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Plate or nail fixations have been applied to the repair of clavicle fractures. However, it is quite difficult to fairly evaluate the different clavicle fixation techniques owing to variations in the bone anatomy, bone quality, and fracture pattern. The purpose of this study was to investigate the biomechanical performances of different fixation techniques applied to a clavicle fracture using the finite element method. A simplified single-clavicle model and a complete human upper-body skeleton model were developed in this study. Three types of plate fixations, namely, superior clavicle plate, anterior clavicle plate, and clavicle anatomic spiral fixations, and one nail fixation, a titanium elastic nail fixation, were investigated and compared. The plate fixation techniques have a better fixation stability compared to the nail fixation technique. However, the nail fixation technique shows lower bone stress and can reduce the risk of a peri-implant fracture compared to the plate fixation techniques. Increasing the number of locking screws for the clavicle plate system can reduce the implant stress. Insertion of the bone plate into the anterior site of the clavicle or a multi-plane fixation is recommended to achieve the required biomechanical performance. A plate fixation revealed a relatively better fixation stability, and a nail fixation showed a lower risk of a peri-implant fracture.

Evaluations are vital to quantify the functionalities of athletic footwear, such as the performance of slip resistance, shock absorption, and rebound. Computational technology has progressed to become a promising solution for accelerating product development time and providing customized products in order to keep up with the competitive contemporary footwear market. In this research, the effects of various tread pattern designs on traction performance in a normal gait were analyzed by employing an approach that integrated computational simulation and gait analysis. A state-of-the-art finite element (FE) model of a shoe was developed by digital sculpting technology. A dynamic plantar pressure distribution was automatically applied to interpret individualized subject conditions. The traction performance and real contact area between the shoe and the ground during the gait could be characterized and predicted. The results suggest that the real contact area and the structure of the outsole tread design influence the traction performance of the shoe in dry conditions. This computational process is more efficient than mechanical tests in terms of both cost and time, and it could bring a noticeable benefit to the footwear industry in the early design phases of product development.

The pelvis is one of the most stressed areas of the human musculoskeletal system due to the transfer of truncal loads to the lower extremities. Sacroiliac joint injury may lead to abnormal joint mechanics and an unstable pelvis. Various fixation techniques have been evaluated and discussed. However, it may be difficult to investigate each technique due to variations in bone quality, bone anatomy, fracture pattern, and fixation location. Additionally, the finite element method is one useful technology that avoids these variations. Unfortunately, most previous studies neglected the effects of the lumbar spine and femurs when they investigated the biomechanics of pelvises. Thus, the aim of this study was to investigate the biomechanical performance of intact, injured, and treated pelvises using numerical and experimental approaches. Three-dimensional finite element models of the spine-pelvis-femur complex with and without muscles and ligaments were developed. The intact pelvis, the pelvis with sacroiliac joint injury, and three types of pelvic fixation techniques were analyzed. Concurrently, biomechanical tests were conducted to validate the numerical outcomes using artificial pelvises. Posterior iliosacral screw fixation showed relatively better fixation stability and lower risks of implant failure and pelvic breakage than sacral bar fixation and a locking compression plate fixation. The present study can help surgeons and engineers understand the biomechanics of intact, injured, and treated pelvises. Both the simulation technique and the experimental setup can be applied to investigate different pelvic injuries.

Femoral shaft fractures can be treated using retrograde interlocking nailing systems; however, fracture nonunion still occurs. Dynamic fixation techniques, which remove either the proximal or distal locking screws, have been used to solve the problem of nonunion. In addition, a surgical rule for dynamic fixation techniques has been defined based on past clinical reports. However, the biomechanical performance of the retrograde interlocking nailing systems with either the traditional static fixation technique or the dynamic fixation techniques has not been investigated by using nonlinear numerical modeling. Three-dimensional nonlinear finite element models were developed, and the implant strength, fixation stability, and contact area of the fracture surfaces were evaluated. Three types of femoral shaft fractures (a proximal femoral shaft fracture, a middle femoral shaft fracture, and a distal femoral shaft fracture) fixed by three fixation techniques (insertion of all the locking screws, removal of the proximal locking screws, or removal of the distal locking screws) were analyzed. The results showed that the static fixation technique resulted in sufficient fixation stability and that the dynamic fixation techniques decreased the failure risk of the implant and produced a larger contact area of the fracture surfaces. The outcomes of the current study could assist orthopedic surgeons in comprehending the biomechanical performances of both static and dynamic fixation techniques. In addition, the surgeons could also select a fixation technique based on the specific patient situation using the numerical outcomes of this study.

