Sample size considerations in soft tissue biomechanics.

Biomechanical experiments help link tissue morphology with load-deformation characteristics. A tissue-dependent minimum sample number is indispensable to obtain accurate material properties. Stress-strain properties were retrieved from human dura mater and scalp skin, exemplifying two distinct soft tissues. Minimum sample sizes necessary for a stable estimation of material properties were obtained in a simulation study. One-thousand random samples were sequentially drawn for calculating the point at which a majority of the estimators settled within a corridor of stability at given tolerance levels around a 'complete' reference for the mean, median and coefficient of variation. Stable estimations of means and medians can be achieved below sample sizes of 30 at a ± 20%-tolerance within 80%-conformity for scalp skin and dura. Lower tolerance levels or higher conformity dramatically increase the required sample size. Conformity was barely ever reached for the coefficient of variation. The parameter type appears decisive for achieving conformity. STATEMENT OF SIGNIFICANCE: Biomechanical trials utilizing human tissues are needed to obtain material properties for surgical repair, tissue engineering and modeling purposes. Linking tissue mechanics with morphology helps elucidate form-function relationships, the 'morpho-mechanical link'. For material properties to be accurate, it is vital to examine a minimum number of samples. This number may vary between tissues, and the effects of intrinsic tissue characteristics on data accuracy are unclear to date. This study used data obtained from human dura and skin to compute minimum sample sizes required for estimating material properties at a stable level. It was shown that stable estimations are possible at a ± 20%-tolerance within 80%-conformity below sample sizes of 30. Higher accuracy warrants much higher sample sizes for most material properties.

The dynamic impact behavior of the human neurocranium.

Realistic biomechanical models of the human head should accurately reflect the mechanical properties of all neurocranial bones. Previous studies predominantly focused on static testing setups, males, restricted age ranges and scarcely investigated the temporal area. This given study determined the biomechanical properties of 64 human neurocranial samples (age range of 3 weeks to 94 years) using testing velocities of 2.5, 3.0 and 3.5 m/s in a three-point bending setup. Maximum forces were higher with increasing testing velocities (p ≤ 0.031) but bending strengths only revealed insignificant increases (p ≥ 0.052). The maximum force positively correlated with the sample thickness (p ≤ 0.012 at 2.0 m/s and 3.0 m/s) and bending strength negatively correlated with both age (p ≤ 0.041) and sample thickness (p ≤ 0.036). All parameters were independent of sex (p ≥ 0.120) apart from a higher bending strength of females (p = 0.040) for the 3.5 -m/s group. All parameters were independent of the post mortem interval (p ≥ 0.061). This study provides novel insights into the dynamic mechanical properties of distinct neurocranial bones over an age range spanning almost one century. It is concluded that the former are age-, site- and thickness-dependent, whereas sex dependence needs further investigation.

Topographical mapping of the mechanical characteristics of the human neurocranium considering the role of individual layers.

The site-dependent load-deformation behavior of the human neurocranium and the load dissipation within the three-layered composite is not well understood. This study mechanically investigated 257 human frontal, temporal, parietal and occipital neurocranial bone samples at an age range of 2 to 94 years, using three-point bending tests. Samples were tested as full-thickness three-layered composites, as well as separated with both diploë attached and removed. Right temporal samples were the thinnest samples of all tested regions (median < 5 mm; p < 0.001) and withstood lowest failure loads (median < 762 N; p < 0.001). Outer tables were thicker and showed higher failure loads (median 2.4 mm; median 264 N) than inner tables (median 1.7 mm, p < 0.001; median 132 N, p = 0.003). The presence of diploë attached to outer and inner tables led to a significant reduction in bending strength (with diploë: median < 60 MPa; without diploë: median > 90 MPa, p < 0.001). Composites (r = 0.243, p = 0.011) and inner tables with attached diploë (r = 0.214, p = 0.032) revealed positive correlations between sample thickness and age. The three-layered composite is four times more load-resistant compared to the outer table and eight times more compared to the inner table.

Biomechanical characterization of human temporal muscle fascia in uniaxial tensile tests for graft purposes in duraplasty.

