Alteration of Lower Limb Kinematics and Kinetics due to Bilateral Triple Arthrodesis.

Objectives: The study aimed at discovering the existing differences in lower limb joints' kinematics, and EMG signals of 4 particular muscles of the ankle joint during gait, between normal subjects and patients with bilateral triple arthrodesis. Methods: In this research, a 3D motion analysis system was used and joints' angles were calculated using a MATLAB code, and based on the data collected from markers movements, for patients with bilateral triple arthrodesis and normal subjects. Moreover, the EMG signals of ankle muscles in each subject, and the graphs of mean plus and minus standard deviation of lower limb joint angles and muscles' EMG were calculated by MATLAB. Results: In all patients, an initial ankle eversion and valgus deformity were observed in their knee joints. In addition, for all patients, the maximum knee extension was less than that of the average value of the normal subjects. Furthermore, the results of the electromyography showed that, in all patients, delay occurred in gastrocnemius and soleus muscles in maximum contraction in their EMG signals. Besides, during the early stance phase of gait cycles, the mean value of EMG of peroneus brevis muscle for patients was more than that of normal subjects. Conclusion: Atrophy of four ankle muscles including (soleus, lateral gastrocnemius, tibialis anterior and peroneus brevis), also limitation of joints movement were observed in patients, compared to normal subjects. Based on the results of this work, in order to reduce further musculoskeletal disorders in patients who underwent bilateral triple arthrodesis surgery, there is a serious need to use physiotherapy after the surgery.

The effect of defect size and location on the fracture risk of proximal tibia, following tumor curettage and cementation: An in-silico investigation.

Even though, proximal tibia is a common site of giant cell tumor and bone fractures, following tumor removal, nonetheless very little attention has been paid to affecting factors on the fracture risk. Here, nonlinear voxel-based finite element models based on computed tomography images were developed to predict bone fracture load with defects with different sizes, which were located in the medial, lateral, anterior, and posterior region of the proximal tibia. Critical defect size was identified using One-sample t-test to assess if the mean difference between the bone strength for a defect size was significantly different from the intact bone strength. Then, the defects larger than critical size were reconstructed with cement and the mechanics of the bone-cement interface (BCI) was investigated to find the regions prone to separation at BCI. A significant increase in fracture risk was observed for the defects larger than 20 mm, which were located in the medial, lateral and anterior regions, and defects larger than 25 mm for those located in the posterior region of the proximal tibia. Furthermore, it was found that the highest and lowest fracture risks were associated with defects located in the medial and posterior regions, respectively, highlighting the importance of selecting the initial location of a cortical window for tumor removal by the surgeon. The results of the BCI analysis showed that the location and size of the cement had a direct impact on the extent of damage and its distribution. Identification of critical regions susceptible to separation at BCI, can provide critical comments to surgeons in selecting the optimal cement augmentation technique, which may ultimately prevent unnecessary surgical intervention, such as using screws and pins.

Improving dental implant stability by optimizing thread design: Simultaneous application of finite element method and data mining approach.

STATEMENT OF PROBLEM: Lack of knowledge regarding the optimal design of thread configuration in dental implants, which can offer a satisfactory level of stability in the implant-bone construct, is a significant challenge in the field of dental biomechanics. PURPOSE: The purpose of this finite element analysis study was to identify the optimal thread design by investigating the effects of thread parameters such as thread depth (TD), thread width (TW), and thread pitch (TP), as well as upper (α) and lower (ß) thread angles, on the maximum principal stress in cancellous and cortical bone, maximum von Mises stress in the dental implant, and maximum shear stress at the implant-bone interface. MATERIAL AND METHODS: A finite element model of an alveolar bone segment with a dental implant was developed. The Latin hypercube sampling method was used to generate a dataset of virtual experiments, which were analyzed by using the decision tree method to identify suitable thread designs that minimize mechanical stimuli. Additionally, the effectiveness of thread parameters on stress levels in the bone, implant, and their interface were assessed. RESULTS: The results of this study, verified by comparison with previous literature, indicated that TD, TW, and upper thread angle were the most effective parameters in promoting implant stability. CONCLUSIONS: By analyzing the decision trees, optimum ranges for all the thread parameters were determined as follows: 0.25

Investigation on primary stability of dental implants through considering peri-implant bone damage, caused by small and large deformations: A validated non-linear micro finite element study.

