Finite element analysis of a femur to deconstruct the paradox of bone curvature

A bionic bird jumping grasping structure design based on stm32 development board control

During takeoff and landing, birds bounce and grab with their legs and feet. In this paper,the lower limb structure of the bionic bird is designed with reference to the function of jumping and grasping, and the PID algorithm based on the development module of stm32 development board is used to speed control the lower limb driving element, so that the motor and the bishaft steering gear move with the rate change of sine wave. According to the speed of grasping response time and the size of grasping force, the structure of the bionic bird paw is designed. Based on the photosensitive sensor fixed in the geometric center of the foot, the grasping action of the lower limb mechanism is intelligently controlled. Finally, the kinematic verification of the lower limb structure is carried out by ADAMS. Experiments show that the foot structure with four toes and three toes is more conducive to maintaining the stability of the body while realizing the fast grasping function. In addition, it can effectively improve the push-lift ratio of the bionic ornithopter by adjusting the sinusoidal waveform rate of the motor speed.

Variability in tibia-fibular geometry is associated with increased tibial strain from running loads

Variation in tibial geometry may alter strain magnitude and distribution during locomotion. We investigated the effect of tibia-fibula geometric variations on tibial strain with running loads applied at various speeds. Participant-specific three-dimensional models of the tibia-fibula were created using lower limb computed tomography scans from 30 cadavers. Finite-element models were developed in FEBio, and running loads from 3, 4 and 5 m s-1 were applied to extract effective strain from the tibial shaft. Linear regression models evaluated the relationship between geometric characteristics and effective strain along the tibial shaft. We found a statistically significant positive relationship between: (i) increased thickness of the midshaft to upper tibia with increased condyle prominence and effective strain at points along the distal anterolateral and proximal posterior regions of the tibial shaft; and (ii) increased midshaft cortical thickness and effective strain at points along the medial aspect of the distal tibial shaft. It is possible that increased thickness in the more proximal region of the tibia causes strain to redistribute to areas that are more susceptible to the applied loads. A thickness imbalance between the upper and distal portions of the tibial shaft could have a negative impact on tibial stress injury risk.

Fibular diaphyseal curvature of the Jomon population

This study investigated differences in the fibular diaphyseal curvature between prehistoric Jomon hunter-gatherers and modern Japanese people. A total of 115 skeletal remains of 40 individuals from the Late/Final Jomon period (approximately 4300-2500 years BP) and 75 modern Japanese individuals were included in the analysis. The degree of anteroposterior and mediolateral diaphyseal curvature was measured based on digital photographs taken from the frontal and sagittal planes at every 5% diaphyseal region between the range of 20-80% of the fibular length. Fibular diaphyseal curvature was compared between both populations and sexes, and the correlation between fibular diaphyseal curvature with diaphyseal cross-sectional morphology and body size variables were confirmed. The results showed significant differences in the anteroposterior diaphyseal curvature between the Jomon and modern Japanese populations, and a significantly curved anterior direction was noted for Jomon males and females, compared with modern Japanese males and females. On the contrary, little populational difference was noted in terms of mediolateral diaphyseal curvature. The curvature of the fibular diaphysis showed less correlation with body size variables. Moreover, anteroposterior diaphyseal curvatures were correlated with diaphyseal robustness and had low correlation with diaphyseal shape. A relationship between anteroposterior curvature and diaphyseal cross-sectional morphology, an indicator of habitual activity, was confirmed. This suggests that the fibular curvature is possibly influenced by mechanical loading from daily activities as well.

Humeri under external load: Mechanical implications of differing bone curvature in American otter and honey badger

The mechanical properties of limb long bones are impacted by bone shape and especially curvature, which is therefore likely to be of adaptive value. We use finite element analysis to compare the mechanical properties of humeri of the closely related American otter and honey badger under external loads, and to analyze the significance of bone curvature. We simulate the effects generated by loads applied in directions that differ relative to the humeral longitudinal axes, and then compare the stress characteristics with a series of humerus-inspired abstracted curved structures with increasing ratio (C/R) of eccentricity C to radius of cross section R. The humeri of the two species differ in bone curvature, with C/R of 0.6201 and 0.8752, respectively. Our analysis shows that the peak and mean stress values found within the sampling line of bone models reach a minimum when the directions of loads are 105 ± 5°, and the humerus of the American otter always experienced lower stress values than those of the honey badger in the sampling line. An analysis of stress distribution in abstract curved structures showed the greatest reduction in stress when the direction of external load was equal or greater than 95°. This suggests that the variability of the direction of external loads is an important determinant of bone curvature, and should be accounted for when assessing load carrying capacity. This study provides a basis for biomechanics research and yields insight into the form-function relationship of nature's structural elements within limbs. It potentially contributes to the design of biomimetic robots while also highlighting the functional significance of humeral bone curvature in mammals.