Traditional solid cages have been widely used in posterior lumbar interbody fusion (PLIF) surgery. However, solid cages significantly affect the loading mechanism of the human spine due to their extremely high structural stiffness. Previous studies proposed and investigated porous additive manufactured (AM) cages; however, their biomechanical performances were analyzed using oversimplified bone-implant numerical models. Thus, the aim of this study was to investigate the outer shape and inner porous structure of the AM cages. The outer shape of the AM cages was discovered using a simulation-based genetic algorithm; their inner porous structure was subsequently analyzed parametrically using T10-S1 multilevel spine models. Finally, six types of the AM cages, which were manufactured using selective laser melting, were tested to validate the numerical outcomes. The subsidence resistance of the optimum design was superior to the conventional cage designs. A porous AM cage with a pillar diameter of 0.4mm, a pillar angle of 40°, and a porosity of between 69% and 80% revealed better biomechanical performances. Both the numerical and experimental outcomes can help surgeons to understand the biomechanics of PLIF surgery combined with the use of AM cages. The outer shape of additive manufactured (AM) cages was determined using a simulation-based genetic algorithm; their inner porous structure was subsequently analyzed parametrically using T10-S1 multilevel spine models. Finally, six types of the AM cages fabricated using selective laser melting were tested. The optimum shape design of the AM cage had the highest subsidence resistance compared with the conventional designs. The AM cage with a pillar diameter of 0.4mm, a pillar angle of 40°, and a porosity between 69% and 80% satisfied all biomechanical requirements.Display Omitted The outer shape and inner porous structure of the AM cage could be determined using a simulation-based genetic algorithm and T10-S1 multilevel spine model, respectively.The optimum shape design of the AM cage had the highest subsidence resistance compared with the conventional designs.The AM cage with a pillar diameter of 0.4mm, a pillar angle of 40°, and a porosity between 69% and 80% satisfied all biomechanical requirements.Both the numerical and experimental outcomes can help surgeons to understand the biomechanics of PLIF surgery combined with the use of AM cages.

Study Design: Comparative in vitro biomechanical study and finite element analysis. Objectives: To investigate the bending strength and pullout strength of conical pedicle screws, as compared with conventional cylindrical screws. Summary of Background Data: Transpedicle screw fixation, the gold standard of spinal fixation, is threatened by screw failure. Conical screws can resist screw breakage and loosening. However, biomechanical studies of bending strength have been lacking, and the results of pullout studies have varied widely. Methods: Ten types of pedicle screws with different patterns of core tapering and core diameter were specially manufactured with good control of all other design factors. The stiffness, yielding strength, and fatigue life of the pedicle screws were assessed by cantilever bending tests using high-molecular-weight polyethylene. The pullout strength was assessed by pullout tests using polyurethane foam. Concurrently, 3-dimensional finite element models simulating these mechanical tests were created, and the results were correlated to those of the mechanical tests. Results: In bending tests, conical screws had substantially higher stiffness, yielding strength, and fatigue life than cylindrical screws (P

