Statement of problem Achieving strong and durable fixation remains a major challenge in mandibular reconstruction with patient-specific implants (PSIs). Most prior studies have focused on initial mechanical stability, with limited attention to the time-dependent progression of biological fixation at the bone-implant interface. Purpose The objective of this single-patient study was to investigate the osseointegration dynamics of a mandibular PSI using a mechanoregulation-based finite element model (FEM) to explore how the predicted biological fixation behavior relates to the specific design and screw configuration. It was hypothesized that the model predictions for the spatiotemporal pattern of osseointegration would be in good agreement with postoperative quantitative computed tomography (QCT)-derived periprosthetic bone mineral density (BMD). Material and methods A partial-mandible PSI with an extended fixation wing was designed, fabricated, and implanted in a 19-year-old patient after hemimandibulectomy. A voxel-based FEM was combined with a mechanoregulation algorithm to simulate interfacial tissue maturation over ten 4-week time steps using local micromotion and gap as mechanical stimuli to update a maturity level index (MLI). The final step MLI distribution was compared with 1-year postoperative periprosthetic BMD from QCT, including an element-wise Spearman correlation analysis (α=.05). Results Osseointegration started at the distal portion of the fixation wing and progressed proximally, covering about 30% of the wing area by 24 weeks and over 80% by approximately 36 weeks. The 40-week pattern was consistent with the 1-year QCT-derived BMD distribution, showing a moderate positive correlation (Spearman ρ=0.61, P=.004). Conclusions Simulation of the osseointegration dynamics suggested a distal-to-proximal osseointegration pattern and delayed maturation near the osteotomy edge in the treatment under study. It also indicated that achieving a mechanically competent lamellar interface required longer than the idealized 16-week period.

The bifurcation of the left coronary artery is one of the most critical sites for atherosclerotic plaque development, where rupture initiation can lead to arterial failure and subsequent heart attack. This study aimed to investigate the variation in wall shear stress and von Mises stress at this bifurcation due to plaque formation. A three-dimensional (3D) biomechanical model of a bifurcated coronary artery was developed. Three plaques were modeled for the three branches of the left main (LM), left anterior descending (LAD), and left circumflex (LCx). Fluid-structure interaction (FSI) models were analyzed using the finite element method in ANSYS Fluent. Blood flow was assumed to be laminar, incompressible, and Newtonian in nature. Results showed that wall shear stress peaked at the entrance of the bifurcation in each branch, and both wall shear stress and von Mises stress increased with plaque height. Interestingly, longer plaques were associated with reduced von Mises stress within the arterial wall. These findings provide insight into stress distribution patterns that may contribute to plaque vulnerability and arterial rupture risk.

BACKGROUND:Estimation of lumbar spinal loads is important for understanding low back pain, guiding ergonomic interventions, and informing surgical and rehabilitation planning. Historically, intradiscal pressure (IDP) provided one of the few internal in vivo measures of disc loading; more recently, telemetry, musculoskeletal (MS) modeling, finite element (FE) analysis, hybrid MS-FE approaches, displacement/control-based methods, and AI surrogates have expanded the toolbox for estimating spinal loads. MATERIAL AND METHODS:We present a narrative perspective review based on a literature search in PubMed, Scopus, and Web of Science using terms related to spinal loads, IDP, telemeterized implants, MS modeling, FE analysis, hybrid MS-FE coupling, displacement/control-based methods, wearable/EMG-based approaches, and AI/machine learning surrogates. Human lumbar studies and methodological contributions relevant to load estimation or validation were included; animal models were excluded. RESULTS:Invasive approaches (needle-based IDP, discography, intra-abdominal pressure, and telemeterized implants) provide task-dependent internal pressures or forces in small, selected cohorts and now primarily serve as benchmarks for model validation. MS models estimate segmental compression, shear, and net moments from motion and EMG, with typical L4-L5 compressive forces of ∼1-2 kN in relaxed standing and ∼3-5 kN during common lifting tasks. FE and hybrid MS-FE simulations resolve how these loads are distributed across discs, facets, and ligaments and relate segmental forces to internal stresses. Displacement-driven/control-based models and emerging AI/wearable-based surrogates provide additional non-invasive pathways for task-specific lumbar load estimation. CONCLUSIONS:This methods-focused synthesis outlines how invasive data support MS, FE, hybrid, and AI-based approaches and highlights recurring challenges in muscle redundancy, constitutive and parameter uncertainty, limited in vivo benchmarks, and heterogeneous model reporting. Within this framework, IDP is best regarded as an internal benchmark rather than a stand-alone metric of "spinal load" which is more fully described by compression, shear, moments, and internal stresses.

