The vertebrate skeleton consists of over 200 individual bones, each with its own unique shape, size and function. We study the role of intrauterine muscle-induced mechanical loads in determining the three-dimensional morphology of developing bones. Analysis of the force-generating capacity of intrauterine muscles in mice revealed that developing bones are subjected to significant and progressively increasing mechanical challenges. To evaluate the effect of intrauterine loads on bone morphogenesis and the contribution of the emerging shape to the ability of bones to withstand these loads, we monitored structural and mineral changes during development. Using daily micro-CT scans of appendicular long bones we identify a developmental program, which we term preferential bone growth, that determines the specific circumferential shape of each bone by employing asymmetric mineral deposition and transient cortical thickening. Finite element analysis demonstrates that the resulting bone structure has optimal load-bearing capacity. To test the hypothesis that muscle forces regulate preferential bone growth in utero, we examine this process in a mouse strain (mdg) that lacks muscle contractions. In the absence of mechanical loads, the stereotypical circumferential outline of each bone is lost, leading to the development of mechanically inferior bones. This study identifies muscle force regulation of preferential bone growth as the module that shapes the circumferential outline of bones and, consequently, optimizes their load-bearing capacity during development. Our findings invoke a common mechanism that permits the formation of different circumferential outlines in different bones.

The baculum is an extraskeletal bone located in the penis of a few species in several orders of mammals such as carnivores, insectivores, rodents, bats and primates. 

This study aims to describe the structure, architecture and mechanical properties of the canine baculum. To this end canine bacula from castrated and uncastrated dogs were collected and examined by light microscopy, micro-computed tomography (microCT) scanning, histological staining, and mechanical testing. Their mineral density and mechanical properties were compared with those of a typical skeletal bone (the radius) in the same dog. Furthermore, a numerical model of a representative baculum was created and its mechanical performance analyzed using the finite element method, in order to try to elucidate its function. 

Examination of light microscopy images of transverse sections shows that the baculum consists of a typical sandwich structure, with two cortical plates separated, and joined, by loose cancellous bone. MicroCT scans reveal that the mineral density is lower in the baculum than in the radius, both in castrated as well as in uncastrated dogs, resulting in much lower stiffness. Castration was found to decrease the mineral density in both the baculum and the radius. 

The most likely function of the baculum of the dog is to stiffen the penis to assist intromission, and its much lower mineral density compared to that of the radius may be a mechanism designed to decrease the stiffness somewhat, and thus reduce the risk of fracture during copulation. (C) 2011 Elsevier Inc. All rights reserved.

Whereas detrimental effects of vitamin D deficiency are known over century, the effects of vitamin D receptor activation by 1,25(OH)(2)D-3, the principal hormonal form of vitamin D, on the growing bone and its growth plate are less clear. Currently, 1,25(OH)(2)D-3 is used in pediatric patients with chronic kidney disease and mineral and bone disorder (CKD-MBD) and is strongly associated with growth retardation. Here, we investigate the effect of 1,25(OH)(2)D-3 treatment on bone development in normal young rats, unrelated to renal insufficiency. Young rats received daily i.p. injections of 1 mu g/kg 1,25(OH)(2)D-3 for one week, or intermittent 3 mu g/kg 1,25(OH)(2)D-3 for one month. Histological analysis revealed narrower tibial growth plates, predominantly in the hypertrophic zone of 1,25(OH)(2)D-3-treated animals in both experimental protocols. This phenotype was supported by narrower distribution of aggrecan, collagens II and X mRNA, shown by in situ hybridization. Concomitant with altered chondrocyte maturation, 1,25(OH)(2)D-3 increased chondrocyte proliferation and apoptosis in terminal hypertrophic cells. In vitro treatment of the chondrocytic cell line ATDC5 with 1,25(OH)(2)D-3 lowered differentiation and increased proliferation dose and time-dependently. Micro-CT analysis of femurs from 1-week 1,25(OH)(2)D-3-treated group revealed reduced cortical thickness, elevated cortical porosity, and higher trabecular number and thickness. 1-month administration resulted in a similar cortical phenotype but without effect on trabecular bone. Evaluation of fluorochrome binding with confocal microscopy revealed inhibiting effects of 1,25(OH)(2)D-3 on intracortical bone formation. This study shows negative effects of 1,25(OH)(2)D-3 on growth plate and bone which may contribute to the exacerbation of MBD in the CKD pediatric patients.

