Biomechanical Evaluation of a Newly Developed Functional-Grade Composite Material for Pedicle Screws.

OBJECTIVE: Pedicle screw and rod systems are widely employed in spine surgeries and loosening due to insufficient mechanical stimulation on the bone is frequently encountered in pedicle screws. This mechanical stimulation problem also arises due to the high rigidity of the implant material. This study aimed to develop new pedicle screws with composite material to solve the pedicle screw loosening problem. METHODS: The vertebrae and vertebral disk were modeled in three dimension using computerized tomography images obtained from a patient. A commercially available pedicle screw was modeled using Fusion software, and all models were assembled in accordance with the surgical procedure. Pedicle screw models were also divided radially and longitudinally to resemble functionally graded materials, which are composite materials. The load was applied to the top of the T12 vertebra and the screw-vertebral system was fixed to the bottom of the L1 vertebra. RESULTS: The strain results on the vertebrae were examined according to the mechanostat theorem. According to the results, functionally graded material (FGM) pedicle screw decreased the strain on the vertebral bones, and the positive effects on the bone were determined when using the radially functionally graded screws. The maximum stress values were also examined to determine the strengths of all the models. CONCLUSION: In conclusion, FGM pedicle screw decreased the strain on the bone which is an important parameter for the loosening failure according to the study. The other important conclusion is that FGM pedicle screw can be the solution to the loosening of the screw but not in all vertebrae.

The relationship between passion and athlete identity in sport: the mediating and moderating role of dedication.

BACKGROUND: In addition to the fact that the concept of passion in sports plays a significant role in the formation of the identity concept of athletes, the dedication of athletes to the sports branches they are interested in also has a significant impact on their passion for the sport they are interested in as well as their identity as an athlete. In this direction, the research aims to investigate the role of dedication as a mediator and moderator in the relationship between athlete identity and passion in sport. METHODS: The research was designed using the quantitative research technique of relational surveying. As data collection instruments for the research, the athlete identity scale, the passion in sport scale, and the sports commitment scale were utilized. 237 amateur and professional athletes, of which 142 were male and 95 were female (Mage = 22.7), participated voluntarily in the study by random sampling. The data were analyzed with the PROCESS and Jamovi programs in order to examine the direct and indirect effects. RESULTS: Significant effects of sports passion on commitment and athlete identity were found. Since both dedication and athlete identity had a significant effect on passion for sports, it was determined that passion for sports continues to influence athlete identity through the medium of dedication. The moderator significance of medium, high, and low values of devotion was determined. ETHICS APPROVAL NUMBER: 226394, date of registration: 03/11/2022. CONCLUSION: On the basis of the results of the statistical analyses, it was determined that the concept of dedication has a mediating and moderating effect on the relationship between sports passion and athlete identity.

Biomechanical evaluation of intramedullary retrograde nail and dynamic condylar screw used in unstable distal femoral fractures.

Distal femur fractures are a common problem in orthopedics. Intramedullary retrograde nails (IRN) and dynamic condylar screws (DCS) are generally used for the treatment of these fractures. In this study, it was aimed to mechanically evaluate and compare these two implants used for the treatment of distal femur fractures. In this study, an AOOTA 33C1.3 fracture was created on the intact femur obtained from computed tomography images. The fractures were fixed with DCS and IRN. Then the created models were imported into the ANSYS Workbench for finite element analysis to determine the most convenient mechanical fixation type. The distal region of the femur was loaded considering 75 kg-f, and the created models were constrained in all directions from the femoral head. The intact femur was also analyzed to compare it with the DCS and IRN fixation models. The von Mises stress, strain, and displacement results were examined to determine the damage risk. According to the results, the risk of damage is lower in the model of fixation with IRN. The normal strain distribution in the model fixed with IRN is closer to the model of an intact femur. For this reason, the risk of stress shielding in IRN fixation is less than in DCS fixation. However, the fracture lines were more stable in the fixation with the DCS. In conclusion, fracture fixation with IRN is mechanically more suitable for distal femur fractures in terms of fracture healing.

The Impact of Regular Exercise on Life Satisfaction, Self-Esteem, and Self-Efficacy in Older Adults.