Macroevolutionary trends in theropod dinosaur feeding mechanics

Theropod dinosaurs underwent some of the most remarkable dietary changes in vertebrate evolutionary history, shifting from ancestral carnivory^1-3 to hypercarnivory^4,5 and omnivory/herbivory,^6-9 with some taxa eventually reverting to carnivory.^10-12 The mandible is an important tool for food acquisition in vertebrates and reflects adaptations to feeding modes and diets.^13,14 The morphofunctional modifications accompanying the dietary changes in theropod dinosaurs are not well understood because most of the previous studies focused solely on the cranium and/or were phylogenetically limited in scope,^12,15-21 while studies that include multiple clades are usually based on linear measurements and/or discrete osteological characters.^8,22 Given the potential relationship between macroevolutionary change and ontogenetic pattern,²³ we explore whether functional morphological patterns observed in theropod mandibular evolution show similarities to the ontogenetic trajectory. Here, we use finite element analysis to study the mandibles of non-avialan coelurosaurian theropods and demonstrate how feeding mechanics vary between dietary groups and major clades. We reveal an overall reduction in feeding-induced stresses along all theropod lineages through time. This is facilitated by a post-dentary expansion and the development of a downturned dentary in herbivores and an upturned dentary in carnivores likely via the "curved bone effect." We also observed the same reduction in feeding-induced stress in an ontogenetic series of jaws of the tyrannosaurids Tarbosaurus and Tyrannosaurus, which is best attributed to bone functional adaptation. This suggests that this common tendency for structural strengthening of the theropod mandible through time, irrespective of diet, is linked to "functional peramorphosis" of bone functional adaptations acquired during ontogeny.

Ontogenetic changes in femoral cross-sectional geometry during childhood locomotor development

OBJECTIVES

The femur is a major weight-bearing bone that is variably loaded throughout growth as children transition through locomotory states prior to the attainment of a mature bipedal gait. Here, we document ontogenetic trends in femoral cross-sectional geometry (CSG) and explore how changes in loading regime may impact the structural arrangement of cortical bone along the length of the developing diaphysis.

MATERIALS AND METHODS

Micro-CT scans of 110 immature femora were generated from a documented archaeological sample ranging in age from birth to 8.5 years old. CSG properties indicative of relative bone strength and bending rigidity were analyzed from cross-sections extracted at 35%, 50% and 65% of total intermetaphyseal length.

RESULTS

Infants experience a marked redistribution of cortical bone between birth and 7 months facilitating a more advantageous mechanical structure for early load bearing behaviors as bone is displaced further from the section centroid. Early walkers are characterized by a mediolaterally reinforced cross-section that becomes more circular as gait continues to develop.

DISCUSSION

During ontogeny the femur undergoes distinct morphological phases, which correspond with changes in loading regime. This study illustrates the importance of loading conditions in shaping immature bone morphology. Nonmechanical factors such as changes in hormonal environmental can also impact on this dynamic.

Terrestrial acclimation and exercise lead to bone functional response in Polypterus senegalus pectoral fins

The ability of bones to sense and respond to mechanical loading is a central feature of vertebrate skeletons. However, the functional demands imposed on terrestrial and aquatic animals differ vastly. The pectoral girdle of the basal actinopterygian fish Polypterus senegalus was previously shown to exhibit plasticity following terrestrial acclimation, but the pectoral fin itself has yet to be examined. We investigated skeletal plasticity in the pectoral fins of P. senegalus after exposure to terrestrial loading. Juvenile fish were divided into three groups: a control group was kept under aquatic conditions without intervention, an exercised group was also kept in water but received daily exercise on land, and a terrestrial group was kept in a chronic semi-terrestrial condition. After 5 weeks, the pectoral fins were cleared and stained with Alcian Blue and Alizarin Red to visualize cartilage and bone, allowing measurements of bone length, bone width, ossification and curvature to be taken for the endochondral radial bones. Polypterus senegalus fin bones responded most strongly to chronic loading in the terrestrial condition. Fish that were reared in a terrestrial environment had significantly longer bones compared with those of aquatic controls, wider propterygia and metapterygia, and more ossified metapterygia and medial radials, and they showed changes in propterygial curvature. Exercised fish also had longer and more ossified medial radials compared with those of controls. Polypterus senegalus fin bones exhibit plasticity in response to novel terrestrial loading. Such plasticity could be relevant for transitions between water and land on evolutionary scales, but key differences between fish and tetrapod bone make direct comparisons challenging.

