A Mouse Femoral Ostectomy Model to Assess Bone Graft Substitutes

The shortcomings of autografts and allografts in bone defect healing have prompted researchers to develop suitable alternatives. Numerous biomaterials have been developed as bone graft substitutes each with their own advantages and disadvantages. However, in order to test if these biomaterials provide an adequate replacement of the clinical standard, a clinically representative animal model is needed to test their efficacy. In this chapter, we describe a mouse model that establishes a critical sized defect in the mid-diaphysis of the femur to evaluate the performance of bone graft substitutes. This is achieved by performing a femoral ostectomy and stabilization utilizing a femoral plate and titanium screws. The resulting defect enables the bone regenerative potential of bone graft substitutes to be investigated. Lastly, we provide instruction on assessing the torsional strength of the healed femurs to quantitatively evaluate the degree of healing as a primary outcome measure.

Finite element modelling of the developing infant femur using paired CT and MRI scans

Bone finite element (FE) studies based on infant post-mortem computed tomography (CT) examinations are being developed to provide quantitative information to assist the differentiation between accidental and inflicted injury, and unsuspected underlying disease. As the growing skeleton contains non-ossified cartilaginous regions at the epiphyses, which are not well characterised on CT examinations, it is difficult to evaluate the mechanical behaviour of the developing whole bone. This study made use of paired paediatric post mortem femoral CT and magnetic resonance imaging (MRI) examinations at two different stages of development (4 and 7 months) to provide anatomical and constitutive information for both hard and soft tissues. The work aimed to evaluate the effect of epiphyseal ossification on the propensity to shaft fractures in infants. The outcomes suggest that the failure load of the femoral diaphysis in the models incorporating the non-ossified epiphysis is within the range of bone-only FE models. There may however be an effect on the metaphysis. Confirmation of these findings is required in a larger cohort of children.

A comparative evaluation of tibial metaphyseal-diaphyseal angle changes between physiologic bowing and Blount disease

The purpose of this study was to estimate the rate of spontaneous improvement in tibial metaphyseal-diaphyseal angle (TMDA) in physiologic bowing in comparison to that in Blount disease and to provide reference values of TMDA for monitoring patients with highly suspected to have Blount disease.We retrospectively reviewed patients with physiologic bowing meeting the following criteria:(1) TMDA greater than 9° before 36 months of age at initial evaluation;(2) two or more standing long bone radiographs available; and(3) follow-up conducted up to resolution of deformity.Patients with Blount disease had(1) more than 2 standing long bone radiographs obtained before 36 months of age and(2) underwent no treatment during the period in which these images were obtained.TMDA measurements were obtained from 174 patients with physiologic bowing and 32 patients with Blount disease. Rates of TMDA improvement were adjusted by multiple factors using a linear mixed model, with sex and laterality as fixed effects and age and individual patients as the random effects.In the physiologic bowing group, TMDA improved significantly, by 3° per 6 months and by 6° per year. Changes in TMDA were not significant in the Blount disease group.Knowing the rate of TMDA change can be helpful for physicians seeking to monitor infants with suspected as having Blount disease with a high TMDA and to avoid unnecessary repeat radiographic evaluations.

Fractional fetal thigh volume in the prediction of normal and abnormal fetal growth during the third trimester of pregnancy

Background

Currently, 2-dimensional ultrasound estimation of fetal size rather than fetal growth is used to define fetal growth restriction, but single estimates in late pregnancy lack sensitivity and may identify small for gestational age rather than growth restriction. Single or longitudinal measures of 3-dimensional fractional thigh volume may address this problem.

Objective

We sought to derive normal values for 3-dimensional fractional thigh volume in the third trimester, determine if fractional thigh volume is superior to 2-dimensional ultrasound biometry alone for detecting fetal growth restriction, and determine whether individualized growth assessment parameters have the potential to identify fetal growth restriction remote from term delivery.

Study Design

This was a longitudinal prospective cohort study of 115 unselected pregnancies in a tertiary referral unit (St Mary’s Hospital, Manchester, United Kingdom). Standard 2-dimensional ultrasound biometry measurements were obtained, along with fractional thigh volume measurements (based on 50% of the femoral diaphysis length). Measurements were used to calculate estimated fetal weight (Hadlock). Individualized growth assessment parameters and percentage deviations in longitudinally measured biometrics were determined using a Web-based system (iGAP; http://iGAP.research.bcm.edu). Small for gestational age was defined <10th and fetal growth restriction <3rd customized birthweight centile. Logistic regression was used to compare estimated fetal weight (Hadlock), estimated fetal weight (biparietal diameter–abdominal circumference–fractional thigh volume), fractional thigh volume, and abdominal circumference for the prediction of small for gestational age or fetal growth restriction at birth. Screening performance was assessed using area under the receiver operating characteristic curve.