Cell manipulation and separation play a pivotal role in the diagnosis and treatment of different types of cancer. Separation can occur on a micro and/or macro scale. The size of the red blood cells (RBCs) has a major role in anisocytosis disease, and any change in the size of the RBCs can impair their primary function, which is transporting oxygen and carbon dioxide. This study aims to simulate the mechanism of RBCs separation by application of external dielectrophoretic forces, and to gain a better understanding of separation data before any attempt to manufacture separation devices. Here, the simulation for the separation of three kinds of biological particles and the determination of a range of sizes for separation purposes has been investigated. The results show that the dielectrophoretic force is sensitive to particle size, and this force increases with the elevation of the particle size, causing the particles to be separated. Moreover, a size range was obtained for an effective separation. The findings may be used to improve the separation process in biomedical applications.

The utilization of a plate-screw system is a prevalent osteosynthesis technique widely employed for the fixation of mandibular fractures. While comparable findings exist regarding the impact of using locking and non-locking screws on the mandibular bone, conflicting results have been reported concerning their effect on stress distribution in the plate and screws. This study investigates the influence of locking and non-locking plate-screw systems on mandibular fracture fixation using finite element analysis, incorporating a 3D scanned jawbone geometry. Results indicate that locking screws exhibit a more uniform stress distribution while experiencing higher stress values compared to non-locking screws. Furthermore, the maximum stress in non-locking plates is lower than that in locking plates. In fact, replacing the locking screws with non-locking ones reduces the maximum stress in the plate by 62.5% and in the screw by 8.8%, respectively. Considering displacement in screws, findings indicate that the superiority of locking or non-locking screws depends on their location relative to the fracture.

Understanding the dynamic response of the intervertebral disc (IVD) is crucial for developing synthetic and engineered tissues to treat disc degeneration or injury. However, limited studies have investigated the effects of loading mode and rate on the IVD's global mechanical response. This study explores the time-dependent behavior of the IVD, focusing on the viscoelastic properties of the annulus fibrosus (AF) and nucleus pulposus (NP). By examining how various periodic loading rates influence the disc's biomechanical behavior in both in vitro and in silico environments, this research aims to enhance our understanding of the IVD's dynamic performance under cyclic loading conditions. In vitro experiments were conducted on 16 sheep lumbar motion segments subjected to cyclic loading for 60min at frequencies of 0.25, 0.5, 1, and 2.5Hz and pressures ranging from 0.1 to 0.8MPa. The findings revealed that increasing loading frequencies led to higher dynamic stiffness and reduced disc height and area displacement. Finite element analysis (FEA) demonstrated strong agreement between numerical models and experimental results, validating the assumed biomechanical properties under periodic loads. This study found that dynamic stiffness increases at higher frequencies due to interactions between the solid matrix and fluid flow within the disc. The insights gained from this work provide valuable information about the behavior of IVDs under dynamic loading, with potential implications for improving clinical treatments and advancing research in spinal biomechanics.

Background: The biomechanical impacts of Conventional Open Surgery (COS) versus Minimally Invasive Surgery (MIS) fusion techniques on adjacent segments and their potential role in developing Adjacent Segment Disease (ASD) remain uncertain for spondylolisthesis.Objective: This study aimed to investigate the impact of MIS and COS fusion surgeries on adjacent spinal segments for spondylolisthesis, through on muscle injury and developing ASD.Material and Methods: This prospective and non-randomized controls study used a validated musculoskeletal model to compare the biomechanical effects of COS and MIS L4/L5 fusion surgery on patients with spondylolisthesis. The model incorporated kinematic data from 30 patients who underwent each surgery. A sitting task was simulated to model post-operative muscle atrophy, and the analysis focused on changes in biomechanics of adjacent spinal segments.Results: Lumbar flexion was significantly greater (201%) in MIS vs. COS, despite similar pelvic tilt. Consequently, Lumbopelvic Rhythm (LPR) also increased in MIS (133%). Both techniques altered inter-segmental moments. While inter-joint load was higher in COS, only the lower joint’s compressive load was significantly greater (67%). Additionally, MIS required lower overall muscle force with reduced loads and passive moment on spinal joints compared to COS. Conclusion: This study demonstrates that MIS fusion preserves physiological LPR better than COS. MIS maintains normal spinal curvature and maintains lumbar lordosis. While open surgery can lead to abnormal curvature and increased muscle forces to compensate for spinal stability. The study emphasizes the importance of paraspinal muscles in influencing spinal load distribution during MIS compare to COS.

