A new design for the humerus fixation plate using a novel reliability-based topology optimization approach to mitigate the stress shielding effect.

BACKGROUND: Due to high stiffness, metal fixation plates are prone to stress shielding of the peri-prosthetic bones, leading to bone loss. Therefore, it has become important to design implants with reduced rigidity but increased load-carrying capacity. Considering the uncertainties in the parameters affecting the implant-bone structure is critical in making more reliable implant designs. In this study, a Response Surface Method based Reliability-based Topology Optimization approach was proposed to design a fixation plate for humerus fracture having less stiffness than the conventional plate. METHODS: The design of the fixation plate was described as an Reliability-based Topology Optimization problem in which the probabilistic constraint was replaced with a meta-model generated using the Kriging method. The artificial humerus bone model was scanned, and the 3D simulation model was used in the finite element analysis required in the solution. The optimum plate was manufactured using Selective Laser Melting. Both designs were experimentally compared in terms of rigidity. FINDINGS: The volume of the conventional plate was reduced from 2512.5 mm3 to 1667.3 mm3; nevertheless, the optimum plate had almost one-third less rigidity than the conventional plate. The probability of failure of the conventional plate was computed as 0.994. However, this value was almost half for the optimum fixation plate. Interpretation The studies showed that the new fixation plate design was less rigid but more reliable than the conventional one. The computation time required to have the optimum plate was reduced by one-tenth by applying the Response Surface Method for the Reliability-based Topology Optimization problem.

Designing and in vitro testing of a novel patient-specific total knee prosthesis using the probabilistic approach.

In order to prevent failure as well as ensure comfort, patient-specific modelling for prostheses has been gaining interest. However, deterministic analyses have been widely used in the design process without considering any variation/uncertainties related to the design parameters of such prostheses. Therefore, this study aims to compare the performance of patient-specific anatomic Total Knee Arthroplasty (TKA) with off-the-shelf TKA. In the patient-specific model, the femoral condyle curves were considered in the femoral component's inner and outer surface design. The tibial component was designed to completely cover the tibia cutting surface. In vitro experiments were conducted to compare these two models in terms of loosening of the components. A probabilistic approach based on the finite element method was also used to compute the probability of failure of both models. According to the deterministic analysis results, 103.10 and 21.67 MPa von Mises stress values were obtained for the femoral component and cement in the anatomical model, while these values were 175.86 and 25.76 MPa, respectively, for the conventional model. In order to predict loosening damage due to local osteolysis or stress shield, it was determined that the deformation values in the examined cement structures were 15% lower in the anatomical model. According to probabilistic analysis results, it was observed that the probability of encountering an extreme value for the anatomical model is far less than that of the conventional model. This indicates that the anatomical model is safer than the conventional model, considering the failure scenarios in this study.

A new porous fixation plate design using the topology optimization.

Fixation plates are used to accelerate the biological healing process in the damaged area by providing mechanical stabilization for fractured bones. However, they may cause mechanical and biological complications such as aseptic loosening, stress shielding effect and necrosis during the treatment process. The aim of this study, therefore, was to reduce mechanical and biological complications observed in conventional plate models. For this purpose, an optimum plate geometry was obtained using the finite element based topology optimization approach. An optimum and functionally graded porous model were obtained for the plates used for transverse fractures of diaphysis in long bones. This model was combined with a functional graded porous cage structure, and thus a new generation porous implant model was proposed for fixation plates. In order to determine the performance of the optimum plate model, it was produced by additive manufacturing. Three models; i.e. conventional, optimum and porous fixation plates were statically tested, and they were compared experimentally and numerically using the finite element analysis (FEA). The porous model can be considered as the most suitable option since it requires less invasive inputs, and might lead minimum necrosis formation due to having lesser contact surface with the bone.

Triad of foot deformities and its conservative treatment: With a 3D customized insole.

