The resistance of goose (Anser anser f. domestica) eggs to damage was determined by measuring the average rupture force, specific deformation and rupture energy during their compression at different compression speeds (0.0167, 0.167, 0.334, 1.67, 6.68 and 13.36 mm/s). Eggs have been loaded between their poles (along X axis) and in the equator plane (Z axis). The greatest amount of force required to break the eggs was required when eggs were loaded along the X axis and the least compression force was required along the Z axis. This effect of the loading orientation can be described in terms of the eggshell contour curvature. The rate sensitivity of the eggshell rupture force is higher than that observed for the Japanese quail's eggs.

• MeSH
• biomechanika MeSH
• husy * MeSH
• pevnost v tlaku * MeSH
• povrchové vlastnosti MeSH
• testování materiálů * MeSH
• vaječná skořápka MeSH
• vejce * MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

PURPOSE: Investigation of trabecular bone strength and compaction is important for fracture risk prediction. At 1-2% compressive strain, trabecular bone undergoes strain softening, which may lead to numerical instabilities and mesh dependency in classical local damage-plastic models. The aim of this work is to improve our continuum damage-plastic model of bone by reducing the influence of finite element mesh size under large compression. METHODOLOGY: This spurious numerical phenomenon may be circumvented by incorporating the nonlocal effect of cumulated plastic strain into the constitutive law. To this end, an over-nonlocal implicit gradient model of bone is developed and implemented into the finite element software ABAQUS using a user element subroutine. The ability of the model to detect the regions of bone failure is tested against experimental stepwise loading data of 16 human trabecular bone biopsies. FINDINGS: The numerical outcomes of the nonlocal model revealed reduction of finite element mesh dependency compared with the local damage-plastic model. Furthermore, it helped reduce the computational costs of large-strain compression simulations. ORIGINALITY: To the best of our knowledge, the proposed model is the first to predict the failure and densification of trabecular bone up to large compression independently of finite element mesh size. The current development enables the analysis of trabecular bone compaction as in osteoporotic fractures and implant migration, where large deformation of bone plays a key role.

• MeSH
• algoritmy MeSH
• biologické modely * MeSH
• biomechanika fyziologie   MeSH
• fraktury kostí MeSH
• kosti a kostní tkáň fyziologie   MeSH
• lidé MeSH
• pevnost v tlaku fyziologie   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Biophysical loading of the elbow and wrist is a potential reason for chronic lesions in gymnastics and present a real concern for coaches, scientist and clinicians. Previous research has identified injury risk factors during round-off (RO) skills in elite female gymnasts. The aim of this study was to investigate key elbow and wrist joint injury risk factors during different techniques of fundamental cartwheel (CW) and RO skills performed by young female artistic gymnasts. Seventeen active young female gymnasts performed 30 successful trials of both CW and RO from a hurdle step with three different hand positions (parallel (10), T-shape (10) and reverse (10)). Synchronised kinematic (240 Hz) and kinetic (1200 Hz) data were collected for each trial. One-way repeated measures ANOVA and effect size (ES) were used for statistical analysis. The results showed statistically significant differences (P < .05) and large ES (>0.8) among hand positions for peak vertical ground reaction force (VGRF), peak elbow compression force, peak wrist compression force, elbow internal adduction moment and wrist dorsiflexion angle. In conclusion, the parallel and reverse techniques increase peak VGRF, elbow and wrist compression forces, and elbow internal adduction moment. These differences indicate that the parallel and reverse techniques may increase the potential of elbow and wrist injuries in young gymnasts compared with the T-shape technique; this is of particular importance with the high frequency of the performance of these fundamental skills.