Primary stability of a dental implant is defined as its ability to resist the applied load without showing excessive damage in peri-implant bone, which is a prerequisite for secondary stability, and consequently for implantation success. The main goal of this study was to develop a validated micro-finite element (µFE) approach to assess the primary stability of dental implants in terms of stiffness, stiffness reduction, and irreversible displacement of the bone-implant system, subjected to an increasing step-wise quasi-static compressive loading-unloading test. The µFE models were generated based on the µCT images of bone, taken from extracted bovine tibia trabecular bone samples after drilling and implantation. A tissue constitutive model was considered for trabecular bone by describing elasto-plasticity with a modified von Mises yield criterion and element deletion technique to account for trabecular bone damage behavior. Then, the obtained force-displacement curves from the simulation were compared with the in-vitro mechanical test curves to evaluate the validity of the model. The results showed that the proposed µFE model could be properly predict the bone-implant system mechanical response in terms of irreversible displacement (R2 = 0.99), stiffness (R2 = 0.77), and stiffness reduction (R2 = 0.72) of the bone-implant construct for all the applied displacements without a significant difference from the unit slope and zero intercept of the QQ-plot (p-value<0.05). Moreover, a qualitative agreement was seen between the peri-implant bone damage predicted by the µFE model and the observed from µCT images. The adopted methodology used in this study can predict the mechanical failure response of the bone-implant system, which can be employed as a representative tool to study the effects of various dental implant design parameters on the primary stability with the ultimate goal of optimizing dental implants design.

The effects of material and structural properties of the periodontal ligament in mechanical function of tooth-PDL-bone complex in dental trauma: A sensitivity study using finiteelement analysis.

Periodontal ligament (PDL) plays a crucial role in transferring load from tooth to its adjacent bone, and its role is more pronounced in case of trauma, due to its shock-absorbing character, which has not been fully understood yet. Different constitutive models have correlated mechanical function of PDL with its anisotropic, inhomogeneous, non-linear elastic nature, and it was variably modeled using Finite Element (FE) simulations of dental trauma. Furthermore, since capturing accurate dimension of PDL is difficult, various thicknesses were considered for PDL in FE reconstruction process. In this study, the sensitivity of FE analyses to variation in mechanical properties, including a large range of elastic properties for a linear elastic model, also a hyper-elastic material model, and various thicknesses of PDL was investigated by developing a CT-based FE model of tooth-PDL-bone complex. Results of this study highlighted the crucial role of PDL in absorption and dissipation of energy, as well as in stress distribution within alveolar bone during dental trauma. It was observed that as Young's modulus of PDL decreases and its thickness increases, its shock-absorbing capacity would be escalated. Moreover, it was found that inclusion of PDL reduces the maximum von Mises stress exerted on the alveolar bone by about 60% in some areas, compared to the case in which the PDL is absent. Results of this work underscore the need of presenting comprehensive constitutive models to describe mechanical behavior of PDL, with the goal of understanding the behavior of a tooth-PDL-bone complex in pathological conditions, such as trauma.

Optimization of thread configuration in dental implants through regulating the mechanical stimuli in neighboring bone.

BACKGROUND AND OBJECTIVE: The threads, as the most critical component of dental implants, transfer the imposed occlusal loads to the adjacent bone. Moreover, regulation of the mechanical stimuli in the implant adjacent bone is crucial to maximize the bone-implant construct stability. An optimal thread design can be resulted when the distribution of mechanical stimuli within the bone, and at the implant-bone interface, lie in an advised confined range. In this work, with the goal of finding the optimal thread design, which can provide the maximum level of stability, the effects of thread parameters, namely, thread depth, thread width, and thread pitch, together with upper and lower thread angles, on maximum principal strain within the cortical and cancellous bone, and shear strain at the implant-bone interface, were investigated. METHODS: In this study, the response surface methodology (RSM), due to the central composite design (CCD), was employed to obtain a set of 53 experiments. Following that, they were numerically simulated using the finite element method (FEM). The polynomial regression model was then used to predict the response functions based on the magnitude of thread parameters. The effectiveness of each thread parameter was also evaluated through statistical tools. Moreover, the non-dominated sorting genetic algorithm (NSGA-II) was performed to find the optimum dimensions of the thread. RESULTS: Through comparing the results obtained from analyzing initial and optimized configuration of threads, it was shown that the latter causes a reduction in the maximum principal strains in cancellous and cortical bones by about 25% and 30%, respectively, which is in favor of making a higher quality bone, and thus greater stability in dental implant-bone construct. Moreover, the maximum shear strains at the implant-bone interface in different planes were reduced by about 40%, in the optimized thread, compared with the initial design. CONCLUSIONS: The optimized design found in this study is a buttress thread with a fine pitch, but deep thread, which keeps the mechanical stimuli in a safe range to grant an acceptable level of stability.

