Biomechanical characteristics of ligament injuries in the knee joint during impact in the upright position: a finite element analysis.

BACKGROUND: Our study aims to examine stress-strain data of the four major knee ligaments-the anterior cruciate ligament (ACL), the posterior cruciate ligament (PCL), the medial collateral ligament (MCL), and the lateral collateral ligament (LCL)-under transient impacts in various knee joint regions and directions within the static standing position of the human body. Subsequently, we will analyze the varying biomechanical properties of knee ligaments under distinct loading conditions. METHODS: A 3D simulation model of the human knee joint including bone, meniscus, articular cartilage, ligaments, and other tissues, was reconstructed from MRI images. A vertical load of 300 N was applied to the femur model's top surface to mimic the static standing position, and a 134 N load was applied to the impacted area of the knee joint. Nine scenarios were created to examine the effects of anterior, posterior, and lateral external forces on the upper, middle, and lower regions of the knee joint. RESULTS: The PCL exhibited the highest stress levels among the four ligaments when anterior loads were applied to the upper, middle, and lower parts of the knee, with maximum stresses at the PCL-fibula junction measuring 59.895 MPa, 27.481 MPa, and 28.607 MPa, respectively. Highest stresses on the PCL were observed under posterior loads on the upper, middle, and lower knee areas, with peak stresses of 57.421 MPa, 38.147 MPa, and 26.904 MPa, focusing notably on the PCL-tibia junction. When a lateral load was placed on the upper knee joint, the ACL showed the highest stress 32.102 MPa. Likewise, in a lateral impact on the middle knee joint, the ACL also had the highest stress of 29.544 MPa, with peak force at the ACL-tibia junction each time. In a lateral impact on the lower knee area, the LCL had the highest stress of 22.279 MPa, with the highest force at the LCL-fibula junction. Furthermore, the maximum stress data table indicates that stresses in the ligaments are typically higher when the upper portion of the knee is affected compared to when the middle and lower parts are impacted. CONCLUSIONS: This study recommends people avoid impacting the upper knee and use the middle and lower parts of the knee effectively against external forces to minimize ligament damage and safeguard the knee.

Combining the probabilistic finite element model and artificial neural network to study nutrient levels in the human intervertebral discs.

BACKGROUND: Diffusion distance and diffusivity are known to affect nutrient transport rates, but the probabilistic analysis of these two factors remains vacant. There is a lack of effective tools to evaluate disc nutrient levels. METHODS: Five-hundred-disc samples with different combinations of morphological and water content parameters were generated, which were used to evaluate nutrient levels in unloaded and loaded states. Spearman correlation coefficients between inputs and responses were calculated. Artificial neural networks were trained to predict nutrient concentrations based on the dataset generated by the probabilistic finite element model. FINDINGS: In unloaded and loaded states, the minimum oxygen concentration of nucleus pulposus was negatively correlated with disc height (r = -0.83, p < 0.01 and r = -0.76, p < 0.01, respectively), and the minimum glucose concentration of annulus fibrosus was positively correlated with its water content (r = 0.68, p < 0.01 and r = 0.73, p < 0.01, respectively). The maximum lactate concentration of cartilage endplate was affected by endplate thickness (r = 0.94, p < 0.01 and r = 0.95, p < 0.01, respectively). For trained neural networks, nutrient concentrations could be well predicted, with coefficients of determination greater than 0.95 and mean absolute percentage errors less than 5 %. INTERPRETATION: This study underscores the importance of disc height, annulus fibrosus water content, and endplate thickness in regulating nutrient levels, and precise control of these parameters should be prioritized in the design of tissue-engineered discs. Moreover, artificial neural networks might be a promising tool for evaluating nutrient levels.

Inverse Identification of Constitutive Model for GH4198 Based on Genetic-Particle Swarm Algorithm.

