Juan Alfonso Beltrán-Fernández

Assessment of the Structural Integrity of C3–C5 Cervical Porcine Vertebrae Model Based on 2D Classic CAD, 3D Scanner and 3D Computed Tomography

In this chapter, the biomechanical behavior of C3–C5 porcine cervical vertebrae is analyzed. The objective of this evaluation is to establish the advantages and limitations of three numerical procedures when a compressive load is applied. In a first stage, a damaged C4 vertebral body is instrumented with a bone graft and a titanium alloy (Ti-6A1-4V) cervical plate fixed with titanium alloy screws. In the second stage, the biomechanical integrity of a healthy C3–C5 unit is studied. The required numerical models were created with three different techniques; these are 2D Computer Tomography (CT), 3D ZScan and CT scanning with a Siemens Emotion system. This was done in conjunction with Pro-E Wildfire 4.0, Scan IP 3.1, UGS NX-4 and Geomagics R 10 codes. Lateral displacements among the upper and lower surfaces of the vertebral bodies and the bone graft, as well as the von Misses stresses, were calculated. Numerical differences from the biomechanical models are discussed. In order to establish a performance criterion, the results obtained were compared against those obtained for the case of the instrumented C3–C5 unit. In order to establish helpful criteria to optimize the therapeutic procedures before a surgery is performed, the analysis of the results was focused to demonstrate that DICOM methodology can be applied when a biomechanical simulation for a patient is required. It is possible, to apply this technique safely as it is not invasive and geometrical parameters are obtained directly from a tomography taken at a hospital. On the other hand, classical CAD models and Z scan methodology has shown to be useful when specimens are numerically analyzed.

Biomechanical Characterization of a Cervical Corporectomy using Porcine Specimens, following an Experimental Approach

In this paper, the interaction among cervical vertebrae, a cervical plate and a bone graft implant, which is developed in a Corporectomy, is analyzed in an experimental form. In the case of specific damaged vertebra, its replacement is one of the alternative solutions. However, the displacement between the vertebral adjacent facets and the bone graft is a critical parameter which has to be evaluated in order to ensure the stability of the spine. Besides, it is advisable to make a precise evaluation of the structural integrity of the arrangement. For this study, porcine cervical vertebrae (C3-C5) were instrumented in order to replace a damaged C4 vertebra. This arrangement was tested under compression. The experimental observations were complemented with a numerical model. The displacements between the vertebral facets and the bone graft were measured. They are lower than 3 mm in order to develop stability in the spine. Besides, the proposed arrangement has structural integrity and the surgical procedure is simplified, as no wires are used.

Biomechanics and Numerical Evaluation of Cervical Porcine Models Considering Compressive Loads Using 2-D Classic Computer Tomography CT, 3-D Scanner and 3 -D Computed Tomography

In this paper the biomechanical behavior and numerical evaluation results of three C3-C5 porcine cervical models created with different modeling techniques are shown. The objective of this evaluation is to know the differences between the biomechanical effects on a bone graft, which replaces a damaged C4 vertebral body, a titanium alloy (Ti-6A1-4V) cervical plate, used to isolate the C4 damaged vertebra, and the influence on the compressive loads on the complete and instrumented C3-C5 cervical model. The biomechanical integrity of the healthy C3 and C5 vertebral body after the fixation of the cervical plate using titanium alloy screws is considered. Besides, 2-D Computer Tomography classic technique, 3-D Scanner Z-Corp 700 and a CT scanning Philips Brilliance system was used to create the three FEM models. In addition, 3-D Software as Pro-E Wildfire 4.0, ScanIP 3.1, UGS NX-4 and Geomagics R 10.0 was used to create specific numerical model. Main displacements and von Misses stresses between the upper and lower surfaces of the vertebral bodies and the bone graft and the influence of the titanium alloy (Ti-6A1-4V) screws on the vertebral body of C3 and C5 were evaluated. The contribution of this study is to optimize the actual surgical technique once the numerical results on the FEM model have been analyzed. In other words, the numerical disparity between classic CT techniques versus 3-D modern techniques is established.