Teeth adopt a variety of different morphologies, each of which is presumably optimized for performing specific functions during feeding. It is generally agreed that the enamel cap is a crucial element in controlling the mechanical behavior of mammalian teeth under load. Incisors are particularly interesting in terms of structure-function relations, as their role in feeding is that of the 'first bite'. However, little is known how incisor cap morphology is related to tooth deformation. In the present paper we examine the mechanical behavior of mandibular central incisors in the cercopithecine primate Macaca mulatta under loads similar to those encountered during ingestion. We map three-dimensional displacements on the labial surface of the crown as it is compressed, using electronic speckle pattern interferometry (ESPI), an optical metrology method. In addition, micro-computed tomography is used to obtain data regarding the morphology of the enamel cap, which in the M. mulatta lower incisors exhibits missing or very little enamel on the lingual face. The results showed that although compressed along a longitudinal axis, deformation in the incisors mostly occurred in the lingual direction and orthogonal to the direction of the applied load. Both isolated, embedded teeth and teeth in the mandible showed considerable lingual deformation. Incisor deformation in the mandible was generally greater, reflecting the additional freedom of movement enabled by the supporting structures. We show that the association with adjacent teeth in the arch is significant for the behavior of the tooth under load. Finally, loading two teeth simultaneously in the mandible showed that they work as one functional unit. We suggest that these results demonstrate the importance of enamel cap morphology in directing deformation behavior; an ability stemming from the stiffness of the enamel cap overlying the more pliable dentin.

Bone is a dynamic tissue that is continually undergoing a process of remodeling - an effect due to the interplay between bone resorption by osteoclasts and bone formation by osteoblasts. When new bone is deposited, some of the osteoblasts are embedded in the mineralizing collagen matrix and differentiate to osteocytes, forming a dense network throughout the whole bone tissue. Here, we investigate the extent to which the organization of the osteocyte network controls the collagen matrix arrangement found in various bone tissues. Several tissue types from equine, ovine and murine bone have been examined using confocal laser scanning microscopy as well as polarized light microscopy and back-scattered electron imaging. From comparing the spatial arrangements of unorganized and organized bone, we propose that the formation of a highly oriented collagen matrix requires an alignment of osteoblasts whereby a substrate layer provides a surface such that osteoblasts can align and, collectively, build new matrix. Without such a substrate, osteoblasts act isolated and only form matrices without long range order. Hence, we conclude that osteoblasts synthesize and utilize scaffold-like primary tissue as a guide for the deposition of highly ordered and mechanically competent bone tissue by a collective action of many cells. (C) 2010 Elsevier Inc. All rights reserved.

Study Design. In vitro compressive load-displacement experiments on intact rat lumbar vertebrae and on the same vertebrae after part of their trabecular bone was removed. 

Objective. To determine the contribution of the trabecular bone component to the stiffness and strength of rat lumbar vertebrae. 

Summary of Background Data. Vertebral fractures are common in the aging population, possibly resulting from the deterioration of the mechanical properties of vertebral bone. Studies of the contribution of trabecular bone to the mechanical behavior of whole vertebra were published, but yielded mixed results. Here, we propose a novel optical metrology approach to address this important question. 

