Bone Tissue Density Research Articles

Influence of Bone Tissue Density and Elasticity on Ultrasound Propagation: An In Vitro Study

Ultrasound (US) waves are mechanical vibrations that are applied to a material--bone tissue--in order to study its properties, that is, density, elasticity, and structure. In this study we evaluated in which way density and elasticity of the spongy bone influenced the transmission of 1.25 MHz US pulses. Twelve cylindrical specimens (diameter, 8 mm; height, 5 mm) excised from phalanxes of pig were decalcified with 0.5 M EDTA for different times (0, 2, and 5 days). During these periods, the samples underwent the following investigations: US transmission, density, and elasticity measurements. To assess the homogeneity of decalcification, the cross-sections of some samples were microradiographed. A detailed analysis of the US signal received was performed using velocity, Fourier analysis, and some parameters typical of signal processing technique. A good correlation was found between US velocity and density (r2 = 0.70); a lower correlation was found between velocity and elasticity (r2 = 0.59). If density and elasticity are considered simultaneously, the correlation with the US velocity improves significantly (r2 = 0.84). Fourier analysis enabled us to observe a shift of the main frequency toward lower values as the decalcification process advanced. We also observed that in the regressions weighted for density, US velocity correlated poorly with elasticity (r2 = 0.16), whereas signal processing parameters maintain a good correlation with elasticity (ultrasound peak amplitude [UPA], r2 = 0.48; slope, r2 = 0.62). In this study, it has been observed that when using a signal processing technique to analyze US pulses, it is possible to identify some parameters that are related in different ways to density and to elastic properties of bone. Our results show the potentiality of US technique to separate information on bone density and elasticity that X-ray-based densitometric methods do not provide.

Properties of growing trabecular ovine bone

Our aim was to determine the relationship between age and the mechanical and physical properties of trabecular bone, to describe the patterns in which the variations in these properties take place, and to investigate the influence of the physical properties on the mechanical characteristics of trabecular bone during growth. We used 30 lambs in three age groups and 20 sheep in two age groups. Cubes of subchondral bone were cut from the proximal tibia according to a standardised protocol. We performed non-destructive compression tests of the specimens in three orthogonal directions and compression tests to failure in the axial direction. The physical properties of the specimens were also determined. The data were correlated with age and compared in skeletally immature and mature animals. Multiple regression analyses were performed between the mechanical and the physical properties. Age correlated positively with elastic modulus, bone strength, energy absorption to failure, elastic energy, mechanical anisotropy ratio, tissue density, apparent density, apparent ash density, and bone mineral content, and inversely with ultimate strain, viscoelastic energy absorption, relative energy loss, the collagen content of bone and the percentage porosity. The values of all variables were significantly different in the skeletally mature and immature groups. The apparent density of trabecular bone tissue was found to be the major predictor of its compressive mechanical properties. Together with the content of bone muscle and bone collagen, the apparent density could explain 84% of the variation in the elastic modulus, whereas only a small portion of the variation in ultimate strain could be explained by the variation in apparent density.

Material properties assignment to finite element models of bone structures: a new method

Finite element analysis (FEA) is widely adopted to investigate the mechanical behaviour of bone structures. Computed tomography (CT) data are frequently used to generate FE models of bone. If properly calibrated, CT images are capable of providing accurate information about the bone morphology and tissue density. The aim of this work was to develop a special program able to read a CT data set as well as the FEA mesh generated from it, and to assign to each element of the mesh the material properties derived from the bone tissue density at the element location. The program was tested on phantom data sets and was adopted to evaluate the effects of the discrete description of the bone material properties. A three-dimensional FE model was generated automatically from a 16 bit CT data set of a distal femur acquired in vivo. The strain energy density (SED) was evaluated for each model element for increasing model complexity (number of different material cards assigned to the model). The computed SED were strongly dependent on the material mapping strategy.

A theoretical model to predict distribution of the fabric tensor and apparent density in cancellous bone.