Measurement of bone damage caused by quasi-static compressive loading-unloading to explore dental implants stability: Simultaneous use of in-vitro tests, µ-CT images, and digital volume correlation.

Primary stability of dental implants is the initial mechanical engagement of the implant with its adjacent bone. Implantation and the subsequent loading may cause mechanical damage in the peripheral bone, which ultimately reduces the stability of the implant. This study aimed at evaluating primary stability of dental implants through applying stepwise compressive displacement-controlled, loading-unloading cycles to obtain overall stiffness and dissipated energy of the bone-implant structure; and quantifying induced plastic strains in surrounding bone using digital volume correlation (DVC) method, through comparing µCT images in different loading steps. To this end, dental implants were inserted into the cylindrical trabecular bones, then the bone-implant structure was undergone step-wise loading-unloading cycles, and µCT images were taken in some particular steps, then comparison was made between undeformed and deformed configurations using DVC to quantify plastic strain within the trabecular bone. Comparing stiffness reduction and dissipated energy values in different loading steps, obtained from the force-displacement curve in each loading step, revealed that the maximum displacement of 0.16 mm can be deemed as a safe threshold above which damages in peri-implant bone started to increase considerably (p < 0.05). In addition, it was found here that peri-implant bone strain linearly increased with decreasing bone-implant stiffness (p < 0.05). Moreover, strain concentration in peri-implant bone region showed that the plastic strain in trabecular bone spread up to a distance of about 2.5 mm away from the implant surface. Research of this kind can be used to optimize the design of dental implants, with the ultimate goal of improving their stability, also to validate in-silico models, e.g., micro-finite element models, which can help gain a deeper understanding of bone-implant construct behavior.

The correlation between osseointegration and bonding strength at the bone-implant interface: In-vivo & ex-vivo investigations on hydroxyapatite and hydroxyapatite/titanium coatings.

This study investigated the effects of hydroxyapatite (HA) and hydroxyapatite/titanium (HA/Ti) coatings on osseointegration and bonding strength at the bone-implant interface. The coatings were made using air plasma spray (APS), and three study groups were examined: 1) Uncoated commercial pure titanium (CP-Ti) rods; 2) HA-coated CP-Ti rods, and 3) Composite of 50 %wt HA + 50 %wt Ti coated CP-Ti rods. The rods were implanted into the distal femurs and proximal tibias of fifteen New Zealand white rabbits, and 8 weeks after the implantation, the samples were harvested. The results of pull-out tests showed that the ultimate strength of HA and HA/Ti coatings were significantly greater than the uncoated samples (P < 0.05). Moreover, even though the histological evaluations showed significantly greater osseointegration of HA/Ti composite coatings compared with HA coatings (P < 0.05), nonetheless, the composite of HA/Ti offers no significant increase in the ultimate strength, stiffness, and bonding strength at the bone-implant interface, compared with the HA group (P > 0.05). Thus, in an eight-week study, there was no linear correlation between the osseointegration and the bonding strength at the bone-implant interface. The results of this work may imply that the extent of osseointegration at the bone-implant interface does not necessarily determine the value of the bonding strength at the bone-implant interface. It is speculated that, in a longer-term study, a greater quality of bone formation may occur during osseointegration, between the implant and its adjacent bone, which can lead to a more enhanced bonding strength, compared with the 8-weeks post-surgery follow up.