BACKGROUND/OBJECTIVES:Sarcopenia, characterized by age-related muscle loss, impacts functional performance and mobility. This study compares sarcopenia prevalence and physical fitness outcomes among older adults using four criteria from European and Asian Working Groups. METHODS:A total of 377 community-dwelling older adults all of Taiwanese ethnicity, were recruited for this study. They completed seven functional assessment tests. Descriptive statistics and various tests were used to compare variables between older adults with and without sarcopenia. Correlation and logistic regression analyses, along with the area under the curve, were performed to evaluate relationships between sarcopenia criteria and functional assessments, as well as the impact of functional performance on sarcopenia classification. Statistical significance was set at p < .05. RESULTS:The prevalence of sarcopenia varied with different criteria: European Working Group on Sarcopenia in Older People (EWGSOP)-2 (3.7%), EWGSOP-1 (39.0%), Asian Working Group for Sarcopenia (AWGS)-2 (11.1%), and AWGS-1 (6.6%). The study found generally low but statistically significant correlations between functional tests and sarcopenia factors. The receiver operating characteristic analysis results indicated that the functional test set by logistic regression model achieved an area under the curve of 0.787 under EWGSOP-2, 0.686 under EWGSOP-1, 0.728 under AWGS-2, and 0.751 under AWGS-1. Patients with sarcopenia consistently performed worse in functional tests, and area under the curve values indicated the effectiveness of functional tests in distinguishing sarcopenia. CONCLUSION:This study highlights the variability in sarcopenia prevalence and functional implications among older adults using different European and Asian criteria, emphasizing the importance of context-driven diagnostic criteria. Significance/Implications: The findings of this study can highlight the need for selecting appropriate sarcopenia criteria to enhance screening accuracy, functional assessment, and targeted interventions for older adults in clinical practice.

Cervical spondylotic myelopathy (CSM) is rising in the aging population. This study evaluated conventional versus home-based exercise interventions with a head-mounted device in 75 patients. Participants were divided into conventional (N = 36) and home-based (N = 39) groups, assessed pre-surgery, 3-months post-surgery, and after an eight-week intervention. Outcomes included numeric pain rating scale (NRS), neck disability index (NDI), cervical spine range of motion (ROM), neck muscle strength, muscle activation during movement, and cervical proprioception. A two-way mixed ANOVA was used to explore the main effects and interactions between groups and time points. ANCOVA adjusted for potential baseline differences. Both groups improved in NRS (P = 0.003), NDI (P = 0.001), and ROM in flexion (P < 0.001) and extension (P < 0.001) after exercise, while the home-based group showed significantly greater ROM in rotation (left, P = 0.026; right, P = 0.006), greater muscle strength (flexors, P < 0.001; extensors, P < 0.001), and lower sternocleidomastoid muscle activation (P < 0.001). The home-based group exhibited lower reposition errors post-exercise than the conventional group (Variable error during extension, P < 0.001; root mean square error during flexion, left and right rotation, P < 0.001 for all). The home-based intervention with a head-mounted device showed superior outcomes in mobility, muscle strength, proprioception, and muscle activation, surpassing pre-surgery levels and enhancing quality of life for CSM patients.

This study compared biomechanical impacts of conventional open surgery (COS) and minimally invasive surgery (MIS) for spondylolisthesis using a musculoskeletal model with in-vivo data from 31 patients undergoing L4-L5 fusion. Pre- and post-operative conditions with simulated muscle injury were analyzed, focusing on kinematics, muscle forces, and adjacent segment loading. Both methods altered lumbosacral parameters, but COS caused greater lumbar-pelvic rhythm reduction (60% vs. 14%), largely due to decreased trunk flexion. MIS showed increased multifidus contribution and reduced adjacent loading, though it raised upper segment passive moment and compression. Findings suggest MIS better preserves stability and favorable biomechanics than COS.

