A physical model for simulating fusion of impaction-grafted morselized cancellous bone

This article describes a method to simulate fusion of morselized cancellous bone. The morselized cancellous bone is mixed with an epoxy adhesive, in empirically determined proportions. The mixture is then impacted into a construct. When the epoxy cures, the morselized material fuses into a cohesive, contiguous structure with a compressive modulus equivalent to that of intact cancellous bone. This model can be used to study biomechanical aspects of fused impaction grafts.     

Cancellous and cortical morselized allograft in revision total hip replacement: A biomechanical study of implant stability

To restore femoral intramedullary bone stock loss in revision surgery of failed total hip arthroplasties, impacted morselized cancellous allograft is recommended. This study investigated the mechanical properties of both impacted cortical (group A) and cancellous (group B) morselized bone graft for reconstruction of femoral bones. Ten matched pairs of fresh frozen human femora were prepared by over-reaming to create a smooth-walled cortical shell. Each pair had one cortical and one cancellous impacted morselized allograft and cement. Stem subsidence was evaluated by a cyclic axial load, which was applied by a servohydraulic test. The stem subsidence was measured for initial subsidence (subsidence at the first 1000 cycles), the total axial subsidence (subsidence at the end of cycles under load) and the final axial subsidence (subsidence after the unloading phase). Torque test was measured by torsional loads through the prosthetic femoral heads. Total axial subsidence was significantly higher in group B (mean: 1.32+/-0.32 mm) compared to group A (mean: 0.94+/-0.26 mm) (P<0.01).There was no significant difference between the two groups in terms of initial subsidence (P=0.09) and final axial subsidence.The mean maximum torque before failure was 39.5+/-22.2 N-m for the cortical morselized allograft and 32.5+/-18.1N-m for cancellous.We concluded that impacted morselized cortical bone graft used for reconstruction of contained femoral bone loss in revision hip arthroplasty, may reduce the stem subsidence. Further animal experimentation for mechanical and histological evaluation of in vivo application is warranted.     

Particle size influence in an impaction bone grafting model. Comparison of fresh-frozen and freeze-dried allografts

BackgroundImpaction bone grafting with large particles is considered as mechanically superior to smaller morsels. Interest of freeze-dried irradiated bone for impaction bone grafting has been observed with small particles. Influence of bone process on other particle sizes still needed to be assessed.Material and methodsTwenty-four osteoarthrotic femoral heads were used to prepare fresh-frozen and freeze-dried irradiated cancellous bone. Each group was divided into four batches of different particle sizes, each batch containing 18 samples. The different particle sizes were obtained with a Retsch Cross Beater Mill SK 100, Noviomagus rotating bone mills with two sizes of rasps and a Luer bone rongeur. Bone grafts were impacted in a contained cylinder. Stiffness was monitored during impaction.ResultsFreeze-dried irradiated grafts showed higher stiffness than fresh-frozen bone whatever the size of the particles. Large particles obtained with the rongeur and the large rasp from the Noviomagus bone mill were mechanically superior than small particles up to 30 impactions.InterpretationLarge particles offer better mechanical performance as a greater magnitude of force would be required to deform and break the particles. Freeze-dried irradiated bone brittleness reduces this advantage after 30 impactions. Large particles embrittlement leads to similar mechanical results as small particles at higher impaction rate. This may account for partial collapse of the graft layer in clinical situation when impaction rate is lower. This model supports the use of small particles obtained with thin rasp bone mill when freeze-dried irradiated bone for impaction bone grafting and large particles obtained with the Rongeur when fresh-frozen bone is available.     