Early post-operative performance of an anatomically designed hybrid thread interference screw for ACL reconstruction: A comparative study.

Although the anterior cruciate ligament (ACL) reconstruction using interference screw is a well-accepted surgical procedure, patients still suffer graft failure in the initial rehabilitation phase. Graft fixation stability of a newly designed anatomical hybrid thread tapered interference screw (AHTTIS) was compared with a conventional standard one (CSIS) by conducting in-vitro mechanical tests. According to the CSIS manufacturer's instruction, eight tapered bone tunnels, matching AHTTIS geometry, and eight straight cylindrical tunnels were drilled in artificial bone blocks. Bovine tendon grafts were fixed using AHTTIS and CSIS in their corresponding bone tunnels. Each graft was subjected to a pre-load, a dynamic cyclic sinusoidal tensile load, and a tensile pullout load. Aggregate graft displacement relative to the bone tunnel under dynamic cyclic load, load corresponding to a 3 mm displacement; load and displacement at yield and ultimate failure of the graft; and graft-bone-screw stiffness resulted from pullout tests were recorded. There were no significant differences between recorded parameters of the two groups, except the graft displacements relative to the bone tunnel at ultimate failure load (8.35 ± 3.03 mm versus 5.28 ± 1.37 mm) and at the yield point (7.73 ± 3.02 mm versus 4.59 ± 1.25 mm) (P < 0.05), which were both significantly greater for the AHTTIS group. Considering all tests were made in the worst-case scenario of fixation of an interference screw, i.e., the employed synthetic bone just mimicked cancellous bone, graft fixation with the AHTTIS is practical. However, in the case of employing high strain rate loads on AHTTIS, further considerations are needed to reduce the side effect of slippage of the graft.

Osteosynthesis of diaphyseal tibia fracture with locking compression plates: A numerical investigation using Taguchi and ANOVA.

Performance of the locking compression plate (LCP) is a multifactorial function. The control parameters of plating, such as geometries, material properties, and physical constraints of the LCP components, affect basic functions associated with the bone fixation, including the extent of stress shielding and subsequent bone remodeling, strength and stability of the bone-LCP construct, and performance of secondary bone healing. The main objectives of this research were as follows: (1) to find the appropriate values of control parameters of an LCP construct to achieve the optimized performance throughout bone healing; and (2) to unravel relationships between LCP parameters and the LCP's performance. Different values for the plate/screw modulus of elasticity (E), plate width (W), plate thickness (T), screw diameter (D), bone-plate offset (O), and screw configuration (C), as six control parameters, were considered at five different levels. Taguchi method was adopted to create trial combinations of control parameters and determining the best set of parameters, which can optimize the overall performance of the LCP. All design cases were analyzed using the finite element method. The optimal set of control parameters consisting of 150 GPa, 12 mm, 4 mm, 5.5 mm, 2 mm, and 123,678 were determined for E, W, T, D, O, and C, respectively. Furthermore, ANOVA was used to rank the most influential parameters on each function of the LCP fixation. In the overall performance of the LCP fixation, E, D, T, C, W, and O showed a contribution percentage of 46%, 22%, 10%, 11%, 8%, and 3%, respectively.

Dental implants' stability dependence on rotational speed and feed-rate of drilling: In-vivo and ex-vivo investigations.

This study aimed to explore the effects of drilling rotational speed and feed-rate on the stability of dental implants through in-vivo and ex-vivo experiments. To this end, a total of 16 identical dental implants were inserted in the mandible of four dogs. The osteotomies were made with two drilling rotational speeds, i.e., 800 and 1500 rpm, and two different feed-rates, i.e., 1 and 2 mm/s. Implant stability quotients (ISQs) were recorded immediately after inserting implants and then each week for four subsequent weeks. Then, all animals were euthanized, and a bone sample containing the implants was extracted from each hemi-mandible for the pull-out test. A two-way ANOVA was performed for ISQs, and pull-out strengths (PoS), and the significance level was set to <0.05. The effect of rotational speed and feed-rate, used in this study, on the primary stability quotients was not significant (P > 0.05). Increasing the rotational speed from 800 to 1500 rpm significantly increased both ISQ and PoS values at the end of the 4th week after the implantation (P = 0.022 and P = 0.001, respectively). Moreover, by decreasing the feed-rate from 2 to 1 mm/s, a significant increase in PoSs of the dental implants was observed four weeks after the implantation (P = 0.019). Results of this study showed that either by increasing drilling rotational speed, here from 800 to 1500 rpm, or by reducing feed-rate, here from 2 to 1 mm/s, the secondary stability would be reinforced. Further investigations are needed to see if and how the conclusions made in this study can be generalized.

