Biomechanical Investigation Research Articles

A ‘Speed—Difficulty—Accuracy’ Model Following a General Trajectory Motor Task with Spatial Constraints: An Information-Based Model

Accuracy in executing a motor task, i.e., in following a given trajectory under geometrical constraints, is of great interest in work operations as well as in biomechanics applications. In the framework of the Fitts’ law research on motor tasks, experimental studies usually refer to simple trajectories which are of low interest in practical applications. Furthermore, available models lack predicting accuracy in executing motor tasks since do not systematically investigate effects of both speed and task difficulty (index of difficulty (ID)). In this paper, the authors propose a ‘Speed-ID-Accuracy’ model aiming at overcoming abovementioned limits. The model is of general validity as is based on an information-based formulation of a trajectory ID; the model proposed put into relation accuracy in task execution with a general trajectory and with the speed of task execution. Modeling accuracy, defined as standard deviation of the endpoint position, is carried out by regressing data available in the literature. The model proposed proves to be more accurate than the classical ‘Speed-Accuracy’ model in fitting available data. Such a result has been found in both numerical cases relating to ‘tunnel’ and ‘circular’ traveling tasks. Limits of data from field experiments are stressed out and future research field of investigations in work environment and biomechanics are figured out.

Introducing a Custom-Designed Volume-Pressure Machine for Novel Measurements of Whole Lung Organ Viscoelasticity and Direct Comparisons Between Positive- and Negative-Pressure Ventilation.

Asthma, emphysema, COVID-19 and other lung-impacting diseases cause the remodeling of tissue structural properties and can lead to changes in conducting pulmonary volume, viscoelasticity, and air flow distribution. Whole organ experimental inflation tests are commonly used to understand the impact of these modifications on lung mechanics. Here we introduce a novel, automated, custom-designed device for measuring the volume and pressure response of lungs, surpassing the capabilities of traditional machines and built to range size-scales to accommodate both murine and porcine tests. The software-controlled system is capable of constructing standardized continuous volume-pressure curves, while accounting for air compressibility, yielding consistent and reproducible measures while eliminating the need for pulmonary degassing. This device uses volume-control to enable viscoelastic whole lung macromechanical insights from rate dependencies and pressure-time curves. Moreover, the conceptual design of this device facilitates studies relating the phenomenon of diaphragm breathing and artificial ventilation induced by pushing air inside the lungs. System capabilities are demonstrated and validated via a comparative study between ex vivo murine lungs and elastic balloons, using various testing protocols. Volume-pressure curve comparisons with previous pressure-controlled systems yield good agreement, confirming accuracy. This work expands the capabilities of current lung experiments, improving scientific investigations of healthy and diseased pulmonary biomechanics. Ultimately, the methodologies demonstrated in the manufacturing of this system enable future studies centered on investigating viscoelasticity as a potential biomarker and improvements to patient ventilators based on direct assessment and comparisons of positive- and negative-pressure mechanics.

Development and validation of a finite-element musculoskeletal model incorporating a deformable contact model of the hip joint during gait

Musculoskeletal models provide non-invasive and subject-specific biomechanical investigations of the musculoskeletal system. In a musculoskeletal model, muscle forces contribute to the deformation and kinematics of the joint which in turn would alter moment arms of muscles and ground reaction forces and thus affect the prediction of muscle forces and contact forces and contact mechanics of the joint. By far, deformable contact models of the hip have not been considered in musculoskeletal models, and the role of kinematics and deformation within the hip in muscle forces and hip contact mechanics is unknown. In this study, an FE musculoskeletal model including bones, joints and muscles of the lower extremity was developed. A deformable contact model of the hip joint was incorporated and coupled into the musculoskeletal model. Joint angles and ground reaction forces during gait were used as inputs. Optimization minimizing the sum of muscle stresses squared was performed directly to the FE musculoskeletal model in order to simultaneously solve muscle forces and contact forces and contact stresses of the hip joint within a single framework. The calculated hip contact forces corresponded well to the in vivo measurement data. The maximum hip contact stress was 6.5 MPa and occurred at weight-acceptance. The influence of kinematics and deformation in the hip on muscles forces and hip contact forces was minimal and not sensitive to variations in the thickness and properties of the joint cartilage during gait. This suggests that the uncoupled approach in which the hip contact forces and contact mechanics are simulated in separate frameworks would serve as an effective and efficient alternative for subject-specific modelling of the hip. This study provides guidance for the level of complexity needed for future hip models and can be used to evaluate biomechanical changes of the musculoskeletal system following interventions.

