Biomechanical Evaluation of Temporomandibular Joint Reconstruction Using Individual TMJ Prosthesis Combined with a Fibular Free Flap in a Pediatric Patient.

The main aim of this study was to perform a complex biomechanical analysis for a custom-designed temporomandibular joint (TMJ) prosthesis in combination with a fibular free flap in a pediatric case. Numerical simulations in seven variants of loads were carried out on 3D models obtained based on CT images of a 15-year-old patient in whom it was necessary to reconstruct the temporal-mandibular joints with the use of a fibula autograft. The implant model was designed based on the patient's geometry. Experimental tests on a manufactured personalized implant were carried out on the MTS Insight testing machine. Two methods of fixing the implant to the bone were analyzed-using three or five bone screws. The greatest stress was located on the top of the head of the prosthesis. The stress on the prosthesis with the five-screw configuration was lower than in the prosthesis with the three-screw configuration. The peak load analysis shows that the samples with the five-screw configuration have a lower deviation (10.88, 0.97, and 32.80%) than the groups with the three-screw configuration (57.89 and 41.10%). However, in the group with the five-screw configuration, the fixation stiffness was relatively lower (a higher value of peak load by displacement of 171.78 and 86.46 N/mm) than in the group with the three-screw configuration (where the peak load by displacement was 52.93, 60.06, and 78.92 N/mm). Based on the experimental and numerical studies performed, it could be stated that the screw configuration is crucial for biomechanical analysis. The results obtained may be an indication for surgeons, especially during planning personalized reconstruction procedures.

Analysis of the effects of mandibular reconstruction based on microvascular free flaps after oncological resections in 21 patients, using 3D planning, surgical templates and individual implants.

INTRODUCTION: Post- resection defects in the area of the head and neck frequently result in functional impairment of the masticatory system and unaesthetic outcome in the facial appearance. In pediatric population they exert a devastating effect on speech development, breathing and facial growth leading to secondary deformations which are extremely challenging in reconstruction by means of conventional surgery protocols. MATERIAL AND METHODS: 21 patients (14 males/ 7 females) aged 4-17 years old, treated between 2015 and 2019 due to malignant/benign tumors or congenital deformities requiring mandible resection were enrolled in the study. All patients underwent Virtual Surgical Planning (VSP), mandible tumor resection with use surgery guides and defect reconstruction with microvascular bone graft supported with custom implants. Postoperatively, 3D models used for the planning and postoperative 3D model of the reconstructed mandible were compared using authors method based on easily measurable morphometric measurements (3 angles, 3 linear dimensions), allowing a three-dimensional quantitative assessment of postoperative outcomes of the surgery. Linear regression analysis and one-way analysis of variance were used to evaluate the clinical material. The difference was considered significant if p < 0.05. RESULTS: Free fibula flap (FFF) was most commonly used type of the reconstruction of the pediatric mandible. The average maximum deviation for the analyzed cases was 7.7 mm, and the average minimum deviation was -6.09 mm, however without significant differences and the postoperative position of the mandible condyle was comparable to the position designed in the 3DVSP preoperatively. Position of the whole reconstructed mandible by means of individually planned grafts and plates provided comparable position of the ramus and mandible body and no chin deviation as the differences between the pre-operative axial and sagittal angles and their post-operative equivalents were insignificant (p > 0,05). CONCLUSIONS: This study confirms applicability of the 3DVSP in pediatric craniomaxillofacial surgery. Preoperative planning of the osteotomies, grafting technique and production of the individualized guides and implants provides precise tumor resection and immediate reconstruction adjusted to the specific anatomy of the pediatric patients.

Wall shear stress gradient is independently associated with middle cerebral artery aneurysm development: a case-control CFD patient-specific study based on 77 patients.

BACKGROUND: Previously published computational fluid dynamics (CFD) studies regarding intracranial aneurysm (IA) formation present conflicting results. Our study analysed the involvement of the combination of high wall shear stress (WSS) and a positive WSS gradient (WSSG) in IA formation. METHODS: We designed a case-control study with a selection of 38 patients with an unruptured middle cerebral artery (MCA) aneurysm and 39 non-aneurysmal controls to determine the involvement of WSS, oscillatory shear index (OSI), the WSSG and its absolute value (absWSSG) in aneurysm formation based on patient-specific CFD simulations using velocity profiles obtained from transcranial colour-coded sonography. RESULTS: Among the analysed parameters, only the WSSG had significantly higher values compared to the controls (11.05 vs - 14.76 [Pa/mm], P = 0.020). The WSS, absWSSG and OSI values were not significantly different between the analysed groups. Logistic regression analysis identified WSS and WSSG as significant co-predictors for MCA aneurysm formation, but only the WSSG turned out to be a significant independent prognosticator (OR: 1.009; 95% CI: 1.001-1.017; P = 0.025). Significantly more patients (23/38) in the case group had haemodynamic regions of high WSS combined with a positive WSSG near the bifurcation apex, while in the control group, high WSS was usually accompanied by a negative WSSG (14/39). From the analysis of the ROC curve for WSSG, the area under the curve (AUC) was 0.654, with the optimal cut-off value -0.37 Pa/mm. The largest AUC was recognised for combined WSS and WSSG (AUC = 0.671). Our data confirmed that aneurysms tend to form near the bifurcation apices in regions of high WSS values accompanied by positive WSSG. CONCLUSIONS: The development of IAs is determined by an independent effect of haemodynamic factors. High WSS impacts MCA aneurysm formation, while a positive WSSG mainly promotes this process.