Methods. The bodies of intact rat lumbar vertebrae and the bodies of the same vertebrae after part of their trabecular bone was removed were loaded within their elastic region in a wet environment. The amount of trabecular bone removed was determined by micro-computer tomography scanning. Deformation maps of the dorsal vertebral surface of the intact and manipulated vertebrae were obtained using an optical metrology method, and compared. Intact and manipulated vertebrae were also loaded to failure in compression and their strengths and stiffness were compared. 

Results. The preferred trabecular orientation was found to be along the anterior-posterior axis, which is similar to humans. Removal of up to 42% of the trabecular tissue in the intact vertebrae did not significantly affect lumbar vertebral stiffness. However, removal of even smaller amounts of the intact trabecular tissue significantly reduced vertebral strength. 

Conclusion. Trabeculae in rat lumbar vertebrae fulfill an important role in failure resistance (strength), but have little or no effect on the deformational behavior (stiffness) of the bone. These results differ from previous results we reported for rat femora, where removal of trabecular bone surprisingly increased the stiffness of the whole bone, and suggest that trabecular tissue may have different functions depending on anatomic location, bone function and morphology, and mode of loading.

Many studies have described the effects of exercise restriction on the mammalian skeleton. In particular, human and animal models have shown that reduction in weight bearing leads to generalised bone loss and deterioration of its mechanical properties. The aim of this study was to assess the effect of prolonged exercise restriction coupled with heavy Calcium demands on the micro-structural, compositional and mechanical properties of the avian skeleton. The tibiae and humeri of 2-year-old laying hens housed in conventional caging (CC) and free-range (FIR) housing systems were compared by mechanical testing and micro-computed tomography (mu CT) scanning. Analyses of cortical, cancellous and medullary bone were performed. 

Mechanical testing revealed that the tibiae and humeri of birds from the FIR group had superior mechanical properties relative to those of the CC group, and mu CT scanning indicated larger cortical and lower medullary regions in FR group bones. Cancellous bone analysis revealed higher trabecular thickness and a higher bone volume fraction in the FR group, but no difference in mineral density. The biomechanical superiority of bones from the FR group was primarily due to structural rather than compositional differences, and this was reflected in both the cortical and cancellous components of the bones. The study demonstrated that prolonged exercise restriction in laying hens resulted in major structural and mechanical effects on the bird skeleton. (C) 2008 Elsevier Ltd. All rights reserved.

This study examines the question of whether the stiffness (Young's modulus) of secondary osteonal cortical bone is different in compression and tension. Electronic speckle pattern interferometry (ESPI) is used to measure concurrently the compressive and tensile strains in cortical bone beams tested in bending. ESPI is a non-contact method of measuring surface deformations over the entire region of interest of a specimen, tested wet. The measured strain distributions across the beam, and the determination of the location of the neutral axis, demonstrate in a statistically-robust way that the tensile Young's modulus is slightly (6%), but significantly greater than that of the compressive Young's modulus. it is also shown that within a relatively small bone specimen there are considerable variations in the modulus, presumably caused by structural inhomogeneities. (C) 2008 Elsevier Ltd. All rights reserved.

Using electronic speckle pattern interferometry minipig molars were tested under load inside the bone socket and when embedded in a stiff polymer. It is demonstrated that the molar bends in the direction of the load in both configurations even at low loads. This shows that the intrinsic reaction of the tooth crown to load is complemented by the structures supporting the tooth.

To describe the location of the lateral thoracic artery (LTA), determine dimensions of an axial pattern flap based on this artery, and report use of this flap in 2 cats. 

Ex vivo study and case reports. 

Cat cadavers (n=8); cats (n=2) with thoracic limb skin defects. 

Dissection of the LTA was carried out on 1 side of each cadaver and the contralateral side was used for injection studies. In 4 specimens, the LTA was cannulated and injected with positive contrast material and the flap was raised and radiographed. In 4 specimens, the flap was injected with methylene blue. Adequacy of flap injection was subjectively evaluated and leakage of methylene blue from the cut edge was noted. 

