A finite-element facial model for simulating plastic surgery

A Review of Image-Based Simulation Applications in High-Value Manufacturing

Image-Based Simulation (IBSim) is the process by which a digital representation of a real geometry is generated from image data for the purpose of performing a simulation with greater accuracy than with idealised Computer Aided Design (CAD) based simulations. Whilst IBSim originates in the biomedical field, the wider adoption of imaging for non-destructive testing and evaluation (NDT/NDE) within the High-Value Manufacturing (HVM) sector has allowed wider use of IBSim in recent years. IBSim is invaluable in scenarios where there exists a non-negligible variation between the 'as designed' and 'as manufactured' state of parts. It has also been used for characterisation of geometries too complex to accurately draw with CAD. IBSim simulations are unique to the geometry being imaged, therefore it is possible to perform part-specific virtual testing within batches of manufactured parts. This novel review presents the applications of IBSim within HVM, whereby HVM is the value provided by a manufactured part (or conversely the potential cost should the part fail) rather than the actual cost of manufacturing the part itself. Examples include fibre and aggregate composite materials, additive manufacturing, foams, and interface bonding such as welding. This review is divided into the following sections: Material Characterisation; Characterisation of Manufacturing Techniques; Impact of Deviations from Idealised Design Geometry on Product Design and Performance; Customisation and Personalisation of Products; IBSim in Biomimicry. Finally, conclusions are drawn, and observations made on future trends based on the current state of the literature.

Geometrical model establishment and preoperative evaluation on A-T flap design: Finite element method-based computer-aided simulation on surgical operation processes

Objective

A-T flap has been extensively applied to repair dermal soft tissue defects. The flap design completely depends on the experience of doctors. Herein, we explored the approach of analyzing the reasonability of A-T flap design and performed a simulation of operation processes by computer-aided technology. Afterward, the finite element analysis software (MSC.Marc/Mentat) was used to establish the simulation model, based on which the computer simulation of flap suturing and release state in A-T flap surgery was performed.

Methods

A geometrical model of the A-T flap was established, and the length-width ratio of the flap, maximum suture distance, and suture area that could influence the postoperative suture effects of the flap were analyzed. The reasonable surgical planning for A-T flap design based on the crossing constraint relationship was achieved. The simulation model was established by the finite element analysis software (MSC.Marc/Mentat), based on which computer simulation of flap suture and release state of A-T flap in surgery processes were performed. The flap's stress and deformation distribution results confirmed the applicability of the A-T flap design method proposed in the present study.

Results

When the apex angle of the A-T flap was 60 degrees, the suture area was the smallest, and the flap design had the highest practicability.

Conclusion

Computer-assisted preoperative assessment, which has high clinical value, could provide a theoretical basis for A-T flap design in clinical practice.

A computer based facial flaps simulator using projective dynamics

BACKGROUND AND OBJECTIVES

Interactive surgical simulation using the finite element method to model human skin mechanics has been an elusive goal. Mass-spring networks, while fast, do not provide the required accuracy.

METHODS

This paper presents an interactive, cognitive, facial flaps simulator based on a projective dynamics computational framework. Projective dynamics is able to generate rapid, stable results following changes to the facial soft tissues created by the surgeon, even in the face of sudden increases in skin resistance as its stretch limit is reached or collision between tissues occurs. Our prior work with the finite element method had been hampered by these considerations. Surgical tools are provided for; skin incision, undermining, deep tissue cutting, and excision. A spring-like "skin hook" is used for retraction. Spring-based sutures can be placed individually or automatically placed as a row between cardinal sutures.

RESULTS

Examples of an Abbe/Estlander lip reconstruction, a paramedian forehead flap to the nose, a retroauricular flap reconstruction of the external ear, and a cervico-facial flap reconstruction of a cheek defect are presented.

CONCLUSIONS

Projective dynamics has significant advantages over mass-spring and finite element methods as the physics backbone for interactive soft tissue surgical simulation.