• MeSH
• biomechanika MeSH
• dítě MeSH
• gymnastika fyziologie   MeSH
• lidé MeSH
• loketní kloub fyziologie   MeSH
• poranění lokte MeSH
• poranění z opakovaného přetěžování MeSH
• poranění zápěstí MeSH
• rizikové faktory MeSH
• sportovci MeSH
• sportovní úrazy MeSH
• zápěstní kloub fyziologie   MeSH
• zatížení muskuloskeletálního systému * MeSH
• Check Tag
• dítě MeSH
• lidé MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH

OBJECTIVE: To evaluate and compare the viscoelastic properties of dentine and resin-based dental materials by bulk compressive test and the Burgers model. MATERIALS AND METHODS: Sound dentine, three resin composites as well as a resin-based cement were prepared into cylindrical specimens (n = 8). A bulk compressive creep test was applied with a constant load of 300 N (23.9 MPa) for 2 h, followed by another 2 h recovery. The maximum strain, creep stain, percentage of recovery and permanent set was measured using a linear variable displacement transducer. The viscoelastic properties were characterized via the Burgers model, and the instantaneous elastic, viscous as well as elastic delayed deformation were separated from the total strain. Data were analysed via ANOVA (or Welch's Test) and Tukey (or Games-Howell Test) with a significance level of 0.05. RESULTS: Sound dentine presented the lowest maximum strain, creep strain, permanent set and the highest percentage of recovery, followed by 3 resin composites with comparable parameters, while the cement showed a significantly higher maximum strain, permanent set and lower percentage of recovery (p < 0.001). The Burgers model presented acceptable fits for characterization viscoelastic processes of both dentine and resin-based dental materials. Viscous and elastic delayed strain of dentine was significantly lower than those for tested materials (p < 0.001) with the highest instantaneous elastic strain percentage. Similar viscous and delayed strain was found among the 4 resin-based materials (p > 0.05). SIGNIFICANCE: Sound dentine exhibited superior creep stability compared to resin-based dental materials. The viscous deformation in sound dentine could be ignored when loading parallel to dentine tubules.

• MeSH
• analýza zatížení zubů MeSH
• dentin MeSH
• lidé MeSH
• pružnost MeSH
• složené pryskyřice * MeSH
• testování materiálů MeSH
• zubní materiály * MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

• MeSH
• biomechanika účinky záření   statistika a číselné údaje   MeSH
• chondrocyty fyziologie   patologie   MeSH
• finanční podpora výzkumu jako téma MeSH
• kloubní chrupavka anatomie a histologie   fyziologie   MeSH
• lidé MeSH
• tělesná námaha fyziologie   MeSH
• Check Tag
• lidé MeSH

Osseointegration is paramount for the longevity of dental implants and is significantly influenced by biomechanical stimuli. The aim of the present study was to assess the micro-strain and displacement induced by loaded dental implants at different stages of osseointegration using finite element analysis (FEA). Computational models of two mandible segments with different trabecular densities were constructed using microCT data. Three different implant loading directions and two osseointegration stages were considered in the stress-strain analysis of the bone-implant assembly. The bony segments were analyzed using two approaches. The first approach was based on Mechanostat strain intervals and the second approach was based on tensile/compression yield strains. The results of this study revealed that bone surrounding dental implants is critically strained in cases when only a partial osseointegration is present and when an implant is loaded by buccolingual forces. In such cases, implants also encounter high stresses. Displacements of partially-osseointegrated implant are significantly larger than those of fully-osseointegrated implants. It can be concluded that the partial osseointegration is a potential risk in terms of implant longevity.

• MeSH
• analýza metodou konečných prvků MeSH
• analýza zatížení zubů metody   MeSH
• biologické modely * MeSH
• biomechanika MeSH
• lidé MeSH
• mandibula fyziologie   MeSH
• mechanický stres MeSH
• osteointegrace fyziologie   MeSH
• počítačové zpracování signálu MeSH
• rentgenová mikrotomografie MeSH
• zubní implantáty * MeSH
• Check Tag
• lidé MeSH
• mužské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Due to the internal structure of the knee joint, the ability to characterize and quantify the dynamic response of the meniscal tissue directly in vivo is highly problematic. The main purpose of this study was to investigate the behaviour of the meniscus under loading conditions. Four healthy young females were included. To obtain T2* values in the meniscus, the vTE sequence was used with 10 echoes ranging from 0.8 to 10.1 ms. Submilisecond first echo time is a great advantage of vTE sequence allowing for precise mapping of relatively short T2*. The two-parametric least squares fitting procedure was used to calculate T2* pixel-wise. A custom-made diamagnetic apparatus was developed to simulate stress conditions on the lower limb in a conventional MR scanner. vTE T2* was performed in five consecutive scans, 6:10 min apart. Three different compartments of the medial and lateral meniscus were segmented. The differences at the different time-points were calculated. A constant increase of T2* times after compression was statistically significant in the anterior horn of the medial meniscus. T2* mapping with variable echo time sequence might be a satisfactorily sensitive technique to detect the changes of meniscus physiology under loading conditions in vivo.

