Search Results (383)

Background: Closing extraction spaces with clear aligners remains a significant biomechanical challenge, frequently involving difficulties in sagittal control, torque expression, and intra-arch anchorage. Although various sequential or phased retraction strategies exist, the Caterpillar Motion protocol has not yet been formally defined. This clinical report describes the Caterpillar Motion staging protocol and illustrates its application through representative extraction cases, rather than providing a systematic review or experimental comparison. Case Presentation: Two adult patients with extraction-based malocclusions were treated using the Caterpillar Motion staging protocol. Case 1 involved bimaxillary first-premolar extractions with maximum anchorage requirements and periodontal limitations in the mandibular incisors. Case 2 presented as a full Class II malocclusion requiring maxillary first-premolar extractions with moderate anchorage for sagittal camouflage. In both cases, tooth movement was organized into alternating functional groups, with waves limited to 2 mm of sagittal closure. Discussion: The Caterpillar Motion protocol reduces the risk of aligner bowing effect, increases effective crown engagement, and redistributes anchorage demands by preventing simultaneous shortening of both arch extremities. Both cases demonstrated controlled anterior retraction, stable posterior anchorage, and favorable root parallelism. Conclusions: Caterpillar Motion offers a biomechanically coherent and clinically reproducible staging strategy for clear aligner extraction therapy. Further controlled studies are needed to validate its advantages over traditional linear and en-masse protocols. Full article

Lower-limb rehabilitation exoskeletons must balance biomechanical compatibility, structural safety, and low mass to enable practical, repeatable gait assistance. This paper proposes a planar pantograph-derived exoskeleton leg driven by a Chebyshev Lambda linkage and develops an integrated workflow from mechanism synthesis to manufacturable optimization and experimental verification. A mannequin-coupled multibody model was built in MSC ADAMS to evaluate joint kinematics, end-point (foot) trajectories, and joint reaction forces under multiple scenarios (fixed-frame, ramp, stair ascent, and inclined-plane walking). The extracted joint loads were transferred to a parametric finite element model in ANSYS Workbench 2019, where response surface surrogates and a multi-objective genetic algorithm (MOGA) were used to minimize mass under stiffness and strength constraints. For the optimized load-bearing link, the selected minimum-mass design reached a component mass of 0.542 kg while respecting the imposed structural limits, i.e., a maximum total deformation below 0.2 mm and a maximum equivalent (von Mises) stress below 50 MPa (e.g., ~0.188 mm deformation and ~39 MPa stress in the optimal candidate). A rapid prototype was manufactured by 3D printing and experimentally evaluated using CONTEMPLAS high-speed video tracking, providing measured X_M(t) and Y_M(t) trajectories and joint-angle histories for quantitative comparison with simulations via RMSE metrics. Full article

Finite element analysis is widely used to study spinal biomechanics and to compare surgical strategies under controlled loading conditions. By allowing variation in alignment, fixation, and implant design, these models provide insight into stress redistribution and motion changes that are difficult to isolate experimentally. This review examines spine surgery-focused finite element studies published between 2018 and 2024, with emphasis on interbody fusion techniques, adjacent segment mechanics, and implant-related stress behavior. Across lumbar fusion models, constructs incorporating anterior column support demonstrate lower posterior instrumentation stress than posterior-only approaches, with lateral lumbar interbody techniques showing reduced rod and screw stresses across multiple loading conditions compared with posterior lumbar interbody or posterolateral fusion constructs. In the cervical spine, comparisons of plated and zero-profile anterior cervical discectomy and fusion devices show smaller increases in adjacent-level motion and intradiscal pressure with zero-profile constructs, alongside higher localized stress at fixation interfaces. More recent studies apply finite element methods to implant optimization, alignment planning, and patient-specific modeling. Together, these findings suggest that finite element analysis is increasingly used to support surgical planning and implant design, with continued advances in validation and patient-specific simulation likely to strengthen its clinical relevance. Full article