Implications of Applying New Technology in Cosmetic and Reconstructive Facial Plastic Surgery

The field of facial plastic and reconstructive surgery is privy to a myriad of technological advancements. As innovation in areas such as imaging, computer applications, and biomaterials progresses at breakneck speed, the potential for clinical application is endless. This review of recent progress in the implementation of new technologies in facial plastic surgery highlights some of the most innovative and impactful developments in the past few years of literature. Patient-specific surgical modeling has become the gold standard for oncologic and posttraumatic reconstructive surgery, with demonstrated improvements in operative times, restoration of anatomical structure, and patient satisfaction. Similarly, reductions in revision rates with improvements in learner technical proficiency have been noted with the use of patient-specific models in free flap reconstruction. In the cosmetic realm, simulation-based rhinoplasty implants have drastically reduced operative times while concurrently raising patient postoperative ratings of cosmetic appearance. Intraoperative imaging has also seen recent expansion in its adoption driven largely by reports of eradication of postoperative imaging and secondary-often complicated-revision reconstructions. A burgeoning area likely to deliver many advances in years to come is the integration of bioprinting into reconstructive surgery. Although yet to clearly make the translational leap, the implications of easily generatable induced pluripotent stem cells in replacing autologous, cadaveric, or synthetic tissues in surgical reconstruction are remarkable.

Simulation in Cleft Surgery

A number of digital and haptic simulators have been developed to address challenges facing cleft surgery education. However, to date, a comprehensive review of available simulators has yet to be performed. Our goal is to appraise cleft surgery simulators that have been described to date, their role within a simulation-based educational strategy, the costs associated with their use, and data supporting or refuting their utility.

Location-specific mechanical response and morphology of facial soft tissues

The facial tissue of 9 healthy volunteers (m/f; age: 23-60y) is characterized at three different locations using a procedure combining suction measurements and 18MHz ultrasound imaging. The time-dependent and multilayered nature of skin is accounted for by adopting multiple loading protocols which differ with respect to suction probe opening size and rate of tissue deformation. Over 700 suction measurements were conducted and analyzed according to location-specific mechanical and morphological characteristics. All corresponding data are reported and made available for facial tissue analysis and biomechanical modeling. Higher skin stiffness is measured at the forehead in comparison to jaw and parotid; these two regions are further characterized by lower creep deformation. Thicker tissue regions display a tendency towards a more compliant and less dissipative response. Comparison of superficial layer thickness and corresponding mechanical measurements suggests that connective tissue density determines the resistance to deformation in suction experiments.

Computer Simulation and Digital Resources for Plastic Surgery Psychomotor Education

Contemporary plastic surgery residents are increasingly challenged to learn a greater number of complex surgical techniques within a limited period. Surgical simulation and digital education resources have the potential to address some limitations of the traditional training model, and have been shown to accelerate knowledge and skills acquisition. Although animal, cadaver, and bench models are widely used for skills and procedure-specific training, digital simulation has not been fully embraced within plastic surgery. Digital educational resources may play a future role in a multistage strategy for skills and procedures training. The authors present two virtual surgical simulators addressing procedural cognition for cleft repair and craniofacial surgery. Furthermore, the authors describe how partnerships among surgical educators, industry, and philanthropy can be a successful strategy for the development and maintenance of digital simulators and educational resources relevant to plastic surgery training. It is our responsibility as surgical educators not only to create these resources, but to demonstrate their utility for enhanced trainee knowledge and technical skills development. Currently available digital resources should be evaluated in partnership with plastic surgery educational societies to guide trainees and practitioners toward effective digital content.

A Real-Time Local Flaps Surgical Simulator Based on Advances in Computational Algorithms for Finite Element Models

BACKGROUND

This article presents a real-time surgical simulator for teaching three- dimensional local flap concepts. Mass-spring based simulators are interactive, but they compromise accuracy and realism. Accurate finite element approaches have traditionally been too slow to permit development of a real-time simulator.