This study employed the correlational survey model to examine how regular exercise influenced life satisfaction, self-esteem, and self-efficacy in men over 65. The study sample included a total of 215 participants, of whom 110 exercised regularly (for at least 45 min, three times a week), while 105 engaged in no physical exercise. Regular exercisers were found to score significantly higher on life satisfaction, self-esteem, and self-efficacy scales as compared to non-exercisers. These scores also increased significantly with age and prolonged exercise history. A moderate and positive correlation was detected between life satisfaction, self-esteem, and self-efficacy among regular exercisers, while non-exercisers showed low to moderate correlations. The findings suggest that regular exercise can enhance life satisfaction, self-esteem, and self-efficacy in the elderly male population. Such effects appear to be associated with greater age and lifetime exercise history, highlighting the value of regular physical exercise in improving the quality of life among older adults.

Effects of the internal contact surfaces of dental implants on screw loosening: A 3-dimensional finite element analysis.

STATEMENT OF PROBLEM: The effects of the internal contact surfaces of dental implants on screw loosening have yet to be investigated. PURPOSE: The purpose of this 3-dimensional finite element analysis (FEA) study was to evaluate and compare the mechanical effects of the abutment implant angle (θ), the abutment screw head diameter (D), and the abutment screw length (L) on screw loosening. MATERIAL AND METHODS: A total of 27 models presenting various mechanical scenarios were built by using combinations of 3 different θ (30 degrees, 45 degrees, and 60 degrees), D (2.65 mm, 2.75 mm, and 2.85 mm), and L (4 mm, 5 mm, and 6 mm). In FEA, a static test with a 200-N force inclined 30 degrees in the implant axial direction was applied to the upper surface of the abutment to evaluate and compare the maximum von Mises stresses of the implant components and the maximum total deformation in all models. In addition, modal analysis was applied to identify the natural frequencies in all models under free (unforced) vibration, and a Kruskal-Wallis statistical test (α=.05) was performed, followed by multiple pairwise comparisons by using the Dunn test. RESULTS: The Kruskal-Wallis test found a significant influence of the θ on implant stress, total deformation, and natural frequency (P<.001). For example, increasing the θ from 30 degrees to 45 degrees and 60 degrees can considerably reduce the model's natural frequencies to 18% and 26%, respectively. Similarly, the test underscored the significant impact of the D on both abutment screw stress and abutment stress (P=.010 and P=.002, respectively). However, the L appeared to have no significant effect on any of the dependent variables (P>.05). CONCLUSIONS: The θ and the D significantly influenced the stresses of dental implant components, total deformation, and natural frequency of the model, which may impact the mechanical stability of the screw joint. However, the L does not appear to affect these values significantly.

Metatarsal bone model production using 3D printing and comparison of material properties with results obtained from CT-based modeling and real bone.

Using a real bone is very important to find correct results for the biomechanical studies. However, it is very difficult to find the real bone and sometimes artificial bone models can be preferred instead of real bone. The aim of this study is to obtain an easy-to-manufacture, easy-to-customize and inexpensive method the artificial first metatarsal bone model that is similar material properties with the real bone. 3D printer technology was used to produce the artificial bone model. First metatarsal bone was modeled using MIMICS software to produce and determined the mechanical properties. The bone mechanical properties were calculated via MIMICS software using computer tomography images. 3D bone models were produced in different infill density and infill pattern to determine the real bone mechanical properties using 3D printer. The infill density of the bone model was adjusted as 20%, 40%, and 60%. Five different infill pattern types were used as grid, cubic, triangle, trihexagon, and gyroid. The produced models were subjected to torsional test and the elasticity modulus of all models were obtained. The results of the elasticity modulus of all produced (artificial) and modeled (calculated) bone were compared and the optimum bone model was obtained. The optimum infill density and infill pattern was determined as 40% and trihexagon, respectively.

Evaluation of the Relation Between Preload Values and Pull-Out Force of the Cortical Screw Used in Bone Fracture.

