another. The interaction between the sternum and pectus bar was modelled by tangential sliding contact condition using penalty friction formulation with the coefficient of friction of 0.05 as well as normal hard contact pressure-overclosure condition. The analysis was performed by the dynamic implicit solver in Abaqus v6.12 (SIMULIA, RI, USA). 2.3 Biomechanical Parameters and Simulation Verification In this study, von Mises stress was chosen as the biomechanical metric for stress analysis of the thoracic cage, since it is a scalar variable defined in terms of all individual stress components, thus, a good representative of the state of stresses. It has also been commonly utilized in numerous biomechanical studies in the literature 18, 19 for the measurement of skeletal stress intensity. Another commonly used variable in the finite element analyses of bone and tissue failure is the maximum principal strain, which has been identified as an indicator for bone fracture 20, 21, and as such, it was therefore included in the analysis of this study. Moreover, in order to verify the validity 5 Tse, K. M.*, Tan, L, B., Lee, S. J., Rasheed, M. Z., Tan, B. K. and Lee, H. P.* (2018). Feasibility of using computer simulation to predict the postoperative outcome of the minimally invasive Nuss procedure: Simulation prediction vs. postoperative clinical observation. Journal of Plastic, Reconstructive & Aesthetic Surgery. doi: 10.1016/j.bjps.2018.05.026

Preprint of the FE predictions, the predicted sternal elevations from the simulation, in both the mid-sagittal plane and transverse plane were obtained and were compared against those measured from postoperative CT images of the same patient (with postoperative Haller index of 2.31), at 3 years after the Nuss procedure. It should be noted that the sternal elevation in this study is defined as the anterior-posterior distance of the sternum measured from the central transverse axis of the vertical column (known as sternovertebral distance). This will provide a robust quantitative validation with the post-surgical outcome. 3. Results 3.1 Stress and Strain Analysis The predicted stress and strain of the thorax model were evaluated. Figure 3 shows the predicted von Mises stress contour plot experienced by the postoperative thorax. It can be seen that maximum von Mises stress of 132.6 MPa occurred at the 2nd to 5th ribs, towards the posterior regions in close proximity to the vertebral column. In contrast, the costal cartilage and sternum remained to experience relatively low stress throughout the process. The highest stressed regions were near the sternocostal joints and costochondral joints, with maximum von Mises stress of approximately 2 MPa. The strain distribution presented in Figure 4 shows that the costal cartilages near the xiphoid process experienced the highest strain of 0.47. The magnitude of strain in other regions of the thoracic cage turned out to much lower than the strain experienced in the costal cartilages. In addition, the sternal contact pressure with the pectus bar was found to about 20 MPa after the turning process and was observed to be confined at only 3 areas on the anterior part of the pectus bar as shown in Figure 5. 3.2 Comparison between the Simulated Prediction and the Post-Surgical Outcome The predicted sternal contour in the mid-sagittal plane was obtained from the 50 interior surface nodes of the mid-sternum (Figure 6). With the assumption that the vertical column remains unchanged through the Nuss procedure 11, the deviations at each of these exterior surface nodes, from the vertical column reference axis along the anterior-posterior direction were measured. This sternal contour along the mid-sternum surface path was plotted against that of the postoperative CT images (Figure 6). The pectus corrective bar raised the PE sternum, displacing the xiphoid process by about 20 mm, as shown in Figure 6. The FE-predicted mid-sagittal sternal contour matched very well with the postoperative position of the sternum in the CT images. A detailed quantitative evaluation was shown in Table 2, with the FE prediction underestimating the postoperative mid-sagittal sternovertebral elevation by only 3%.