Background: Knee osteoarthritis (KOA) is a major cause of pain, mobility limitation, and increased fall risk among older adults. Gait dysfunction, characterized by spatiotemporal and kinematic alterations, is a key functional consequence of KOA. While sagittal-plane gait deviations are well-established, multiplanar kinematic changes—particularly in the frontal and transverse planes—remain less clearly understood. This study aimed to compare three-dimensional gait characteristics between older adults with and without KOA. Methods: Ninety older adults (45 with KOA and 45 controls) completed gait assessments using a VICON™ motion capture system. Participants walked at a self-selected speed along a straight walkway without turning movements during data collection. Spatiotemporal parameters and lower-limb joint kinematics (hip, knee, and ankle) were recorded during key gait phases: initial contact, mid-stance, toe-off, and mid-swing. Group comparisons were performed using independent t-tests with statistical significance set at p < 0.05. Results: Compared with controls, participants with KOA demonstrated significantly slower gait velocity (p = 0.001), reduced cadence (p = 0.020), shorter stride length (p = 0.011), increased step time (p = 0.006), prolonged double support time (p = 0.009), and reduced single support time (p = 0.012). Kinematic analysis revealed greater knee adduction at initial contact (p = 0.001), reduced hip adduction (p = 0.002) and greater knee adduction (p = 0.003) during mid-stance, and increased ankle plantarflexion at toe-off (p = 0.004) in the KOA group. No significant between-group differences were observed during the mid-swing phase. Conclusions: Older adults with KOA exhibit distinct spatiotemporal and multiplanar kinematic gait alterations, particularly during weight-bearing phases. These changes may reflect adaptive gait patterns associated with joint dysfunction rather than definitive compensatory mechanisms. Three-dimensional gait analysis may provide valuable biomechanical insights to support early identification of mobility impairments and inform targeted rehabilitation planning in individuals with KOA. Full article

Rotator cuff suture anchors have traditionally been inserted at the 45° “deadman” angle, but this recommendation was largely derived from single-row constructs and may not reflect the biomechanics of contemporary double-row suture bridge repairs. This study compared the biomechanical performance and stress distribution of medial row anchors inserted at 45° versus 90° in a double-row suture bridge construct. Sixteen ovine humeri with intact infraspinatus tendons were randomized to 45° or 90° medial anchor insertion (n = 8 each), and double-row suture bridge repair was performed using 3.5 mm metallic and PEEK anchors. Specimens underwent uniaxial tensile testing (10-N preload, 5 mm/min) to failure, measuring yield load, failure load, displacement, stiffness, and energy absorption; additionally, a CT-based finite element model of the human humerus assessed von Mises stress, strain, and deformation under 200 N loading. Mean failure load was 161.96 ± 50.99 N for 45° and 185.61 ± 60.97 N for 90° (p = 0.447), and stiffness was 31.63 ± 8.18 N/mm versus 36.79 ± 9.26 N/mm (p = 0.291). Displacement at failure was greater with 90° insertion (8.11 ± 0.51 mm vs. 6.65 ± 0.83 mm; p = 0.002), while energy absorption was higher but not significantly different (p = 0.255). Finite element analysis demonstrated lower bone von Mises stress with 90° insertion (14.03 MPa) compared with 45° (24.77 MPa), with similar deformation. In double-row suture bridge repair, 90° medial anchor insertion provides comparable fixation strength to that at 45° while reducing bone stress, suggesting a biomechanical advantage. Full article