Posterolateral Plate Fixation with Pantalarlock® is More Stable than Nail Fixation in Tibiotalocalcaneal Arthrodesis in a Biomechanical Cadaver Study

Category:Ankle; Ankle ArthritisIntroduction/Purpose:Despite the promising results of ankle joint arthroplasty, the tibiotalocalcaneal (TTC) arthrodesis remains an established procedure in treatment of combined pathology of the ankle and subtalar joint. Despite the promising results in biomechanical investigations, nonunion rates of up to 24% are described in recent studies. The objective of this work was a comparative study of the biomechanical properties of the posterolateral plate fixation with retrograde intramedullary nail fixation.Methods:Twenty four fresh-frozen human lower leg specimens (12 pairs) were used for the comparative biomechanical testing. Every specimen was preconditioned with 100N over 200 cycles. After every 250 cycles the force was increased by 50N from 200 to 600N. This was followed by cyclic loading in dorsi-/plantiflexion with 800N for 3000 cycles. All specimens were subjected to bone densitometry (DXA) and computed tomography.Results:Significantly higher number of spacimens with nails (4) failed during the cycling testing in dorsi-/plantarflexion and futher two during the cyclic testing with 800N. Two specimens with plates failed during the cyclic testing with 800N. Statistical analysis showed that the specimens with the plate were significantly more stable in each test direction. The Pearson correlation demonstrated for the specimens with plate a linear relationship between the stiffness and the determined bone density.Conclusion:We expect a considerable reduction of the pseudarthrosis rate and shorten the postoperative treatment phase in clinical set up and appropriate advantages in the treatment of high risk patients with severe deformity of the ankle, bone defects, neuropathic deformity, poor bone quality and osteoporosis. The choice of most predictable and stable implant is essential for the successful fusion. In conclusion, the posterolateral plate ostesynthesis for TTC arthrodesis is significantly stiffer compared to the nail osteosynthesis in osteoporotic bone model.

Interobserver reliability of the Gehweiler classification and treatment strategies of isolated atlas fractures: an internet-based multicenter survey among spine surgeons

PurposeAtlas (C1) fractures are commonly rated according to the Gehweiler classification, but literature on its reliability is scarce. In addition, evaluation of fracture stability and choosing the most appropriate treatment regime for C1-injuries are challenging. This study aimed to investigate the interobserver reliability of the Gehweiler classification and to identify whether evaluation of fracture stability as well as the treatment of C1-fractures are consistent among spine surgeons.MethodsComputed tomography images of 34 C1-fractures and case-specific information were presented to six experienced spine surgeons. C1-fractures were graded according to the Gehweiler classification, and the suggested treatment regime was recorded in a questionnaire. For data analyses, SPSS was used, and interobserver reliability was calculated using Fleiss’ kappa (κ) statistics.ResultsWe observed a moderate reliability for the Gehweiler classification (κ = 0.50), the evaluation of fracture stability (κ = 0.50), and whether a surgical or non-surgical therapy was indicated (κ = 0.53). Type 1, 2, 3a, and 5 fractures were rated stable and treated non-surgically. Type 3b fractures were rated unstable in 86.7% of cases and treated by surgery in 90% of cases. Atlas osteosynthesis was most frequently recommended (65.4%). Overall, 25.8% of type 4 fractures were rated unstable, and surgery was favoured in 25.8%.ConclusionWe found a moderate reliability for the Gehweiler classification and for the evaluation of fracture stability. In particular, diverging treatment strategies for type 3b fractures emphasise the necessity of further clinical and biomechanical investigations to determine the optimal treatment of unstable C1-fractures.