Mandibular fractures are among the most serious injuries to the maxillofacial region, with controversy surrounding their diagnosis, classification, and management Fixation mini-plate systems are commonly used for treatment of mandibular fractures. Previous studies have examined plate configurations with various locking systems. However, the impact of plate thickness on the performance of unlocking screw mechanisms has not been investigated in the literature. Also, there exist conflicting findings concerning the impact of the locking and unlocking screw mechanisms on the concentration of stress within the screws. This study investigates the effect of plate thickness and plate-screw locking mechanisms on the performance of the fixation system using the finite element analysis. The complex relation between jawbone thickness and occurred cracks or fractions made us build a precised model for investigating the fixation patterns. Results showed that the locking screw mechanism reduced the von Miss stress in the buccal and lingual regions of the bone. Increasing the plate thickness also decreased the von Miss stress and maximum pressure in the bone. The unlocking screws application resulted in lower values of stress and displacement in the plate and screws compared to the locking screws. Moreover, while using a plate with a higher thickness resulted in a pronounced decrease in plate von Mises stress, it led to a higher stress on the screws. The study investigated crack propagation by analyzing bone density, which was directly related to age and an individual's lifestyle. This method enables a more precise use of the viscoelastic characteristics of mandibular bones tailored to everyone. The outcomes of this study indicated that the locking screw mechanism demonstrated enhanced features in light of the reduced stress on the bone. Nevertheless, the screws and plate experienced an elevated stress level using this mechanism.

Osteoarthritis (OA) is a degenerative condition that impacts synovial joints, particularly the knee joint, impairing patients’ capacity to engage in regular physical activity. Regrettably, there is no remedy for this musculoskeletal condition. Currently, numerous researchers focus on developing ways to model individualized risks for the initiation and progression of osteoarthritis and assess the impact of various conservative preventive measures. Finite element analysis (FEA) is now known as a potential technique for the management of knee osteoarthritis. The FEA pipeline comprises three recognized phases: pre-processing, processing, and post- This study aims to introduce an innovative concept in the customization of knee prosthesis, considering the anatomical characteristics influencing osteoarthritis, to enhance treatment efficacy. We posited that anatomical parameters in simplified knee models can be adjusted so that the estimation of the tissue mechanical response from a parametric model matches that of a model with precise geometry. Consequently, we want to integrate simpler models with individualized modeling to provide successful treatment solutions that will help clinicians identify individuals at high risk of knee OA and provide more conservative treatments for patients.

Background:Osteoarthritis is a degenerative condition that impacts synovial joints, particularly the knee joint. Researchers regard Finite Element Analysis as a promising technique for managing knee osteoarthritis. However, these models often depend on input geometry from one or more individuals, feature complex interfaces, and require a significant amount of time, which makes them unsuitable for clinical use and reduces their reliability. Purpose:This study aims to assess the effectiveness of the personalized parametric model technique in predicting the knee joint's mechanical response, taking into account anatomical variables that influence osteoarthritis. Methods:A 3D model of the knee was created from CT images of a patient with knee osteoarthritis. Lateral, anterior, and posterior knee radiographs were obtained from twenty-six subjects to customize the geometric parameters of the developed parametric model. The knee geometry was parameterized using Ansys software. The models used six parameters to represent the articular surface of the tibial plateau, its slope, and variables attached to the medial and lateral femoral condyles. Parametric FE models were created individually by applying the ground reaction force diagram to each model. Results:Mean maximum von Mises stress was higher in the OA group than in the control group. Simulations of the patients in the OA group indicated that the mean von Mises stress at the articular surfaces diminished with an increase in tibial plateau tilt. Also, individual geometry-specific models exhibited varying responses, thereby confirming the significance of taking personalized geometry into account. Conclusion:Personalized models can be used to simulate mechanical responses and specifically evaluate the effect of the tibial plateau tilt. This work presented an innovative method for creating individualized finite element models of osteoarthritic knees, which can be used as a practical and effective tool in clinical environments.