Background/Objectives: To characterize sectoral corneal thickness (CT) profiles in eyes with primary open-angle glaucoma (POAG) compared with healthy eyes and to evaluate potential associations between CT, retinal nerve fiber layer (RNFL) thickness, and optic disc rim area (RA). Methods: In this cross-sectional study, 192 participants (91 with POAG and 101 controls) contributed 297 eyes (145 glaucoma eyes and 152 control eyes). All participants underwent comprehensive ophthalmological examination and spectral-domain optical coherence tomography (OCT; Optovue Solix, Fremont, CA, USA) to obtain peripapillary RNFL measurements, optic disc rim area, and corneal pachymetry maps across five sectors (central, superior, inferior, temporal, and nasal). Repeated-measures correlation analyses were used to assess within-subject associations between CT and RA, and generalized estimating equation (GEE) models were applied to evaluate independent associations between CT, glaucoma status, disease severity, and RNFL thickness while adjusting for relevant covariates. Results: Eyes with POAG exhibited significantly thinner corneas across all sectors compared with controls (all p < 0.05), with the greatest differences observed in the superior (median 607.0 μm vs. 640.0 μm, p < 0.001) and temporal (562.0 μm vs. 579.5 μm, p < 0.001) regions. Average RNFL thickness and rim area were also significantly reduced in glaucoma eyes (all p < 0.001). However, no independent associations between sectoral CT and RNFL thickness or RA were observed after adjustment for multiple comparisons. Although nominal associations between thinner inferotemporal CT and reduced RNFL thickness were observed in unadjusted analyses, these did not remain statistically significant after false discovery rate correction. In multivariable GEE models, glaucoma diagnosis and greater disease severity were consistently associated with reduced RNFL thickness (β range: −11.0 to −42.2 μm; all p < 0.001), whereas CT was not independently associated with RNFL thickness (all adjusted p > 0.07). Conclusions: Sectoral corneal thickness is significantly reduced in eyes with POAG but does not independently correlate with RNFL thickness or optic disc rim area after adjustment for confounding factors. These findings support the concept that corneal thinning reflects structural and biomechanical susceptibility to glaucoma rather than serving as a marker of established neuroretinal damage severity. Further longitudinal studies incorporating comprehensive biomechanical assessments are warranted to clarify the role of corneal structure in glaucoma pathophysiology. Full article

Background: Cubital Tunnel Syndrome (CuTS) is the second-most common compressive neuropathy of the upper limb, traditionally associated with prolonged elbow flexion, trauma, or anatomical constraints. With the widespread adoption of smartphones, sustained upper-limb postures have emerged as potential novel risk factors for ulnar nerve compression. This retrospective study aimed to investigate the potential correlation between smartphone use patterns and the development of CuTS. Methods: A retrospective observational study was conducted on 100 subjects recruited between 2021 and 2024, including 50 patients with EMG-confirmed CuTS who underwent surgical decompression and 50 matched controls without clinical or electrophysiological evidence of ulnar neuropathy. Demographic variables, daily smartphone use (h/day), predominant activity type, and habitual posture during device handling were collected through clinical records and questionnaires. Group comparisons were performed using t-tests and Chi-square analyses, with significance set at p < 0.05. Results: Daily smartphone use was higher in the CuTS group compared with controls (4.94 ± 1.8 vs. 4.04 ± 1.5 h/day), although the difference did not reach statistical significance (p = 0.0716). Posture during device use showed a significant association with CuTS: 82% of affected patients reported using smartphones with the elbow flexed, compared with 56% of controls, whereas supportive postures were less frequent among CuTS patients (16% vs. 38%) (p = 0.019). No significant differences were found between groups regarding smartphone activity type (p = 0.858). Conclusions: Smartphone use may contribute to ulnar nerve compression primarily through ergonomically disadvantageous postures, particularly sustained elbow flexion, rather than total usage time. These findings highlight a modifiable behavioral risk factor relevant to the rising prevalence of CuTS in the digital era. Increased clinical attention to device-handling habits and public-health strategies promoting ergonomic posture may support CuTS prevention. Prospective and biomechanically informed studies are warranted to further elucidate causal mechanisms. Unmeasured confounders (e.g., occupational and sleep-related elbow flexion) may influence these associations. Full article