Short-term load bearing capacity of osteochondral autografts implanted by the mosaicplasty technique: an in vitro porcine model

Articular surface congruency and graft stability are considered essential factors in the success of osteochondral grafting; however, quantitative measures of short-term load bearing capacity of grafts implanted by the mosaicplasty technique have not been reported. The purpose of this study was to develop a live tissue in vitro model to examine short-term fixation strength of mosaicplasty autografts immediately after and 1 week following graft implantation. Cylindrical osteochondral autografts were implanted in vitro by the mosaicplasty technique on five pairs of porcine femoral condyles within one and a half hours of animal sacrifice. Immediately following the surgical procedure, graft push-in and pull-out strength tests as well as indentation tests to determine modulus of the surrounding cancellous bone were performed on half of the specimens from the distal femurs of each animal. The remaining specimens, matched for location in the contralateral leg, were incubated in culture medium for 7 days prior to performing the same set of mechanical tests. Averaged push-in and pull-out graft fixation strength decreased 44% from 135.7 to 75.5N over the 7-day period, while no change in modulus was detected in the surrounding cancellous bone. These in vitro results demonstrate a substantial deterioration of short-term fixation strength of mosaicplasty grafts from the immediate post-operative state. Such a reduction in short-term graft load bearing capacity may pose a threat to the surgically established articular surface congruency and blood vessels formed during the early stages of the healing response.     

The use of Irradiated Allografts in Posterior Spinal Fusion for Healed Tubercular Kyphosis in Children

Post-tubercular spinal kyphosis in children is not only cosmetically unacceptable but functionally disabling as well, as with the progression of the deformity there is a very significant risk of late onset paraplegia. We present our preliminary results in a prospective study of 12 cases of healed post-tubercular kyphosis in children treated with isolated posterior spinal fusion using irradiated allografts and autogenous cancellous grafts.The study included 12 patients of healed post-tubercular kyphosis documented by clinical, radiological and haematological criteria, with >2 spine at risk signs radiologically. The mean age was 7 years. In situ posterior spinal fusion with irradiated allografts and autogenous cancellous bone graft without any instrumentation was done for all the patients. The total follow-up is 5 years (mean 2.8 years).Eight patients (66%) showed a correction of the kyphosis, 3 patients (25%) were static and only 1 patient showed worsening of the deformity. Eleven patients had sound fusion and 1 patient had good fusion but a pseudoarthrosis at the lower vertebral level.Good posterior fusion was achieved because of the judicious use of morcellised, irradiated cancellous allografts with autogenous cancellous grafts. The proposed mechanism of correction is selective anterior column growth vis-à-vis posterior fused mass leading to gradual self-correction and remodelling.Conclusion. In situ posterior spinal fusion with irradiated allografts is a simple, safe, easily reproducible, less morbid surgical procedure with good results which may alter the long term disability of the patients.     

Comparison of contamination of femoral heads and pre-processed bone chips during hip revision arthroplasty

With bone impaction grafting, cancellous bone chips made from allograft femoral heads are impacted in a bone defect, which introduces an additional source of infection. The potential benefit of the use of pre-processed bone chips was investigated by comparing the bacterial contamination of bone chips prepared intraoperatively with the bacterial contamination of pre-processed bone chips at different stages in the surgical procedure. To investigate baseline contamination of the bone grafts, specimens were collected during 88 procedures before actual use or preparation of the bone chips: in 44 procedures intraoperatively prepared chips were used (Group A) and in the other 44 procedures pre-processed bone chips were used (Group B). In 64 of these procedures (32 using locally prepared bone chips and 32 using pre-processed bone chips) specimens were also collected later in the procedure to investigate contamination after use and preparation of the bone chips. In total, 8 procedures had one or more positive specimen(s) (12.5 %). Contamination rates were not significantly different between bone chips prepared at the operating theatre and pre-processed bone chips. In conclusion, there was no difference in bacterial contamination between bone chips prepared from whole femoral heads in the operating room and pre-processed bone chips, and therefore, both types of bone allografts are comparable with respect to risk of infection.     