The cutaneous location of the LTA caudal to the triceps muscle was confirmed. Mean flap size was 8.7 cm x 15.5 cm for a mature, averaged-sized cat. Perfusion of the entire flap was demonstrated and viability of the flap was confirmed in 2 clinical cases. 

The LTA flap is useful for repair of skin defects of the brachium and antebrachium in cats. 

The LTA flap is an alternative technique for repair of skin defects involving the thoracic limb of cats.

Data regarding the segmental inertial properties of the dog are currently unavailable, although such parameters are needed for dynamic analyses of canine motion. The purpose of this study was to measure the segmental inertial properties in three medium sized dogs of average build using magnetic resonance imaging. The parameters included the mass, location of centre of mass and moments of inertia for each body segment. The normalised results will serve as a preliminary foundation for various biomechanical studies in dogs, although further study is required to characterise them for specific dog breeds and to determine how they may be affected by age and gender. (C) 2008 Elsevier Ltd. All rights reserved.

Classical mechanical methods for testing whole bone have been critically assessed in a previous review where their limitations in terms of precision, accuracy and the amount of data yielded were described. This article describes the use of optical metrology methods and their novel adaptation to the study of whole bone response to mechanical load. Such methods overcome many of the limitations of mechanical testing: they do not require contact with the tested sample, are non-destructive, can be conducted on wet samples, and results comprise deformation maps of entire surfaces. The concepts upon which each method is based are reviewed. and examples of their use in biomechanical studies of bone are presented. Potential future applications that are expected to make significant contributions to the understanding of whole bone mechanics are outlined. (c) 2007 Elsevier Ltd. All rights reserved.

Mice phenotypes are invaluable for understanding bone formation and function, as well as bone disease. The elastic modulus is an important property of bones that can provide insights into bone quality. The determination of the elastic modulus of mouse cortical bone is complicated by the small dimensions of the bones. Whole bone bending tests are known to under estimate the elastic modulus compared to nanoindentation tests. The latter however provides information oil extremely localized areas that do not necessarily correspond to the bulk elastic modulus under compression. 

This study presents a novel method for determining the bulk or effective elastic modulus of mouse cortical bone using the femur. We use Electronic Speckle Pattern Interferometry (ESPI), an optical method that enables the measurement of displacements oil the bone surface, as it is compressed under water. This data is combined with geometric information obtained from micro-CT to calculate the elastic modulus. Roughly tubular cortical bone segments (2 mm) were cut from the diaphyses of femora of four week old C57BL/6 (86) female mice and compressed axially using a mechanical tension-compression device. Displacements in the loading direction were mapped oil the bone Surface after loading the specimen. A linear regression of the displacement vs. axial-position enabled the calculation of the effective strain. Effective stress was calculated using force (N) data from the system's load cell and the mean cross-sectional area of the sample as determined by micro-CT. The effective elastic modulus (E) Was Calculated from the Stress to strain ratio. The method was shown to be accurate and precise using a standard material machined to similar dimensions as those of the mouse femoral segments. 

Diaphyses Of Mouse femora were shown to have mean elastic moduli of 10.4 +/- 0.9 GPa for femora frozen for eight months, 8.6 +/- 1.4 GPa for femora frozen for two weeks and 8.9 +/- 1.1 GPa for the fresh femora. These values are much higher thin those measured using three-point bending, and lower than values reported in the literature based oil nanoindentation tests from mice bones of the same age. We show that this method can be used to accurately and precisely measure the effective elastic modulus of mouse cortical bone. (C) 2009 Elsevier Inc. All rights reserved.