Results

There was a better correlation between fractional thigh volume and estimated fetal weight ((biparietal diameter–abdominal circumference–fractional thigh volume) obtained at 34-36 weeks with birthweight than between 2-dimensional biometry measures such as abdominal circumference and estimated fetal weight (Hadlock). There was also a modest improvement in the detection of both small for gestational age and fetal growth restriction using fractional thigh volume–derived measures compared to standard 2-dimensional measurements (area under receiver operating characteristic curve, 0.86; 95% confidence interval, 0.79–0.94, and area under receiver operating characteristic curve, 0.92; 95% confidence interval, 0.85–0.99, respectively).

Conclusion

Fractional thigh volume measurements offer some improvement over 2-dimensional biometry for the detection of late-onset fetal growth restriction at 34-36 weeks.

A method for estimating gestational age of fetal remains based on long bone lengths

The estimation of gestational age (GA) in fetal human remains is important in forensic settings, particularly to assess fetal viability, in addition to often being the only biological profile parameter that can be assessed with some accuracy for non-adults. The length of long bone diaphysis is one of the most frequently used methods for fetal age estimation. The main objective of this study was to present a simple and objective method for estimating GA based on the measurements of the diaphysis of the femur, tibia, fibula, humerus, ulna, and radius. Conventional least squares regression equations (classical and inverse calibration approaches) and quick reference tables were generated. A supplementary objective was to compare the performance of the new formulae against previously published models. The sample comprised 257 fetuses (136 females and 121 males) with known GA (between 12 and 40 weeks) and was selected based on clinical and pathological information. All measurements were performed on radiographic images acquired in anonymous clinical autopsy records from spontaneous and therapeutic abortions in two Portuguese hospitals. The proposed technique is straightforward and reproducible. The models for the GA estimation are exceedingly accurate and unbiased. Comparisons between inverse and classical calibration show that both perform exceptionally well, with high accuracy and low bias. Also, the newly developed equations generally outperform earlier methods of GA estimation in forensic contexts. Quick reference tables for each long bone are now available. The obtained models for the estimation of gestational age are of great applicability in forensic contexts.

[The effect of tibial transphyseal reinforcement on the growth and response of leg tissues]

Transphyseal reinforcement of right intact tibia performed with thin steel rods in six mongrel dogs at the age of six months. Contralateral segment served as control. The leg growth and blood supply studied under the created conditions for the next six months. Radiographic, physiologic (surface thermometry, photoplethysmography), and statistical methods used for studying. The significant effect of transphyseally inserted rods on the leg longitudinal growth and blood supply has not been revealed. The changes in natural shape-formation oftibial proximal and distal meta-epiphyses observed influenced by the transphyseal rods in the experiment. In order to evaluate the tissue response and the degree of the functional activity of leg bone meta-epiphyseal zones the most informative areas considered to be the following: the area of medial malleolus in the early period of physiological growth completion, and the area of the tibial lateral condyle--at the late stage.

Differential effects of exercise on tibial shaft marrow density in young female athletes

CONTEXT

Increased mechanical loading can promote the preferential differentiation of bone marrow mesenchymal stem cells to osteoblastogenesis, but it is not known whether long-term bone strength-enhancing exercise in humans can reduce marrow adiposity.

OBJECTIVE

Our objective was to examine whether bone marrow density (MaD), as an estimate of marrow adiposity 1) differs between young female athletes with contrasting loading histories and bone strengths and 2) is an independent predictor of bone strength at the weight-bearing tibia.

DESIGN

Mid-tibial MaD, cortical area (CoA), total area, medullary area, strength strain index (SSI), and cortical volumetric bone mineral density (vBMD) (total, endocortical, midcortical, and pericortical) was assessed using peripheral quantitative computed tomography in 179 female athletes involved in both impact and nonimpact loading sports and 41 controls aged 17-40 years.

RESULTS

As we have previously reported CoA, total area, and SSI were 16% to 24% greater in the impact group compared with the controls (all P < .001) and 12% to 18% greater than in the nonimpact group (all P < .001). The impact group also had 0.5% higher MaD than the nonimpact and control groups (both P < .05). Regression analysis further showed that midtibial MaD was significantly associated with SSI, CoA, endocortical vBMD, and pericortical vBMD (P < .05) in all women combined, after adjusting for age, bone length, loading groups, medullary area, muscle cross-sectional area, and percent fat.