A precise Johnson-Cook (J-C) constitutive model is the foundation for precise calculation of finite-element simulation. In order to obtain the J-C constitutive model accurately for a new cast and forged alloy GH4198, an inverse identification of J-C constitutive model was proposed based on a genetic-particle swarm algorithm. Firstly, a quasi-static tensile test at different strain rates was conducted to determine the initial yield strength A, strain hardening coefficient B, and work hardening exponent n for the material's J-C model. Secondly, a new method for orthogonal cutting model was constructed based on the unequal division shear theory and considering the influence of tool edge radius. In order to obtain the strain-rate strengthening coefficient C and thermal softening coefficient m, an orthogonal cutting experiment was conducted. Finally, in order to validate the precision of the constitutive model, an orthogonal cutting thermo-mechanical coupling simulation model was established. Meanwhile, the sensitivity of J-C constitutive model parameters on simulation results was analyzed. The results indicate that the parameter m significantly affects chip morphology, and that the parameter C has a notable impact on the cutting force. This study addressed the issue of missing constitutive parameters for GH4198 and provided a theoretical reference for the optimization and identification of constitutive models for other aerospace materials.

Modelling and Characterisation of Orthotropic Damage in Aluminium Alloy 2024.

The aim of the work presented in this paper was development of a thermodynamically consistent constitutive model for orthotopic metals and determination of its parameters based on standard characterisation methods used in the aerospace industry. The model was derived with additive decomposition of the strain tensor and consisted of an elastic part, derived from Helmholtz free energy, Hill's thermodynamic potential, which controls evolution of plastic deformation, and damage orthotopic potential, which controls evolution of damage in material. Damage effects were incorporated using the continuum damage mechanics approach, with the effective stress and energy equivalence principle. Material characterisation and derivation of model parameters was conducted with standard specimens with a uniform cross-section, although a number of tests with non-uniform cross-sections were also conducted here. The tests were designed to assess the extent of damage in material over a range of plastic deformation values, where displacement was measured locally using digital image correlation. The new model was implemented as a user material subroutine in Abaqus and verified and validated against the experimental results for aerospace-grade aluminium alloy 2024-T3. Verification was conducted in a series of single element tests, designed to separately validate elasticity, plasticity and damage-related parts of the model. Validation at this stage of the development was based on comparison of the numerical results with experimental data obtained in the quasistatic characterisation tests, which illustrated the ability of the modelling approach to predict experimentally observed behaviour. A validated user material subroutine allows for efficient simulation-led design improvements of aluminium components, such as stiffened panels and the other thin-wall structures used in the aerospace industry.

Classification of ossicular fixation based on a computational simulation of ossicular mobility.

Ossicular fixation disturbs the mobility of the ossicular chain and causes conductive hearing loss. To diagnose the lesion area, otologists typically assess ossicular mobility through intraoperative palpation. Quantification of ossicular mobility and evidence-based diagnostic criteria are necessary for accurate assessment of each pathology, because diagnosis via palpation can rely on the surgeons' experiences and skills. In this study, ossicular mobilities were simulated in 92 pathological cases of ossicular fixation as compliances using a finite-element (FE) model of the human middle ear. The validity of the ossicular mobilities obtained from the FE model was verified by comparison with measurements of ossicular mobilities in cadavers using our newly developed intraoperative ossicular mobility measurement system. The fixation-induced changes in hearing were validated by comparison with changes in the stapedial velocities obtained from the FE model with measurements reported in patients and in temporal bones. The 92 cases were classified into four groups by conducting a cluster analysis based on the simulated ossicular compliances. Most importantly, the cases of combined fixation of the malleus and/or the incus with otosclerosis were classified into two different surgical procedure groups by degree of fixation, i.e., malleo-stapedotomy and stapedotomy. These results suggest that pathological characteristics can be detected using quantitatively measured ossicular compliances followed by cluster analysis, and therefore, an effective diagnosis of ossicular fixation is achievable.

A humeral intracondylar fissure elevates maximum principal bone strain in the humeral condyle and lateral epicondylar crest in French Bulldogs.