This study aims to examine the relation between pull-out strength and preload values of the cortical screw used in bone fracture fixation. The research question is that "Does the pull-out strength of the cortical screw used in the bone fracture fixation change with the preload values of the screw change?". To perform this purpose, the finite element method was selected due to its ease to evaluate and calculate the stresses on the whole model. Models of a cortical screw, partial plate, and bone were created using the SolidWorks program. The material properties of the bone were selected orthotropic material type. The bone fixed on the distal and proximal ends. The pull-out forces were applied at the bottom of the plate. The screw that has been loaded ranges from 100 N-700 N as preload. The pull-out forces were determined 200-400-600 N as in the literature. The results show that the pull-out strength of the screw was changed when the preloaded values higher than 400 N. However, it was seen that the pull-out strength does not substantially change when the preload values were lower than 400 N. When the preload values were applied ≥500 N, the maximum von Mises stresses on the screw exceeded the critical strength of the screw material. In conclusion, the critical preload value was determined as 500 N for the optimum pull-out strength.

Biomechanical evaluation of the screw preload values used in the plate placement for bone fractures.

The purpose of this study is to examine the effects of screw preload values on the bone-plate system. The preload value was taken differently in the literature range from 50 N to 3000 N. These preload value were examined in this study. The finite element method was used to calculate the strain and stress on the models. The long bone, plate and screws were modeled as 3D using CAD software. The finite element models were created using Ansys Workbench software. The convergence and validation study were made for the correct results. The 400 N axial load was applied to the proximal end of bone. The distal end of the bone fixed for boundary condition. The preload values were applied to the screws differently. The results of the finite element analysis were compared and evaluated. The results showed that when the preload values increased, the von Mises stresses and strains on the bone and plate system increased. The critical preload value of the screw is the 500 N. The upper values of this critical value can be damaged bone and plate system. The critical region of the bone is the holes where the screw inserted. In conclusion, the preload values of the screw should not exceed the 500 N for the successful fixation.

Evaluation of new hip prosthesis design with finite element analysis.

Cemented and cementless hip prostheses are used in total hip replacement surgery. Short, medium and long term success rates of these hip prostheses are controversial in the literature. Traditional cemented and cementless hip prostheses have advantages and disadvantages affecting the success of the implantation process. In this study, a new design of hip prosthesis is presented considering the advantages and disadvantages of the prostheses. Femur and prostheses were modeled and combined with each other to perform the finite element analysis (FEA). The new design of prosthesis was compared to the conventional prosthesis in terms of mechanical aspects. The evaluation criteria are the maximum von Mises stress and micro-movement of the contact between femur and prosthesis. In conclusion, the new design of prosthesis was found to provide a sufficient amount of primary stability and decreased the risk of stress shielding.

Finite Element Analysis of Short- Versus Long-Segment Posterior Fixation for Thoracolumbar Burst Fracture.

OBJECTIVE: The thoracolumbar (TL) area marks the transition of the rigid thoracic spine into the mobile lumbar spine, and it is considered to be the weakest part of the spine. This study was designed to develop a finite element (FE) model of the TL junction (T9-L3) to provide data that could help the clinician and researcher to answer the question of whether short-segment posterior fixation is sufficient for biomechanical performance. In addition, the aim was to examine whether long-segment posterior fixation carries a greater risk of the development of adjacent segment disease. METHODS: This was a biomechanical finite element model analysis. FE analysis of the spine was conducted with posterior instrumentation under multidirectional loading conditions in order to evaluate the kinematics of the instrumented lumbar spine, as well as stresses in the posterior spinal instrumentation. We analyzed the following: 1) the range of motion of the T9-L3 region; and 2) the von Mises stress nephograms of the pedicle screws, rods, vertebrae, endplates, and intervertebral discs of 2 fixation FE models. RESULTS: Long-segment stabilization was found to be beneficial in terms of reducing total stress on the spine. However, it is possible to reduce the stress on the system by incorporating the spinal fracture into the stabilization system. Therefore, short-segment stabilization is sufficient to create a safe and robust stabilization system and to maintain neighboring intact vertebrae. CONCLUSIONS: Short-segment posterior fixation is sufficient to stabilize fractures at the TL junction, where the spinal fracture is included in the stabilization system.

Medial malleolus fractures: A biomechanical comparison of tension band wiring fixation methods.