Double-level fixator-assisted nailing (DL-FAN)

AIMS

Double-level lengthening, bone transport, and bifocal compression-distraction are commonly undertaken using Ilizarov or other fixators. We performed double-level fixator-assisted nailing, mainly for the correction of deformity and lengthening in the same segment, using a straight intramedullary nail to reduce the time in a fixator.

PATIENTS AND METHODS

A total of 23 patients underwent this surgery, involving 27 segments (23 femora and four tibiae), over a period of ten years. The most common indication was polio in ten segments and rickets in eight; 20 nails were inserted retrograde and seven antegrade. A total of 15 lengthenings were performed in 11 femora and four tibiae, and 12 double-level corrections of deformity without lengthening were performed in the femur. The mean follow-up was 4.9 years (1.1 to 11.4). Four patients with polio had tibial lengthening with arthrodesis of the ankle. We compared the length of time in a fixator and the external fixation index (EFI) with a control group of 27 patients (27 segments) who had double-level procedures with external fixation. The groups were matched for the gain in length, age, and level of difficulty score.

RESULTS

The mean gain in length was statistically similar in the two groups: 3.9 cm (1.5 to 9.0) in the study group and 4.2 cm (3.4 to 5.0) in the control group (p = 0.350). The mean time in a fixator was significantly less in the study group compared with the control group: 8.6 weeks (2.0 to 22.8) versus 30.2 weeks (25.0 to 35.4; p < 0.001). The mean EFI was significantly lower in the study group compared with the control group: 17.7 days/cm (10.6 to 35.6) versus 73.4 days/cm (44.5 to 102.3; p < 0.001). The ASAMI (Association for the Study and Application of the Method of Ilizarov) bone score was excellent in 22, good in four, and fair in one. The ASAMI functional score was excellent in 20 and good in seven. There were no infections, superficial or deep.

CONCLUSION

Double-level osteotomies or two procedures using a custom-made straight nail and external fixation can be used to correct deformities or to treat nonunion or malunion and may be combined with arthrodesis of the ankle with lengthening. It is a reasonably safe procedure that allows accurate and cost-effective treatment with a relatively short time in a fixator.

Comparative Study of Femur Bone Having Different Boundary Conditions and Bone Structure Using Finite Element Method

Background:

Femur bone is an important part in human which basically gives stability and support to carry out all day to day activities. It carries loads from upper body to lower abdomen.

Objective:

In this work, the femur having composite structure with cortical, cancellous and bone marrow cavity is bisected from condyle region with respect to 25%, 50% and 75% of its height. There is considerable difference in the region chosen for fixing all degrees of freedom in the analysis of femur.

Methods:

The CT scans are taken, and 3D model is developed using MIMICS. The developed model is used for static structural analysis by varying the load from 500N to 3000N.

Results:

The findings for 25% bisected femur model report difference in directional deformation less than 5% for loads 2000N and less. In the study comparing fully solid bone and the composite bone, the total deformation obtained for a complete solid bone was 3.5 mm which was 18.7% less than that determined for the composite bone.

Conclusion:

The standardization for fixing the bone is developed. And it is required to fix the distal end always with considering full femur bone.

Changing While Staying the Same: Preservation of Structural Continuity During Limb Evolution by Developmental Integration

More than 150 years since Charles Darwin published "On the Origin of Species", gradual evolution by natural selection is still not fully reconciled with the apparent sudden appearance of complex structures, such as the bat wing, with highly derived functions. This is in part because developmental genetics has not yet identified the number and types of mutations that accumulated to drive complex morphological evolution. Here, we consider the experimental manipulations in laboratory model systems that suggest tissue interdependence and mechanical responsiveness during limb development conceptually reduce the genetic complexity required to reshape the structure as a whole. It is an exciting time in the field of evolutionary developmental biology as emerging technical approaches in a variety of non-traditional laboratory species are on the verge of filling the gaps between theory and evidence to resolve this sesquicentennial debate.