The coexisting of three deformities as hallux valgus, flatfoot, and the calcaneal spur is an undefined medical condition, and it may be called triad of foot deformities (TFD) as a definition for a new disease entity. A customized 3D insole prototype was created by postprocessing of MRI data, and printed by 3D printer technology for the purpose of providing effective and innovative treatment for TFD. A 42 years-old female was clinically examined for TFD findings. All radiological measurements were made on the weightbearing anteroposterior and lateral X-rays. The patient underwent the pedogram (RSscan International, footscan©). MRI images were taken for the purpose of 3D scanning that was used for producing the 3D splint for TFD. AOFAS (American Orthopedic Foot and Ankle Society scores) and FHSQ (Foot Health Status Questionnaire) were used for clinical follow-up. MRI images of the patient were imported to Mimics software in order to create a 3D model using image processing. Thus, Patient-Specific 3D customized silicone orthotic insole that was based on 3D printing technology was produced. The one-simple test was used to compare the results of AOFAS and FHSQ scores. The measurements of radiological measurements were given. On the clinical follow-up, AOFAS was FHSQ scores were obtained. There was a significant difference in terms of AOFAS and FHSQ scores (p ≤ 0.05). As a result of our study; our 3D customized insole was produced at the price of approximately 1/3 of the total cost of three standard medical products. The coexisting of these three deformities may be called triad of foot deformities (TFD). The 3D printer technology enables us to access a customized, personalized conservative treatment option for TFD. The conservative treatment of TFD is possible by a single orthotic insole.

An application of finite element method in material selection for dental implant crowns.

Materials used for dental crowns show a wide range of variety, and a dentist's choice can depend on several factors such as patient desires, esthetics, tooth factors, etc. One of the most important issues for implant surgery is the primary stability and it should be provided to minimize the risks of screw loosening, failed osseointegration, or nonunion. The current study aims to present the Finite Element Analysis (FEA)-based material selection strategy for a dental crown in terms of reducing the aforementioned risks of dental implants. A virtual surgery mandible model obtained using MIMICS software was transferred to the ANSYS and material candidates determined using CES software were compared using FEA. The results indicated that Zr02+Y2O3 (zirconia) has shown a 12.79% worse performance compared to Au83-88/Pt4-12/Pd4.5-6 alloy in terms of abutment loosening. On the other hand, zirconia is the most promising material for dental crowns in terms of the stability of the bone-implant complex. Therefore, it may show the best overall performance for clinical use. Moreover, as suggested in this study, a better outcome and more accurate predictions can be achieved using a patient-specific FEA approach for the material selection process.

Determining the Patient-Specific Optimum Osteotomy Line for Severe Mandibular Retrognathia Patients.

PURPOSE: The purpose of this study is to suggest a patient-specific osteotomy line to optimize the distractor position and thus to minimize the disadvantages of conventional mandibular distraction osteogenesis (MDO) protocols. In addition, this study also aims to compare the conventional MDO protocols with the new MDO protocol proposed in this study in terms of both orthodontic outcomes and mechanical effects of osteotomy level on callus stabilization by means of the finite element method. METHODS: A preoperative patient-specific 3-dimensional bone model was created and segmented by using computed tomography images of an individual patient. Virtual orthodontic set-up was applied to the segmented model prior to the virtual surgery. In order to compare the proposed osteotomy line with the conventional lines used in clinical applications, virtual surgery simulations were performed and callus tissues were modelled for each scenario. The comparison of the success of each osteotomy line was carried out based on the occlusion of the teeth. RESULTS: The osteotomy line determined using the method proposed in this study has resulted in far less malocclusion than the conventional method. Namely, any angular deviation from the optimum osteotomy line determined in this study might result in deep-bite or open-bite. On the other hand, the finite element analysis results have indicated that this deviation also negatively affects the callus stability. CONCLUSION: In order to achieve a better MDO treatment in terms of occlusion of the teeth and the callus stability, the location of the osteotomy line and the distractor position can be computationally determined. The results suggest that MDO protocol developed in this study might be used in clinic to achieve a better outcome from the MDO treatment.