Background Healing of tibial fractures treated by locked nailing is threatened by locking screw failure. However, the effects of the design factors of the screws on their mechanical strength have rarely been studied. Method Three-point bending tests and finite element analyses were used to investigate the bending strength of five types of commercially available tibial locking screws and two types of specially designed screws. Yielding strength and fatigue life measured in bending tests were correlated to total strain energy and maximal tensile stress computed in finite element analyses. Parametric analysis and design optimization were done according to the Taguchi method. Validation studies to assess the stress rising effect of the threads on the fatigue strength were conducted in two types of new screws made of either stainless steel or titanium alloy. Findings The yielding strength of the screws was closely related to their total strain energy, and the logarithm of the fatigue life was closely related to the maximal tensile stress with correlation coefficients of −0.95 and −0.90, respectively. Parametric studies indicated that fatigue strength of the screws was affected mainly by inner diameter (contribution, 63.8%) and root radius (27.8%). The yielding strength was determined primarily by inner diameter (88.5%). Titanium screws had a longer fatigue life than stainless steel screws, especially in screws with larger root radii. Interpretation A screw’s strength is closely related to its design factors. Finite element models, which can reliably reflect the mechanical strength of screws can save time and effort during screw design. Larger root radius can effectively improve the fatigue strength, especially for titanium screws as compared with stainless steel screws.

Anterior cervical discectomy and fusion is a common surgical procedure performed to remove a degenerative or herniated disc in cervical spine. Unfortunately, clinical complications of anterior cervical plate (ACP) systems still occur, such as weak fixation stability and implant loosening. Previous researchers have attempted to ameliorate these complications by varying screw orientations, but the screw orientations are mainly determined according to the investigator's experiences. Thus, the aim of this study was to discover the optimal screw orientations of ACP systems to achieve acceptable fixation stability using finite element simulations and engineering algorithms.Three-dimensional finite element models of C3-T2 multi-level segments with an ACP system were first developed to analyze the fixation stability using ANSYS Workbench 14.5. Then, artificial neural networks were applied to create one objective function, and the optimal screw orientations of an ACP system were discovered by genetic algorithms. Finally, the numerical models and the optimization study were validated using biomechanical tests.The results showed that the optimal design of the ACP system had highest fixation stability compared with other ACP designs. The neuro-genetic algorithm has effectively reduced the time and effort required for discovering for the optimal screw orientations of an ACP system.The optimum screw orientation of the ACP system could be successfully discovered, and it revealed excellent fixation stability for the treatment of cervical degenerative disc disease. This study could directly provide the biomechanical rationale and surgical suggestion to orthopedic surgeons.

Screw loosening can threaten pedicle screw fixation of the spine. Conical screws can improve the bending strength, but studies of their pullout strength as compared with that of cylindrical screws have shown wide variation. In the present study, polyurethane foam with two different densities (0.32 and 0.16 gm/cm3) was used to compare the pullout strength and stripping torque among three kinds of pedicle screws with different degrees of core tapering. Three-dimensional finite element models were also developed to compare the structural performance of these screws and to predict their pullout strength. In the mechanical tests, pullout strength was consistently higher in the higher density foam and was closely related to screw insertion torque (r=0.87 and 0.81 for the high and low density foam, respectively) and stripping torque (r=0.92 and 0.78, respectively). Conical core screws with effective foam compaction had significantly higher pullout strength and insertion torque than cylindrical core screws (p

Objective. To investigate the bone holding power of tibial locking screws. Design. The bone holding power was assessed by mechanical testing and finite element analysis. Background. Screw loosening might threaten fracture fixation and bone healing. Methods. In mechanical tests, six types of different tibial locking screws were inserted into low-density polyurethane foam tubes, which simulated osteoporotic bone. The screws were pushed out of the foam bone by an axial load, and the maximal pushout load was recorded. In finite element analysis, three-dimensional finite element models with a nonlinear contact interface between the screws and the bones were created to simulate the mechanical testing. The total strain energy of the bone and total reaction force of the screws were recorded. The contribution of the design factors was analyzed by the Taguchi method. Results. In the mechanical tests, foam bone was stripped by the screw threads without screw deformation. The testing results were closely related to those of finite element analysis. The Taguchi analysis showed that the descending order of contribution of the design factors was outer diameter, pitch, half angle, and inner diameter. Root radius and thread width had minimal effects. Conclusions. The bone holding power of the screws could be reliably assessed by finite element models, which could analyze the effects of all the design factors independently and were potentially applicable to screws with irregular thread patterns. RelevanceThe finite element models built in this study may help manufacturers in evaluating new designs of locking screws and assist surgeons in selecting suitable devices for patients with severe osteoporosis.