Preprint Table 2: Comparison of the mid-sagittal and transverse sternovertebral deviations for preoperation, CT-measured & FE-predicted postoperation. Sternovertebral Deviations from the Vertical Column Reference

Mid-Sagittal Sternovertebral Elevation

Transverse Sternovertebral Elevation

Pre-Op (Average)

114.7 mm

125.3 mm

CT-Measured Post-Op (Average)

129.9 mm

140.0 mm

FE-Predicted Post-Op (Average)

125.9 mm

143.7 mm

-3.08%

2.64%

Min. Difference bet. CT-Measured & FEPredicted Post-Op

0.00 mm

1.59 mm

Max. Difference bet. CT-Measured & FEPredicted Post-Op

5.32 mm

3.82 mm

Discrepancy (%)

Since the sternal elevation arisen from the Nuss procedure is two-dimensional, the mediallateral sternal contour in the transverse cross-section near the pectus bar was also traced in a similar way for a complete qualitative analysis (Figure 7). It was shown that the difference between the postoperative CT-measured and FE-predicted lateral deviations was minimal, with the percentage discrepancy being 2.6%. The closeness of results between the FE prediction and CT measurements is evident when the sternal contour plots were superimposed, as shown in both Figures 6 & 7. 4. Discussion The Nuss procedure is considered the most effective and commonly used surgical method for the correction of pectus excavatum (PE) mainly because of its technical ease and minimal invasiveness. However, as aforementioned, there were many uncertainties in the surgical procedure as the outcome solely relies on surgeons’ experience and judgement. Furthermore, when the pectus bar is removed (usually after a period of at least two years), one main disadvantage is the postoperative pain that arises due to the considerable and prolonged stress concentration on the sternum and costal cartilages. It is therefore important to understand the stress occurrence pattern on the thoraces undergoing the operation to alleviate the postoperative pain. The current study employed the finite element method (FEM) to simulate the entire Nuss procedure including the flipping process of the pectus bar, on a preoperative PE patient-specific thorax model. To the authors’ knowledge, there is no reported numerical study, simulating the flipping process of the pectus bar in the Nuss procedure, which has a significant effect on the 7 Tse, K. M.*, Tan, L, B., Lee, S. J., Rasheed, M. Z., Tan, B. K. and Lee, H. P.* (2018). Feasibility of using computer simulation to predict the postoperative outcome of the minimally invasive Nuss procedure: Simulation prediction vs. postoperative clinical observation. Journal of Plastic, Reconstructive & Aesthetic Surgery. doi: 10.1016/j.bjps.2018.05.026

Preprint predicted biomechanical parameters. The PE patient-specific thorax model presented in this work also allowed the biomechanical stress and strain of the thoracic cage, arisen in the Nuss procedure, which cannot be measured in-vivoly, to be obtained. In this study, the predicted patterns and magnitudes of stress and strain, shown in Figures 6 & 7 appeared to concur with the findings by both Chang et al. 11 as well as Nagasao et al. 9. The FE simulation indicated that relatively high level of stress was found mainly towards the back of the patient, particularly at the thoracic ribs near the vertebral column. This has been suggested as a cause for the association to scoliosis and complains of back pain by patients 11, 22. Moreover, the costal cartilages near the sternal xiphoid process and the costochondral joints were found to experience stress level that was just slightly lower than both the tensile and compressive fracture loads in the control group in Feng et al. 23. This inferred that the structural integrity of the thoracic cage may be a cause for concern. As for the strain distribution, the converse was observed, with the bilateral concentration of maximum principal strain found on the costal cartilages at the sternocostal joints (between the sternum and costal cartilages) and costochondral joints (between costal cartilages and rib cage). The high strain values in the costal cartilages could be explained by their vastly lower stiffness as compared to that of the bony rib. These intensified strains at the sternocostal joints and costochondral joints were suggested as a cause for concern for the structural stability of the thoracic cage. In fact, these anatomical locations coincided with the micro-damaged regions identified in the postoperative PE patients’ thoraxes in the bone scintigraphy study by Ohno et al. 24. From the contact interaction between the pectus bar and sternum, it could be described that the sternum was simply balancing on the anterior portions of the pectus bar. This observation was consistent with the finding in the literature on the morphology of the sternum, especially one that is pointy or too sharp on the undersurface 7, 25, 26. One cause for concern is that the set-up may be inherently unstable and may over-elevate the sternum, especially in the sunken sternum cases with asymmetrical deformity 25. This would require more stabilizers and preoperative planning. Hence, the use of a predictive numerical tool (particularly the FEM) and patient-specific biomechanical model will allow the clinicians to foresee such excessive movements that can be detrimental to the patient. Moreover, these tools aid the clinicians in deciding on the initial deformed shape and size of the pectus bar as well as the optimal position for placing the corrective bar. Overall, the model prediction of the mid-sagittal and transverse sternal shape matched very well with that of the postoperative thorax. Moreover, to the authors’ knowledge, the current study is the only one that provides a quantitative comparison with postoperative measurement. This quantitative comparison of the mid-sagittal and transverse sternovertebral elevation between the FE prediction and the postoperative measurement from CT images, also confirms the validity of our study. This in turns demonstrates the feasibility of using the FEM to predict the surgical outcome of the Nuss procedure, providing a basis for the future development or integration of these predictive tools with a surgical planner to enhance surgical management of PE.