METHODS

A new computational formulation of the finite element method has been applied to a simulated surgical environment. The surgical operators of retraction, incision, excision, and suturing are provided for three-dimensional operation on skin sheets and scalp flaps. A history mechanism records a user's surgical sequence. Numerical simulation was accomplished by a single small-form-factor computer attached to eight inexpensive Web-based terminals at a total cost of $2100. A local flaps workshop was held for the plastic surgery residents at the University of Wisconsin hospitals.

RESULTS

Various flap designs of Z-plasty, rotation, rhomboid flaps, S-plasty, and related techniques were demonstrated in three dimensions. Angle and incision segment length alteration advantages were demonstrated (e.g., opening the angle of a Z-plasty in a three-dimensional web contracture). These principles were then combined in a scalp flap model demonstrating rotation flaps, dual S-plasty, and the Dufourmentel Mouly quad rhomboid flap procedure to demonstrate optimal distribution of secondary defect closure stresses.

CONCLUSIONS

A preliminary skin flap simulator has been demonstrated to be an effective teaching platform for the real-time elucidation of local flap principles. Future work will involve adaptation of the system to facial flaps, breast surgery, cleft lip, and other problems in plastic surgery as well as surgery in general.

Plasticine Model: An Useful Surgical Training in Plastic Surgery

OBJECTIVE

To help surgical trainees reach a deep understanding of plastic operations, we developed and evaluated an economical and convenient model using plasticine for plastic surgical training.

METHODS

From Sep of 2012 to Dec of 2014, we invited 57 medical interns to participate in a program designed for the qualitative evaluation of this model. In this program, 57 interns were asked to simulate certain surgical operations under guidance of the experienced staff of our department using the plasticine model. The value of the plasticine model was evaluated through questionnaire surveys. Their acceptance of the plasticine model, as well as the benefits and the flaws, was evaluated by the questionnaire survey.

RESULTS

All the participants completed the training session as well as the questionnaire, all of whom felt that the plasticine model had increased their familiarity with the surgical procedure they were assigned. By remodeling plasticine, the trainees understood either the brief surgical procedures or some confusing operative details in plastic surgery. In the questionnaire surveys, the trainees showed considerable consensus with the training program. The flaws of this method were also listed. The flaws generally reflected that "it is difficult to model into a vivid image" and "it is not suitable for all the operation".

CONCLUSIONS

Overall, the plasticine model is accepted by the participants in this survey. This model is economical and versatile, and could be used as a complementary training tool for novices in simulated operation training of plastic surgery.

NO LEVEL ASSIGNED

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266.

Image fusion in preoperative planning

This article presents a comprehensive overview of generating a digital Patient-Specific Anatomic Reconstruction (PSAR) model of the craniofacial complex as the foundation for a more objective surgical planning platform. The technique explores fusing the patient's 3D radiograph with the corresponding high-precision 3D surface image within a biomechanical context. As taking 3D radiographs has been common practice for many years, this article describes various approaches to 3D surface imaging and the importance of achieving high-precision anatomical results to simulate surgical outcomes that can be measured and quantified. With the PSAR model readily available for facial assessment and virtual surgery, the advantages of this surgical planning technique are discussed.

Creating a virtual surgical atlas of craniofacial procedures: Part I. Three-dimensional digital models of craniofacial deformities

BACKGROUND

Three-dimensional digital animation can enable surgeons to create anatomically accurate, virtual models of normal and pathologic human anatomy. From these models, surgical procedures can be digitally performed, recorded, and distributed as a teaching tool or as a virtual surgical atlas. The idea of a virtual surgical atlas has recently become a part of contemporary surgical teaching. In the field of craniofacial surgery, no such educational tool exists. Presented is the first part of the creation of a virtual atlas of craniofacial surgical procedures: the three-dimensional digital modeling of pathologic deformities commonly treated by craniofacial surgeons.