The human temporal muscle fascia (TMF) is used frequently as a graft material for duraplasty. Encompassing biomechanical analyses of TMF are lacking, impeding a well-grounded biomechanical comparison of the TMF to other graft materials used for duraplasty, including the dura mater itself. In this study, we investigated the biomechanical properties of 74 human TMF samples in comparison to an age-matched group of dura mater samples. The TMF showed an elastic modulus of 36 ± 19 MPa, an ultimate tensile strength of 3.6 ± 1.7 MPa, a maximum force of 16 ± 8 N, a maximum strain of 13 ± 4% and a strain at failure of 17 ± 6%. Post-mortem interval correlated weakly with elastic modulus (r = 0.255, p = 0.048) and the strain at failure (r = - 0.306, p = 0.022) for TMF. The age of the donors did not reveal significant correlations to the TMF mechanical parameters. Compared to the dura mater, the here investigated TMF showed a significantly lower elastic modulus and ultimate tensile strength, but a larger strain at failure. The human TMF with a post-mortem interval of up to 146 h may be considered a mechanically suitable graft material for duraplasty when stored at a temperature of 4 °C.

Wrist at risk? - Considerations derived from a novel experimental setup to assess torques during hip reaming with potential implications on the orthopedic surgeons' health.

Orthopedic surgeons endure high physical stresses when performing surgery, as large forces and torques are applied commonly. Occupational risks are consequently higher when compared to other surgical disciplines. One example is the reaming of the acetabula during total hip arthroplasty, using customized instruments. This surgery may predispose the surgeon to overuse-related wrist pathology. In this study, torques acting along the reaming tool were measured, and the resulting forces applied to the orthopedic surgeons' wrists were estimated based on the measured torque data from hip reaming. Different reamer sizes and tool velocities were analyzed to determine how both parameters may influence the torques applied at the surgeon's wrist. Using a highly standardized setup, torques were measured while the reamer was pushed into the acetabula to remove cartilage. Maximum torques and stoppage torques at blocking of the reamer were compared between feed rates and reamer sizes. Peak values of the maximum torques along the reamer axis averaged 1.5-1.8 Nm. No significant difference between maximum torques and reamer sizes was found. A significant difference in maximum torques was noted between feed rates with a large effect (p = 0.010; η2 = 0.214) and a large interaction effect (p = 0.017; η2 = 0.186). Based on this experimental setup, it can be hypothesized that the impulsive behavior of the torque when the milling tool reaches the subchondral lamella could potentially contribute to wrist pathology. These preliminary data warrant further study. Consequently, torque limiters should be implemented in reamers to minimize the risk of occupation-related pathology to the wrist.

Surface coating and speckling of the human iliotibial tract does not affect its load-deformation properties.

Stochastic surface patterns form an important requirement to facilitate digital image correlation and to subsequently quantify material properties of various tissues when loaded and deformed without artefacts arising from material slippage. Depending on the samples' natural colour, a surface pattern is created by speckling with colour or dye only, or it requires combined surface coating and speckling before to enhance the contrast, to facilitate high-quality data recording for mechanical evaluation. However, it is unclear to date if the colours deployed for coating and speckling do significantly alter the biomechanical properties of soft tissues. The given study investigated the biomechanical properties of 168 human iliotibial tract samples as a model for collagen-rich soft tissues, separated into four groups: untreated, graphite speckling only, water-based coating plus graphite speckling and solvent-based coating plus graphite speckling following a standardized approach of application and data acquisition. The results reveal that elastic modulus, ultimate tensile strength and strain at maximum force of all groups were similar and statistically non-different (p ≥ 0.69). Qualitatively, the speckle patterns revealed increasing contrast differences in the following order: untreated, graphite speckling only, water-based coating plus graphite speckling and solvent-based coating plus graphite speckling. Conclusively, both coating by water- and solvent-based paints, as well as exclusive graphite speckling, did not significantly influence the load-deformation parameters of the here used human iliotibial tract as a model for collagen-rich soft tissues. In consequence, water- and solvent-based coating paints seem equally suitable to coat collagen-rich soft tissues for digital image correlation, resulting in suitable speckle patterns and unbiased data acquisition.

Load-deformation characteristics of acellular human scalp: assessing tissue grafts from a material testing perspective.