P2. To cross or not to cross: a biomechanical investigation of crossing cervicothoracic junction in posterior cervical laminectomy and fusion

BACKGROUND CONTEXT Lower stopping point for the construct in posterior cervical laminectomy and fusion (PCLF) that involves the cervico-thoracic junction is highly debated. Constructs with C7 as lowest instrumented vertebra (LIV) have been implicated in higher incidence of adjacent level disease and junctional kyphosis, but the literature is not conclusive about these findings and many studies claim in difference in adjacent level disease or PJK. PURPOSE To investigate the biomechanical implications of having C7 as the lowest instrumented vertebra versus crossing the cervico-thoracic junction. STUDY DESIGN/SETTING Biomechanical cadaveric study PATIENT SAMPLE N/A OUTCOME MEASURES N/A METHODS Human cadaveric specimens of full subaxial cervical spine and torso with intact ribcage were used for the study. Six degrees of freedom pure-moment simulator were used to test the specimens in Flexion-Extension (FE), Lateral Bending (LB) and Axial Rotation (AR). Torque-controlled protocol (2.5 Nm, 1.5o/s) was utilized for testing of the intact specimens, while displacement control (based on the angle values obtained from the intact testing) was used for testing the constructs. After the intact testing, C3–7 laminectomy was performed in a standard fashion, and three different fusion constructs were tested in the same specimen: C3–C7, C3–T1, C3–T2. Optic tracking system was used to record range of motion (ROM) and intradiscal pressure (IDP) monitors with custom LabView based software was used to study the intradiscal pressures at the levels adjacent to the fusion constructs. Univariate analysis along with multivariate model was used to analyze the differences between the three constructs. RESULTS A total of nine cadaveric specimens were included in the study. There was partial IDP data missing on one of the specimens and the data was unreliable (statistical outlier on the other specimen) those specimens were excluded from the IDP analysis. ROM data were available for all nine specimens. There was a statistically significant difference in an absolute increase in the adjacent segment range of motion in both torque-controlled and displacement-controlled protocol on FE between constructs stopping at C7 and the ones stopping at T1 or T2. There was also a statically significant difference in absolute increase in the IDP using displacement-control protocol at the adjacent level in FE between constructs stopping at C7 and the ones stopping at T1 or T2. There was no statistically significant difference between changes in the ROM or IDP at the adjacent level in LB or AR. There was also no statistically significant difference in absolute change in ROM or IDP at the adjacent level between constructs stopping at T1 and T2, although a trend was towards lower increase in ROM and IDP with C3–T2 construct. CONCLUSIONS This is the first definitive biomechanical study demonstrating a significant difference in the increase in both ROM and IDP at the adjacent level for constructs terminating at C7 versus the ones crossing the cervico-thoracic junction. These findings suggest higher stress on the adjacent levels with likely implications for the adjacent level disease and PJK for multilevel constructs that involve C7 and do not cross the cervico-thoracic junction. FDA DEVICE/DRUG STATUS QUARTEX (Globus Medical) (Approved for this indication)

Influence of glenosphere diameter and lateralization on instability of reverse shoulder arthroplasty

Abstract Background Prosthetic replacement of the proximal humerus with reverse shoulder arthroplasty (RSA) is an established means of treatment. Due to its unique biomechanical characteristics, RSA can restore shoulder function to a satisfying level in the case of cuff tear arthropathy, arthritis, and fractures. However, complications are frequent in RSA, one of the more common being implant instability with dislocation. The present study investigated the influence of glenosphere diameter and metaglene lateralization using a unique test setup. Methods Seven fresh-frozen cadaveric specimens of the shoulder were thawed and dissected. The subscapularis muscle, the infraspinatus, and the three heads of the deltoid muscle were fixed to a pulley system. After implanting an RSA in different configurations (38/42 mm glenosphere with lateralization of +0 mm, +5 mm, or +10 mm), the implants were dislocated using selective muscle pull. The frequency of dislocations depending on the prosthesis configuration was documented. Results The larger glenosphere diameter of 42 mm showed less dislocations than the diameter of 38 mm (39 vs. 46). Lateralization of +0, +5 mm, and +10 mm showed 26, 29, and 30, dislocations, respectively. Dislocation via pull on the infraspinatus muscle was most frequent. None of the results reached statistical significance. Conclusion The current investigation used a novel technique for investigating the effect of lateralization and glenosphere diameter on RSA instability. Despite indicating tendencies, the present test setup could not prove the hypothesis that a larger glenosphere diameter and increased lateralization add to stability. The lack of statistical significance could be attributable to the low specimen number. The clinical significance of lateralization and glenosphere diameter should be further assessed in future biomechanical investigations.