Impacted morselized cancellous bone: mechanical effects of defatting and augmentation with fine hydroxyapatite particles

Geotechnical engineering testing techniques were used to study the mechanical properties of morselized cancellous bone (MCB) and the effects of defatting and augmentation with fine hydroxyapatite (HA) particles. Bovine and human cancellous bone was morselized, rinsed, and manually squeezed to remove excess fluid, producing a standard surgical MCB sample that was also used as a control. Some of the MCB was defatted with heat and detergent and mixed with HA particles in ratios ranging from 0% to 100% HA. Compaction tests were used to determine the effects of moisture content and the amount of MCB that can be packed into a confined space. One-dimensional consolidation tests were used to determine the uniaxial strain behavior, confined modulus, and steady-state creep rate. The compaction tests demonstrated that defatting and adding HA particles significantly increased density. The one-dimensional consolidation tests showed that strain was decreased, modulus was increased and the creep rate was decreased by defatting and adding HA.     

Effect of thermodisinfection on mechanic parameters of cancellous bone

Revision surgery of joint replacements is increasing and raises the demand for allograft bone since restoration of bone stock is crucial for longevity of implants. Proceedings of bone grafts influence the biological and mechanic properties differently. This study examines the effect of thermodisinfection on mechanic properties of cancellous bone. Bone cylinders from both femoral heads with length 45 mm were taken from twenty-three 6–8 months-old piglets, thermodisinfected at 82.5 °C according to bone bank guidelines and control remained native. The specimens were stored at ?20 °C immediately and were put into 21 °C Ringer’s solution for 3 h before testing. Shear and pressure modulus were tested since three point bending force was examined until destruction. Statistical analysis was done with non-parametric Wilcoxon, t test and SPSS since p < 0.05 was significant. Shear modulus was significantly reduced by thermodisinfection to 1.02 ± 0.31 GPa from 1.28 ± 0.68 GPa for unprocessed cancellous bone (p = 0.029) since thermodisinfection reduced pressure modulus not significantly from 6.30 ± 4.72 GPa for native specimens to 4.97 ± 2.23 GPa and maximum bending force was 270.03 ± 116.68 N for native and 228.80 ± 70.49 N for thermodisinfected cancellous bone. Shear and pressure modulus were reduced by thermodisinfection around 20 % and maximum bending force was impaired by about 15 % compared with native cancellous bone since only the reduction of shear modulus reached significance. The results suggest that thermodisinfection similarly affects different mechanic properties of cancellous bone and the reduction of mechanic properties should not relevantly impair clinical use of thermodisinfected cancellous bone.     

Prediction of femoral head collapse in osteonecrosis

The femoral head deteriorates in osteonecrosis. As a consequence of that, the cortical shell of the femoral head can buckle into the cancellous bone supporting it. In order to examine the buckling scenario we performed numerical analysis of a realistic femoral head model. The analysis included a solution of the hip contact problem, which provided the contact pressure distribution, and subsequent buckling simulation based on the given contact pressure. The contact problem was solved iteratively by approximating the cartilage by a discrete set of unilateral linear springs. The buckling calculations were based on a finite element mesh with brick elements for the cancellous bone and shell elements for the cortical shell. Results of 144 simulations for a variety of geometrical, material, and loading parameters strengthen the buckling scenario. They, particularly, show that the normal cancellous bone serves as a strong supporting foundation for the cortical shell and prevents it from buckling. However, under the development of osteonecrosis the deteriorating cancellous bone is unable to prevent the cortical shell from buckling and the critical pressure decreases with the decreasing Young modulus of the cancellous bone. The local buckling of the cortical shell seems to be the driving force of the progressive fracturing of the femoral head leading to its entire collapse. The buckling analysis provides an additional criterion of the femoral head collapse, the critical contact pressure. The buckling scenario also suggests a new argument in speculating on the femoral head reinforcement. If the entire collapse of the femoral head starts with the buckling of the cortical shell then it is reasonable to place the reinforcement as close to the cortical shell as possible.     

Modeling of summation of individual twitches into unfused tetanus for various types of rat motor units.