Acellular matrices seem promising scaffold materials for soft tissue regeneration. Biomechanical properties of such scaffolds were shown to be closely linked to tissue regeneration and cellular ingrowth. This given study investigated uniaxial load-deformation properties of 34 human acellular scalp samples and compared these to age-matched native tissues as well as acellular dura mater and acellular temporal muscle fascia. As previously observed for human acellular dura mater and temporal muscle fascia, elastic modulus (p = 0.13) and ultimate tensile strength (p = 0.80) of human scalp samples were unaffected by the cell removal. Acellular scalp samples showed a higher strain at maximum force compared to native counterparts (p = 0.02). The direct comparison of acellular scalp to acellular dura mater and temporal muscle fascia revealed a higher elasticity (p < 0.01) and strain at maximum force (p = 0.02), but similar ultimate tensile strength (p = 0.47). Elastic modulus and ultimate tensile strength of acellular scalp decreased with increasing post-mortem interval. The elongation behavior formed the main biomechanical difference between native and acellular human scalp samples with elastic modulus and ultimate tensile strength being similar when comparing the two.

What is Considered a Variation of Biomechanical Parameters in Tensile Tests of Collagen-Rich Human Soft Tissues? - Critical Considerations Using the Human Cranial Dura Mater as a Representative Morpho-Mechanic Model.

Background and Objectives: Profound knowledge on the load-dependent behavior of human soft tissues is required for the development of suitable replacements as well as for realistic computer simulations. Regarding the former, e.g., the anisotropy of a particular biological tissue has to be represented with site- and direction-dependent particular mechanical values. Contrary to this concept of consistent mechanical properties of a defined soft tissue, mechanical parameters of soft tissues scatter considerably when being determined in tensile tests. In spite of numerous measures taken to standardize the mechanical testing of soft tissues, several setup- and tissue-related factors remain to influence the mechanical parameters of human soft tissues to a yet unknown extent. It is to date unclear if measurement extremes should be considered a variation or whether these data have to be deemed incorrect measurement outliers. This given study aimed to determine mechanical parameters of the human cranial dura mater as a model for human soft tissues using a highly standardized protocol and based on this, critically evaluate the definition for the term mechanical "variation" of human soft tissue. Materials and Methods: A total of 124 human dura mater samples with an age range of 3 weeks to 94 years were uniformly retrieved, osmotically adapted and mechanically tested using customized 3D-printed equipment in a quasi-static tensile testing setup. Scanning electron microscopy of 14 samples was conducted to relate the mechanical parameters to morphological features of the dura mater. Results: The here obtained mechanical parameters were scattered (elastic modulus = 46.06 MPa, interquartile range = 33.78 MPa; ultimate tensile strength = 5.56 MPa, interquartile range = 4.09 MPa; strain at maximum force = 16.58%, interquartile range = 4.81%). Scanning electron microscopy revealed a multi-layered nature of the dura mater with varying fiber directions between its outer and inner surface. Conclusions: It is concluded that mechanical parameters of soft tissues such as human dura mater are highly variable even if a highly standardized testing setup is involved. The tissue structure and composition appeared to be the main contributor to the scatter of the mechanical parameters. In consequence, mechanical variation of soft tissues can be defined as the extremes of a biomechanical parameter due to an uncontrollable change in tissue structure and/or the respective testing setup.

The Effect of the Supplementation of a Diet Low in Calcium and Phosphorus with Either Sheep Milk or Cow Milk on the Physical and Mechanical Characteristics of Bone using A Rat Model.

This study assessed the effect of cow milk (CM) and sheep milk (SM) consumption on the micro-structure, mechanical function, and mineral composition of rat femora in a male weanling rat model. Male weanling rats were fed a basal diet with a 50% reduction in calcium and phosphorus content (low Ca/P-diet) supplemented with either SM or CM. Rats were fed for 28 days, after which the femora were harvested and stored. The femora were analyzed by µ-CT, three-point bending, and inductively coupled plasma-mass spectrometry (ICP-MS). The addition of either milk to the low Ca/P-diet significantly increased (p < 0.05) trabecular bone volume, trabecular bone surface density, trabecular number, cortical bone volume, and maximum force, when compared to rats that consumed only the low Ca/P-diet. The consumption of either milk resulted in a significant decrease (p < 0.05) in trabecular pattern factor, and cortical bone surface to volume ratio when compared to rats that consumed only the low Ca/P-diet. The results were achieved with a lower consumption of SM compared to that of CM (p < 0.05). This work indicates that SM and CM can help overcome the effects on bone of a restriction in calcium and phosphorus intake.