Anterior lumbar plate (ALP) systems have been widely used as an effective interbody fusion device for treating spinal cord compression. However, clinical complications, such as implant loosening and breakage, still occur. Past studies have investigated the effects of the screw orientation on the interfacial strength, but these studies were inconsistent. The purpose of this study was to identify an ALP system with excellent interfacial strength by varying the screw orientation. Three-dimensional finite element models of L4–L5 segments with an ALP system were first constructed. A neurogenetic algorithm, which combines artificial neural networks and genetic algorithms, was subsequently developed to discover the optimum plate design. Finally, biomechanical tests were conducted to validate the results of the finite element models and the engineering algorithm. The results indicated that the interfacial strength of the optimum plate design obtained using the neurogenetic algorithm was excellent compared with the other designs and that all of the locking screws should be inserted divergently. Both the numerical and experimental outcomes can provide clinical suggestions to surgeons and help them to understand the interfacial strength of ALP systems in terms of the screw orientation.

Spinal pedicle screw fixations have been used extensively to treat fracture, tumor, infection, or degeneration of the spine. Cannulated spinal pedicle screws with bone cement augmentation might be a useful method to ameliorate screw loosening. However, cannulated spinal pedicle screws might also increase the risk of screw breakage. Thus, the purpose of this study was to investigate the bending performance of different spinal pedicle screws with either solid design or cannulated design. Three-dimensional finite element models, which consisted of the spinal pedicle screw and the screw's hosting material, were first constructed. Next, monotonic and cyclic cantilever bending tests were both applied to validate the results of the finite element analyses. Finally, both the numerical and experimental approaches were evaluated and compared. The results indicated that the cylindrical spinal pedicle screws with a cannulated design had significantly poorer bending performance. In addition, conical spinal pedicle screws maintained the original bending performance, whether they were solid or of cannulated design. This study may provide useful recommendations to orthopedic surgeons before surgery, and it may also provide design rationales to biomechanical engineers during the development of spinal pedicle screws.

A pedicle screw fixation has been widely used to treat spinal diseases. Clinical reports have shown that the weakest part of the spinal fixator is the pedicle screw. However, previous studies have only focused on either screw breakage or screw loosening. There have been no studies that have addressed the multiobjective design optimization of the pedicle screws. The multiobjective optimization methodology was applied and it consisted of finite element method, Taguchi method, artificial neural networks, and genetic algorithms. Three-dimensional finite element models for both the bending strength and the pullout strength of the pedicle screw were first developed and arranged on an L25 orthogonal array. Then, artificial neural networks were used to create two objective functions. Finally, the optimum solutions of the pedicle screws were obtained by genetic algorithms. The results showed that the optimum designs had higher bending and pullout strengths compared with commercially available screws. The optimum designs of pedicle screw revealed excellent biomechanical performances. The neurogenetic approach has effectively decreased the time and effort required for searching for the optimal designs of pedicle screws and has directly provided the selection information to surgeons.

Optimizing the orthopaedic screws can greatly improve their biomechanical performances. However, a methodical design optimization approach requires a long time to search the best design. Thus, the surrogate objective functions of the orthopaedic screws should be accurately developed. To our knowledge, there is no study to evaluate the strengths and limitations of the surrogate methods in developing the objective functions of the orthopaedic screws. Three-dimensional finite element models for both the tibial locking screws and the spinal pedicle screws were constructed and analyzed. Then, the learning data were prepared according to the arrangement of the Taguchi orthogonal array, and the verification data were selected with use of a randomized selection. Finally, the surrogate objective functions were developed by using either the multiple linear regression or the artificial neural network. The applicability and accuracy of those surrogate methods were evaluated and discussed. The multiple linear regression method could successfully construct the objective function of the tibial locking screws, but it failed to develop the objective function of the spinal pedicle screws. The artificial neural network method showed a greater capacity of prediction in developing the objective functions for the tibial locking screws and the spinal pedicle screws than the multiple linear regression method. The artificial neural network method may be a useful option for developing the objective functions of the orthopaedic screws with a greater structural complexity. The surrogate objective functions of the orthopaedic screws could effectively decrease the time and effort required for the design optimization process.