In this study, carboxymethyl chitosan/gelatin/Akermanite (CMC/GEL/AK)-based scaffolds were prepared for bone tissue regeneration via 3D printing method. The bioactive AK was synthesized and used to fabricate the scaffolds. The AK powder was analysed through scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), and X-ray diffraction (XRD). The porous scaffolds were fabricated and characterized to show their ability in bone tissue engineering (BTE). Degradation rate, swelling ratio, and mechanical properties of the scaffolds containing AK have been significantly increased. The scaffolds possess the interconnected networks with the pore size of about 300–900 μm. The mechanical strength increased up to 2.6 MPa by adding 20

Purpose A personalized model of the knee joint, with adjustable effective geometric parameters for the transplanted autograft diameter in Anterior Cruciate Ligament Reconstruction (ACLR) using the bone-patella-tendon-bone (BPTB) technique, has been developed. The model will assist researchers in understanding how different graft sizes impact a patient’s recovery over time. Methods The study involved selecting a group of individuals without knee injuries and one patient who had undergone knee surgery. Gait analysis was conducted on the control group and the patient at various time points. A 3D model of the knee joint was created using medical images of the patient. Forces and torques obtained from the gait analysis were applied to the model to perform finite element analysis. Results The results of the finite element (FE) analysis, along with kinetic data from both groups, indicate that models with diameters of 7.5 mm and 12 mm improved joint motion during follow-up after ACLR. Additionally, a comparison of the stress applied to the ACL model revealed that a 12 mm autograft diameter showed a more favorable trend in patient recovery during the three follow-up intervals after ACL reconstruction surgery. Conclusion The development of a personalized parametric model with adjustable geometric parameters in ACLR, such as the transplanted autograft diameter, as presented in this study, along with FE using the patient’s kinetic data, allows for the examination and selection of an appropriate autograft diameter for Patella Tendon grafting. This can help reduce stress on the autograft and prevent damage to other knee joint tissues after ACLR.

Morphological changes of the nucleus pulposus (NP) cells occur concomitantly as part of the intervertebral disc (IVD) degeneration and excessive mechanical loading has been speculated as a significant key factor for contributing to such morphological changes. Therefore, we hypothesize that stress exerted on NP cells can cause a deformity of nucleus in response. The changes of cell morphology is observed in degenerative nucleus pulposus. One of the reasons for degeneration of NP is due to overloading of NP especially in the obese population. So the nucleus deformity caused by stress/force is of our study interest. To delineate the effects and role of mechanical stress, we developed a 3D assay using hydrogel cultures with a circular hole generated with needle indentation to simulate a local stress concentration along the edge of the hole. A stressed zone, encompassing 100 mu m of range from the circular edge, is defined based on stress concentration calculation to enable quantitative analysis against the control zone. Our results demonstrated that the circular hole produces stress-induced morphological changes in NP cells. The tangential elongation of NP cells and their nucleus shape changes in the stressed zone are significantly increased compared to the non-stressed control zone. It is proposed that the cell elongation is a direct response to elevated stress within the stressed zone. Subsequently we found the stress induced morphological changes of the NP cells can be significantly reduced by inhibiting ASIC3. This suggests ASIC3 plays an important role of play in mechano-signaling of NP cells.

The anterior cruciate ligament plays a crucial role in maintaining stability within the knee joint, particularly for athletes who frequently experience its rupture. This study presents a novel approach using personalized three-dimensional (3D) parametric finite element modeling of the knee joint to simulate the treatment following anterior cruciate ligament reconstruction (ACLR) in both forward walking (FW) and drop landing (DL) tasks. The study encompasses two distinct cohorts: five healthy athletes and five ACLR patients. Biomechanical motion analysis was conducted on both cohorts, with the ACLR patient group evaluated at 6 and 9 months post-surgery. A comprehensive 3D parametric model of the knee joint was meticulously crafted. The findings reveal a notable reduction in stress on crucial knee structures such as the autograft, meniscus, and cartilages over time for both FW and DL tasks following ACLR, with a reduction in tissue tension of approximately 9.5% and 37% for FW and DL, respectively. This personalized model not only facilitates the investigation of knee joint tissue biomechanics post-ACLR but also aids in estimating the return-to-sports timeline for patients. By accommodating individual tissue geometries and incorporating patient-specific kinetic data, this model enhances our comprehension of post-ACLR biomechanics across various functional tasks, thereby optimizing rehabilitation strategies.