Preprint 6. Competing interests The authors declare that they have no financial and personal relationships with other people or organizations that could inappropriately influence the work. 7. Acknowledgement The authors would like to acknowledge the research support we received from their organizations, National University of Singapore, Mount Elizabeth Medical Centre and Singapore General Hospital. 8. References 1. Nuss D, Kelly RE, Jr., Croitoru DP, Katz ME. A 10-year review of a minimally invasive technique for the correction of pectus excavatum. J Pediatr Surg 1998: 33: 545-52. 2. Kelly RE, Lawson ML, Paidas CN, Hruban RH. Pectus excavatum in a 112-year autopsy series: anatomic findings and the effect on survival. Journal of Pediatric Surgery 2005: 40: 127578. 3. Hebra A. Minimally invasive repair of pectus excavatum. Semin Thorac Cardiovasc Surg 2009: 21: 76-84. 4. Brochhausen C, Turial S, Muller FK, et al. Pectus excavatum: history, hypotheses and treatment options. Interact Cardiovasc Thorac Surg 2012: 14: 801-6. 5. Kowalewski J, Brocki M, Zolynski K. Long-term observation in 68 patients operated on for pectus excavatum: surgical repair of funnel chest. Ann Thorac Surg 1999: 67: 821-4. 6. Nuss D, Kelly Jr RE. Indications and Technique of Nuss Procedure for Pectus Excavatum. Thoracic Surgery Clinics 2010: 20: 583-97. 7. Vegunta RK, Pacheco PE, Wallace LJ, Pearl RH. Complications associated with the Nuss procedure: continued evolution of the learning curve. Am J Surg 2008: 195: 313-6; discussion 16-7. 8. Park HJ, Lee SY, Lee CS, Youm W, Lee KR. The Nuss procedure for pectus excavatum: evolution of techniques and early results on 322 patients. The Annals of Thoracic Surgery 2004: 77: 289-95. 9. Nagasao T, Miyamoto J, Tamaki T, et al. Stress distribution on the thorax after the Nuss procedure for pectus excavatum results in different patterns between adult and child patients. The Journal of Thoracic and Cardiovascular Surgery 2007: 134: 1502-07. 10. Nagasao T, Noguchi M, Miyamoto J, et al. Dynamic effects of the Nuss procedure on the spine in asymmetric pectus excavatum. The Journal of Thoracic and Cardiovascular Surgery 2010: 140: 1294-99.e1. 9 Tse, K. M.*, Tan, L, B., Lee, S. J., Rasheed, M. Z., Tan, B. K. and Lee, H. P.* (2018). Feasibility of using computer simulation to predict the postoperative outcome of the minimally invasive Nuss procedure: Simulation prediction vs. postoperative clinical observation. Journal of Plastic, Reconstructive & Aesthetic Surgery. doi: 10.1016/j.bjps.2018.05.026