Total ankle replacement along with subtalar joint arthrodesis: In-vitro and in-silico biomechanical investigations.

Total ankle replacement (TAR) and subtalar joint (STJ) fusion, are popular treatments for ankle osteoarthritis (OA). Short endurance limits the former, and movement disability comes with the latter. It is hypothesized here that fusion of the STJ can improve the longevity of the TAR prosthesis. In this study, a fresh human cadaver's ankle joint underwent TAR surgery, and strain patterns in the vicinity of prosthesis were recorded after the application of axial compressive load on tibia, resembling stance phase of the gait. Then, STJ of the same sample fused (FTAR), and a similar test procedure was pursued. The obtained strains in the FTAR were smaller than those of the TAR (p < .01). Finite element models of the tested samples were also made, and validated by experimental strains. The validated FE models were then employed to find stress distribution on the tibial plateau and prosthesis compartments. FTAR demonstrated more regular stress profiles in bone-prosthesis interface. Also, maximum von Mises stress in the talar component of the FTAR is approximately half of that in the TAR (8 and 15 MPa, respectively). Based on the results of this study, having a more symmetric load distribution on the prosthesis after STJ fusion, longevity of the TAR may likely increase.

Can the body slope of interference screw affect initial stability of reconstructed anterior cruciate ligament?: An in-vitro investigation.

BACKGROUND: Superior biomechanical performance of tapered interference screws, compared with non-tapered screws, with reference to the anterior cruciate ligament (ACL) reconstruction process, has been reported in the literature. However, the effect of tapered interference screw's body slope on the initial stability of ACL is poorly understood. Thus, the main goal of this study was to investigate the effect of the interference screw's body slope on the initial stability of the reconstructed ACL. METHODS: Based on the best screw-bone tunnel diameter ratios in non-tapered screws, two different tapered interference screws were designed and fabricated. The diameters of both screws were equal to bone tunnel diameter in one-third of their length from screw tip, then they were gradually increased by 1mm, in the lower slope (LSTIS), and 2 mm, in the higher slope (HSTIS) screws. To simulate the ACL reconstruction, sixteen soft tissue grafts were fixed, using HSTIS and LSTIS, in synthetic bone blocks. Through applying sub-failure cyclic incremental tensile load, graft-bone-screw construct's stiffness and graft laxity in each cycle, also through applying subsequent step of loading graft to the failure, maximum load to failure, and graft's mode of failure were determined. Accordingly, the performance of the fabricated interference screws was compared with each other. RESULTS: HSTIS provides a greater graft-bone-screw construct stiffness, and a lower graft laxity, compared to LSTIS. Moreover, transverse rupture of graft fibers for LSTIS, and necking of graft in the HSTIS group were the major types of grafts' failure. CONCLUSIONS: HSTIS better replicates the intact ACL's behavior, compared to LSTIS, by causing less damage in graft's fibers; reducing graft laxity; and increasing fixation stability. Nonetheless, finding the optimal slope remains as an unknown and can be the subject of future studies.

A mechanobiological approach to find the optimal thickness for the locking compression plate: Finite element investigations.