In order to understand whole tooth behavior under load the biomechanical role of enamel and dentin has to be determined. We approach this question by comparing the deformation pattern and stiffness of intact teeth under load with the deformation pattern and stiffness of the same teeth after the enamel has been mechanically compromised by introducing a defect. FE models of intact human premolars, based on high resolution micro-CT scans, were generated and validated by in vitro electronic speckle pattern interferometry (ESPI) experiments. Once a valid FE model was established, we exploit the flexibility of the FE model to gain more insight into whole tooth function. Results show that the enamel cap is an intrinsically stiff biological structure and its morphology dictates the way a whole tooth will mechanically behave under load. The mechanical properties of the enamel cap were sufficient to mechanically maintain almost its entire stiffness function under load even when a small defect (cavity simulating caries) was introduced into its structure and breached the crown integrity. We conclude that for the most part, that enamel and not dentin dictates the mechanical behavior of the whole tooth. (C) 2009 Elsevier Inc. All rights reserved.

In order to understand whole tooth behavior under load the biomechanical role of enamel and dentin has to be determined. We approach this question by comparing the deformation pattern and stiffness of intact teeth under load with the deformation pattern and stiffness of the same teeth after the enamel has been mechanically compromised by introducing a defect. FE models of intact human premolars, based on high resolution micro-CT scans, were generated and validated by in vitro electronic speckle pattern interferometry (ESPI) experiments. Once a valid FE model was established, we exploit the flexibility of the FE model to gain more insight into whole tooth function. Results show that the enamel cap is an intrinsically stiff biological structure and its morphology dictates the way a whole tooth will mechanically behave under load. The mechanical properties of the enamel cap were sufficient to mechanically maintain almost its entire stiffness function under load even when a small defect (cavity simulating caries) was introduced into its structure and breached the crown integrity. We conclude that for the most part, that enamel and not dentin dictates the mechanical behavior of the whole tooth. (C) 2009 Elsevier Inc. All rights reserved.

The objective of this study was to describe seven cases of unilateral bacterial infective coxarthritis from a total of 19 cases of bacterial infective arthritis (BIA), presenting over a two year period. We recorded the history, clinical signs, diagnostic process, treatment and clinical outcome in these cases. The data were obtained,from medical records, review of the radiographs, and telephone follow-up with the owners. All of the dogs in this study had severe chronic osteoarthritis secondary to hip dysplasia, which caused periodic hind limb lameness. They were all admitted with severe acute hind-limb lameness. Pelvic radiographs were performed under general anaesthesia shortly after presentation, followed immediately by orthrocentesis of the affected joint. The synovial fluid was evaluated microscopically by direct smear and a sample was sent for culture and sensitivity. An attempt was not made to drain or lavage the affected joint during the course of treatment. The initial choice of antibiotics was empiric and subsequently modified, as required, based on the sensitivity results. Four of the dogs showed a rapid return to weight-bearing after the initiation of antibiotic treatment, and all of the patients returned to their pre-BIA level of function. Neither recurrent infections nor any adverse sequela requiring further intervention were reported by the owners on telephone follow-up.

Bone is a composite hierarchical structure composed of a cortical shell and inner trabecular tissue. One ofthe most basic questions in whole-bone function is the relative contributions of cortical and trabecular bonetissues to the loaded whole bone. In this study, the manner in which the cortical surfaces of an intact proximal rat femur deform under load is compared to the same femur after some of the trabecular bone inthe distal femoral neck was removed. The surface displacements were measured by electronic speckle pattern interferometry (ESPI) and the extent of trabecular bone removed was determined by high resolution micro-CT scanning. The results show that after damaging the trabecular bone tissue in the distal femoral neck, the manner in which compressive loads are transformed to other regions of the femoral neck changed.The whole bone behaved in a 'stiffer' manner. This demonstrates the importance of connectivity of thetrabeculae and that beyond a certain threshold of damage the normal load-transferring mechanism is impaired. Since these experiments were carried out in a non-contact non-destructive manner in a wet environment and the rat femur was loaded in a close-to physiological manner, we postulate that our results have a direct relevance to the in vivo biomechanical behavior of the femoral neck.