METHODS

Three-dimensional craniofacial models were constructed using Maya 8.5. A skeletally "normal" craniofacial skeleton was first produced from a preexisting digital skull using Bolton tracings as a reference. The remaining soft-tissue elements were then added to create an anatomically complete three-dimensional face. The "normal" model was then deformed in Maya to produce specific craniofacial deformities using computed tomographic scans, cephalograms, and photographs as a reference. One of the craniofacial deformity models was created directly from computed tomographic data.

RESULTS

One model of the normal face and eight pathologic models of craniofacial deformities were created: microgenia, micrognathia, prognathia, temporomandibular joint ankylosis, maxillary hypoplasia, Crouzon syndrome with and without the need for cranial vault expansion, and bicoronal craniosynostosis.

CONCLUSIONS

For the first time, anatomically accurate three-dimensional digital models of craniofacial deformities have been created. The models are the first step in the creation of a virtual surgical atlas of craniofacial procedures.

Three-dimensional imaging and computer simulation for office-based surgery

PURPOSE

Advancements in computers and imaging, especially over the last 10 years, have permitted the adoption of 3-dimensional imaging protocols in the health care field. In addition, the affordability and ease of use of these modalities allow their widespread adoption and use in diagnosis and treatment planning. This is particularly important when the deformities are complex involving both function and esthetics, such as those in the dentofacial area and with orthognathic surgery.

MATERIALS AND METHODS

Image fusion involves combining images from different imaging modalities to create a virtual record of an individual called a patient-specific anatomic reconstruction (PSAR). We describe the system and show its use in 1 case.

RESULTS

Image fusion and, more specifically, PSAR permit a more accurate analysis of deformity as an aid to diagnosis and treatment planning.

CONCLUSION

Three-dimensional imaging and computer simulation can be effectively used for planning office-based procedures. The PSAR can be used to perform virtual surgery and establish a definitive and objective treatment plan for correction of a facial deformity. The end result is improved patient care and decreased expense.

A Web-based, integrated simulation system for craniofacial surgical planning

BACKGROUND

Advances in computing over the last 10 years have rapidly improved imaging and simulation in health care. Implementation of three-dimensional protocols and image fusion techniques are moving diagnosis, treatment planning, and teaching to a next-generation paradigm. In addition, decreasing cost and increasing availability make generalized use of these techniques possible.

METHODS

In this article, the authors present a Web-based, integrated simulation system for craniofacial surgical planning and treatment. Image fusion technology was utilized to create a realistic virtual image that can be manipulated in real time. The resultant data can then be shared over the Internet by distantly located practitioners.

RESULTS

Initial use of this system proved to be beneficial from a planning standpoint and to be accurate as to the reliability of landmark identification. Additional case studies are needed to further document the results of actual surgical simulation.

CONCLUSION

This technology presents significant advantages in surgical planning and education, both of which can improve patient safety and outcomes.

Simulation in plastic surgery training and education: the path forward

SUMMARY

Computer-based training simulators have been used extensively, most notably in flight simulation. Over the past 20 years, surgical simulators have been developed, initially for training of minimally invasive surgery and more recently for open surgical simulation. The key effort in today's surgical simulation field is to develop metrics to evaluate how well the skills learned in a simulator translate to improvement in real surgical skills, execution of procedures, and team cooperation in the operating room. The American College of Surgeons has begun implementing a phased approach to introduce simulation in training and education for general surgery. The authors believe that a similar training plan should be mandated for plastic surgery, to take advantage of the use of computers, virtual reality, and simulation in the training of plastic surgery residents and to explore the value of this technology for continuing medical education and maintenance of certification. This article gives a brief background and history of surgical simulation and its technology, followed by a detailed description of the three phases of the American College of Surgeons' plan and how the authors propose that each phase be implemented, with modifications as applicable for trainees in plastic surgery.