The adaptation of cancellous bone to mechanical forces is well recognized. Theoretical models for predicting cancellous bone architecture have been developed and have mainly focused on the distribution of trabecular mass or the apparent density. The purpose of this study was to develop a theoretical model which can simultaneously predict the distribution of trabecular orthotropy/orientation, as represented by the fabric tensor, along with apparent density. Two sets of equations were derived under the assumption that cancellous bone is a biological self-optimizing material which tends to minimize strain energy. The first set of equations provide the relationship between the fabric tensor and stress tensor, and have been verified to be consistent with Wolff's law of trabecular architecture, that is, the principal directions of the fabric tensor coincide with the principal stress trajectories. The second set of equations yield the apparent density from the stress tensor, which was shown to be identical to those obtained based on local optimization with strain energy density of true bone tissue as the objective function. These two sets of equations, together with elasticity field equations, provide a complete mathematical formulation for the adaptation of cancellous bone.

Effect of antiandrogens casodex and epitestosterone on bone composition in mice

Nonsteroidal antiandrogen casodex and steroidal antiandrogen epitestosterone were administered to intact male mice, and their effect on femoral bones and circulating calcium, phosphate, testosterone, and LH were compared with controls and castrated animals. Pure antiandrogen casodex in a dose used in humans for treatment of prostate cancer decreased the weight of seminal vesicles, organ which is highly sensitive to the androgenic effect, increased insignificantly the concentration of LH and of testosterone, but did not have any effect on bone density or mineral content of bone. Epitestosterone, which not only inhibits the binding of androgens to their receptors but also inhibits the formation of dihydrostestosterone from testosterone, and is reported to interfere with aromatization of testosterone to estrogens, decreased the bone density, ash weight, and calcium and phosphate content of femoral bone tissue significantly, although not to values as low as those seen in castrated animals.

Regular exercise dissociates fat mass and bone density in premenopausal women.

Body weight is one of the principal determinants of bone density and fracture frequency, but there is significant disagreement in the literature regarding the relative contributions of the lean and fat components of body weight to this relationship. As previous studies have not considered the possible role of exercise in soft tissue-bone density interrelationships, we measured areal bone mineral density (BMD), fat mass, and lean mass in eumenorrheic premenopausal women and determined whether the interrelationships of these variables are influenced by the subject's exercise status. Subjects with mean activity levels of more than 140 kilojoules/kg.day (equivalent to undertaking vigorous physical activity for > 1.5 h/week) were classified as exercisers. In the nonexercising subjects (n = 36; age, 36 +/- 8 yr), BMD was markedly weight dependent (0.45 < r < 0.62), and this was contributed to by both fat and lean tissue. Because this finding may have arisen from the mutual dependence of soft tissue mass and areal BMD on body size, fat and lean masses were reexpressed as a percentage of body weight. The percent fat tended to be positively related to areal BMD (0.23 < r < 0.35), whereas the percent lean was inversely related to this index. A second way of obviating the mutual dependence of soft tissue mass and areal BMD on body size is to derive BMD/height as an index of volumetric bone density. This parameter was only related to lean mass in the femur, whereas the correlations with fat mass were little changed. The percent fat was positively (0.29 < r < 0.43) and the percent lean was negatively (-0.43 < r < -0.29) related to BMD/height throughout the skeleton, including the femur. In the exercising subjects (n = 63; age, 33 +/- 8 yr), fat mass and lean mass were unrelated to BMD/height (r < 0.23). However, the percent lean was positively correlated with BMD and BMD/height in the femoral neck (r = 0.28 and r = 0.31, respectively). It is concluded that bone density is only associated with fat mass in sedentary women. In exercisers, femoral neck density is related to lean mass, possibly through the effects of weight-bearing exercise on both of these variables.