BACKGROUND: This study compared the biomechanical properties of three different fixation methods of tension band wirings, used in the treatment of medial malleolus fractures. The first method used an innovative "handmade bent pin" for cerclage fixation. The second method used a U-shaped K-wire to attach the cerclage to the medial tibial cortex. These two novel fixation techniques were compared with the traditional tension band wiring technique which is fixated to the bone by a screw. HYPOTHESIS: Novel fixation techniques of tension band wiring provide stable fixation. MATERIAL AND METHODS: In this study 27 artificial bone models, which medial malleolus fractures were simulated on, were used. Using an electromechanical test device, the force required to pull out each implant was assessed and compared. RESULTS: This study found that; while handmade bent pinning resulted averagely 840.25N (range: 647-1066±118.72) and U-shaped K-wire fixation was 381.71N (range: 176-651±150.2) pull out strength, traditional tension band wiring indicated 871.33N (range: 549-1008±137.74) pull out strength. DISCUSSION: Handmade bent pinning method provide similar results with traditional tension band wiring. Therefore, in suitable cases, it may be an acceptable alternative to traditional tension band wiring techniques when treating malleolar fractures. Although the outcomes of U-shaped K-wire fixation indicated lower than other two groups, the outcomes were comparable with the literature. So while performing tension band wiring, both handmade fixation systems may be used in certain cases. For Orthopaedic surgeons, it is better to know and think about these alternative handmade pinning systems created from simple K-wires during the surgery if needed. LEVEL OF EVIDENCE: IV, Biomechanical trial.

The effect of cement on hip stem fixation: a biomechanical study.

This study presents the numerical analysis of stem fixation in hip surgery using with/without cement methods since the use of cement is still controversial based on the clinical studies in the literature. Many different factors such as stress shielding, aseptic loosening, material properties of the stem, surgeon experiences etc. play an important role in the failure of the stem fixations. The stem fixation methods, cemented and uncemented, were evaluated in terms of mechanical failure aspects using computerized finite element method. For the modeling processes, three dimensional (3D) femur model was generated from computerized tomography (CT) images taken from a patient using the MIMICS Software. The design of the stem was also generated as 3D CAD model using the design parameters taken from the manufacturer catalogue. These 3D CAD models were generated and combined with/without cement considering the surgical procedure using SolidWorks program and then imported into ANSYS Workbench Software. Two different material properties, CoCrMo and Ti6Al4V, for the stem model and Poly Methyl Methacrylate (PMMA) for the cement were assigned. The material properties of the femur were described according to a density calculated from the CT images. Body weight and muscle forces were applied on the femur and the distal femur was fixed for the boundary conditions. The calculations of the stress distributions of the models including cement and relative movements of the contacts examined to evaluate the effects of the cement and different stem material usage on the failure of stem fixation. According to the results, the use of cement for the stem fixation reduces the stress shielding but increases the aseptic loosening depending on the cement crack formations. Additionally, using the stiffer material for the stem reduces the cement stress but increases the stress shielding. Based on the results obtained in the study, even when taking the disadvantages into account, the cement usage is more suitable for the hip fixations.

Comparison of the Lag Screw Placements for the Treatment of Stable and Unstable Intertrochanteric Femoral Fractures regarding Trabecular Bone Failure.

Background. In this study, the cut-out risk of Dynamic Hip Screw (DHS) was investigated in nine different positions of the lag screw for two fracture types by using Finite Element Analysis (FEA). Methods. Two types of fractures (31-A1.1 and A2.1 in AO classification) were generated in the femur model obtained from Computerized Tomography images. The DHS model was placed into the fractured femur model in nine different positions. Tip-Apex Distances were measured using SolidWorks. In FEA, the force applied to the femoral head was determined according to the maximum value being observed during walking. Results. The highest volume percentage exceeding the yield strength of trabecular bone was obtained in posterior-inferior region in both fracture types. The best placement region for the lag screw was found in the middle of both fracture types. There are compatible results between Tip-Apex Distances and the cut-out risk except for posterior-superior and superior region of 31-A2.1 fracture type. Conclusion. The position of the lag screw affects the risk of cut-out significantly. Also, Tip-Apex Distance is a good predictor of the cut-out risk. All in all, we can supposedly say that the density distribution of the trabecular bone is a more efficient factor compared to the positions of lag screw in the cut-out risk.

Evaluation of prebent miniplates in fixation of Le Fort I advancement osteotomy with the finite element method.