Multiple-layered scaffolds with various three-dimensional architectures by the additive manufacturing (AM) have been successfully fabricated and can be used in tissue engineering. This study aimed to investigate the effect of unit cell shape, Struts diameter and number of layers on the mechanical properties of multiple-layered scaffolds with constant porosity. All the lattice scaffolds in cylindrical form (outer diameter of 30 mm and length of 60 mm) were designed and fabricated from 18 various types with 70% porosity and in single, double and triple layers and by Selective Laser Sintering (SLS) method. In all the samples, the outer layers had a higher density compared to the inner layers. The mechanical properties of the scaffolds were determined by the uniform compression test. The stress-strain curves of the samples revealed that as the struts diameter increases, the yield stress increases due to the reduction of manufacturing defects. And the numerical simulations showed that the position of the maximum radial displacement shifts from the middle region to the top and bottom regions of the scaffold with the increase in the number of the layers. Also, a good convergence between the results of the finite element model and the experimental results was observed.

Cement-augmentation is a technique commonly used during posterior lumbar instrumented fusion (PLIF) to reinforce compromised osteoporotic vertebral bone, minimize the risk of loosening screws, enhance stability, and improve overall surgical outcomes. In this study, we introduce a novel segmented vertebral body regional modeling approach to investigate the effects of osteoporosis and cement-augmented lumbar fusion on disc biomechanics at spinal levels adjacent to the fused vertebrae. Using our previously validated personalized-poroelastic-osteoligamentous FE model of the spine, fusion was simulated at L4-L5, and the biomechanics of adjacent levels were studied for 30 patients (non-osteoporotic patients (N = 15), osteoporotic patients (N = 15)). PLIF models, with and without cement-augmentation, were developed and compared after an 8 h-rest period (200 N), following a 16 h-cyclic compressive loading of 500-1000 N (40 and 20 min, respectively). Movement in different directions (flexion/ extension/ lateral bending/ axial rotation) was simulated using 10Nm moment before and after cyclic loading. The material mapping algorithm was validated by comparing the results of voxel-based and parametric models. The FE cement-augmented models, subject to daily activity loading, demonstrated significant differences in disc height loss and fluid loss as compared to non-cemented models. The calculated axial stress and fiber strain values were also significantly higher for these models. This work demonstrates that although osteoporosis does not significantly alter the time-dependent characteristics of adjacent IVDs post-surgery, cement-augmentation increases the risk of adjacent segment disease (ASD) incidence. A holistic understanding of the trade-offs and long-term complex interplay between structural reinforcement modalities, including cement augmentation, and altered biomechanics warrants further investigation.

Degenerative disc disease (DDD), regardless of its phenotype and clinical grade, is widely associated with low back pain (LBP), which remains the single leading cause of disability worldwide. This work provides a quantitative methodology for comparatively investigating artificial IVD degeneration via two popular approaches: enzymatic denaturation and fatigue loading. An in -vitro animal study was used to study the time-dependent responses of forty fresh juvenile porcine thoracic IVDs in conjunction with inverse and forward finite element (FE) simulations. The IVDs were dissected from 6-month-old-juvenile pigs and equally assigned to 5 groups (intact, denatured, low-level, medium-level, high-level fatigue loading). Upon preloading, a sinusoid cyclic load (Peak-to-peak/0.1-to-0.8 MPa) was applied (0.01 -10 Hz), and dynamic-mechanical-analyses (DMA) was performed. The DMA outcomes were integrated with a robust meta-model analysis to quantify the poroelastic IVD characteristics, while specimen-specific FE models were developed to study the detailed responses. The results demonstrated that enzymatic denaturation had a more significantly pronounced effect on the resistive strength and shock attenuation capabilities of the intervertebral discs. This can be attributed to the simultaneous disruption of the collagen fibers and water-proteoglycan bonds induced by trypsin digestion. Fatigue loading, on the other hand, primarily influenced the disc 's resistance to deformation in a frequency-dependent pattern, where alterations were most noticeable at low loading frequencies. This study confirms the intricate interplay between the biochemical changes induced by enzymatic processes and the mechanical behavior stemming from fatigue loading, suggesting the need for a comprehensive approach to closely mimic the interrelated multifaceted processes of human disc degeneration.