Load-deformation properties of the ligament of the head of femur in situ.

The ligament of the head of femur (LHF) or ligamentum teres has been reported to tense during hip adduction and also to provide mechanical stability to the joint. LHF injury is more common in females and also in right hip joints compared with left ones. Although this could be due to leg dominance, pelvic size or muscle strength, there is no study that has looked into these differences. This cadaveric biomechanical study aimed to compare potential differences in the mechanical behavior of the LHF between neutral and 20° adducted hip joints, sex, and sides. Tensile tests of the LHF were performed on 25 hip joints (mean age at death of 85.7 ± 7.5 years; 9 females, 4 males; 13 left, 12 right), positioned either neutrally or in adduction. The maximum force required to rupture the ligament, its strain at failure, tensile strength, linear stiffness, and elastic modulus were obtained and statistically compared between analysis groups. The maximum force the LHF could withstand before rupture averaged 57 ± 37 N, strain at failure of 59 ± 33%, tensile strength of 2.9 ± 1.8 MPa, linear stiffness of 5.4 ± 3.5 N/mm, and elastic modulus of 7.2 ± 3.8 MPa. The LHF length at failure was significantly greater in males compared with females (P = 0.02). Irrespective of joint position, there were no statistical differences in the stress-strain properties of the LHF between females and males, or sides. There may be other anatomical, functional, and demographic factors that could render the ligament tissue vulnerable to injury in these groups. Clin. Anat., 33:705-713, 2020. © 2019 Wiley Periodicals, Inc.

Standardized tensile testing of soft tissue using a 3D printed clamping system.

Biomechanical testing of soft tissues forms the backbone in the experimental validation of tissue engineering and for modelling purposes. The standardized testing of soft tissues requires different experimental protocols and fixtures compared to hard tissues or non-biological materials due to their characteristics. Some of the most commonly-used clamping methods for soft tissue testing affect the tissues' mechanical properties as chemicals are involved to decelerate degradation and autolysis. Moreover, they are unsuitable for standardized and high-throughput testing. Material slippage is also a recurrent unwanted influence on the testing routine with impact on measurement validity. Addressing these issues, this protocol presents a clamping system for simplified testing of biological soft tissues with all necessary components manufactured utilizing 3D printing technology. Templates allow trimming the samples into standardized shapes and sizes while preparation tables facilitate clamping in a fixed distance. The key parts of the system are clamps with a pyramid design, which allow the mounting of biological soft tissues before transferring it into the testing device and minimize material slippage during tensile testing. Flexible holder arms are used to transfer samples from preparation tables into the testing device and simplify positioning. Mechanical testing itself is performed with digital image correlation for precise strain measurements.

Strain-rate sensitive ductility in a low-alloy carbon steel after quenching and partitioning treatment.

We investigate an extraordinarily high ductility in a low alloy carbon steel at an elevated temperature after a quenching and partitioning (Q&P) treatment. The conventional (quenched and tempered) reference material does not show similar behavior. Interestingly, the Q&P treated material's ductility is considerably reduced at increasing strain rates while strength remains almost constant. These results indicate the presence of a diffusion-controlled deformation mechanism at elevated temperatures. Our research shows that interlath retained austenite is more stable during deformation at higher temperatures, resulting in a delayed transformation to martensite and therefore to a more pronounced contribution to plastic deformation at (and in the vicinity of) the many interfaces inherently present in this multi-phase steel.

Mechanical Properties of Human Dura Mater in Tension - An Analysis at an Age Range of 2 to 94 Years.