OBJECTIVE: To investigate whether a humeral intracondylar fissure (HIF) alters bone strain in the French Bulldog humerus, we developed a quantitative CT-based 3-D finite element (FE) model for virtual mechanical testing. We hypothesized that higher strains would be seen in the intracondylar region and lateral epicondylar crest if there was a HIF. METHODS: Patient CT scans from 3 (n = 3) French Bulldogs were selected. Dog 1 had a closed distal physis and no HIF. Dog 2 had an open distal humeral physis but no HIF. Dog 3 had an open distal physis and a HIF. A 3-D FE model was built for FE analysis, and pressure was applied to the humerus over the region that contacts the radial head. RESULTS: The maximum principal bone strain patterns differed in each of the models. A path of strain concentration mimicking the typical pattern of a lateral condylar fracture was only found in dog 3. Maximum principal strain exceeded 1% in parts of the lateral epicondylar crest in all 3 dogs. CONCLUSIONS: We developed a patient-specific, quantitative CT-based 3-D FE model for virtual mechanical testing. We accepted our hypothesis. Strain concentration occurred in the intracondylar region and along the lateral epicondylar crest only when a HIF was present. CLINICAL RELEVANCE: The presence of a HIF in French Bulldogs elevates maximum principal bone strain in this region and alters its path in an FE model, which suggests an increased risk of a lateral humeral condylar fracture.

Finite element analysis part 1 of 2: Influence of short stem implant polyethylene configuration on glenohumeral joint biomechanics.

Purpose: Stress shielding in short-stem arthroplasty can cause critical metaphyseal bone loss. If the size and shape of the humeral shaft are important factors, it is unknown whether the shape of the polyethylene component in reverse shoulder arthroplasty (RSA) affects bone stress around or within the stem. We explored the impact of polyethylene shape on humeral and scapular stress distribution using a finite element model. Methods: We developed a shoulder-specific finite element model. A defined set of muscle forces was applied to simulate movements. An intact rotator cuff state and a superior deficient rotator cuff state were modelled. We used the FX V135 short stem in three conditions: total shoulder arthroplasty (TSA), and RSA with symmetrical and asymmetrical polyethylene (145°/135°). We measured biomechanical markers related to bone stress for different implant sizes. Joint kinematics and the mechanical behaviour of the implant were compared. Results: Rupture of the supraspinatus muscle produced a functionally limited shoulder. The placement of an anatomic TSA with an intact rotator cuff restored function similar to that of a healthy shoulder. RSA in the rotator cuff-deficient shoulder restored function regardless of stem size and polyethylene shape. While stem size had an impact on the stress distribution in the bone and implant, it did not show significant potential for increasing or decreasing overall stress. For the same stem, stress distribution at the humerus is different between TSA and RSA. Polyethylene shape did not alter the transmission of stress to the bone in RSA. Asymmetric polyethylene produced a greater abduction range of motion. Conclusions: In terms of bone stress distribution, smaller stems seemed more appropriate for TSA, while larger stems may be more appropriate for RSA. Polyethylene shape resulted in different ranges of motion but did not influence bone stress. Level of Evidence: Diagnostic Tests or Criteria; Level IV.

Modeling of Dissolving Microneedle-Based Transdermal Drug Delivery: Effects of Dynamics of Polymers in Solution.

Dissolving microneedle (DMN)-assisted transdermal drug delivery (TDD) has received attention from the scientific community in recent years due to its ability to control the rate of drug delivery through its design, the choice of polymers, and its composition. The dissolution of the polymer depends strongly on the polymer-solvent interaction and polymer physics. Here, we developed a mathematical model based on the physicochemical parameters of DMNs and polymer physics to determine the drug release profiles. An annular gap width is defined when the MN is inserted in the skin, accumulating interstitial fluid (ISF) from the surrounding skin and acting as a boundary layer between the skin and the MN. Poly(vinylpyrrolidone) (PVP) is used as a model dissolving polymer, and ceftriaxone is used as a representative drug. The model agrees well with the literature data for ex vivo permeation studies, along with the percent height reduction of the MN. Based on the suggested mathematical model, when loading 0.39 mg of ceftriaxone, the prediction indicates that approximately 93% of the drug will be cleared from the bloodstream within 24 h. The proposed modeling strategy can be utilized to optimize drug transport behavior using DMNs.