Scaling in biomechanical experimentation: a finite similitude approach

Biological experimentation has many obstacles: resource limitations, unavailability of materials, manufacturing complexities and ethical compliance issues; any approach that resolves all or some of these is of some interest. The aim of this study is applying the recently discovered concept of finite similitude as a novel approach for the design of scaled biomechanical experiments supported with analysis using a commercial finite-element package and validated by means of image correlation software. The study of isotropic scaling of synthetic bones leads to the selection of three-dimensional (3D) printed materials for the trial-space materials. These materials conforming to the theory are analysed in finite-element models of a cylinder and femur geometries undergoing compression, tension, torsion and bending tests to assess the efficacy of the approach using reverse scaling of the approach. The finite-element results show similar strain patterns in the surface for the cylinder with a maximum difference of less than 10% and for the femur with a maximum difference of less than 4% across all tests. Finally, the trial-space, physical-trial experimentation using 3D printed materials for compression and bending testing provides a good agreement in a Bland-Altman statistical analysis, providing good supporting evidence for the practicality of the approach.

Young's Modulus and Load Complexity: Modeling Their Effects on Proximal Femur Strain

Finite element analysis (FEA) is a powerful tool for evaluating questions of functional morphology, but the application of FEA to extant or extinct creatures is a non-trivial task. Three categories of input data are needed to appropriately implement FEA: geometry, material properties, and boundary conditions. Geometric data are relatively easily obtained from imaging techniques, but often material properties and boundary conditions must be estimated. Here we conduct sensitivity analyses of the effect of the choice of Young's Modulus for elements representing trabecular bone and muscle loading complexity on the proximal femur using a finite element mesh of a modern human femur. We found that finite element meshes that used a Young's Modulus between 500 and 1,500 MPa best matched experimental strains. Loading scenarios that approximated the insertion sites of hip musculature produced strain patterns in the region of the greater trochanter that were different from scenarios that grouped muscle forces to the superior greater trochanter, with changes in strain values of 40% or more for 20% of elements. The femoral head, neck, and proximal shaft were less affected (e.g. approximately 50% of elements changed by 10% or less) by changes in the location of application of muscle forces. From our sensitivity analysis, we recommend the use of a Young's Modulus for the trabecular elements of 1,000 MPa for the proximal femur (range 500-1,500 MPa) and that the muscular loading complexity be dependent on whether or not strains in the greater trochanter are the focus of the analytical question. Anat Rec, 301:1189-1202, 2018. © 2018 Wiley Periodicals, Inc.

The development of curvature in the porcine radioulna

Long bone curvature in animal limbs has long been a subject of interest and much work has explored why long bones should be curved. However, the ‘when’ and ‘how’ of curvature development is poorly understood. It has been shown that the rat tibia fails to attain its normal curvature if the action of muscles is removed early in life, but it is not clear if this is because the curvature fails to develop or if the bone becomes straighter without the action of muscles. No studies have examined the development of bone curvature in a normally developing quadruped, so this study tracks the course of curvature formation in the radioulna in a series of growing pigs. We also histologically examined the epiphyseal growth plates of these bones to determine if they contribute to the formation of curvature. In all three epiphyseal plates examined, the proliferative zone is thicker and more densely populated with chondrocytes on the cranial (convex) side than the caudal (concave) side. Frost’s chondral modelling theory would suggest that the cranial side of the bone is under more compression than the caudal side, and we conclude that this is due to the action of triceps extending the elbow by pulling on the olecranon process. These results support the idea that bone curvature is an adaptation to habitual loading, where longitudinal loads acting on the curved bone cause bending strains that counter the bending resulting from the habitual muscle action.