Repeated stimulation of motor units (MUs) causes an increase of the force output that cannot be explained by linear summation of equal twitches evoked by the same stimulation pattern. To explain this phenomenon, an algorithm for reconstructing the individual twitches, that summate into an unfused tetanus is described in the paper. The algorithm is based on an analytical function for the twitch course modeling. The input parameters of this twitch model are lead time, contraction and half-relaxation times and maximal force. The measured individual twitches and unfused tetani at 10, 20, 30 and 40 Hz stimulation frequency of three rat motor units (slow, fast resistant to fatigue and fast fatigable) are processed. It is concluded that: (1) the analytical function describes precisely the course of individual twitches; (2) the summation of equal twitches does not follow the results from the experimentally measured unfused tetani, the differences depend on the type of the MU and are bigger for higher values of stimulation frequency and fusion index; (3) the reconstruction of individual twitches from experimental tetanic records can be successful if the tetanus is feebly fused (fusion index up to 0.7); (4) both the maximal forces and time parameters of individual twitches subtracted from unfused tetani change and influence the course of each tetanus. A discrepancy with respect to the relaxation phase was observed between experimental results and model prediction for tetani with fusion index exceeding 0.7. This phase was predicted longer than the experimental one for better fused tetani. Therefore, a separate series of physiological experiments and then, more complex model are necessary for explanation of this distinction.     

Volume maintenance of inlay bone grafts in the craniofacial skeleton

Although the clinical use of inlay bone grafts is widespread in craniofacial surgery, the dynamics of inlay bone grafting to the craniofacial skeleton have never been well characterized. Previous work demonstrated that volume maintenance of bone grafts in the onlay position is a consequence of their microarchitectural features, rather than their embryological origins. The purpose of this study was to investigate whether the properties determining the volume maintenance of bone grafts in the onlay position in the craniofacial skeleton could be extended to bone grafts in the inlay position. It was hypothesized that volume maintenance of an inlay bone graft could be better explained on the basis of the microarchitectural features of the graft (cortical versus cancellous composition), rather than its embryological origin (membranous versus endochondral), and that the primary determinant of bone graft behavior is the interaction between the microarchitectural features of the bone graft and the local mechanical environment in which the bone graft is placed. Cortical and cancellous bone grafts were harvested from the iliac crest (endochondral origin) of 25 New Zealand white rabbits, and cortical bone was harvested from the mandible (membranous origin) of each rabbit. Four 7-mm trephine holes were made in the cranium of each rabbit, posterior to the coronal suture. Each defect was filled with endochondral cortical bone, endochondral cancellous bone, or membranous cortical bone or was left as an ungrafted control specimen. Animals were killed at 3, 8, or 16 weeks. Crania were subjected to micro-computed tomographic and histological assessments. Micro-computed tomographic analysis demonstrated significant increases in actual bone volume from time 0 to the time of death for all types of grafts. Cortical bone demonstrated significant increases in space-occupying volume at all time points. By 16 weeks, no statistically significant difference in either the actual bone volume or the space-occupying volume according to graft type could be detected. There was no resorption of the inlay bone grafts; in fact, all bone types exhibited increased volume. Cancellous bone demonstrated the greatest capacity to increase actual bone volume. All bone graft types seemed to reach a steady-state bone volume, as if controlled by a local regulator. The regulator is likely the local mechanical environment in which the grafts were placed, as corroborated by the findings that the bone grafts seemed to recapitulate the characteristics of the bone in which they were placed, rather than maintaining their native characteristics.     