Age‐related site‐specific modifications in diaphyseal structural properties of the human fibula: Furrows and cross‐sectional geometry

Fibular structure is related to locomotor behavior, which allows an exploration of mobility in past human populations with diaphyseal cross-sectional geometry (CSG). However, bone structure depends on age-related changes. Nonmechanical alterations can affect biomechanical investigations. In this study, we examined how the cortical area and the variables used as functional markers in the fibular diaphysis (i.e., CSG and furrows) change with aging. We predict classic and specific modifications, and we discuss functional interpretations based on bone structure. The sample consisted of 124 individuals of known age in whom the fibular furrow depths were measured with calipers. Microcomputed tomography (micro-CT) scanning of 38 individuals provided CSG (e.g., cortical area, shape index, and robusticity) and fibular furrow indices. CSG was studied at five cross sections taken along the diaphysis. Linear regression analyses and age group comparisons were conducted. The cross-sectional shape summary by fibular furrows and shape index and the total area did not change with aging; in contrast, the cortical area and the robusticity (Zp-std) decreased with age. The decrease in robusticity (Zp-std) with aging is due to the maintenance of total area, which is related to the specific mechanical environment of the fibula, and to the loss of cortical bone and not to the decrease in mechanical stress. This finding is consistent with the lower bone modeling capacity in aged individuals, which also explains the lack of significant changes in the diaphyseal shape. Thus, fibular structure in older individuals is due to a combination of early bone adaptations to stress and aging effects.

Biomechanical effects of posterior pedicle screw-based instrumentation using titanium versus carbon fiber reinforced PEEK in an osteoporotic spine human cadaver model

BackgroundAim of this biomechanical investigation was to compare the biomechanical effects of a carbon fiber reinforced PEEK and titanium pedicle screw/rod device in osteoporotic human cadaveric spine. MethodsTen human fresh-frozen cadaveric lumbar spines (L1-L5) have been used and were randomized into two groups according to the bone mineral density. A monosegmental posterior instrumentation (L3-L4) using titanium pedicle screws and rods was carried out in group A and using carbon fiber reinforced PEEK in group B. A cyclic loading test was performed at a frequency of 3 Hz, starting with a peak of 500 N for the first 2000 cycles, up to 950 N for 100,000 cycles under a general preload with 100 N. All specimens were evaluated with regard to a potential collapse of the implanted pedicle screws. A CT supported digital measurement of cavities around the pedicle at 3 defined measuring points was performed. Finally, the maximum zero-time failure load of all specimens was determined using a universal testing machine (80% Fmax). FindingsRegarding maximum axial force (group A: 2835 N, group B: 3006 N, p = 0.595) and maximum compression (group A: 11.67 mm, group B: 15.15 mm, p = 0.174) no statistical difference could be shown between the two groups. However, significant smaller cavity formation around the pedicle screws could be observed in group B (p = 0.007), especially around the screw tip (p < 0.001). InterpretationCarbon fiber reinforced PEEK devices seem to be advantageous in terms of microscopic screw loosening compared to titanium devices.

Biomechanical and biochemical investigation of erythrocytes in late stage human leptospirosis.