In vivo experimental testing and model identification of human scalp skin

A comprehensive experimental/numerical procedure is formulated and validated for the in vivo characterization of the mechanical properties of human skin and the simulation of reconstructive surgery. The procedure uses in vivo experimental tests on undermined skin flaps, which can be performed during surgery, a numerical model formulated within the framework of nonlinear finite strain elasticity and a nonlinear parameter identification technique for the calibration of the model from indirect measurements. The procedure is applied to characterize the scalp skin tested in Raposio and Nordström (Skin Res. Technol. 4 (1998) 94). The skin is treated as a time independent, isotropic and hyperelastic membrane and the problem is solved through a finite element discretization. The study highlights that the model parameters can be determined with good accuracy using displacement measurements of a few points in the domain.

A surgical simulator for planning and performing repair of cleft lips

The objective of this project was to develop a computer-based surgical simulation system for planning and performing cleft lip repair. This system allows the user to interact with a virtual patient to perform the traditional steps of cleft-lip repair (rotation-advancement technique).

MATERIALS AND METHODS

The system interfaces to force-feedback (haptic) devices to track the user's motion and provide feedback during the procedure, while performing real-time soft-tissue simulation. An 11-day-old unilateral cleft lip, alveolus and palate patient was previously CT scanned for ancillary diagnostic purposes using standard imaging protocols and 1mm slices. High-resolution 3D meshes were automatically generated from this data using the ROVE software developed in-house. The resulting 3D meshes of bone and soft tissue were instilled with physical properties of soft tissues for purposes of simulation. Once these preprocessing steps were completed, the patient's bone and soft tissue data are presented on the computer screen in stereo and the user can freely view, rotate, and otherwise interact with the patient's data in real time. The user is prompted to select anatomical landmarks on the patient's data for preoperative planning purposes, then their locations are compared against that of a 'gold standard' and a score, derived from their deviation from that standard and time required, is generated. The user can then move a haptic stylus and guide the motion of the virtual cutting tool. The soft tissues can thus be incised using this virtual cutting tool, moved using virtual forceps, and fused in order to perform any of the major procedures for cleft lip repair. Real-time soft tissue deformation of the mesh realistically simulates normal tissues and haptic-rate (>1 kHz) force-feedback is provided. The surgical result of the procedure can then be immediately visualized and the entire training process can be repeated at will. A short evaluation study was also performed. Two groups (non-medical and plastic surgery residents) of six persons each performed the anatomical marking task of the simulator four times.

RESULTS

Results showed that the plastic surgery residents scored consistently better than the persons without medical background. Every person's score increased with practice, and the length of time needed to complete the 11 markings decreased. The data was compiled and showed which specific markers consistently took users the longest to identify as well as which locations were hardest to accurately mark.

CONCLUSION

These findings suggest that the simulator is a valuable training tool, giving residents a way to practice anatomical identification for cleft lip surgery without the risks associated with training on a live patient. Educators can also use the simulator to examine which markers are consistently problematic, and modify their training to address these needs.

Real-time finite element modeling for surgery simulation: an application to virtual suturing

Real-time finite element (FE) analysis can be used to represent complex deformable geometries in virtual environments. The need for accurate surgical simulation has spurred the development of many of the new real-time FE methodologies that enable haptic support and real-time deformation. These techniques are computationally intensive and it has proved to be a challenge to achieve the high modeling resolutions required to accurately represent complex anatomies. The authors present a new real-time methodology based on linear FE analysis that is appropriate for a wide range of surgical simulation applications. A methodology is proposed that is characterized by high model resolution, low preprocessing time, unrestricted multipoint surface contact, and adjustable boundary conditions. These features make the method ideal for modeling suturing, which is an element common to almost every surgical procedure. This paper describes constraints in the context of a Suturing Simulator currently being developed by the authors.