Preprint 11. Chang PY, Hsu Z-Y, Chen D-P, Lai J-Y, Wang C-J. Preliminary analysis of the forces on the thoracic cage of patients with pectus excavatum after the Nuss procedure. Clinical Biomechanics 2008: 23: 881-85. 12. Wei Y-b, Shi Y-k, Wang H, Gao Y. Simulation of Nuss Orthopedic for Pectus Excavatum. 2009: 1-4. 13. Wei Y, Sun D, Liu P, Gao Y. Pectus Excavatum Nuss Orthopedic finite element simulation. 2010: 3: 1236-39. 14. Mohr M, Abrams E, Engel C, Long WB, Bottlang M. Geometry of human ribs pertinent to orthopedic chest-wall reconstruction. Journal of Biomechanics 2007: 40: 1310-17. 15. BIOMET. Pectus Bar Pectus Excavatum Correction. 2014: 2014. 16. Li Z, Kindig MW, Kerrigan JR, et al. Rib fractures under anterior-posterior dynamic loads: experimental and finite-element study. J Biomech 2010: 43: 228-34. 17. Wang F, Yang J, Miller K, et al. Numerical investigations of rib fracture failure models in different dynamic loading conditions. Comput Methods Biomech Biomed Engin 2016: 19: 52737. 18. Keyak JH, Rossi SA, Jones KA, Les CM, Skinner HB. Prediction of fracture location in the proximal femur using finite element models. Med Eng Phys 2001: 23: 657-64. 19. Keyak JH, Rossi SA, Jones KA, Skinner HB. Prediction of femoral fracture load using automated finite element modeling. Journal of Biomechanics 1997: 31: 125-33. 20. Schileo E, Taddei F, Cristofolini L, Viceconti M. Subject-specific finite element models implementing a maximum principal strain criterion are able to estimate failure risk and fracture location on human femurs tested in vitro. Journal of Biomechanics 2008: 41: 356-67. 21. Bayraktar HH, Morgan EF, Niebur GL, et al. Comparison of the elastic and yield properties of human femoral trabecular and cortical bone tissue. J Biomech 2004: 37: 27-35. 22. Niedbala A, Adams M, Boswell WC, Considine JM. Acquired thoracic scoliosis following minimally invasive repair of pectus excavatum. The American Surgeon 2003: 69: 530-33. 23. Feng J, Hu T, Liu W, et al. The biomechanical, morphologic, and histochemical properties of the costal cartilages in children with pectus excavatum. Journal of Pediatric Surgery 2001: 36: 1770-76. 24. Ohno K, Morotomi Y, Harumoto K, et al. Preliminary study on the effects of bar placement on the thorax after the nuss procedure for pectus excavatum using bone scintigraphy. Eur J Pediatr Surg 2006: 16: 155-9. 25. Park HJ, Chung W-J, Lee IS, Kim KT. Mechanism of bar displacement and corresponding bar fixation techniques in minimally invasive repair of pectus excavatum. Journal of Pediatric Surgery 2008: 43: 74-78. 10 Tse, K. M.*, Tan, L, B., Lee, S. J., Rasheed, M. Z., Tan, B. K. and Lee, H. P.* (2018). Feasibility of using computer simulation to predict the postoperative outcome of the minimally invasive Nuss procedure: Simulation prediction vs. postoperative clinical observation. Journal of Plastic, Reconstructive & Aesthetic Surgery. doi: 10.1016/j.bjps.2018.05.026

Preprint 26. Lai J-Y, Wang C-J, Chang P-Y. The measurement and designation of the pectus bar by computed tomography. Journal of Pediatric Surgery 2009: 44: 2287-90.


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Figure 1: (A) The patient-specific thorax model and the Nuss procedure simulation; (B) The flipping or turning process of the pectus bar in the Nuss procedure. (Reprinted with kind permission from Felmer, P. J., Pectus Excavatum. Copyright © 2012 by Motion Graphics. https://www.youtube.com/watch?v=0XHs8zoMhXw)


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Figure 2: Loading steps for the turning process of the pectus bar in the Nuss procedure.


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Figure 3: Contour plots of von Mises stress experienced by the thorax before and after the Nuss procedure.


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Figure 4: Contour plots of maximum principal strain experienced by the thorax before and after the Nuss procedure.


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Figure 5: (A) Contact pressure between the sternum and pectus bar after the Nuss procedure; (B) von Mises Stress on the interior sternum after the Nuss procedure.


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Figure 6: Comparison of the sternal contours in the mid-sagittal section before and after the Nuss procedure.


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Figure 7: Comparison of the sternal contours in the transverse section near the pectus bar before and after the Nuss procedure.


Preprint 1 Feasibility of using computer simulation to ...

Preprint 1 Feasibility of using computer simulation to ...

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