Critical evaluation of known bone material properties to realize anisotropic FE-simulation of the proximal femur

PURPOSE: In a meta-analysis of the literature we evaluated the present knowledge of the material properties of cortical and cancellous bone to answer the question whether the available data are sufficient to realize anisotropic finite element (FE)-models of the proximal femur. MATERIAL AND METHOD: All studies that met the following criteria were analyzed: Young's modulus, tensile, compressive and torsional strengths, Poisson's ratio, the shear modulus and the viscoelastic properties had to be determined experimentally. The experiments had to be carried out in a moist environment and at room temperature with freshly removed and untreated human cadaverous femurs. All material properties had to be determined in defined load directions (axial, transverse) and should have been correlated to apparent density (g/cm(3)), reflecting the individually variable and age-dependent changes of bone material properties. RESULTS: Differences in Young's modulus of cortical [cancellous] bone at a rate of between 33% (58%) (at low apparent density) and 62% (80%) (at high apparent density), are higher in the axial than in the transverse load direction. Similar results have been seen for the compressive strength of femoral bone. For the tensile and torsional strengths, Poisson's ratio and the shear modulus, only ultimate values have been found without a correlation to apparent density. For the viscoelastic behaviour of bone only data of cortical bone and in axial load direction have been described up to now. CONCLUSIONS: Anisotropic FE-models of the femur could be realized for most part with the summarized material properties of bone if characterized by apparent density and load directions. Because several mechanical properties have not been correlated to these main criteria, further experimental investigations will be necessary in future.     

Finite element models predict cancellous apparent modulus when tissue modulus is scaled from specimen CT-attenuation

High-resolution architecture-based finite element models are commonly used for characterizing the mechanical behavior of cancellous bone. The vast majority of studies use homogeneous material properties to model trabecular tissue. The objectives of this study were to demonstrate that inhomogeneous finite element models that account for microcomputed tomography-measured tissue modulus variability more accurately predict the apparent stiffness of cancellous bone than homogeneous models, and to examine the sensitivity of an inhomogeneous model to the degree of tissue property variability. We tested five different material cases in finite element models of ten cancellous cubes in simulated uniaxial compression. Three of these cases were inhomogeneous and two were homogeneous. Four of these cases were unique to each specimen, and the remaining case had the same tissue modulus for all specimens. Results from all simulations were compared with measured elastic moduli from previous experiments. Tissue modulus variability for the most accurate of the three inhomogeneous models was then artificially increased to simulate the effects of non-linear CT-attenuation-modulus relationships. Uniqueness of individual models was more critical for model accuracy than level of inhomogeneity. Both homogeneous and inhomogeneous models that were unique to each specimen had at least 8% greater explanatory power for apparent modulus than models that applied the same material properties to all specimens. The explanatory power for apparent modulus of models with a tissue modulus coefficient of variation (COV) range of 21-31% was 13% greater than homogeneous models (COV=0). The results of this study indicate that inhomogenous finite element models that have tissue moduli unique to each specimen more accurately predict the elastic behavior of cancellous cubic specimens than models that have common tissue moduli between all specimens.     

Mechanical properties of compacted morselized cancellous bone graft using one-dimensional consolidation testing

Failures of orthopaedic procedures that use morselized cancellous bone (MCB) graft for load bearing are often due to gross displacement within the graft material. For this reason the mechanical behavior of MCB must be better understood. Our purpose is to present a detailed testing methodology for the mechanical characterization of MCB, and to illustrate how this methodology can be used to study the influence of water and fat content. Complete one-dimensional consolidation testing was performed on bovine cancellous bone processed to represent MCB typically used in surgery (52% water, 31% fat). The one-dimensional consolidation strain under a stress of 1.09 MPa was 30.9% and the confined modulus was 8.0 MPa. The coefficient of consolidation (rate of consolidation) was 2.2×10⁻⁵ cm²/s and the coefficient of secondary strain (steady-state creep rate) was 1.9%. While reducing the water content alone had some influence on properties, reducing the fat content improved both the static and dynamic behavior. A sample of MCB which had fat intentionally minimized and a lower overall moisture content (56% water, 5% fat) demonstrated 23.1% strain, a confined modulus of 9.6 MPa, a coefficient of consolidation of 3.4×10⁻³ cm²/s, and a coefficient of secondary strain of 0.9%. The test methods described in this technical note can be used to evaluate the influence of fluid content on the mechanical behavior of MCB.     