Leptospirosis is a zoonotic disease caused by bacteria of the genus Leptospira, which can cause lipid changes in the erythrocyte membrane. Optical tweezers were used to characterize rheological changes in erythrocytes from patients with leptospirosis in the late stage. Biochemical methods were also used for quantification of plasma lipid, erythrocyte membrane lipid, and evaluation of liver function. Our data showed that the mean elastic constant of erythrocytes from patients with leptospirosis was around 67% higher than the control (healthy individuals), indicating that patient’s erythrocytes were less elastic. In individuals with leptospirosis, several alterations in relation to control were observed in the plasma lipids, however, in the erythrocyte membrane, only phosphatidylcholine showed a significant difference compared to control, increasing around 41%. With respect to the evaluation of liver function of individuals with leptospirosis, there was a significant increase in levels of alanine transaminase (154%) and aspartate transaminase (150%), whereas albumin was 43.8% lower than control (P<0.01). The lecithin-cholesterol acyltransferase fractional activity was 3.6 times lower in individuals with leptospirosis than in the healthy individuals (P<0.01). The decrease of the erythrocyte elasticity may be related to the changes of erythrocyte membrane phospholipids composition caused by disturbances that occur during human leptospirosis, with phosphatidylcholine being a strong candidate in the erythrocyte rheological changes.

Role of Platelet Cytoskeleton in Platelet Biomechanics: Current and Emerging Methodologies and Their Potential Relevance for the Investigation of Inherited Platelet Disorders.

Cytoskeleton is composed of more than 100 proteins and represents a dynamic network of the cellular cytoplasm. Cytoskeletal functions include spatial organization of cellular components, structural connection of the cell with external environment, and biomechanical force generation. Cytoskeleton takes part, at different levels, in all phases of platelet biogenesis: megakaryocyte (MK) differentiation, MK maturation, and platelet formation. In addition, it also plays a major role in each stage of platelet function. Inherited platelet disorders (IPDs) are a group of rare diseases featured by low platelet count and/or impaired platelet function. Over the past decade, the investigation of platelet biomechanics has become a major and highly relevant theme of research due to its implications at every stage of development of human life. The initial use of diverse biophysical techniques (e.g., micropipette aspiration, atomic force and scanning ion conductance microscopy, real-time deformability cytometry) started unraveling biomechanical features of platelets that are expected to provide new explanations for physiological and pathological mechanisms. Although the impact of cytoskeletal alterations has been largely elucidated in various IPDs' pathogenesis, the understanding of their impact on biomechanical properties of platelets represents an unmet need. Regarding IPDs, improving biomechanical studies seems promising for diagnostic and prognostic implications. Potentially, these characteristics of platelets may also be used for the prediction of bleeding risk. This review addresses the current available methods for biophysical investigations of platelets and the possible implementations in the field of IPDs.

Differences in gait analysis and clinical outcome after TightRope\xae or screw fixation in acute syndesmosis rupture: study protocol for a prospective randomized pilot study

BackgroundAnkle sprains and fractures are most common injuries in orthopedic and trauma surgery. The concurrent occurrence of syndesmosis ruptures in these injuries represents a more complex problem, as they often remain undetected.A proper and accurate treatment of injuries of the syndesmosis, both isolated and combined with fractures, is necessary to avoid long-term consequences (chronic instability, cartilage damage, and post-traumatic osteoarthritis). The most popular treatment option is a static screw fixation and the newly developed dynamic TightRope® (Arthrex, Naples, FL, USA).The aim of this pilot study is to compare monitor ankle range of motion and maximum ankle power in gait as functional outcome parameters of instrumented gait analysis, as well as clinical and radiographic outcome for assessing the stabilization of acute syndesmosis rupture with either a static implant (a 3.5 mm metallic screw) or a dynamic device (TightRope®).MethodsThis prospective, randomized, controlled, clinical trial will be carried out at the Center for Orthopedics, Trauma Surgery and Spinal Cord Injury of the University Hospital Heidelberg. Adult patients, who suffer from an acute syndesmosis rupture, both isolated and in combination with fractures of the lateral malleolus (Weber C and Maisonneuve fractures) and who are undergoing surgery at our trauma center will be included in our study. The patients will be randomized to the different treatment options (screw fixation or “TightRope®”). Subsequent to the surgical treatment, all patients will receive the same standardized follow-up procedures including a gait analysis and MRI of the ankle at 6 months follow-up.The primary endpoint of the study is the successful healing of the syndesmosis and biomechanical investigation with gait analysis.DiscussionThe results of the gait analysis from the current study will help to impartially and reliably evaluate the clinical and biomechanical outcome of both treatment options of acute syndesmosis ruptures. We hypothesize that the dynamic fixation provides an equivalent or better biomechanical, clinical, and radiographic outcome in comparison to the screw fixation.Trial registrationGerman Clinical Trials Register (DRKS) DRKS00013562. Registered on July, 12, 2017.