This study aimed at finding the acceptable range, and the optimal value for the locking compression plate (LCP) thickness (THK), through simulating the osteogenic pathway of bone healing, and by checking bone-plate construct's strength and stability. To attain the goals of this research, a multi-objective approach was adopted, which should trade-off between some conflicting objectives. A finite element model of the long bone-plate construct was made first, and validated against an experimental study. The validated model was then employed to determine the initial strength and stability of the bone-plate construct, for the time right after surgery, for various thicknesses of the LCP. Afterward, coupling with a mechano-regulatory algorithm, the iterative process of bone healing was simulated, and follow up was made for each LCP thickness, over the first 16 post-operative weeks. Results of this study regarding the sequence of tissue evolution inside the fracture gap, showed a similar trend with the existing in-vivo data. For the material and structural properties assigned to the bone-plate construct, in this study, an optimal thickness for the LCP was found to be 4.7 mm, which provides an enduring fixation through secondary healing, whereas for an LCP with a smaller or greater thickness, either bone-implant failure, unstable fixation, impaired fracture consolidation, or primary healing may occur. This result is in agreement with a recent study, that has employed a comprehensive optimization approach to find the optimal thickness.

Erratum: 'Corrigendum to "The biomechanical performance of the night-time Providence brace: experimental and finite element investigations" [Heliyon 6 (10) (October 2020) Article e05210]'.

[This corrects the article DOI: 10.1016/j.heliyon.2020.e05210.].

Post-operative fracture risk assessment following tumor curettage in the distal femur: a hybrid in vitro and in silico biomechanical approach.

The distal femur is the predominant site for benign bone tumours and a common site for fracture following tumour removal or cementation. However, the lack of conclusive assessment criterion for post-operative fracture risk and appropriate devices for cement augmentation are serious concerns. Hence, a validated biomechanical tool was developed to assess bone strength, depending on the size and location of artificially created tumorous defects in the distal femora. The mechanics of the bone-cement interface was investigated to determine the main causes of reconstruction failure. Based on quantitative-CT images, non-linear and heterogeneous finite element (FE) models of human cadaveric distal femora with simulated tumourous defects were created and validated using in vitro mechanical tests from 14 cadaveric samples. Statistical analyses demonstrated a strong linear relationship (R2 = 0.95, slope = 1.12) with no significant difference between bone strengths predicted by in silico analyses and in vitro tests (P = 0.174). FE analyses showed little reduction in bone strength until the defect was 35% or more of epiphyseal volume, and reduction in bone strength was less pronounced for laterally located defects than medial side defects. Moreover, the proximal end of the cortical window and the most interior wall of the bone-cement interface were the most vulnerable sites for reconstruction failure.

The biomechanical performance of the night-time Providence brace: experimental and finite element investigations.

The main goal of this study was to investigate the performance of a night-time Providence brace, which alters stress distribution in the growth plates and ultimately result in a reduced Cobb angle, from a biomechanical standpoint, using experimental and in-silico tools. A patient with a mild scoliosis (Cobb angle = 17) was chosen for this study. Applied forces from the Providence brace on the patient's rib cage and pelvis were measured using flexible force pads, and the measured forces were then imported to the generated FE model, and their effects on both curvature and stress distribution were observed. The measured mean forces applied by the brace were 29.4 N, 24.7 N, 22.4 N, and 37.6 N in the posterior pelvis, anterior pelvis, superior thorax, and inferior thorax, respectively, in the supine position. Results of the FE model showed that there is curvature overcorrection, and also Cobb angle was reduced from 17°, in the initial configuration, to 3.4° right after using the brace. The stress distribution, resulted from the FE model, in the patient's growth plate with the brace in the supine position, deviates from that of a scoliotic individual without the brace, and was in favor of reducing the Cobb angle. It was observed that by wearing the night time brace, unbalanced stress distribution on the lumbar vertebrae caused by the scoliotic spine's curvatures, can be somehow compensated. The method developed in this study can be employed to optimize existing scoliosis braces from the biomechanical standpoint.

Stress distribution changes in growth plates of a trunk with adolescent idiopathic scoliosis following unilateral muscle paralysis: A hybrid musculoskeletal and finite element model.