An Analysis of Mandibular Symphyseal Graft Sufficiency for Alveolar Cleft Bone Grafting.

The purpose of this study was to evaluate the sufficiency of the mandibular symphysis as a donor site for unilateral and bilateral alveolar grafting, measuring both the alveolar cleft volume and maximum bone graft volume that can be harvested from the mandibular symphysis using 3-dimensional computed tomography (CT) and software in children and adults. Computed tomography data obtained from 20 unilateral and bilateral cleft lip palates patients in the preoperative period were used in this study. The patients were divided into 2 groups: children (female, n = 5; male, n = 5) and adults (female, n = 5; male, n = 5). The required bone graft volume for grafting and the maximum bone graft volume that can be harvested from the mandibular symphysis were measured based on cone beam CT data and software. The average required bone graft volume (cleft volume) for unilateral alveolar grafting was 963.51 ±â€Š172.31 mm in the children and 1001.21 ±â€Š268.16 mm in the adults. The average required bone graft volume for bilateral alveolar grafting was 1457.82 ±â€Š148.18 mm in the children and 2189.59 ±â€Š600.97 mm in the adults. The average the mandibular symphysis bone graft volume was 819.29 ±â€Š330.85 mm in the children and 2164.9 ±â€Š1095.86 mm in the adults. The results demonstrated that the mandibular symphysis region provided an adequate bone volume for alveolar grafting in adults with unilateral alveolar clefts. However, it is difficult to standardize these results, due to cleft volume and graft volume that could be harvested from the mandibular symphysis are highly variable among individuals.

A New Design for Maximum Conformity of Total Knee Prosthesis to Femur and Tibia.

Total knee arthroplasty (TKA) is a common procedure for treating patients with excessively arthritic knees. Nonetheless, early failure of TKA may occur in the first 5 yr, and up to 20% of TKA procedures can fail after 20 yr. In this study, a new anatomic prosthesis was designed to provide maximum conformity to knee bones and produce less stress and strain, in an effort to avoid possible failure of the prosthesis. Anatomical and conventional knee models were compared on the basis of both geometric conformity and stress and strain results obtained from finite element analysis. To compare geometric conformity, anatomic prosthesis components were manufactured by laser melting, and conventional prosthesis components were fixed to sawbone knee models. The anatomical model yielded up to 50% less contact pressure at the insert, which may indicate potential for reduced wear between insert and femur components. This model also resulted in less principal strain value at the tibial component, considered to be an important parameter to indicate loosening. The anatomical model with a new femur component in the anterior cortex design also yielded less stress at the femoral cortex, when compared to the conventional model. The findings in this study suggest that the anatomic prosthesis model may be a better design alternative to conventional knee prostheses in terms of wear, aseptic loosening, and normal joint biomechanics.

Failure analysis of the cement mantle in total hip arthroplasty with an efficient probabilistic method.

Accurate prediction of long-term behaviour of cemented hip implants is very important not only for patient comfort but also for elimination of any revision operation due to failure of implants. Therefore, a more realistic computer model was generated and then used for both deterministic and probabilistic analyses of the hip implant in this study. The deterministic failure analysis was carried out for the most common failure states of the cement mantle. On the other hand, most of the design parameters of the cemented hip are inherently uncertain quantities. Therefore, the probabilistic failure analysis was also carried out considering the fatigue failure of the cement mantle since it is the most critical failure state. However, the probabilistic analysis generally requires large amount of time; thus, a response surface method proposed in this study was used to reduce the computation time for the analysis of the cemented hip implant. The results demonstrate that using an efficient probabilistic approach can significantly reduce the computation time for the failure probability of the cement from several hours to minutes. The results also show that even the deterministic failure analyses do not indicate any failure of the cement mantle with high safety factors, the probabilistic analysis predicts the failure probability of the cement mantle as 8%, which must be considered during the evaluation of the success of the cemented hip implants.