Anatomical variation of orthotropic elastic moduli of the proximal human tibia

The anatomical variation of orthotropic elastic moduli of the cancellous bone from three human proximal tibiae was investigated using an ultrasonic technique. With this technique, it was possible to measure three orthogonal elastic moduli and three shear moduli from cubic specimens of cancellous bone as small as 8 mm per side. Correlation with mechanical tensile testing has shown this technique to offer a precise measure of cancellous modulus (Eten = 0.94Eult + 144.6 MPa, r2 = 0.96, n = 34). The cancellous bone of the proximal tibia was found to be very inhomogeneous, with the axial modulus ranging between 340 and 3350 MPa. A course map is presented, showing measured Young's moduli as a function of anatomical position. The anisotropy of the cancellous bone, determined by the relative differences between the three orthogonal moduli, was shown to be relatively constant over the entire range of cancellous densities tested. The relationship between the axial elastic modulus and the apparent density was found to be approximately linear, as reported by others for proximal tibial cancellous bone.     

A functional consequence of an ossified mandibular symphysis

According to most recent workers, the presence of fused symphyses in some mammals is explained by the common view that muscle force is transmitted better across a fused, as opposed to an unfused, mandibular symphysis. Recent theoretical work has cast doubt on the importance of fusion for simple force transmission by suggesting that force can also be transmitted efficiently across an unfused symphysis, an expectation that has since been confirmed by a number of observational studies. Perhaps the real significance of symphyseal fusion is that, in animals with upper and lower incisor tooth rows that apply large forces to relatively small resistant food items, muscle force from both sides of the head is reliably available only when the symphysis is fused. Independent movement between the two sides of the lower incisor row, permitted by a patent symphysis, allows the possibility that one side of the lower row will come into contact with the upper incisor row, dissipating all of the muscle force from that side. The dissipation of approximately half of the available jaw muscle force, allowed by a patent symphysis, cannot be ignored when attempting to explain the presence of fused symphyses if one accepts the idea that strong incisor biting is an important element in the masticatory apparatus of those primates and other mammals with fused mandibular symphyses.     

人体颈椎松质骨显微结构和力学性能的区域性差异研究

目的:探讨人体脊柱松质骨骨骼显微结构和力学性能的区域性差异,为松质骨三维结构采样部位的选取提供参考。方法:显微CT扫描6块颈6椎体标本获得三维图像,依据椎体内解剖位置的不同,将松质骨划分为6个位置组:外侧、内侧、腹侧、背侧、头侧和尾侧。利用显微结构参数骨体积分数(Bone volume to tissue volume,BV/TV)、骨表面积和骨体积的比值(Bone surface to bone volume,BS/BV)、骨小梁数量(Trabecular number,Tb.N)、骨小梁厚度(Trabecular thickness,Tb.Th)、骨小梁分离度(Trabecular separation,Tb.Sp)和个体化骨小梁分割方法(Individual trabeculae segmentation,ITS)分析6个位置组内松质骨显微结构,并利用有限元分析,获得6个位置组内松质骨的力学性能参数表观弹性模量和表观剪切模量。分别两两对比外侧和内侧,腹侧和背侧,头侧和尾侧松质骨的显微结构参数(BV/TV、BS/BV、Tb.N、Tb.Th、Tb.Sp和个体化骨小梁分割得到的参数)和力学性能参数(表观弹性模量和表观剪切模量)。结果:头侧和尾侧的主要显微结构参数BV/TV、Tb.Th、Tb.N等和表观弹性模量均存在显著差异(P0.05)。腹侧和背侧、内侧和外侧的主要显微结构参数BV/TV、Tb.Th、Tb.N等无显著差异。外侧和内侧的表观弹性模量在非主方向即内外方向和腹背放上上存在显著差异(P0.05),在主方向即头尾上无显著差异。结论:在实验中采集椎体松质骨样本以及临床上利用高分辨率CT分析椎体松质骨结构时,感兴趣区域要同时涵盖头侧和尾侧。     

Elastic modulus of trabecular bone material

An ultrasonic technique was used to measure both the elastic modulus (Young's modulus) of trabecular bone material and the elastic modulus of the cancellous structure. The average trabecular modulus, measured on specimens obtained from three human and one bovine distal femora, was 13.0 GPa (S.D. 1.47) and 10.9 GPa (S.D. 1.57), respectively. On human specimens the structural elastic modulus was found to be related to the structural (apparent) density raised to the 1.88 power. The elastic modulus from the bovine specimens showed a more linear relationship with the density of the cancellous structure (density raised to the 1.57 power).     