Modelling of a Cervical Plate and Human Cervical Section C3 – C5 under Compression Loading Conditions Using the Finite Element Method

This paper presents the modelling of the effects due to load conditions on the cervical section defined between C3 and C5 after a cervical plate implant is used to transfer the compression loads from C3 to C5 as C4 is considered to be damaged as a result of a medical condition. For this study, three different scenarios which describe the common motion condition of the head-neck system are modelled. The first one refers to the effect of the head weight over the considered section. In the second case the average patient weight is supported by C3 and C5 vertebrae. The last case simulates extreme loading conditions as vertebrae lesions occur when these are compressed beyond its failure limit; the ultimate stress to compression load failure value is applied to C3. The stability and mechanical behaviour of cervical plates under compression loading conditions is evaluated using the Finite Element Method (FEM). Cervical plates are useful to restore stability of the spine by improving the inter-vertebral fusion, particularly when the cervical body has been damaged. The results show that the stresses on the plate and fixation screws, for the three cases, are within the elastic range. Conversely, it has to be considered that cortical and trabecular bone densities vary from one patient to another due to a number of factors, which can influence the fixation conditions of the screws. In the case of this analysis, healthy bone conditions were considered and the obtained results show that the risk of the integrity of the screwimplant- vertebrae system is not compromised.

Optimization of the Design of a Four Bar Mechanism for a Lower Limb Prosthesis Using the Taboo Search Algorithm

In this chapter, the optimization of the design of a four bar mechanism used in polycentric prosthesis with voluntary control is reported. This prosthesis has been used by a male, whose left leg was amputated above the knee. He is 34 years old, weighs 78 kg and is 1.75 m tall. One of the objectives of this optimization was to fulfill the requirements of his anthropometric characteristics. The taboo search algorithm was used for this purpose. In this case, the lengths of the links were determined, following an inverse analysis. The objective function was the minimization of the error between the target trajectory of the instantaneous center of rotation (ICR) and the path followed by ICR of the four bar mechanism. This curve is very important because it is related with the kinematic and the forces that are developed in the gait cycle. Therefore, it is expected that the amputee individual develop a natural gait cycle with this prosthesis. In the final stage, 1,900 iterations were carried out and the lengths of the bars were augmented by 0.01 mm. The lengths of the links of the optimized mechanism are the following: Bar 1 = 43 mm; Bar 2 = 55.5 mm; Bar 3 = 59 mm and Bar 4 = 29 mm. With this information, the prosthesis was manufactured and adapted to the patient.

Biomechanical evaluation of a corporectomy in porcine lumbar specimens using flexible polymer belts

This paper presents the experimental results of a biomechanical evaluation in lumbar porcine specimens (L2–L4), instrumented with flexible polymer belts, under fatigue and tensile loading. The clinical effect called facetary arthrosis is evaluated. An experimental analysis was carried on 3 lumbar porcine specimens. In two of them, polyamide belts are fixed on the interspinous ligament from L2 to L4. Specimens are taken from pigs which are 6 month old. For the present work, the stiffness reduction of the spine and the biomechanical behaviour of the belts in conjunction with the interspinous ligament are evaluated. The purpose is to determine the failure conditions for the elements of the specimen (vertebral disk, supra and intraspinous ligament and vertebral body). Under static loading, which is the base line case, the elements of the specimen failed as a typical healthy structure. While in the fatigue combined with static loading, the element failed in different order. Additionally, the stiffness changed in accordance with the fatigue loading conditions. Because of the simplicity of this alternative technique, a high level of the structural integrity is preserved, as no holes are made on the spinous process in order to insert the fixation screws. Furthermore, there is a cost reduction.

Design and Manufacturing of Prosthesis of a Jaw for a Young Patient with Articular Ankylosis

