The Use of Finite Element Method Analysis for Modeling Different Osteotomy Patterns and Biomechanical Analysis of Craniosynostosis Correction.

PURPOSE: Several post-processing algorithms for 3D visualization of the skull in craniosynostosis with their specific advantages and disadvantages have been already described. The Finite Element Method (FEM) described herein can also be used to evaluate the efficacy of the cutting patterns with respect to an increase in the projected surface area under assumed uniform loading of the manipulated and cut bone segments. METHODS: The FEM analysis was performed. Starting with the classic cranial osteotomies for bifrontal craniotomy and orbital bandeau a virtually mirroring of the unaffected triangular shaped frontal bone was performed to achieve a cup-shaped sphere of constant thickness of 2.5 mm with a radius of 65 mm. Mechanical properties required for the analysis were Young's modulus of 340 MPa and Poisson's ratio of 0.22. Four different cutting patterns from straight to curved geometries have been projected onto the inner surface of the sphere with a cutting depth set to 2/3rds of the shell thickness. The necessary force for the deformation, the resulting tensions and the volume loss due to the osteotomy pattern were measured. RESULTS: Better outcomes were realized with pattern D. The necessary force was 73.6% smaller than the control group with 66N. Best stress distribution was achieved. Curved cutting patterns led to the highest peak of stress and thus to a higher risk of fracture. Straight bone cuts parallel to the corners or to the thighs of the sphere provided a better distribution of stresses with a small area with high stress. Additionally, also with pattern D a surface increase of 20.7% higher than reference was registered. CONCLUSION: As a proof of concept for different cutting geometries for skull molding in the correction of craniosynostosis, this computational model shows that depending of the cutting pattern different biomechanical behavior is achieved.

Quantitative 3D soft tissue analysis of symmetry prior to and after unilateral cleft lip repair compared with non-cleft persons (performed in Cambodia).

OBJECT: The aim of this study was to evaluate the clinical application of three-dimensional (3D) imaging and morphological analysis with subsequent individual therapy planning and postoperative 3D symmetry control in comparison with data from non-cleft persons. DESIGN: This was a prospective study using a 3D surface-imaging and evaluation system in cleft patients and non-cleft persons. The pre- and postoperative 3D facial profiles were recorded from the patients using a 3D laser scanner. The preoperative 3D image was analyzed qualitatively and quantitatively for an individual therapy planning. On the basis of ratios and scores, based on empirical regions of interest, the technique of cleft repair was designed individually. The postoperative result was evaluated regarding symmetry. The surgically created soft tissue shift was defined quantitatively and visualized with vectors. The postoperative symmetry was compared with 3D data from a group of non-cleft persons of the same ethnical group. PATIENTS: Eleven patients (mean age 13.8 years, median 13, minimum 2, maximum 41 years) with either a unilateral isolated cleft lip, a cleft lip and alveolus or a complete unilateral cleft lip, alveolus and palate and 25 non-cleft persons (8 children between 4 and 12 years, 17 adults (9 men, 8 women) between 18 and 50 years). All these persons investigated were Asians of Khmer origin. RESULTS: The analysis permitted quantitative 3D evaluation. The 3D anthropometric data of the non-cleft Khmer persons were collected and named the gold standard of symmetry in this ethnical group. All postoperative 3D images reached symmetrical values within the range of the normal cohort. Soft tissue shifts from pre- to postoperative sites could be visualized. CONCLUSION: A new method for registration was described enabling follow-up registration in patients when growing older. This 3D soft tissue analysis can be a useful tool in quantitative analysis and objective follow-up control in cleft patients. It offers deeper insight into the complex morphology to be treated and could contribute to individualisation of surgical procedures.