Realistic human head models are of great interest in traumatic brain injury research and in the forensic pathology courtroom and teaching. Due to a lack of biomechanical data, the human dura mater is underrepresented in head models. This study provides tensile data of 73 fresh human cranial dura mater samples retrieved from an area between the anterior middle and the posterior middle meningeal artery. Tissues were adapted to their native water content using the osmotic stress technique. Tensile tests were conducted under quasi-static uniaxial testing conditions with simultaneous digital image correlation. Human temporal dura mater is mechanically highly variable with regards to its elastic modulus of 70 ± 44 MPa, tensile strength of 7 ± 4 MPa, and maximum strain of 11 ± 3 percent. Mechanical properties of the dura mater did not vary significantly between side nor sex and decreased with the age of the cadaver. Both elastic modulus and tensile strength appear to have constant mechanical parameters within the first 139 hours post mortem. The mechanical properties provided by this study can help to improve computational and physical human head models. These properties under quasi-static conditions do not require adjustments for side nor sex, whereas adjustments of tensile properties accompanied with normal aging may be of interest.

An Investigation on the Correlation between the Mechanical Properties of Human Skull Bone, Its Geometry, Microarchitectural Properties, and Water Content.

With increasingly detailed imaging and mechanical analysis, modalities need arises to update methodology and assessment criteria for skull bone analysis to understand how bone microarchitecture and the presence of attached tissues may affect the response to mechanical load. The main aim was to analyze the effect of macroscopic and microstructural features, as well as periosteal attachment, on the mechanical properties of human skull bone. Fifty-six skull specimens from ethanol-phenoxyethanol-embalmed cadavers were prepared from two human cadavers. Assuming symmetry of the skull, all samples from one-half each were stripped of periosteum and dura mater, while the soft tissues were kept intact on the remaining samples on the contralateral side. The specimens were analyzed using microcomputed tomography to assess trabecular connectivity density, total surface area, and volume ratio. The specimens were loaded under three-point bend tests until fracture with optical co-registration. The bone fragments were then lyophilized to measure their water content. With increasingly detailed imaging and mechanical analysis modalities, there is a need to update methodology and assessment criteria for skull bone analysis to understand how the bone microarchitecture and the presence of attached tissues may affect the response to mechanical load. The mechanical properties were negatively correlated to bone thickness and water content. Conversely, most microarchitectural features did not influence either mechanical parameter. The correlation between mechanical response data and morphologic properties remains similar between the results of embalmed tissues presented here and fresh osseous tissue from literature data. The findings presented here add to the existing methodology to assess human skull for research purposes. The interaction between most microarchitectural features in ethanol-phenoxyethanol-embalmed embalmed skull samples and bending stress appear to be minute.

A biomechanical comparison between human calvarial bone and a skull simulant considering the role of attached periosteum and dura mater.

PURPOSE: Current forensic analysis of blunt force trauma relies on the use of cadaveric or animal tissues, posing ethical and reproducibility concerns. Artificial substitutes may help overcome such issues. However, existing substitutes exhibit poor anatomic and mechanical biofidelity, especially in the choice of skull simulant material. Progress has been made in identifying materials that have similar mechanical properties to the human skull bone, with the potential to behave similarly in mechanical loading. AIMS: To compare the biomechanical properties of the human calvarial bone with an epoxy resin-based simulant material. Data collected was also used to analyse the effect of periosteal attachment on the mechanical properties of skull bone compared with that of the counterpart samples. METHODS: Fifty-six human skull bone specimens were prepared from two cadaveric heads. Half of these specimens were removed of periosteum and dura mater as the PR (periosteum removed) group, whereas periosteum was left attached in the PA (periosteum attached) group. Duplicates of the bone specimens were fabricated out of an epoxy resin and paired in corresponding PR and PA groups. The specimens were loaded under three-point bending tests until fracture with image-based deformation detection. RESULTS: Comparison of the epoxy resin and skull specimens yielded similarity for both the PR and PA groups, being closer to the PA group (bending modulus resin PR 2665 MPa vs. skull PR 1979 MPa, resin PA 3165 MPa vs. skull PA 3330 MPa; maximum force resin PR 574 N vs. skull PR 728 N, resin PA 580 N vs. skull PA 1034 N; strain at maximum force resin PR 2.7% vs. skull PR 5.1%, resin PA 2.3% vs. skull PA 3.5%, deflection at maximum force resin PR 0.5 mm vs. skull PR 0.8 mm, resin PA 0.5 mm vs. skull PA 1.0 mm). Bending strength was significantly lower in the resin groups (resin PR 43 MPa vs. skull PR 55 MPa, resin PA 44 MPa vs. skull PA 75 MPa). Moreover, the correlations of the mechanical data exhibited closer accordance of the PR group with the epoxy resin compared with the PA group with the epoxy resin. CONCLUSIONS: The load-deformation properties of the epoxy resin samples assessed in this study fell within a closer range to the skull specimens with PR  than with PA. Moreover, the values obtained for the resin fall within the reference range for skull tissues in the literature suggesting that the proposed epoxy resin may provide a usable artificial substitute for PA but does not totally represent the human skull in its complex anatomical structure.