Nonequilibrium bone remodelling: Changes of mass density and of the axes of anisotropy

This paper is concerned with some aspects of bone tissue remodelling brought about by a change of the daily loading history. The mathematical model of remodelling is based on the assumption that every deformation state corresponds with a single thermodynamically balanced state of bone tissue and that the rate of changes of all parameters characterizing the bone tissue is determined by its strain history. It is assumed that the rate of the change of the bone tissue density depends on the history of the difference between the equilibrium and the actual densities. If we know the experimentally ascertained relation between the equilibrium density and the formation deformation state, we can compute from the derived integral equation the density at any moment of time. The equilibrium orientation of the principal axes of anisotropy is coaxial with the principal axes of strain. The position of the equilibrium and actual systems of the axes of anisotropy with regard to the reference coordinate system can be expressed at any moment by the vectors of rotation of these systems. If we assume small rotations, the rate of rotation of the system of axes of anisotropy can be expressed by the history of the difference of these vectors. From the strain history and the derived vector integral equation it is possible to compute the vector determining the spatial orientation of the principal axes of anisotropy at any moment of time.

The effect of grip strength on radial bone in postmenopausal women.

This communication explores the correlation in 255 postmenopausal women of grip strength to bone tissue density (BTD) and cross-sectional area (CSArea) of the radius. While grip strength correlated cross-sectionally with the baseline measures of both BTD and CSArea, grip strength affected differentially the changes that transpired in the two bone parameters over the 3 years of the study. Thus, the increases in the CSArea of the radius were significantly enhanced by higher grip strength, while BTD losses were not. Since the power of muscle contraction is a factor in the mechanical loading of a bone, it is argued that the differential effects of grip strength on the two bone parameters of the radius suggest that moderate loading can effect favorable changes in the geometry of the bone, without necessarily affecting changes in BTD.

Instrumentation and techniques in bone density measurement

Bone disease represents one of the most common diseases in the western world. Often the result is rarefied bone tissue, which leads to a loss in bone strength and is a precursor to clinical osteoporosis. Many different techniques have been used to determine the density of bone tissue at the most important clinical sites in the skeleton for diagnosis of the disease. Measurement of total attenuation or scattering of a radiation beam, attenuation of ultrasonic beams and the activation through neutron irradiation have all been used. This review first considers the skeletal changes that need to be monitored and then considers each technique in turn. When comparing the success of these different approaches accuracy, precision, site of measurement, patient convenience, sensitivity and radiation hazard must all be taken into account.

Stiffness of compact bone: Effects of porosity and density

Stiffness of compact bone is found to be highly and nonlinearly dependent on its porosity, its complement, bone volume fraction and apparent density. Elastic modulus decreases as a power (0.55) of increasing porosity and increases both as a power of increasing bone tissue volume (10.92) and increasing apparent density (7.4). These data indicate that small changes in the amount or density of compact bone tissue exert a more pronounced influence on its stiffness than would similar changes in trabecular bone.

Developments in the Use of X-Rays in Body Composition Analysis

Quantitative assay of body components in the living human is a subject of keen interest. Measurement of such fractions on superficial view seems a simple analysis problem. In fact, the opposite is true. The ‘specimen’ is not amenable to the usual destructive analytical procedures. Due to its importance, a continued effort has been mounted to assay the most basic of such components. This paper and bibliography traces the recent applications of penetrating radiation for such analysis.Some of the fractions whose measurement has been attempted are; bone mineral, adiposity (lipid to lean ratio), body hydration, tissue density, voids and spaces (i.e. lung). The importance of quantitative analysis of such gross components is apparent when taking mineralization as example.

ROENTGEN CHANGES IN EARLY RHEUMATOID ARTHRITIS. WRISTS--HANDS--FEET.