Introduction: The relationship between load and the structure and mechanical Properties of mature bones has been thoroughly described. In contrast, this relationship has been studied much less in immature bones, which consist of bony tissue and cartilaginous growth plate, during the postnatal period. This paper describes the effect of an externally applied load on the bones of young fast-growing chicks; in particular, we examine the effect on the growth plate, which regulates longitudinal bone growth, and the consequences in terms of bone structural and mechanical properties. Materials and methods: The tibial growth plates from chicks subjected to external load and control chicks, immediately after loading and following 5 days of load release, were studied by histological staining and quantitative PCR. The contralateral tibiae were mechanically tested by three-point bending and their structural features determined by micro-CT. Results: At the end of the external loading period, the tibias of the experimental group were shorter and their growth plate narrower than in controls. However, at this time point, effects were not yet apparent in the bones' structural or mechanical parameters. After a further 5 days of no external load, bones and growth plates of the experimental group demonstrated the phenomenon of 'catch-up': the thickness of the growth plate exceeded that of the control; however the relative expression of genes controlling chondrocyte differentiation (collagen II and X) did not change, while the expression of factors related to growth-plate ossification (osteopontin, alkaline phosphatase) and cartilage and bone calcification (matrix and bone Gla proteins) was upregulated as a result of the catch-up process. At this time, however, the tibiae of the experimental group showed inferior mechanical and structural Properties relative to the Control group. Conclusion: External loading during bone elongation negatively affects the mechanical and Structural properties of the skeleton. The effect is first noticeable in the growth plate, which regulates bone growth, and is exhibited in the bone phenotype after a lag period. (c) 2008 Elsevier Inc. All rights reserved.

The mechanical behaviour of material bone can be completely described by a group of material properties. The mechanical behaviour of the entire bone organ, however, is much more difficult to predict; it is the result both of the properties of the material of which it is made, and of the geometric spatial architecture in which this is arranged. 

This review first describes material bone in terms of its complex, graded and hierarchical structure. Basic concepts used in the field of mechanics of materials are defined and explained and then used to describe the mechanical properties of whole bone. Some clinical implications of these properties are provided. Commonly used mechanical testing methods for the study of the mechanical behaviour of whole bone are reviewed and the technical difficulties associated with them are discussed. (C) 2007 Elsevier Ltd. All rights reserved.

Background. In the context of osteoporosis, important determinants of the fracture risk are the apparentstrength and stiffness of cancellous bone, as well as its brittleness and energy absorption capacity. Standard medical imaging, however, cannot measure these mechanical properties directly. Consequently, an estimation of the risk for fracture is made by correlating relative density or mineral density at a skeletal site with statistics of fracture occurrence, which provides limited and partial indications on fracture risks. Abetter method for evaluating the patient-specific mechanical properties of cancellous bone is therefore required. 

Methods. In order to asses the mechanical properties of vertebral cancellous bone, we developed a finite element parametric model of lattice trabecular architecture that, in the future, will be suitable for use withbone imaging modalities. The model inputs are apparent morphological parameters (trabecular thickness and trabecular separation) and the bone mineral density. We conducted uniaxial compression tests on 36 canine vertebral cancellous bone specimens (C7 and L1) to validate model predictions of strength and stiffness in vitro. 

Findings. Predictions of strength and stiffness matched the experimental results within relative absolute errors of 17.7% and 12.8%, respectively (average of differences between model-predicted and measured values, divided by the average of measured values). We also employed the model for evaluation of strengthand stiffness of human L1 and L5 vertebrae and found mean strength of 1.67 MPa (confidence interval 0.42 MPa) and mean elastic modulus of 190 MPa (confidence interval 50 MPa), which are well within the range ofpreviously reported apparent strength and stiffness properties. 

Interpretation. The present model can be used to improve medical imaging-based evaluation of the spine inosteoporotic individuals by providing more specific information on the individual bone's susceptibility to fracture once clinical bone scans will be able to provide more reliable measures of trabecular thickness and separation. (c) 2006 Elsevier Ltd. All rights reserved.