Algorithmic tools for real-time microsurgery simulation††This paper is based on earlier work appearing in (Brown et al., 2001a,b)

Today, there is growing interest in computer surgical simulation to enhance surgeons' training. This paper presents a simulation system based on novel algorithms for animating instruments interacting with deformable tissue in real-time. The focus is on computing the deformation of a tissue subject to external forces, and detecting collisions among deformable and rigid objects. To achieve real-time performance, the algorithms take advantage of several characteristics of surgical training: (1) visual realism is more important than accurate, patient-specific simulation; (2) most tissue deformations are local; (3) human-body tissues are well damped; and (4) surgical instruments have relatively slow motions. Each key algorithm is described in detail and quantitative performance-evaluation results are given. The specific application considered in this paper is microsurgery, in which the user repairs a virtual severed blood vessel using forceps and a suture (micro-anastomosis). Microsurgery makes it possible to demonstrate several facets of the simulation algorithms, including the deformations of the blood vessel and the suture, and the collisions and interactions between the vessel, the forceps, and the suture. Validation of the overall microsurgery system is based on subjective analysis of the simulation's visual realism by different users.

Preshaped hydroxyapatite tricalcium-phosphate implant using three-dimensional computed tomography in the reconstruction of bone deformities of craniomaxillofacial region

We prepared solid life-sized models and templates of implants based on three-dimensional computed tomography data in six cases with a bone deformity of the craniomaxillofacial region. After simulation surgery using these models and templates, the preshaped hydroxyapatite-tricalcium phosphate (HAP-TCP) implants were prepared to fill in the facial bone defects, and implantation was performed. Consequently, implants fitted the individual bone defects, and satisfactory facial contouring was obtained in five cases. In one case with severe cutaneous scarring in the grafted site, it was necessary to reduce the volume of the preshaped HAP-TCP implant during surgery. In conclusion, the three-dimensional, solid, life-sized model and template are useful for preoperative detailed simulation, and the use of preshaped HAP-TCP implants based on the template probably contributes to successful reconstruction of complex facial bone deformities and to the reduction of surgical invasion, resulting in achievement of better results.

Three-dimensional facial simulations and measurements: changes of facial contour and units associated with facial expression

Recent innovations in laser scanning technology provide a potentially useful technique for accurate three-dimensional documentation of the face. In this study, linear and area measurements of the facial contour and facial units have been recorded in a variety of chosen facial postures using surface laser scanning combined with three-dimensional lighting techniques on seven healthy volunteers and three patients with facial nerve paralysis. Three-dimensional surface measurement of the face was taken using a laser light scanner. Computer graphics lighting techniques were used to produce facial images constituted by highlights and shadows, which emboss facial contour and units. Then quantitative measurement of changes in facial angles and areas were made to analyze morphological changes of the face accompanying facial expression. Changes of angles and widths of the cheek and nasal units were found to be associated with dimensional changes imposed by the action of the underlying mimetic muscles. This system has potential value for both dynamic monitoring and evaluation of facial contour, units, and movement.

Computer assisted oral and maxillofacial surgery--a review and an assessment of technology

Advances in the basic scientific research within the field of computer assisted oral and maxillofacial surgery have enabled us to introduce features of these techniques into routine clinical practice. In order to simulate complex surgery with the aid of a computer, the diagnostic image data and especially various imaging modalities including computer tomography (CT), magnetic resonance imaging (MRI) and Ultrasound (US) must be arranged in relation to each other, thus enabling a rapid switching between the various modalities as well as the viewing of superimposed images. Segmenting techniques for the reconstruction of three-dimensional representations of soft and hard tissues are required. We must develop ergonomic and user friendly interactive methods for the surgeon, thus allowing for a precise and fast entry of the planned surgical procedure in the planning and simulation phase. During the surgical phase, instrument navigation tools offer the surgeon interactive support through operation guidance and control of potential dangers. This feature is already available today and within this article we present a review of the development of this rapidly evolving technique. Future intraoperative assistance takes the form of such passive tools for the support of intraoperative orientation as well as so-called 'tracking systems' (semi-active systems) which accompany and support the surgeons' work. The final form are robots which execute specific steps completely autonomously. The techniques of virtual reality and computer assisted surgery are increasingly important in their medical applications. Many applications are still being developed or are still in the form of a prototype. It is already clear, however, that developments in this area will have a considerable effect on a surgeon's routine work.