Prediction of track performance in competitive BMX riders using laboratory measures

Identifying key physiological factors is essential in cycling; however, the unique nature of BMX decreases the validity and transferability of research findings from other cycling disciplines. Therefore, this study highlighted the physical and physiological characteristics of BMX riders that could influence track performance. Fifteen sub-elite BMX riders (male n = 12; age 18.3 ± 3.3 and female n = 3; 17.7 ± 5.7 years) undertook a battery of laboratory tests on three different occasions, including body composition, upper and lower body strength, flexibility, sprint and aerobic capacity measures. On a separate day, participants completed three full lap sprints on an outdoor BMX track. Correlation and multiple linear regression analyses were performed to develop predictive models of performance across the laboratory tests and race time. The final model indicated power to weight ratio, relative back-leg-chest strength and arm span explained ~87% of the variability in finish time (adjusted R2 = 0.87, p &lt; .01). These findings highlighted the importance of a multidimensional approach for developing BMX race performance. Coaches should prioritise these variables in their training programs and selection of future talents. However, further physiological and biomechanical investigation is needed to validate current findings, particularly among elite riders.

Biomechanical investigation of the effect of pedicle-based hybrid stabilization constructs: A finite element study.

Hybrid stabilization is widely performed for the surgical treatment of degenerative disk diseases. Pedicle-based hybrid stabilization intends to reduce fusion-associated drawbacks of adjacent segment degeneration, construct failure, and pseudoarthrosis. Recently, many types of pedicle-based hybrid stabilization systems have been developed and optimized, using polymeric devices as an adjunct for lumbar fusion procedures. Therefore, the purpose of this study was to evaluate the effect of new pedicle-based hybrid stabilization on bending stiffness and center of rotation at operated and adjacent levels in comparison with established semirigid and rigid devices in lumbar fusion procedures. A validated three-dimensional finite element model of the L3-S1 segments was modified to simulate postoperative changes during combined loading (moment of 7.5 N m + follower load of 400 N). Two models instrumented with pedicle-based hybrid stabilization (Dynesys Transition Optima, NFlex), semirigid system (polyetheretherketone), and rigid fixation system (titanium rod (Ti) were compared with those of the healthy and degenerated models. Contact force on the facet joint during extension increased in fusion (40 N) with an increase of bending stiffness in Dynesys and NFlex. The center of rotation shifted in posterior and cranial directions of the fused level. The centers of rotation in the lower lumbar spine is segment dependent and altered with the adopted construct. The bending stiffness was varied from 1.47 N m/° in lateral bending for the healthy model to 5.75 N m/° for the NFlex stabilization, which had the closest center of rotation, compared to the healthy center of rotation. Locations of center of rotation, stress, and strain distribution varied according to construct design and materials used. These data could help understand the biomechanical effects of current pedicle-based hybrid stabilization on the behavior of the lower lumbar spine.

Influence of foot posture on immediate biomechanical responses during walking to variable-stiffness supported lateral wedge insole designs