Background: Alpine skiing imposes high biomechanical demands on the lower limbs, which are further amplified in individuals with transfemoral amputation due to prosthetic constraints. This study aimed to quantify three-dimensional knee flexion asymmetries during alpine skiing turns in transfemoral amputee skiers compared with non-disabled controls. Methods: Five unilateral transfemoral amputee skiers (intervention group) and five non-disabled ski instructors (control group) performed six left and six right turns on a skiing simulator under laboratory conditions. Knee flexion angles at the apex of each turn were analyzed using three-dimensional motion capture. Intra-individual differences between the prosthetic and intact limbs were assessed using paired comparisons, and inter-individual differences between groups were evaluated using independent statistical tests (p < 0.05), performed in IBM SPSS Statistics. Results: Intra-individual analysis revealed significant knee flexion asymmetries (p < 0.05) in almost all amputee participants at the apex of both left (mean difference = 7.74°, 95% CI: 3.38–12.09) and right turns (mean difference = 4.36°, 95% CI: 2.66–6.06). In the control group, asymmetries were smaller and reached significance only for the inside leg in both turns (mean difference = 4.02°, 95% CI: 2.51–5.54). Inter-individual comparisons demonstrated significant differences between the groups for both turning directions. During left turns (prosthetic limb on the inside), the largest difference was observed for the inside leg (26.9°, p < 0.001), while the smallest difference occurred for the outside leg (12.1°, p = 0.013). During right turns (prosthetic limb on the outside), the largest difference was found for the outside leg (19.0°, p < 0.001), with a smaller but still significant difference for the inside leg (14.0°, p < 0.001). Conclusions: Transfemoral amputee skiers exhibit a turning strategy that is qualitatively comparable to that of non-disabled skiers; however, it is characterized by a reduced knee flexion range of motion. These limitations appear to be primarily influenced by prosthesis mechanics and user-specific skill levels rather than by a fundamentally different movement strategy. Full article

The paw pad is an outstanding cushioning structure, which demonstrates nonlinear mechanical characteristics when subjected to pressure. Nonlinear mechanical characteristics are generally considered to be related to the viscoelastic properties of the material. However, the relationship between its nonlinear mechanical properties and the morphological characteristics of the paw pad remains unknown. In this study, morphological data, mechanical data, and finite element simulation methods were integrated to explore how the unique shape of the paw pads enables them to exhibit excellent cushioning performance. The research findings indicate that the paw pad exhibits an irregular morphology. Nevertheless, its cross-sectional area increases in proportion to the increase in the paw pad height, presenting a linear gradient relationship (R² = 0.99). Two comparison models with the same volume and height but different morphologies as the paw pad model, were designed for finite element simulation. The finite element static analysis shows that the influence of morphology is mainly reflected in the early deformation process, while the influence of viscoelastic material properties is reflected in the later load-bearing capacity. The finite element dynamic analysis shows that compared with the comparison models, the paw pad model has a more stable force during the impact process, without an instantaneous impact force at the initial contact moment. Moreover, the peak normal ground reaction force (GRF) component under different impact speeds is lower than that of the comparison models, demonstrating better buffering effects. The research results can provide inspiration and a biomechanical basis for the morphological design of buffering units. Full article

Interface interaction mechanics analysis is of great significance for robot-assisted insertion surgery in minimally invasive surgery and therapy. Previous work indicates that the accurate modeling of soft tissue puncture forces plays a crucial role in surgical planning, robotic needle insertion, and biomechanical simulation, which can give insights useful for physicians to guide and operate assisted robots. The objective of this study is to develop a dynamic multi-component force model that integrates cutting force, stiffness resistance, and frictional interaction to characterize needle–soft tissue interaction during puncture. A dynamic force model is proposed, and a lateral periodic disturbance mechanism is introduced into the simulation framework in order to enhance the robustness and realism of the model under micro-manipulation scenarios. The model has been validated using a series of controlled puncture experiments on porcine liver and renal tissues under varying insertion angles (15°, 30°, 45°) and speeds (0.5 mm/s, 1.5 mm/s, 2.5 mm/s). Corresponding finite element simulations were also conducted using ANSYS software. The agreement between simulation and experiment has been quantitatively evaluated by comparing force–depth and force–time curves, and the statistical significance of the impact of angle and speed on puncture forces has been assessed using ANOVA and Tukey’s HSD tests. Quantitative comparison demonstrated strong consistency, with the optimal case reaching a coefficient of determination (R²) value of 0.96 and Root Mean Square Error (RMSE) below 0.13 N after incorporating a 0.05 mm lateral perturbation. Statistical analysis confirmed the impact of angle and speed on puncture force responses (p < 0.05). Furthermore, comparative analysis revealed that porcine liver exhibits more consistent biomechanical behavior than renal tissue, particularly under perturbation-enhanced simulation. This study successfully establishes a dynamic multi-component force model for soft tissue puncture, validated with high fidelity against experimental data. The incorporated lateral disturbance mechanism enhanced the model’s realism. This work can provide a reliable foundation for the future design of intelligent robot-assisted puncture systems and high-fidelity simulation-based training platforms. Full article