Rheumatoid arthritis is a systemic disease which locally involves the joint synovial membrane. The alterations of soft tissue, cartilage, and bone are secondary to the pathologic changes occurring within this very dynamic structure (Table I). This communication will describe the most pertinent radiologic findings in the earliest phases which may assist the clinician in making the diagnosis. It is imperative that the radiologist recognize these early changes so that proper therapeutic measures may be instituted promptly and effectively. The soft-tissue alterations must be studied carefully since they may be the first findings apparent and in some instances may be demonstrated radiographically before physical signs are evident. The characteristic early erosive bone changes in this disease will be described and correlated with the clinical and pathologic findings. Material The roentgen findings have been reviewed in a group of 250 early adult rheumatoid patients. The diagnosis was made according to criteria set forth by the American Rheumatism Association (12). Standard equipment has been employed with careful technic stressed to emphasize soft-tissue detail where possible. During the past three years, it has been routine in all cases to include a postero-anterior projection of the hands, wrists, and feet, as well as lateral studies of the feet, regardless of symptomatology. Undoubtedly a more extensive survey would be helpful, but perhaps not practical. The hands, wrists, and feet often assist in establishing the differential diagnosis even though these joints may be asymptomatic at the time. Bywaters (3) in an excellent review in 1960 stated: “We have not found projection of value, ”which in general is true. In some instances, however, supine views are necessary in addition to the standard prone projection to visualize metacarpal phalangeal joints of the hand. We have also found lateral and tangential projections of specific joints useful in detecting subtle changes. Review of Literature The importance of soft-tissue structure has been stressed many times previously, but this concept has apparently fallen into disrepute. Ferguson (7) in 1936 stated: “Roentgenograms for the detection of rheumatoid arthritis should depict the soft-tissue shadows as clearly as the bone shadows. In rheumatoid arthritis, particularly in the early stages, there are changes in the soft tissues at the joints and changes in relative density of bone and soft tissue which are important and can be detected only if the soft tissues are clearly pictured.” Ferguson recommended “that the hands, feet, knees, and the lumbar spine be examined in every case in which doubt as to the diagnosis existed regardless of the presence or absence of clinical evidence of disease in the region mentioned.”

THE PATHOGENESIS AND TREATMENT OF DELAYED UNION AND NON-UNION

1. The mechanism of non-union of fractures of the tibia, common to all clinical circumstances of this condition, is fibrinoid degeneration of connective tissue in the interior of the callus. Fibrinoid forms when the bone injury has been extensive, has been complicated by infection, or has been difficult to immobilize. The process appears to be similar to that seen in chronic adventitious bursitis. If motion and friction are not controlled, fibrinoid degeneration continues indefinitely, and a permanent pseudarthrosis may develop. Immobilization acts as a deterrent to the formation of fibrinoid and permits the refilling of the defect with new fibrocartilaginous callus. 2. Fibrinoid is not a simple barrier to osteogenesis; it indicates a defective callus. Fibrinoid fails to draw osteogenesis from the periosteum and endosteum across the fracture gap. According to interpretations of the newer theory of osteogenesis, it lacks the ability of cartilage and fibrocartilage to promote new-bone formation by induction. 3. The effect of open operations on fresh fractures is to increase the volume of damaged bone which has to be absorbed and replaced before the fracture can unite and permit full weight-bearing on the leg. Comminuted fractures of the shaft of the human adult tibia should be considered non-operable fractures during the first six months of healing, because the trauma added by surgery exceeds the normal capacity for bone regeneration in this area of the skeleton. 4. Bone-grafting, without excision of the fibrocartilaginous callus, may be applied successfully in ununited fractures of the tibia before eighteen months of healing. Excision of the pseudarthrosis, osteotomy of the fibula, and telescoping of the fracture ends are advisable in ununited fractures after eighteen months. All of the standard surgical procedures of onlay, inlay, or intramedullary bone grafts are capable of producing union with the aid of one additional year of immobilization of the fracture, but the success of the operation is determined by the proliferative reaction of the bone ends, not the bone graft. If the bone ends are in close contact, the function of the graft appears to be that of an inductor. 5. Recurrence of sepsis is the chief cause of failure of all types of bone-graft operations. Roentgenograms which show a diffuse increase in density of bone tissue three or four centimeters above and below the fracture line indicate latent sepsis. In such cases six months, or even two years, without drainage is not a safe period of waiting to permit a bone-graft operation. Only synostosis operations which avoid the fracture site are free of risks of further damage to the bone ends by infection. 6. Radical leg-shortening procedures are an alternative to amputation and may be applicable in old ununited fractures with large soft-tissue defects after repeated failure of bone-grafting operations.