• MeSH
• dospělí MeSH
• kloubní chrupavka * diagnostické zobrazování   MeSH
• kolenní kloub MeSH
• lidé MeSH
• magnetická rezonanční tomografie metody   MeSH
• menisky tibiální * diagnostické zobrazování   fyziologie   MeSH
• zátěžový test * MeSH
• zobrazování trojrozměrné MeSH
• Check Tag
• dospělí MeSH
• lidé MeSH
• ženské pohlaví MeSH
• Publikační typ
• kazuistiky MeSH
• práce podpořená grantem MeSH

The aim of the study was to determine if sex differences exist in the key elbow and wrist joint injury risk factors during different cartwheel (CW) and round-off (RO) techniques performed by young male and female artistic gymnasts. Sixteen active young gymnasts (8 males and 8 females) performed 30 successful trials of CW and RO with three different hand positions (parallel (10), T-shape (10) and reverse (10)). Synchronised kinematic and kinetic data were collected for each trial. Two-way repeated measures ANOVA (3 × 2, technique × sex) and effect-sizes (ES) were used for statistical analysis. In conclusion, female gymnasts exhibited greater normalised peak vertical ground reaction forces (VGRF), elbow and wrist compression forces and elbow internal adduction moments during CW and RO skills compared with male gymnasts. In both sexes, the parallel and reverse techniques increased peak VGRF, elbow and wrist compression forces and the elbow internal adduction moment. Increased elbow flexion resulted in decreased peak VGRF, elbow compression forces and elbow internal adduction moment. Injury risk factors including elbow extension and internal adduction moment with axial compression force suggest that a CW and RO in reverse and parallel techniques can be hazardous especially for young female gymnasts.

• MeSH
• biomechanika MeSH
• dítě MeSH
• gymnastika zranění   fyziologie   MeSH
• kinetika MeSH
• lidé MeSH
• loketní kloub fyziologie   MeSH
• motorické dovednosti fyziologie   MeSH
• poranění lokte MeSH
• poranění zápěstí patofyziologie   MeSH
• rizikové faktory MeSH
• sexuální faktory MeSH
• studie pohybu a času MeSH
• zápěstní kloub fyziologie   MeSH
• Check Tag
• dítě MeSH
• lidé MeSH
• mužské pohlaví MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH

OBJECTIVE: Translation of the contact zone in articulating joints is an important component of joint kinematics, yet rarely investigated in a biological context. This study was designed to investigate how sliding contact areas affect cartilage mechanobiology. We hypothesized that higher sliding speeds would lead to increased extracellular matrix mechanical stress and the expression of catabolic genes. DESIGN: A cylindrical Teflon indenter was used to apply 50 or 100 N normal forces at 10, 40, or 70 mm/s sliding speed. Mechanical parameters were correlated with gene expressions using a multiple linear regression model. RESULTS: In both loading groups there was no significant effect of sliding speed on any of the mechanical parameters (strain, stress, modulus, tangential force). However, an increase in vertical force (from 50 to 100 N) led to a significant increase in extracellular matrix strain and stress. For 100 N, significant correlations between gene expression and mechanical parameters were found for TIMP-3 (r(2) = 0.89), ADAMTS-5 (r(2) = 0.73), and lubricin (r(2) = 0.73). CONCLUSIONS: The sliding speeds applied do not have an effect on the mechanical response of the cartilage, this could be explained by a partial attainment of the "elastic limit" at and above a sliding speed of 10 mm/s. Nevertheless, we still found a relationship between sliding speed and gene expression when the tissue was loaded with 100 N normal force. Thus despite the absence of speed-dependent mechanical changes (strain, stress, modulus, tangential force), the sliding speed had an influence on gene expression.