Anterior lumbar interbody fusion (ALIF) with cylindrical cages and supplemental posterior fixation has been widely used for internal disc derangement. However, most researchers have focused on single-level ALIF. Therefore, the biomechanical performance of various fixation constructs after two-level ALIF is not well characterized. This research used three-dimensional finite element models (FEM) with a nonlinear contact analysis to evaluate the initial biomechanical behavior of five types of fixation devices after two-level ALIF (L3/L4, L4/L5) under six loading conditions. These fixation constructs included a three-level pedicle screw and rod, a two-level translaminar facet screw, a two-level transfacet pedicle screw, a bisegmental pedicle screw and rod, and a bisegmental pedicle screw and rod with cross-linking. The FEM's developed in this study demonstrate that, compared to the other four types of posterior fixation constructs analyzed, the three-level pedicle screw and rod provide the best biomechanical stability. Both two-level facet screw fixation constructs showed unfavorable loading in lateral bending. For the construct of the three-level pedicle screw and rod, the middle-segment pedicle screw should not be omitted even though a cross-link is used. The two-level ALIF models with cages and posterior fixation constructs that we developed can be used to evaluate the initial biomechanical performance of a wide variety of posterior fixation devices prior to surgery.

Improper design of vertebral body cages may seriously affect the interface strength and cause the lose of fixation for a vertebral body replacement. This research used a FEM-based Taguchi method to investigate the effects of various factors to find the robust design of the body cage. Three-dimensional finite element models with a nonlinear contact analysis have been developed to simulate the pullout strength of the body cage. Then, the Taguchi robust design method was used to evaluate the spike design. In a situation without bone fusion, the spike row, the spike oblique, and the spike height were especially important factors. The optimum combination has been found to be the pyramidal spike type, a spike height of 2 mm, a spike diameter of 2.2 mm, an oblique geometry, 11 rows per 28 mm, and an inner diameter of 10 mm. In a situation with bone fusion, the spike row, the spike height, and the inner diameter were the most significant factors. Here, the optimum combination has been found to be the conical spike type, a spike height of 2 mm, a spike diameter of 2.2 mm, an oblique geometry, 11 rows per 28 mm, and an inner diameter of 20 mm. The finite element analyses could be used to predict the interface stiffness of the body cages. The FEM-based Taguchi methods have effectively decreased the time and effort required for evaluating the design variables of implants and have fairly assessed the contribution of each design variable.

Breakage or loosening of locking screws may impair fracture fixation or bone healing in locked nailing of tibial fractures. Bending strength and bone holding power, two important design objectives of locking screws, may conflict with each other. The present study used multiobjective optimization with a genetic algorithm to investigate the optimal designs with respect to these two objectives. Three-dimensional finite element models for analyzing bending strength and bone holding power of locking screws were created first. Through use of a Taguchi L25 orthogonal array, two objective functions were developed by least-squares regression analyses. Then, the trade-off solutions between the two objectives known as Pareto optima were explored by a weighted-sum aggregating approach under geometric constraints. The objective functions, reliably reflecting the finite element results, were valid for multiobjective studies. The Pareto fronts of the screws with 4.5-mm and 5.0-mm outer diameters were similar. The “knee” region of the Pareto front, characterized by the fact that a small improvement in either objective will cause a large deterioration in the other objective, might be the favored choice of optimal designs. The commercially available locking screws compared with the Pareto optima were found to be dominated designs and could be improved. In conclusion, the multiobjective optimization with a genetic algorithm was useful for optimization of locking screw design with many variables and conflicting objectives. Choosing an optimal design requires a thorough knowledge of the inherent problems. This method could reduce the time, cost, and labor associated with the screw development process. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res