Forelimb bone curvature in terrestrial and arboreal mammals

It has recently been proposed that the caudal curvature (concave caudal side) observed in the radioulna of terrestrial quadrupeds is an adaptation to the habitual action of the triceps muscle which causes cranial bending strains (compression on cranial side). The caudal curvature is proposed to be adaptive because longitudinal loading induces caudal bending strains (increased compression on the caudal side), and these opposing bending strains counteract each other leaving the radioulna less strained. If this is true for terrestrial quadrupeds, where triceps is required for habitual elbow extension, then we might expect that in arboreal species, where brachialis is habitually required to maintain elbow flexion, the radioulna should instead be cranially curved. This study measures sagittal curvature of the ulna in a range of terrestrial and arboreal primates and marsupials, and finds that their ulnae are curved in opposite directions in these two locomotor categories. This study also examines sagittal curvature in the humerus in the same species, and finds differences that can be attributed to similar adaptations: the bone is curved to counter the habitual muscle action required by the animal’s lifestyle, the difference being mainly in the distal part of the humerus, where arboreal animals tend have a cranial concavity, thought to be in response the carpal and digital muscles that pull cranially on the distal humerus.

Curvature reduces bending strains in the quokka femur

This study explores how curvature in the quokka femur may help to reduce bending strain during locomotion. The quokka is a small wallaby, but the curvature of the femur and the muscles active during stance phase are similar to most quadrupedal mammals. Our hypothesis is that the action of hip extensor and ankle plantarflexor muscles during stance phase place cranial bending strains that act to reduce the caudal curvature of the femur. Knee extensors and biarticular muscles that span the femur longitudinally create caudal bending strains in the caudally curved (concave caudal side) bone. These opposing strains can balance each other and result in less strain on the bone. We test this idea by comparing the performance of a normally curved finite element model of the quokka femur to a digitally straightened version of the same bone. The normally curved model is indeed less strained than the straightened version. To further examine the relationship between curvature and the strains in the femoral models, we also tested an extra-curved and a reverse-curved version with the same loads. There appears to be a linear relationship between the curvature and the strains experienced by the models. These results demonstrate that longitudinal curvature in bones may be a manipulable mechanism whereby bone can induce a strain gradient to oppose strains induced by habitual loading.

Influence of Regional Difference in Bone Mineral Density on Hip Fracture Site in Elderly Females by Finite Element Analysis

Hip fracture is a kind of osteoporotic fractures in elderly patients. Its important monitoring indicator is to measure bone mineral density (BMD) using DXA. The stress characteristics and material distribution in different parts of the bones can be well simulated by three-dimensional finite element analysis. Our previous studies have demonstrated a linear positive correlation between clinical BMD and the density of three-dimensional finite element model of the femur. However, the correlation between the density variation between intertrochanteric region and collum femoris region of the model and the fracture site has not been studied yet. The present study intends to investigate whether the regional difference in the density of three-dimensional finite element model of the femur can be used to predict hip fracture site in elderly females. The CT data of both hip joints were collected from 16 cases of elderly female patients with hip fractures. Mimics 15.01 software was used to reconstruct the model of proximal femur on the healthy side. Ten kinds of material properties were assigned. In Abaqus 6.12 software, the collum femoris region and intertrochanteric region were, respectively, drawn for calculating the corresponding regional density of the model, followed by prediction of hip fracture site and final comparison with factual fracture site. The intertrochanteric region/collum femoris region density was [(1.20 ± 0.02) × 10(6)] on the fracture site and [(1.22 ± 0.03) × 10(6)] on the non-fracture site, and the difference was statistically significant (P = 0.03). Among 16 established models of proximal femur on the healthy side, 14 models were consistent with the actual fracture sites, one model was inconsistent, and one model was unpredictable, with the coincidence rate of 87.5 %. The intertrochanteric region or collum femoris region with lower BMD is more prone to hip fracture of the type on the corresponding site.

Curved bones: An adaptation to habitual loading

Why are long bones curved? It has long been considered a paradox that many long bones supporting mammalian bodies are curved, since this curvature results in the bone undergoing greater bending, with higher strains and so greater fracture risk under load. This study develops a theoretical model wherein the curvature is a response to bending strains imposed by the requirements of locomotion. In particular the radioulna of obligate quadrupeds is a lever operated by the triceps muscle, and the bending strains induced by the triceps muscle counter the bending resulting from longitudinal loads acting on the curved bone. Indeed the theoretical model reverses this logic and suggests that the curvature is itself a response to the predictable bending strains induced by the triceps muscle. This, in turn, results in anatomical arrangements of bone, muscle and tendon that create a simple physiological mechanism whereby the bone can resist the bending due to the action of triceps in supporting and moving the body. The model is illustrated by contrasting the behaviour of a finite element model of a llama radioulna to that of a straightened version of the same bone. The results show that longitudinal and flexor muscle forces produce bending strains that effectively counter strains due to the pull of the triceps muscle in the curved but not in the straightened model. It is concluded that the curvature of these and other curved bones adds resilience to the skeleton by acting as pre-stressed beams or strainable pre-buckled struts. It is also proposed that the cranial bending strains that result from triceps, acting on the lever that is the radioulna, can explain the development of the curvature of such bones.