Study on Prestressed Concrete Beams Strengthened with External Unbonded CFRP Tendons.

This study builds a refined finite element (FE) model to research the flexural behavior of a reinforced beam with prestressed CFRP tendons. The precision of the FE model is validated through a comparison with the experimental outcomes. The numerical findings align well with the experimental outcomes, encompassing the failure mode, load-deflection curve, load-strain curves of concrete, steel reinforcements and CFRP tendons. The variances between predicted values and experimental results are within 10%. Leveraging the verified FE model, an extensive parametric study has been carried out to examine the effects of various parameters, including the CFRP tendon prestress, the CFRP tendon diameter, the deviator layout, the anchorage height and the prestressing strand prestress. Leveraging the findings from the parametric study, some refined design recommendations are proposed for practical reinforcement applications: Increasing the CFRP tendon prestress in practical reinforcement designs is recommended; CFRP tendons with larger diameters are recommended for use in practical reinforcement designs; Employing a linear CFRP tendon profile for reinforcement is not considered optimal in practical applications; The prestress loss in the prestressing strands of PC beams should be considered in practice.

Numerical Investigation on the Influence of Turbine Rotor Parameters on the Eddy Current Sensor for the Dynamic Blade Tip Clearance Measurement.

Eddy current sensors are increasingly being used to measure the dynamic blade tip clearance in turbines due to their robust anti-interference capabilities and non-contact measurement advantages. However, the current research primarily focuses on enhancing the performance of eddy current sensors themselves, with few studies investigating the influence of turbine rotor parameters on the measurements taken by these sensors for dynamic blade tip clearance. Hence, this paper addresses this gap by using COMSOL Multiphysics 6.2 software to establish a finite model with circuit interfaces. Additionally, the model's validity was verified through experiments. This model is used to simulate the voltage output of the sensor and the measurement of dynamic blade tip clearance under various rotor parameters. The results indicate that the length and number of blades, as well as the hub radius, significantly affect the sensor voltage output in comparison to rotation speed. Furthermore, we show that traditional static calibration methods are inadequate for measuring dynamic blade tip clearance using eddy current sensors. Instead, it is demonstrated that incorporating rotor parameters into the calibration of eddy current sensors can enhance the accuracy of dynamic blade tip clearance measurements.

An Investigation of the Energy-Absorption Characteristics of Thin-Walled Polymer Composite C-Channels: Experiment and Stacked Shell Simulation.

Polymer composite materials are increasingly used in civil aircraft structures. The failure mode and energy-absorption characteristics of polymer composite structures have garnered significant attention from academia and industry. For thin-walled polymer composite C-channels with layups of [0/90]3s, [45/-45]3s, and [45/90/-45/0]3, low-speed axial compression tests were performed to investigate the failure modes, failure mechanisms, and energy-absorbing characteristics. After parametric studies using [0] and [90] single-element models, stacked shell models of thin-walled composite C-channels were established using the Lavadèze single-layer damage constitutive model, Puck 2000, and Yamada Sun failure criteria. The results show that these thin-walled composite C-channels exhibit a stable progressive crushing process with a local buckling failure mode, encompassing local buckling, fiber break-age, matrix cracks, delamination, and corner cracking. The stacked shell model demonstrates reasonable agreement with the progressive crushing process of thin-walled composites, accurately capturing interlayer matrix failure and interface delamination cracking behavior. A comparison of the specific energy absorption (SEA) and mean crushing force (Fmean) between the simulation and test results yields a difference of less than 6%, indicating a strong correlation between the simulation results and the experimental energy-absorbing characteristics. It also shows that a deep understanding of the parameters is helpful for accurate numerical modeling.

Inverse Method to Determine Parameters for Time-Dependent and Cyclic Plastic Material Behavior from Instrumented Indentation Tests.