Lumbar interbody fusion is widely performed for degenerative, deformity-related, and instability-associated spinal conditions. Yet, reported outcomes remain variable across grafting strategies and surgical techniques. While advances in instrumentation and cage design improve immediate construct stability, successful arthrodesis depends on early graft behavior within the interbody environment. This includes positional stability, interface contact, and load transfer prior to mature bone formation. Synthetic bone graft substitutes are commonly used to supplement or replace autograft. However, the clinical literature describing these materials is heterogeneous with respect to composition, structural presentation, surgical context, and outcome reporting. This narrative review synthesizes clinical, translational, and biomechanical studies published between 2019 and 2025 that evaluate synthetic bone graft substitutes used in adult lumbar interbody fusion. Rather than comparing individual products or reported fusion rates, grafts are organized by material class and examined through early mechanical events such as graft migration, loss of graft–endplate contact, and cage subsidence. Across recent studies, variability in fusion definitions, imaging modalities, postoperative timepoints, and documentation of early mechanical events limits direct comparison and quantitative synthesis. These findings highlight the need for improved reporting consistency and greater emphasis on engineering-relevant variables in future investigations. Full article

An injury to the elbow’s lateral ulnar collateral ligament (LUCL) is an orthopedic emergency that can impair joint stability and functional biomechanics throughout the upper extremity. The development and application of synthetic ligament substitutes, particularly short-chain-length and medium-chain-length polyhydroxyalkanoate (SCL-PHA and MCL-PHA) co-polymers, represent a promising innovation for lateral elbow stabilization. This experimental cadaveric study aimed to (1) compare biomechanical parameters of torque and angular rotation among control, damage, repair, and reconstruction groups and (2) compare stress and strain responses across the same groups. Twenty-four cadaveric elbows were allocated among six experimental conditions. The control group consisted of intact elbows (n = 4), while the damage group (n = 4) involved transection of the anterior capsule and extensor carpi radialis brevis (ECRB) to simulate ligament injury. The repair group (n = 4) underwent anterior capsular suturing. The reconstruction group (n = 12) was divided into three subgroups: palmaris longus (PL) autograft alone, PL with SCL-PHA co-polymer augmentation, and PL with MCL-PHA augmentation. Biomechanical testing measured maximum torque, angular displacement, shear stress, and strain, with statistical analysis conducted using descriptive statistics, one-way ANOVA, and post hoc multiple comparisons. The results demonstrated that maximum torque (F = 24.930, p < 0.001) and maximum shear stress (F = 8.130, p < 0.001) significantly differed among groups. The control group exhibited the highest mechanical performance (30.700 ± 9.368 Nm and 0.880 ± 0.216 MPa), whereas the damage group showed the lowest values (10.300 ± 2.904 Nm and 0.210 ± 0.073 MPa). The reconstruction group using palmaris longus with SCL-PHA co-polymer reinforcement (RC-PLSCL) demonstrated torque (29.550 ± 7.656 Nm) and shear stress (0.610 ± 0.206 MPa) comparable to those of the control group (p > 0.05), indicating near-physiological mechanical behavior. These findings suggest that SCL-PHA co-polymer augmentation offers superior biomechanical restoration relative to standard repair and other reconstruction strategies, highlighting its potential as an advanced biomaterial for ligament reconstruction in LUCL injuries. Full article