This study aimed to investigate changes occurred in the stress distribution in the growth plates (GPs) of a trunk with adolescent idiopathic scoliosis (AIS) following unilateral muscle paralysis. We hypothesized that weakening the appropriately chosen muscles on the concave side can decelerate AIS deformity progression. Muscle forces and reaction loads were estimated by an optimization-driven musculoskeletal (MS) model of adolescents with a normal- and an AIS trunk, and then applied on the finite element model of GPs of L1 through L4. Different set patterns of 95% reduction in the strength of the concave-side longissimus thoracis pars thoracic (LGPT), multifidus lumborum (MFL), and LGPT + MFL muscles were performed in the MS models. Results of this study showed that weakening of the concave-side MFL and LGPT muscles rendered a 35% correction in the symptomatic axial rotation of the AIS spine, and a reduction of about 25% in the compressive von Mises stress on the concave side of GPs, respectively, which can decelerate the deformity progression. It was observed that unilateral muscle weakening caused a compensatory activation of the rest of muscles to retain the spine stability. The intradiscal pressures and ratio between the rotations toward either side of the scoliotic spine, found here, matched well with some recent in-vivo investigations. One of the applications of the stability-based MS model of AIS spine with unilaterally weakened muscles presented in this study is to optimize the performance of the currently used braces. To fortify the presented therapeutic approach, experiments should be done on scoliotic animals.

Fixation of distal tibia fracture through plating, nailing, and nailing with Poller screws: A comparative biomechanical-based experimental and numerical investigation.

The goal of this study was to investigate two commonly used methods of fixation of distal metaphyseal tibia fractures, plating and nailing as well as the less frequently employed nailing with Poller screws, from a biomechanical perspective. Despite numerous studies, the best method to repair fractures of tibia the remains up for of debate. This study includes an in vitro experimental phase on human cadaveric tibias followed by a finite element analysis. In the experimental phase, under partial weight-bearing axial loading, the axial stiffness of the bone-implant construct and interfragmentary movements for each of the fixation methods, bone-plate, bone-nail, and bone-nail-Poller screw, were measured and compared with each other. Shear interfragmentary movement and stress distribution in the bone-implant construct for the three mentioned fixation methods were also determined from FE models and compared with each other. Results of in vitro experiments, i.e., the exertion of axial loading on the tibia-plate, tibia-nail, and tibia-nail-Poller screw, showed that utilization of tibia-nail and tibia-nail-Poller screw led to a stiffer bone-implant construct, and consequently, lower interfragmentary movement, compared to the tibia-plate construct (p values for tibia-nail and tibia-nail-Poller screw, and for both axial stiffness and interfragmentary movement, compared to those of tibia-plate construct, were less than 0.05). Numerical analyses showed that nailing produced less undesirable shear interfragmentary movement, compared to the plating, and application of a Poller screw decreased the shear movements, compared to tibia-nail. Furthermore, using the finite element analysis, maximum von Mises stress of adding a screw in tibia-nail, tibia-plate, and tibia-nail-Poller screw, was found to be: 51.5, 78.6, and 60.5 MPa, respectively. The results of this study suggested that from a biomechanical standpoint, nailing both with and without a Poller screw is superior to plating for the treatment of distal tibia fractures.

Linear Momenta Transferred to the Dental Implant-Bone and Natural Tooth-PDL-Bone Constructs Under Impact Loading: A Comparative in-vitro and in-silico Study.

During dental trauma, periodontal ligament (PDL) contributes to the stability of the tooth-PDL-bone structure. When a dental implant is inserted into the bone, the dental implant-bone construct will be more prone to mechanical damage, caused by impact loading, than the tooth-PDL-bone construct. In spite of the prevalence of such traumas, the behavioral differences between these two constructs have not been well-understood yet. The main goal of this study was to compare the momentum transferred to the tooth-PDL-bone and dental implant-bone constructs under impact loading. First, mechanical impact tests were performed on six canine mandibles of intact (N = 3) and implanted (N = 3) specimens using a custom-made drop tower apparatus, from release heights of 1, 2, and 3 cm. Next, computed tomography-based finite element models were developed for both constructs, and the transferred momenta were calculated. The experimental results indicated that, for the release heights of 1, 2, and 3 cm, the linear momenta transferred to the dental implant-bone construct were 33.1, 31.0, and 27.5% greater than those of the tooth-PDL-bone construct, respectively. Moreover, results of finite element simulations were in agreement with those of the experimental tests (error <7.5%). This work tried to elucidate the effects of impact loading on the dental implant-bone and tooth-PDL-bone constructs using both in-vitro tests and validated in-silico simulations. The findings can be employed to modify design of the current generation of dental implants, based on the lessons one can take from the biomechanical behavior of a natural tooth structure.