Water-content related alterations in macro and micro scale tendon biomechanics.

Though it is known that the water content of biological soft tissues alters mechanical properties, little attempt has been made to adjust the tissue water content prior to biomechanical testing as part of standardization procedures. The objective of this study was to examine the effects of altered water content on the macro and micro scale mechanical tissues properties. Human iliotibial band samples were obtained during autopsies to osmotically adapt their water content. Macro mechanical tensile testing of the samples was conducted with digital image correlation, and micro mechanical tests using atomic force microscopy. Analyses were conducted for elastic moduli, tensile strength, and strain at maximum force, and correlations for water content, anthropometric data, and post-mortem interval. Different mechanical properties exist at different water concentrations. Correlations to anthropometric data are more likely to be found at water concentrations close to the native state. These data underline the need for adapting the water content of soft tissues for macro and micro biomechanical experiments to optimize their validity. The osmotic stress protocol provides a feasible and reliable standardization approach to adjust for water content-related differences induced by age at death, post-mortem interval and tissue processing time with known impact on the stress-strain properties.

Tissue biomechanics of the human head are altered by Thiel embalming, restricting its use for biomechanical validation.

Thiel embalming is a well-known method of anatomical fixation giving lifelike optical and haptic tissue properties. Beyond these characteristics, Thiel embalming may also be a promising method to provide lifelike tissues for validation purposes of human head biomechanics. Recent investigations using Thiel-embalmed human tissues of the upper and lower limb yielded contradicting biomechanical results on fixation-induced changes in the tissues' load-deformation behavior. It is to date unclear if Thiel embalming may have a softening or stiffening effect on human soft tissues or no global effect on biomechanics compared to the fresh state, with the latter being the most desirable outcome. The given study aimed at assessing the effects of Thiel embalming on the uniaxial tensile properties of human head soft tissues. Age-matched fresh and Thiel-embalmed dura mater, temporalis muscle, temporalis muscle fascia, and scalp samples were examined. Dura, fascia, and scalp samples showed significantly different elastic moduli compared to fresh tissues (all P < 0.01). The observed ultimate tensile strength supports the theory of an increased collagen crosslinking of the embalmed tissues when compared to the fresh state. Thiel-embalmed muscles failed any tensile testing approach as a result of the muscles dissolving due to the embalming. Furthermore, collagen integrity seems altered in scanning electron microscopy by the Thiel embalming, limiting their use for ultrastructural failure analyses. Thiel-embalmed soft tissues may consequently not serve to reflect the biomechanical properties of the human head. Consequently, the application of Thiel embalming should be limited to preliminary tests for biomechanical purposes. Clin. Anat. 32:903-913, 2019. © 2019 Wiley Periodicals, Inc.

In Silico Pelvis and Sacroiliac Joint Motion: Refining a Model of the Human Osteoligamentous Pelvis for Assessing Physiological Load Deformation Using an Inverted Validation Approach.