Indentation is a versatile method to assess the hardness of different materials along with their elastic properties. Recently, powerful approaches have been developed to determine further material properties, like yield strength, ultimate tensile strength, work-hardening rate, and even cyclic plastic properties, by a combination of indentation testing and computer simulations. The basic idea of these approaches is to simulate the indentation with known process parameters and to iteratively optimize the initially unknown material properties until just a minimum error between numerical and experimental results is achieved. In this work, we have developed a protocol for instrumented indentation tests and a procedure for the inverse analysis of the experimental data to obtain material parameters for time-dependent viscoplastic material behavior and kinematic and isotropic work-hardening. We assume the elastic material properties and the initial yield strength to be known because these values can be determined independently from indentation tests. Two optimization strategies were performed and compared for identification of the material parameters. The new inverse method for spherical indentation has been successfully applied to martensitic steel.

Misalignment Assembly Effect on the Impact Mechanical Response of Tandem Nomex Honeycomb-Core Sandwich Structures.

To optimize the assembly methods of honeycomb structures and enhance their design flexibility, this study investigated the impact mechanical responses of tandem honeycomb-core sandwich structures with varying misalignment assembly lengths. Impact tests were conducted across different energy levels on single-layer and tandem honeycomb-core sandwiches to observe their impact processes and failure behaviors. Our findings indicate that tandem honeycomb cores significantly enhance the impact resistance compared with single-layer configurations, even though a misaligned assembly can deteriorate this property. A finite element model was developed and validated experimentally; the model showed good agreement with the experiments, thereby allowing the simulation and evaluation of the impact responses. Herein, we reveal that specific misalignment lengths can either increase or decrease the impact resistance, providing insights into improving the resilience of tandem honeycomb-core structures. Our results not only contribute to enhancing the impact resistance of honeycomb-core sandwich structures but also offer a valuable basis for their practical applications in engineering.

Calibration of Aseptic Loosening Simulation for Coatings Osteoinductive Effect.

The risk of aseptic loosening in cementless hip stems can be reduced by improving osseointegration with osteoinductive coatings favoring long-term implant stability. Osseointegration is usually evaluated in vivo studies, which, however, do not reproduce the mechanically driven adaptation process. This study aims to develop an in silico model to predict implant osseointegration and the effect of induced micromotion on long-term stability, including a calibration of the material osteoinductivity with conventional in vivo studies. A Finite Element model of the tibia implanted with pins was generated, exploiting bone-to-implant contact measures of cylindrical titanium alloys implanted in rabbits' tibiae. The evolution of the contact status between bone and implant was modeled using a finite state machine, which updated the contact state at each iteration based on relative micromotion, shear and tensile stresses, and bone-to-implant distance. The model was calibrated with in vivo data by identifying the maximum bridgeable gap. Afterward, a push-out test was simulated to predict the axial load that caused the macroscopic mobilization of the pin. The bone-implant bridgeable gap ranged between 50 µm and 80 µm. Predicted push-out strength ranged from 19 N to 21 N (5.4 MPa-3.4 MPa) depending on final bone-to-implant contact. Push-out strength agrees with experimental measurements from a previous animal study (4 ± 1 MPa), carried out using the same implant material, coated, or uncoated. This method can partially replace in vivo studies and predict the long-term stability of cementless hip stems.

Alveolar wall hyperelastic material properties determined using alveolar cluster model with experimental stress-stretch and pressure-volume data.

Micro-scale models of lung tissue have been employed by researchers to investigate alveolar mechanics; however, they have been limited by the lack of biofidelic material properties for the alveolar wall. To address this challenge, a finite element model of an alveolar cluster was developed comprising a tetrakaidecahedron array with the nominal characteristics of human alveolar structure. Lung expansion was simulated in the model by prescribing a pressure and monitoring the volume, to produce a pressure-volume (PV) response that could be compared to experimental PV data. The alveolar wall properties in the model were optimized to match experimental PV response of lungs filled with saline, to eliminate surface tension effects and isolate the alveolar wall tissue response. When simulated in uniaxial tension, the model was in agreement with reported experimental properties of uniaxial tension on excised lung tissue. The work presented herein was able to link micro-scale alveolar response to two disparate macroscopic experimental datasets (stress-stretch and PV response of lung) and presents hyperelastic properties of the alveolar wall for use in alveolar scale finite element models and multi-scale models. Future research will incorporate surface tension effects, and investigate alveolar injury mechanisms.