Comparative effects of alendronate and alfacalcidol on cancellous and cortical bone mass and bone mechanical properties in ovariectomized rats.

The purpose of the present study was to compare the effects of alendronate and alfacalcidol on cancellous and cortical bone mass and bone mechanical properties in ovariectomized rats. Twenty-six female Sprague-Dawley rats, 7 months of age, were randomized by the stratified weight method into four groups: the sham-operated control (Sham) group and the three ovariectomy (OVX) groups, namely, OVX + vehicle, OVX + alendronate (2.5 mg/kg, p.o., daily), and OVX + alfacalcidol (0.5 mug/kg, p.o., daily). At the end of the 8-week experimental period, bone histomorphometric analyses of cancellous bone at the proximal tibial metaphysis and cortical bone at the tibial diaphysis were performed, and the mechanical properties of the femoral distal metaphysis and femoral diaphysis were evaluated. OVX decreased cancellous bone volume per total tissue volume (BV/TV), and the maximum load of the femoral distal metaphysis, as a result of increases in serum osteocalcin (OC) levels, and also the number of osteoclasts (N.Oc), osteoclast surface (OcS) and bone formation rate (BFR) per bone surface (BS), and BFR/BV, without any effect on cortical area (Ct Ar), or maximum load of the femoral diaphysis. Alendronate prevented this decrease in cancellous BV/TV by suppressing increases in N.Oc/BS, OcS/BS, BFR/BS, and BFR/BV, without any apparent effect on Ct Ar, or maximum load of the femoral distal metaphysis and femoral diaphysis. On the other hand, alfacalcidol increased cancellous BV/TV, Ct Ar, and the maximum load of the femoral distal metaphysis and femoral diaphysis, by mildly decreasing trabecular BFR/BV, maintaining trabecular mineral apposition rate and osteoblast surface per BS, increasing periosteal and endocortical BFR/BS, and preventing an increase in endocortical eroded surface per BS. The present study clearly showed the differential skeletal effects of alendronate and alfacalcidol in ovariectomized rats. Alendronate prevented OVX-induced cancellous bone loss by suppressing bone turnover, while alfacalcidol improved cancellous and cortical bone mass and bone strength by suppressing bone resorption and maintaining or even increasing bone formation.     

Elastic moduli, yield stress, and ultimate stress of cancellous bone in the canine proximal femur

Elastic moduli, yield stress and ultimate compressive stress were determined for cancellous bone from the femoral head and neck regions of the canine femur. Unconfined compression tests were performed on 5 mm cubic samples which were cut from two femurs. Elastic moduli were measured in three orthogonal directions, and the yield stress and ultimate stress were measured along the proximal-distal axis. The results from this investigation support previous assumptions that the mechanical behavior of canine cancellous bone is qualitatively similar to human cancellous bone. The canine cancellous bone was observed to be anisotropic in elastic modulus. For two thirds of the cubic specimens tested, the elastic modulus was largest in the load-bearing, proximal-distal direction. A linear relationship between yield stress and elastic modulus was observed for canine bone, as is typical of human bone. A similar linear relationship between ultimate stress and elastic modulus was observed. Thus, for canine bone as well as for human bone, failure appears to be governed by a strain level which is position independent. The yield strain of 0.0259 and ultimate strain of 0.0288 for canine bone were both less than the yield strain of 0.0395 reported for human bone.