BackgroundNovel designs of lateral wedge insoles with arch support can alter walking biomechanics as a conservative treatment option for knee osteoarthritis. However, variations in foot posture may influence individual responses to insole intervention and these effects are not yet known. Research questionHow does foot posture influence biomechanical responses to novel designs of lateral wedge insoles with arch support? MethodsThis exploratory biomechanical investigation categorized forty healthy volunteers (age 23–34) into pronated (n = 16), neutral (n = 15), and supinated (n = 9) foot posture groups based on the Foot Posture Index. Three-dimensional gait analysis was conducted during walking with six orthotic insole conditions: flat control, lateral wedge, uniform-stiffness arch support, variable-stiffness arch support, and lateral wedge + each arch support. Frontal plane knee and ankle/subtalar joint kinetic and kinematic outcomes were compared among insole conditions and foot posture groups using a repeated measures analysis of variance. ResultsThe lateral wedge alone and lateral wedge + variable-stiffness arch support were the only insole conditions effective at reducing the knee adduction moment. However, the lateral wedge + variable-stiffness arch support had a smaller increase in peak ankle/subtalar eversion moment than the lateral wedge alone. Supinated feet had smaller ankle/subtalar eversion excursion and moment impulse than neutral and pronated feet, across all insole conditions. SignificanceSupinated feet have less mobile ankle/subtalar joints than neutral and pronated feet and, as a result, may be less likely to respond to biomechanical intervention from orthotic insoles. Supported lateral wedge insoles incorporating an arch support design that is variable-stiffness may be better than uniform-stiffness since reductions in the knee adduction moment can be achieved while minimizing increases in the ankle/subtalar eversion moment.

Variable Fixation Technology Provides Rigid as Well as Progressive Dynamic Fixation: A Biomechanical Investigation.

A new locking-screw technology, the Variable Fixation Locking Screw (VFLS; Biomech Innovations), was developed with the aim of promoting secondary fracture-healing. The VFLS features a resorbable sleeve that progressively decreases its mechanical properties and mass during the fracture-healing time. In this study, we investigated whether the VFLS can provide rigid as well as progressive dynamic fixation. The interfragmentary stability provided by the VFLS was tested in a simulated fracture-gap model and compared with that provided by standard locking or by a combination of both technologies under compression and torsional loading. Tests were performed with an intact sleeve (initial condition) and after its chemical dissolution. An optical measurement system was used to characterize interfragmentary movements. The axial stiffness did not differ significantly among groups in the initial condition. Sleeve resorption significantly decreased construct stiffness. The torsional stiffness of the samples instrumented with the VFLS was lower than that of the control group. The degradation of the sleeve resulted in a significant increase in axial displacement recorded at both the cis and trans cortices. In samples featuring combined technologies, this increase was about 12% to 20% at the trans cortex and about 50% to 60% at the cis cortex. In samples featuring VFLS technology only, this increase was about 20% to 37% at the trans cortex and about 70% to 125% at the cis cortex. The initial stability offered by the VFLS is equivalent to that of standard locking-screw technology. The resorption of the degradable sleeve leads to effective and reproducible fracture-gap dynamization, progressively varying the way the fracture gap is strained and the magnitude of the strain. The VFLS provides rigid and progressive dynamic fixation in vitro. Such variable stability might have beneficial effects in terms of triggering and boosting secondary fracture-healing.

The role of biceps loading and muscle activation on radial head stability in anterior Monteggia injuries: An in vitro biomechanical study

IntroductionLittle evidence-based information is available to direct the optimal rehabilitation of patients with anterior Monteggia injuries. Purpose of the StudyThe aims of this biomechanical investigation were to (1) quantify the effect of biceps loading and (2) to compare the effect of simulated active and passive elbow flexion on radial head stability in anterior Monteggia injuries. Study DesignIn vitro biomechanical study. MethodsSix cadaveric arms were mounted in an elbow motion simulator. The effect of biceps loading, simulated active and passive elbow flexion motions was examined with application of 0N, 20N, 40N, 60N, 80N, and 100N of load. Simulated active and passive elbow flexion motions were then performed with the forearm supinated. Radial head translation relative to the capitellum was measured using an optical tracking system. After testing the intact elbows, the proximal ulna was osteotomized and realigned using a custom jig to simulate an anatomical reduction. We then sequentially sectioned the anterior radiocapitellar joint capsule, annular ligament, quadrate ligament, and the proximal and middle interosseous membrane to simulate soft tissue injuries commonly associated with anterior Monteggia fractures. ResultsGreater magnitudes of biceps loading significantly increased anterior radial head translation. However, there was no significant difference in radial head translation between simulated active and passive elbow flexion except in the final stage of soft tissue sectioning. There was a significant increase in anterior radial head translation with progressive injury states with both isometric biceps loading and simulated active and passive motion. ConclusionsOur results demonstrate that anatomic reduction of the ulna may not be sufficient to restore radial head alignment in anterior Monteggia injuries with a greater magnitude of soft tissue injury. In cases with significant soft tissue injury, the elbow should be immobilized in a flexed and supinated position to allow relaxation of the biceps and avoid movement of the elbow in the early postoperative period.