Development of a continuum-based, meshless, finite element modeling approach for representation of trabecular bone indentation.

Implant subsidence into the underlying trabecular bone is a common problem in orthopaedic surgeries; however, the ability to pre-operatively predict implant subsidence remains limited. Current state-of-the-art computational models for predicting subsidence have issues addressing this clinical problem, often resulting from the size and complexity of existing subject-specific, image-based finite element (FE) models. The current study aimed to develop a simplified approach to FE modeling of subject-specific trabecular bone indentation resulting from implant penetration. Confined indentation experiments of human trabecular bone with flat- and sharp-tip indenters were simulated using FE analysis. A generalized continuum-level approach using a meshless smoothed particle hydrodynamics (SPH) approach and an isotropic crushable foam (CF) material model was developed for the trabecular bone specimens. Five FE models were generated with CF material parameters calibrated to cadaveric specimens spanning a range of bone mineral densities (BMD). Additionally, an alternative model configuration was developed that included consideration of bone marrow, with bone and marrow material parameters assigned to elements randomly according to bone volume (BV%) measurements of experimental specimens, owing to the non-uniform nature of trabecular bone tissue microstructure. Statistical analysis found significant correlation between the shapes of the numerical and experimental force-displacement curves. FE models accurately captured the bone densification patterns observed experimentally. Inclusion of marrow elements offered improved response prediction of the flat-tip indenter tests. Ultimately, the developed approach demonstrates the ability of a generalizable continuum-level SPH approach to capture bone variability using clinical bone imaging metrics without needing detailed image-based geometries, a significant step towards simplified subject-specific modeling of implant subsidence.

Validated 3D finite-element model of the Risso's dolphin (Grampus griseus) head anatomy demonstrates gular sound reception and channelling through the mandibular fats.

Like other odontocetes, Risso's dolphins actively emit clicks and passively listen to the echoes during echolocation. However, the head anatomy of Risso's dolphins differs from that of other odontocetes by a unique vertical cleft along the anterior surface of the forehead and a differently-shaped lower jaw. In this study, 3D finite-element sound reception and production models were constructed based on computed tomography (CT) data of a deceased Risso's dolphin. Our results were verified by finding good agreement with experimental measurements of hearing sensitivity. Moreover, the acoustic pathway for sounds to travel from the seawater into the dolphin's tympanoperiotic complexes (TPCs) was computed. The gular reception mechanism, previously discovered inDelphinus delphisandZiphius cavirostris, was also found in this species. The received sound pressure levels and relative displacement at TPC surfaces were compared between the cases with and without the mandibular fats or mandible. The results demonstrate a pronounced wave-guiding role of the mandibular fats and a limited bone-conductor role of the mandible. For sound production modelling, we digitally filled the cleft with neighbouring soft tissues, creating a hypothetical 'cleftless' head. Comparison between sound travelling through a 'cleftless' head vs. an original head indicates that the distinctive cleft plays a limited role in biosonar sound propagation.

Embedded finite element modeling of the mechanics of brain axonal fiber tracts under head impact conditions.

Investigating and understanding the biomechanical kinematics and kinetics of human brain axonal fibers during head impact process is crucial to study the mechanisms of Traumatic Axonal Injury (TAI). Such a study may require the explicit incorporation of brain fiber tracts into the host brain in order to distinguish the mechanical states of axonal fibers and brain tissue. Herein we extend our previously developed human head model by using an embedded element method to include fiber tracts reconstructed from diffusion tensor images in a host brain with the purpose of numerically tracking the deformation state of axonal fiber tracts during a head impact simulation. The updated model is validated by comparing its prediction of intracranial pressures with experimental data, followed by a thorough study of the effects of element types used for fiber tracts and the stiffness ratios of fiber to host brain. The validated model is also used to predict and visualize the damaged region of fiber tracts during the head impact process based on different injury criteria. The model is promising in tracking the state of fiber tracts and can add more objective functions such as axonal fiber deformation if used in the future design optimization of head protective equipment such as a football helmet.