The stability of segments after Le Fort I osteotomy first attracted the researcher's interest when the surgical concept was conceived. Prebent plates are the ultimate modification of plate systems in craniofacial surgery; they have two right angles and are available in different lengths for use in maxillary advancement surgery. For this research, cone-beam computed tomography (CBCT) images of a male patient were obtained and scanned, and a 3D maxillary bone was created. Conventional Le Fort I osteotomies with 5 and 10 mm advancements were performed on both the cortical and trabecular bone using the Surgical Simulation Module of Mimics software; 1.7 mm Leibinger standard orthognathic 5-hole L plates and 1.7 mm Leibinger orthognathic advancement 11-hole prebent plates were adapted to the fragments. Displacement of the segment, the von Mises (VM) stresses (on the titanium miniplates) and the maximum principal (MP) stresses (on the bone) were evaluated for each configuration. Prebent plates offer a good alternative to the conventional two plate system, except in operations where maxillary advancement exceeds 5 mm. Surgical procedures that include advancement exceeding 5 mm or vertical position changes remain controversial and further studies are needed.

Evaluation of contact characteristics of a patient-specific artificial dysplastic hip joint.

This study addresses the results of the experimental measurements for the contact surface areas and contact pressure distributions of a dysplastic hip joint. The hip joint consists of pelvis, proximal femur and artificial cartilages for both acetabulum and femoral head. The dysplastic hip joint is modeled in three dimensional (3D) form using the computerized tomography (CT) images obtained in vivo of an adult female patient. The modeled hip joint components are manufactured as a non-natural dysplastic hip joint using different materials and manufacturing processes. The dysplastic hip joint produced is subjected to compression forces experimentally to measure the contact surface area and contact pressure distributions between the femoral head and acetabulum using the pressure sensitive Fuji film. Different types of specific fixtures and molds are designed and manufactured to produce the dysplastic hip joint components and perform the experimental studies. The measured results using a non-natural dysplastic hip joint are compared with relevant results reported in current literature considering the peak and mean contact pressure values. Therefore, the obtained results showed that the non-natural dysplastic hip models can be generated and replaced to determine the contact characteristics for an elusive cadaveric model. In conclusion, the artificial models might be useful to understand the contact pressure distributions and potential changes in surface pressure contours and their effects on the stress distributions.

The effect of proximal tibial corrective osteotomy on menisci, tibia and tarsal bones: a finite element model study of tibia vara.

BACKGROUND: Proximal tibial open wedge osteotomy (PTO) is a corrective operation used in the surgery of lower extremities and is applied to patients with varus deformities for sufficient correction. The aim of the study was to evaluate whether the PTO can achieve decreased stress-bearing on the tibia and tarsal bones in addition to correcting the mechanical axis of the lower limb in patients with tibia vara. METHODS: Three-dimensional (3D) solid modelling of the lower extremity was carried out using computed tomography (CT) and magnetic resonance (MR)-containing images of all of the bony elements and non-bony structures. PTO was applied to the obtained deformed model in the computer environment and the correction was carried out. RESULTS: Stress distributions in menisci, tibia and tarsal bones were calculated. With respect to loading on the tarsal bones, the maximum equivalent stresses on all bones decreased except for the navicula in the PTO-simulated model in the current study. CONCLUSION: These results clearly indicate that PTO can achieve decreased stresses on the tarsal bones in patients with tibia vara.

Stress distribution comparisons of foot bones in patient with tibia vara: a finite element study.

Blount's disease, or tibia vara, is the most common cause of pathologic genu varum in children and adolescents. Changes in the loading of knee structures such as tibial articular cartilage, menisci and subcondral bone are well documented in case of genu varum. But the mechanical effects of this condition on foot bones are still questionable. In this study, the authors hypothesized that stress distributions on foot bones might increase in patients with tibia vara when compared with patients who had normal lower extremity mechanical axis. Three-dimensional (3D) finite element analyses of human lower limb were used to investigate and compare the loading on foot bones in normal population and patient with tibia vara. The segmentation software, MIMICS was used to generate the 3D images of the bony structures of normal and varus malalignment lower extremity. Except the spaces between the adjacent surface of the phalanges fused, metatarsals, cuneiforms, cuboid, navicular, talus and calcaneus bones were independently developed to form foot and ankle complex. Also femur, tibia and fibula were modeled utilizing mechanical axis. ANSYS version 14 was used for mechanical tests and maximum equivalent stresses (MES) were examined. As a result of the loading conditions, in varus model MES on talus, calcaneus and cuboid were found higher than in normal model. And stress distributions changed through laterally on middle and fore foot in varus deformity model.