Background: The integration of advanced 3D scanning and additive manufacturing technologies in stroke rehabilitation offers promising advancements in the design and production of ankle-foot orthoses. These technological innovations are progressively recognized for their potential to provide more precise and customized orthotic solutions for individuals with stroke-related impairments. Objectives: The primary aim of this study was to biomechanically test and validate the effectiveness of custom ankle-foot orthoses produced through additive manufacturing technology using data captured by a novel photogrammetric scanning system. The customized orthosis was compared with a standard prefabricated orthosis to assess their relative effectiveness in improving gait dynamics and patient satisfaction in stroke rehabilitation. Methods: Participants with equinovarus deformity, a common consequence of stroke, were fitted with custom ankle-foot orthoses, alongside conventional prefabricated orthoses. The study utilized the Qualisys^® motion analysis system for comprehensive biomechanical gait analysis, and the QUEST questionnaire was employed to capture participant feedback on both types of orthoses. Detailed comparisons of gait dynamics were conducted using Statistical Parametric Mapping with each orthosis. Results: The study revealed notable kinematic and kinetic differences between the custom and prefabricated orthoses. The custom orthoses demonstrated superior performance in enhancing gait efficiency, symmetry, and safety. Patient feedback favored the customized orthoses over the prefabricated variants, with higher scores in comfort, fit, and overall effectiveness. Conclusions: This research underscores the effectiveness of custom orthoses produced through additive manufacturing technology for stroke rehabilitation. By offering a comprehensive evaluation of orthotic interventions and establishing a comparative framework, the study serves as a reference point for future research, advocating for a more personalized and evidence-based approach in orthotic design for improving the quality of life of stroke survivors. Full article

Fractures of the pelvic ring are among the most severe injuries in orthopaedic practice and Tile type C lesions are characterized by complete disruption of the posterior arch with both vertical and rotational instability. The optimal construct for posterior ring fixation remains a matter of debate. The aim of this study was to compare, by means of finite element analysis, the biomechanical performance of three different methods of osteosynthesis for Tile type C1.2 pelvic ring fractures: a transiliac plate, one iliosacral screw and two anterior reconstruction plates on the sacroiliac joint. A three-dimensional model of an intact pelvis was reconstructed from computed tomography images of a healthy adult male. A Tile type C1.2 injury pattern was created virtually, and three fixation constructs were designed in Ansys SpaceClaim according to manufacturer specifications. All materials were assumed to be homogeneous, isotropic and linearly elastic. Vertical loads of 400 N and 800 N were applied to the sacral endplate to simulate partial and full weight bearing, while the acetabular regions were constrained to represent standing stance. In this study, mechanical stability was operationally defined as resistance to global displacement under applied vertical load, with lower displacement indicating higher construct stiffness. Construct stiffness, total deformation and von Mises stress were assessed for bone and implants. For both loading conditions, the iliosacral screw construct showed the lowest overall displacement and provided the greatest stiffness. The transiliac plate construct presented larger displacements, whereas the anterior reconstruction plate construct provided intermediate stability with higher stresses at the sacroiliac joint. Among the analyzed constructs, the iliosacral screw provided the greatest stiffness and lowest overall displacement, suggesting superior mechanical performance under vertical loading conditions. Full article

Self-organizing systems arise in complex biomechanical structures, human locomotion, and neural control hierarchies, yet quantitative methods for describing order formation and loss of stability remain limited. This study develops a mathematical framework for analyzing self-organization using entropy-based measures, indicators of chaotic dynamics, and network-theoretic structure. The approach (the LET framework) combines Lyapunov exponents with entropy families and graph metrics (algebraic connectivity, Load-Path Heterogeneity Index) to: (i) examine transitions between ordered and disordered states, (ii) assess sensitivity to perturbations, and (iii) characterize structural coherence in evolving cervical spine kinematics. Analytical models and computational validations are presented for cervical stability and post-operative Adjacent Segment Disease (ASD) using the Branney–Breen dataset. The findings indicate that entropy and chaos measures identify regime shifts and the emergence of a “stability corridor” more clearly than task-oriented indices, and provide finer resolution of dynamical variability within self-organizing processes. Network metrics complement these results by linking local segmental interactions to global structural fragility transfer. The study shows that entropy, chaos indicators, and network structure together form a consistent basis for describing self-organization in biomechanical systems, enabling quantitative comparison of dynamical regimes and improved interpretation of emergent pathological behavior. The approach utilizes a hybrid kinematic surrogate model to resolve passive and active components, bypassing direct force measurements by employing viscoelastic mechanotransduction principles. Full article