Introduction. Computational modeling of the human pelvis using the finite elements (FE) method has become increasingly important to understand the mechanisms of load distribution under both healthy and pathologically altered conditions and to develop and assess novel treatment strategies. The number of accurate and validated FE models is however small, and given models fail resembling the physiologic joint motion in particular of the sacroiliac joint. This study is aimed at using an inverted validation approach, using in vitro load deformation data to refine an existing FE model under the same mode of load application and to parametrically assess the influence of altered morphology and mechanical data on the kinematics of the model. Materials and Methods. An osteoligamentous FE model of the pelvis including the fifth lumbar vertebra was used, with highly accurate representations of ligament orientations. Material properties were altered parametrically for bone, cartilage, and ligaments, followed by changes in bone geometry (solid versus 3 and 2 mm shell) and material models (linear elastic, viscoelastic, and hyperelastic isotropic), and the effects of varying ligament fiber orientations were assessed. Results. Elastic modulus changes were more decisive in both linear elastic and viscoelastic bone, cartilage, and ligaments models, especially if shell geometries were used for the pelvic bones. Viscoelastic material properties gave more realistic results. Surprisingly little change was observed as a consequence of altering SIJ ligament orientations. Validation with in vitro experiments using cadavers showed close correlations for movements especially for 3 mm shell viscoelastic model. Discussion. This study has used an inverted validation approach to refine an existing FE model, to give realistic and accurate load deformation data of the osteoligamentous pelvis and showed which variation in the outcomes of the models are attributed to altered material properties and models. The given approach furthermore shows the value of accurate validation and of using the validation data to fine tune FE models.

Consumption of sheep milk compared to cow milk can affect trabecular bone ultrastructure in a rat model.

Cow milk has a positive effect on bone health due to the effects of its protein, fat, lipid, vitamin, and mineral components. Sheep milk contains a unique composition of all of these components. However, to the best of our knowledge the benefits of sheep milk in relation to bone development have not been studied. The aim of the present study was to determine the effects of the consumption of sheep milk in comparison to cow milk on the structural and physical characteristics of growing bone in a rat model. Newly weaned male rats were fed either cow milk, sheep milk or sheep milk diluted to the same total solids content as cow milk for 28 days in addition to a basal chow. At the end of the feeding period animals were euthanized, the femora harvested and stored. The femora were analysed by µ-CT, mechanical bending tests, and ICP-MS. Rats consuming sheep milk in the trial were found to have significantly higher trabecular bone surface density and trabecular bone surface to volume ratio (p < 0.05) when compared to the rats consuming cow milk. No significant differences were observed in the mechanical properties and the mineral composition of the bones (p > 0.05). With the exception of Rb, which was found to be present in higher concentrations in rats consuming sheep milk (p < 0.05). Our results indicate that consumption of sheep milk may positively influence the structural integrity of bone, which may result in an enhancement of bone health.

Physiological in vitro sacroiliac joint motion: a study on three-dimensional posterior pelvic ring kinematics.

The sacroiliac joint (SIJ) is a well-known source of low back and pelvic pain, of increasing interest for both conservative and surgical treatment. Alterations in the kinematics of the pelvis have been hypothesized as a major cause of SIJ-related pain. However, definitions of both the range and the extent of physiological movement are controversial, and there are no clear baseline data for pathological alterations. The present study combined a novel biomechanical setup allowing for physiological motion of the lumbosacral transition and pelvis without restricting the SIJ movement in vitro, combined with optical image correlation. Six fresh human pelvises (81 ± 10 years, three females, three males) were tested, with bodyweight-adapted loading applied to the fifth lumbar vertebra and both acetabula. Deformation at the lumbopelvises was determined computationally from three-dimensional image correlation data. Sacroiliac joint motion under the loading of 100% bodyweight primarily consisted of a z-axis rotation (0.16°) and an inferior translation of the sacrum relative to the ilium (0.32 mm). Sacroiliac joint flexion-extension rotations were minute (< 0.02°). Corresponding movements of the SIJ were found at the lumbosacral transition, with an anterior translation of L5 relative to the sacrum of -0.97 mm and an inferior translation of 0.11 mm, respectively. Moreover, a flexion of 1.82° was observed at the lumbosacral transition. Within the innominate bone and at the pubic symphysis, small complementary rotations were seen around a vertical axis, accounting for -0.10° and 0.11°, respectively. Other motions were minute and accompanied by large interindividual variation. The present study provides evidence of different SIJ motions than reported previously when exerted by physiological loading. Sacroiliac joint kinematics were in the sub-degree and sub-millimeter range, in line with previous in vivo and in vitro findings, largely limited to the sagittal rotation and an inferior translation of the sacrum relative to the ilium. This given physiological loading scenario underlines the relevance of the lumbosacral transition when considering the overall motion of the lumbopelvis, and how relatively little the other segments contribute to overall motion.