In this work, the design and manufacture of a new jaw prosthesis for a young patient with articular Ankylosis is reported. The required models were obtained with a Computed Axial Tomography (CAT) in conjunction with computed aided design (CAD) and engineering codes. Several tomography slices were taken in digital format (DICOM). Each slice was processed with Scan IP, CATIA and Solidworks. The main objective of this study is to show the digital and a physical processing for manufacturing the desired model, taking into account the anthropometry of the young patient, who expects to receive this fixation as a maxillary implant. The STL and FEM model allowed creating biomechanical prototypes in order to adjust the disorders that this young patient has suffered by three incorrect medical procedures. It will allow manufacture the final mold by using of a quick prototyping printer system (dust). This prosthesis will be created as an only piece, and the main body will be created by a strong, low weight and polymeric material Poly(methyl methacrylate)—(PMMA), while a low friction metal will be considered for the condylar joint. The expectation for this final implant requires the approval of the Specialty Hospital “La Raza” (IMSS) in order to be installed on the patient. For this purpose, biomechanical engineering procedure and 3D manufacturing quick prototyping was used for the prototype. The clinical case discussed in this paper is related to a 17-year-old individual. He was treated in the area of maxillofacial and plastic surgery. The severity of the deformation was based on congenital disease. Calcium hydroxyapatite, Poly(methyl Methacrylate) polymers and stainless steel, which are highly biocompatible materials, were used for this purpose. It is very important to mention that this procedure avoided the employment of bone tissue taken from the ribs and cranial regions as in other research publications referred. As a result of this research, a unique 3D personalized jaw model could be presented in order to be fixed in the patient.

Biomechanical Design of a Vertebral Distractor for Fractured Bodies Useful in Kyphoplasty

Nowadays, vertebral fractures represent a worldwide health problem. In the last decade, several advances in the development of techniques for the treatment of these fractures have been reported. These are the special surgery techniques called “vertebral augmentation techniques”. The purpose of this paper is to show a definitive design of a biomechanically assembled mechanism which has the function of separating the collapsed walls of the fractured vertebral body and to aid to get the necessary space to fix an implant. The function of this mechanism was tested under the surgical technique called “Kyphoplasty”, which is necessary in the treatment of vertebral fractures. With this design the intention is that the mechanism has functional characteristics such as: do to not leave it permanent taken into the fractured vertebral body as well as to have the ability to separate the collapsed walls of the healthy adjacent vertebral body. It is expected to be reusable a finite number of times after a sterilization process. The design methodology used was the QFD (The quality function deployment), and a final concept design was obtained. Some lumbar vertebrae porcine specimens (8 months old of the Duroc breed) were used in order to know the mechanical strength, necessary for the design of the mechanism. The final design of the device will be analyzed by the finite element method (FEM), in order to know the mechanical behavior under simulated working conditions. These studies will provide the necessary data which will be the main support to decide the best material to propose for the final mechanism and its manufacturing. However, these FEM results are not reported on this paper .

Numerical Study in Biomodels of Maxillofacial Prosthesis (Cancer and Osteonecrosis Cases)

This work shows a methodology to successfully generate an anatomically appropriate mandibular prosthesis for two patients with different conditions affecting the bone: cancer and necrosis. A common technique for bio-modeling was used in both cases, which includes tomographic slices of 0.5 mm for each clinical case. As a result of the processing a stereolithographic model was performed using two different techniques, were the affected area was reconstructed. In the osteonecrosis case, with the use of auxiliary guide paths and drawings in the CATIA platform a 3D model was produced, achieving a partial replacement with lateral support; while in the cancer case a left lateral replacement with the ramus was produced by reconstructing surfaces and patterns of the required area in PowerShape® and Solidworks® platforms. The region to replace was defined by the surgical expertise of a maxillofacial physician. Both cases were printed in acrylonitrile butadiene styrene (ABS) polymer producing a three-dimensional model, which was adjusted by the maxillofacial surgeon and subsequently integrated into a compound that includes cyanoacrylate with low toxicity, calcium powder, hydroxyapatite and isophthalic resin as a fundamental basis. The models were analyzed numerically using the same conditions that will be applied mechanically and clinically in order to obtain preliminary information on stress concentration zones and material deformation.

Numerical and experimental evaluation of the residual stress relaxation and the influence zone due to application of the crack compliance method

This paper presents the results concerning an evaluation of the crack compliance method. The research was focused on the relaxation caused by a cut induced to obtain the data required to calculate the residual stress field. The main objective in this research is to establish the optimum place to cut in a specimen that has suffered a failure and how extended is the zone of relaxed stresses. It has been recognized that a crack vanishes the beneficial or detrimental effects of the residual stress fields. This research has been performed in a numerical and experimental way, so results can be compared and FEM on this topic can be assessed.