Morphological and Hemodynamic Risk Factors for Middle Cerebral Artery Aneurysm: a Case-Control Study of 190 Patients.

This study analyzed morphometric and hemodynamic parameters of aneurysmal and non-aneurysmal middle cerebral artery (MCA) bifurcations and their relationship with optimal values derived from the principle of minimum work (PMW). The study included 96 patients with MCA aneurysm and 94 controls. Aneurysm patients presented with significantly higher values of the radius and cross-sectional area of the MCA trunk, angle between the post-bifurcation branches (α angle) and volume flow rate (VFR) and had significantly lower values of junction exponent and pulsatility index than the controls. The Φ1 and Φ2 angles (angles between the MCA trunk axis and the larger and smaller branch, respectively) and α angle in all groups were significantly larger than the optimal PMW-derived angles. The most important independent predictors of MCA aneurysm were junction exponent (odds ratio, OR = 0.42), α angle (OR = 1.07) and VFR (OR = 2.36). Development of cerebral aneurysms might be an independent effect of abnormalities in hemodynamic and morphometric factors. The risk of aneurysm increased proportionally to the deviation of morphometric parameters of the bifurcation from their optimal PMW-derived values. The role of bifurcation angle in aneurysm development needs to be explained in future research as the values of this parameter in both aneurysm patients and non-aneurysmal controls in were scattered considerably around the PMW-derived optimum.

Evaluation of the impact of decellularization and sterilization on tensile strength transgenic porcinedermal dressings.

PURPOSE: The aim of this paper was to evaluate which method of acellularization and sterilization is optimal, in the meaning of which processes have the least impact on the deterioration of mechanical properties of porcine tissues used for xenogeneic applications. METHODS: The static tensile probe was conducted for 80 skin specimens obtained from transgenic swine, which are used as a wound dressing for skin recipient. Obtained data were subsequently analyzed with the use of statistical methods. RESULTS: It was found that Young's modulus for the samples after the sterilization process for the dispase substance and the mixed method (SDS + trypsin) were statistically significantly changed. In the case of dispase, Young's modulus value before the sterilization process was 12.4 MPa and after the value increased to 28.0 MPa. For the mixed method (SDS + trypsin) before the sterilization process Young's modulus value was 5.6 MPa and after it was increased to 6.3 MPa. The mixed method (SDS + trypsin) had the slightest effect on changing the mechanical properties of the samples before and after the sterilization process. CONCLUSIONS: It was confirmed that different methods of acellularization and the process of sterilization have an influence on the change of mechanical properties of the skin of transgenic swine. In the authors' opinion, the mixed method (SDS + trypsin) should be recommended as the best one for the preparation of transgenic porcine dermal dressings because it ensures a smaller probability of dressing's damage during a surgical procedure.

Modeling and biomechanical analysis of craniosynostosis correction with the use of finite element method.

Craniosynostosis is a skull malformation because of premature fusing of one or more cranial sutures. The most common types of craniosynostosis are scaphocephaly (with the sagittal suture fused) and trigonocephaly (with the metopic suture fused). In this paper we describe and discuss how finite element analysis and three-dimensional modeling can be used for preoperative planning of the correction of craniosynostosis and for the postoperative evaluation of the treatment results. We used the engineering software MIMICS MATERIALISE to obtain three-dimensional geometry from computed tomography scans, and applied finite element method for the sake of biomechanical analysis. These simulations help to improve the surgical treatment, making it more accurate, safer, and faster.

Biomechanical aspects of preoperative planning of skull correction in children with craniosynostosis.

Craniosynostosis is a birth defect that causes one or more sutures on a baby's head to close earlier than normal. In effect the growing brain determines an abnormal skull shape and, which is more important and more dangerous, it causes an elevated intracranial pressure. The only treatment for children with craniosynostosis is surgical cranioplasty. More extensive procedures yield excellent results, particularly in older children with moderate to severe deformity. However, in children undergoing more extensive reconstructions an essential requirement is blood transfusion. They are also put at risk of complications. In this paper, the authors propose a method of preoperative planning based on three-dimensional modelling and biomechanical investigations. We used Mimics, 3-matic and ANSYS software for the process. The proposed preoperative planning improved the preoperative knowledge of deformation, shortened the time of surgery, and subsequently reduced blood loss during the procedure.