BONE BIOMECHANICAL MODELING BASED ON CELLULAR STRUCTURE: METHODS AND EVALUATION

The aim of this study is to establish a biomechanical model of bone on the basis of cellular structure and then to evaluate its accuracy for the clinical application. The thighbone of swine was scanned by computed tomography (CT). The resulting sectional images were input into MIMICS10.01 to generate a three-dimensional geometric model. A biomechanical model of bone was built on the basis of cellular structure, and calculations of the model were implemented in MATLAB with the finite element method. With this cellular mechanics model, axial compression load was simulated, and load–axial and load–transverse strain at the measurement points were detected. To evaluate the model, a mechanics model derived from an empirical formula was simulated under the same conditions, and an actual biomechanical experiment was also conducted. The simulated results obtained from the two models were then compared with the test results, indicating that the simulated results for the cellular model were closer to the test results than those for the empirical mechanics model. Therefore, the proposed cellular mechanics model shows advantages in accuracy and scope of application for bone modeling.

In vivo strains in the femur of the nine-banded armadillo (Dasypus novemcinctus)

The capacity of limb bones to resist the locomotor loads they encounter depends on both the pattern of those loads and the material properties of the skeletal elements. Among mammals, understanding of the interplay between these two factors has been based primarily on evidence from locomotor behaviors in upright placentals, which show limb bones that are loaded predominantly in anteroposterior bending with minimal amounts of torsion. However, loading patterns from the femora of opossums, marsupials using crouched limb posture, show appreciable torsion while the bone experiences mediolateral (ML) bending. These data indicated greater loading diversity in mammals than was previously recognized, and suggested the possibility that ancestral loading patterns found in sprawling lineages (e.g., reptilian sauropsids) might have been retained among basal mammals. To further test this hypothesis, we recorded in vivo locomotor strains from the femur of the nine-banded armadillo (Dasypus novemcinctus), a member of the basal xenarthran clade of placental mammals that also uses crouched limb posture. Orientations of principal strains and magnitudes of shear strains indicate that armadillo femora are exposed to only limited torsion; however, bending is essentially ML, placing the medial aspect of the femur in compression and the lateral aspect in tension. This orientation of bending is similar to that found in opossums, but planar strain analyses indicate much more of the armadillo femur experiences tension during bending, potentially due to muscles pulling on the large, laterally positioned third trochanter. Limb bone safety factors were estimated between 3.3 and 4.3 in bending, similar to other placental mammals, but lower than opossums and most sprawling taxa. Thus, femoral loading patterns in armadillos show a mixture of similarities to both opossums (ML bending) and other placentals (limited torsion and low safety factors), along with unique features (high axial tension) that likely relate to their distinctive hindlimb anatomy.

Biomechanical analysis of the annular ligament in Monteggia fractures using finite element models

Background

The pathogenesis of Monteggia injuries remains controversial. The current study biomechanically explored the pathological changes during Monteggia fractures using finite element analysis.

Methods

Two cadaveric forearm specimens underwent computed tomography in both the prone and supine positions. The images were imported to Mimics to construct three-dimensional images. The obtained models of the annular ligaments were assembled onto the bones. Two thin gaps were produced at the proximal third of the ulna to simulate a Monteggia fracture. The models were analyzed mechanically. The initial fracture process was simulated by constraining the distal portions of the radius and ulna and the dorsal fracture sites of the ulna. The mechanical changes of the annular ligament in the two positions were observed and compared.

Results

In the prone position, the maximum Z-axial displacement of the annular ligament was close to that along the Y-axis, although with a significant difference (P < 0.01). In the supine position, the X-axial displacement dramatically increased (P < 0.01), while it was noticeably decreased along the Z-axis (P < 0.01).

Conclusions

Biomechanical changes may partially explain the pathological changes in the annular ligament during Monteggia fractures; longitudinal displacement of the radial head causes it to slip out of the annular ligament while the ligament remains intact.