• Publikační typ
• časopisecké články MeSH

PURPOSE OF THE STUDY The study aimed to draw up a diagnosis and treatment guidelines for the management of the most common compression fractures of the thoracolumbar spine in children. MATERIAL AND METHODS Between 2015 and 2017, pediatric patients with a thoracolumbar injury aged 0-12 years were followed up in the University Hospital in Motol and the Thomayer University Hospital. The age and gender of the patient, injury etiology, fracture morphology, number of injured vertebrae, functional outcome (VAS and ODI modified for children), and complications were assessed. An X-ray was performed in all patients, in indicated cases also an MRI scan was done, and in more severe cases a CT scan was obtained as well. RESULTS The average vertebral body kyphosis in patients with one injured vertebra was 7.3° (range 1.1°-12.5°). The average vertebral body kyphosis in patients with two injured vertebrae was 5.5° (range 2.1°-12.2°). The average vertebral body kyphosis in patients with more than two injured vertebrae was 3.8° (range 0.2°-11.5°). All patients were treated conservatively in line with the proposed protocol. No complications were observed, no deterioration of the kyphotic shape of the vertebral body was reported, no instability occurred, and no surgical intervention had to be considered. DISCUSSION Pediatric spine injuries are in most cases treated conservatively. Surgical treatment is opted for in 7.5-18% of cases, in dependence on the evaluated group of patients, age of the patients and philosophy of the department concerned. In our group, all patients were treated conservatively. CONCLUSIONS 1. To diagnose F0 fractures, two unenhanced orthogonal view X-rays are indicated, whereas MRI examination is not routinely performed. In F1 fractures, an X-ray is indicated, and an MRI scan is considered based on the age and extent of injury. In F2 and F3 fractures, an X-ray is indicated and subsequently the diagnosis is confirmed by MRI, in F3 fractures also a CT scan is performed. 2. In young children (under 6 years of age), in whom an MRI procedure would require general anaesthesia, MRI is not routinely performed. 3. In F0 fractures, crutches or a brace are not indicated. In F1 fractures, verticalization using crutches or a brace is considered in dependence on the patient's age and extent of injury. In F2 fractures, verticalization using crutches or a brace is indicated. 4. In F3 fractures, surgical treatment is considered, followed by verticalization using crutches or a brace. In case of conservative treatment, the same procedures as in F2 fractures are applied. 5. Long-term bed rest is contraindicated. 6. Duration of spinal load reduction (restriction of sports activities, or verticalization using crutches or a brace) in F1 injuries is 3-6 weeks based on the age of the patient, it increases with the age, with the minimum being 3 weeks. 7. Duration of spinal load reduction (verticalization using crutches or a brace) in F2 and F3 injuries is 6-12 weeks based on the age of the patient, it increases with the age, with the minimum being 6 weeks. Key words: pediatric spine injury, thoracolumbar compression fractures, children trauma treatment.

• MeSH
• bederní obratle diagnostické zobrazování   chirurgie   MeSH
• dítě MeSH
• fraktury páteře * diagnostické zobrazování   etiologie   MeSH
• hrudní obratle diagnostické zobrazování   chirurgie   MeSH
• kojenec MeSH
• kompresivní fraktury * diagnostické zobrazování   etiologie   MeSH
• kyfóza * chirurgie   MeSH
• lidé MeSH
• novorozenec MeSH
• předškolní dítě MeSH
• výsledek terapie MeSH
• Check Tag
• dítě MeSH
• kojenec MeSH
• lidé MeSH
• novorozenec MeSH
• předškolní dítě MeSH
• Publikační typ
• anglický abstrakt MeSH
• časopisecké články MeSH