Virtual reality for dermatologic surgery: virtually a reality in the 21st century

In the 20th century, virtual reality has predominantly played a role in training pilots and in the entertainment industry. Despite much publicity, virtual reality did not live up to its perceived potential. During the past decade, it has also been applied for medical uses, particularly as training simulators, for minimally invasive surgery. Because of advances in computer technology, virtual reality is on the cusp of becoming an effective medical educational tool. At the University of Washington, we are developing a virtual reality soft tissue surgery simulator. Based on fast finite element modeling and using a personal computer, this device can simulate three-dimensional human skin deformations with real-time tactile feedback. Although there are many cutaneous biomechanical challenges to solve, it will eventually provide more realistic dermatologic surgery training for medical students and residents than the currently used models.

Pre-surgical CT/FEA for craniofacial distraction: I. Methodology, development, and validation of the cranial finite element model

Recently, surgeons have begun to treat serious congenital craniofacial deformities including craniosynostoses with mechanical devices that gradually distract the skull. As a prospective means of treatment planning for such complex deformities, FE models derived from routine preoperative CT scans (CT/FEA) would provide ideal patient specific engineering analyses. The purpose of this study was to assess the dimensional and predictive accuracy of the CT/FEA process through the development of a 3D model of a dry human calvarium subjected to two-point distraction ex vivo. Comparative skull measurements revealed that CT/FEA construction error did not exceed 1% for transcranial dimensions, and the thickness error did not exceed 8.66% or 0.31 mm. CT/FEA strain predictions for the central region of the skull, between the distraction posts, were not statistically different from homologous gage values at P < 0.05. Peripherally, however, the strain fields were less well behaved and the FE predictions showed only general qualitative agreement with gage recordings.

Presurgical finite element analysis from routine computed tomography studies for craniofacial distraction: II. An engineering prediction model for gradual correction of asymmetric skull deformities

Finite element analysis from routine computed tomography studies (CT/FEA) allows clinicians to predict the mechanical and anatomic consequences of specific distraction systems before human application. A realistic three-dimensional CT/FEA engineering model of an actual plagiocephalic infant with unicoronal synostosis was developed using 4215 parabolic triangular shell elements and intracranial pressure conditions ranging from 10 to 20 mmHg. The completed finite element analysis model was used to predict the anatomic outcome of multiaxial distraction delivered by hypothetical patterns of rod and node distraction units. The predictions for the various patterns of distraction units were also compared quantitatively with respect to force, stress, strain, and intracranial volume. Best anatomic corrections were achieved with bilateral patterns of distraction units that simultaneously elongated the ipsilateral cranium and shortened the contralateral cranium. Greatest strain levels were experienced within the osteotomy callus, greatest stress levels at the appliance anchorage sites, and the greatest rod force at the ipsilateral lower coronal position.

The finite element method as a research and teaching tool in the analysis of local skin flaps

BACKGROUND

The finite element analysis (FEA) is a recently introduced method in biomechanics that permits modeling of complex structures considering them as an aggregate of small elements. Skin flaps are highly suggested to be amenable to the continuum mechanic laws that underly the development of FEA.

OBJECTIVE

A combination of "large deformation analysis," based on FEA with the criteria for skin flap selection, was attempted.

METHODS

Serial defects were experimentally created on piglet skin stripes, which were consequently covered through designing appropriate flaps. Skin samples were modeled after the development of a computer FEA program and they were scanned by incorporating their photographs.

RESULTS AND CONCLUSION

On the graphic interfaces the flap movement, the closure of the defect, and the whole deformation were found to match with the skin stripe postincisional alterations. This work permits the prediction and offers planning guides for different skin reconstructions.