A COUPLED EXPERIMENTAL AND NUMERICAL APPROACH TO CHARACTERIZE THE ANISOTROPIC MECHANICAL BEHAVIOR OF AORTIC TISSUES

Nowadays, the investigation of aortic wall biomechanics is a fundamental tool in clinical research and vascular prosthesis design. This study aims at analyzing the biomechanical behavior of aortic tissues using a coupled experimental and computational approach. Considering the typical fiber-reinforced configuration of aortic tissues, uni-axial tensile tests along six different loading directions were performed on specimens from pig aorta. Starting from the obtained experimental data, a suitable constitutive framework was defined and a methodology for the identification of the constitutive parameters was developed using the inverse analysis of mechanical tests. Transversal stretch versus loading stretch and nominal stress versus loading stretch curves were evaluated, showing the anisotropic and nonlinear mechanical behavior determined by tissue conformation with fibers distributed along preferential directions. In detail, experimental data showed different mechanical responses between longitudinal and circumferential directions, with a greater tissue stiffness along the longitudinal one. The reliability of the developed constitutive framework was evaluated by the comparison between experimental data and model results. The mentioned analysis can be considered as a useful tool for the development of reliable computational models, which allow a better understanding of the pathophysiology of cardiovascular diseases and can be applied for a proper planning of surgical procedures.

Biomechanical effects of screw orientation and plate profile on tibial condylar valgus osteotomy - Finite-element analysis

Tibial condylar valgus osteotomy (TCVO) is a type of open wedge high tibial osteotomy for correcting intra-articular deformities of medial knee osteoarthritis. However, there are no implant design and related biomechanical investigations specifically for TCVO. This study aims to investigate the effects of the proximal screw direction and plate profile on the biomechanical behaviors of the TCVO construct. Based on computed tomography images, the tibia model with TCVO was simulated. Four variations (straight and contoured plate profile × convergent and divergent proximal screw direction) with two loading conditions (compressive loads and torsional load) were compared by finite-element method. Fracture risk and construct stability were chosen as the comparison indices. For both loading conditions, the fracture risk of screw, plate and bone was the lowest in straight plate with divergent screw direction (SD), while contoured plate with convergent screw direction (CC) was the highest. Similar results were found in construct stability, SD allowed the smallest micromotions of the L-shaped opening gap, but CC allowed the highest. Divergent screw direction can decrease fracture risk of all components and provide better construct stability, while contoured plate profile seems like to have converse effects. If stability is the major concern, straight plate with divergent screw is recommended for patients with heavy load demands. Contoured plate may be suitable for skinny patients that can reduce the soft tissue irritation.

Computational Biomechanics: In-Silico Tools for the Investigation of Surgical Procedures and Devices.

Biomechanical investigations of surgical procedures and devices are usually developed by means of human or animal models. The exploitation of computational methods and tools can reduce, refine, and replace (3R) the animal experimentations for scientific purposes and for pre-clinical research. The computational model of a biological structure characterizes both its geometrical conformation and the mechanical behavior of its building tissues. Model development requires coupled experimental and computational activities. Medical images and anthropometric information provide the geometrical definition of the computational model. Histological investigations and mechanical tests on tissue samples allow for characterizing biological tissues’ mechanical response by means of constitutive models. The assessment of computational model reliability requires comparing model results and data from further experimentations. Computational methods allow for the in-silico analysis of surgical procedures and devices’ functionality considering many different influencing variables, the experimental investigation of which should be extremely expensive and time consuming. Furthermore, computational methods provide information that experimental methods barely supply, as the strain and the stress fields that regulate important mechano-biological phenomena. In this work, general notes about the development of biomechanical tools are proposed, together with specific applications to different fields, as dental implantology and bariatric surgery.