Optimal tooth sectioning using a surgical handpiece and elevator: a finite element study of horizontally deeply impacted mandibular third molars.

OBJECTIVES: To conduct a finite element analysis of the impact of different variables on tooth sectioning efficiency and trauma to surrounding tissues when utilizing high-speed surgical handpieces and elevators. METHODS: CBCT data from the horizontally impacted third mandibular molar (M3M) of a patient were utilized to establish digital models of the M3M, adjacent M2M, and surrounding bone. To simulate tooth sectioning, a 3D finite element model was established with the following variables: remaining tooth tissue thickness (1-5 mm), tooth section fissure width (1-3 mm), elevator depth in fissure (2-6 mm), elevator position (buccal, lingual, central), elevator width (2-5 mm), and application of force (rotating, levering). Using this model, the distribution of stress on the M3M and the surrounding tissue was assessed while measuring tooth sectioning efficiency and trauma to the surrounding tissue. RESULTS: Factors associated with uniform stress at the site of sectioning included thin (≤ 3 mm) remaining tooth tissue, appropriate fissure width (~ 2 mm), a wide (≥ 4 mm) elevator, and central elevator positioning. Levering the elevator yielded greater stress on the M3M than rotating force. Greater sectioning efficiency was associated with increased stress placed on the distobuccal side of M2M. CONCLUSIONS: Tooth sectioning efficiency can be improved by adjusting the high-speed surgical handpiece and elevator. However, it is important to remain attentive to the trauma to which adjacent teeth are exposed during this process. CLINICAL SIGNIFICANCE: These results offer guidance for approaches to improving operator efficiency and reducing trauma to surrounding tissues during tooth sectioning.

Auditory nerve fiber excitability for alternative electrode placement in the obstructed human cochlea: electrode insertion in scala vestibuli versus scala tympani.

Objective. The cochlear implant (CI) belongs to the most successful neuro-prostheses. Traditionally, the stimulating electrode arrays are inserted into the scala tympani (ST), the lower cochlear cavity, which enables simple surgical access. However, often deep insertion is blocked, e.g. by ossification, and the auditory nerve fibers (ANFs) of lower frequency regions cannot be stimulated causing severe restrictions in speech understanding. As an alternative, the CI can be inserted into the scala vestibuli (SV), the other upper cochlear cavity.Approach. In this computational study, the excitability of 25 ANFs are compared for stimulation with ST and SV implants. We employed a 3-dimensional realistic human cochlear model with lateral wall electrodes based on aµ-CT dataset and manually traced fibers. A finite element approach in combination with a compartment model of a spiral ganglion cell was used to simulate monophasic stimulation with anodic (ANO) and cathodic (CAT) pulses of 50µs.Main results. ANO thresholds are lower in ST (mean/std =µ/σ= 189/55µA) stimulation compared to SV (µ/σ= 323/119µA) stimulation. Contrary, CAT thresholds are higher for the ST array (µ/σ= 165/42µA) compared to the SV array (µ/σ= 122/46µA). The threshold amplitude depends on the specific fiber-electrode spatial relationship, such as lateral distance from the cochlear axis, the angle between electrode and target ANF, and the curvature of the peripheral process. For CAT stimulation the SV electrodes show a higher selectivity leading to less cross-stimulation of additional fibers from different cochlear areas.Significance. We present a first simulation study with a human cochlear model that investigates an additional CI placement into the SV and its impact on the excitation behavior. Results predict comparable outcomes to ST electrodes which confirms that SV implantation might be an alternative for patients with a highly obstructed ST.