CONCLUSION

In young female athletes, tibial bone MaD was associated with loading history and was an independent predictor of tibial bone strength. These findings suggest that an exercise-induced increase in bone strength may be mediated via reduced bone marrow adiposity and consequently increased osteoblastogenesis.

Biomechanical properties of the mid-shaft femur in middle-aged hypophysectomized rats as assessed by bending test

Both stiffness and strength of bones are thought to be controlled by the "bone mechanostat". Its natural stimuli would be the strains of bone tissue (sensed by osteocytes) that are induced by both gravitational forces (body weight) and contraction of regional muscles. Body weight and muscle mass increase with age. Biomechanical performance of load-bearing bones must adapt to these growth-induced changes. Hypophysectomy in the rat slows the rate of body growth. With time, a great difference in body size is established between a hypophysectomized rat and its age-matched control, which makes it difficult to establish the real effect of pituitary ablation on bone biomechanics. The purpose of the present investigation was to compare mid-shaft femoral mechanical properties between hypophysectomized and weight-matched normal rats, which will show similar sizes and thus will be exposed to similar habitual loads. Two groups of 10 female rats each (H and C) were established. H rats were 12-month-old that had been hypophysectomized 11 months before. C rats were 2.5-month-old normals. Right femur mechanical properties were tested in 3-point bending. Structural (load-bearing capacity and stiffness), geometric (cross-sectional area, cortical sectional area, and moment of inertia), and material (modulus of elasticity and maximum elastic stress) properties were evaluated. The left femur was ashed for calcium content. Comparisons between parameters were performed by the Student's t test. Average body weight, body length, femur weight, femur length, and gastrocnemius weight were not significantly different between H and C rats. Calcium content in ashes was significantly higher in H than in C rats. Cross-sectional area, medullary area, and cross-sectional moment of inertia were higher in C rats, whereas cortical area did not differ between groups. Structural properties (diaphyseal stiffness, elastic limit, and load at fracture) were about four times higher in hypophysectomized rats, as were the bone material stiffness or Young's modulus and the maximal elastic stress (about 7×). The femur obtained from a middle-aged H rat was stronger and stiffer than the femur obtained from a young-adult C rat, both specimens showing similar size and bone mass and almost equal geometric properties. The higher than normal structural properties shown by the hypophysectomized femur were entirely due to changes in the intrinsic properties of the bone; it was thus stronger at the tissue level. The change of the femoral bone tissue was associated with a high mineral content and an unusual high modulus of elasticity and was probably due to a diminished bone and collagen turnover.

Increasing participation of sclerostin in postnatal bone development, revealed by three-dimensional immunofluorescence morphometry

Confocal immunofluorescence tiling imaging revealed the spatio-temporal distributions of osterix and sclerostin in femurs from 3-day-old, 2-week-old and 4-week-old rats to be reciprocally exclusive at the tissue level. Further quantitative three-dimensional immuno fluorescence morphometry demonstrated the increasing distribution of sclerostin in the osteocytic lacuno-canalicular system specifically in diaphysis, which paralleled the cooperative participation and depletion of osterix and β-catenin in adjacent periosteum cells. Treating MC3T3-E1 cells with BIO (a GSK3 inhibitor) induced the stabilization of β-catenin and nuclear translocation of osterix, and negatively regulated osteocalcin/BGLAP and Dmp1. These results collectively demonstrate that the increasing distribution of sclerostin in diaphyseal cortical bone appears to be involved in the attenuation of osterix and β-catenin in adjacent periosteum cells, thus possibly contributing to osteoblast maturation and reducing the osteoblast formation at this bone site. Our confocal microscopy-based imaging analyses provide a comprehensive and detailed view of the spatio-temporal distribution of sclerostin, β-catenin and osterix at the tissue to subcellular level in a coherent manner, and uncovered their spatio-temporal cooperation in postnatal bone development, thus providing evidence that they link skeletogenic growth and functional bone development.

Micro and macroarchitectural changes at the tibia after botulinum toxin injection in the growing rat

The aim of this study was to analyze bone microarchitecture and macroarchitecture of tibia in a disuse model in growing rats. Eight-weeks-old Copenhagen rats were injected intramuscularly with 1.5 units BTX in the quadriceps muscle of the right hind limb. Saline injection was done at the left hind limb to serve as control. Five rats were killed at day 1 and represented the baseline group (D1), 5 rats were killed at day 14 (D14), 5 at day 21 (D21), 5 at day 28 (D28) and 5 at day 35 (35). For each group, muscle surface, parameters of bone microarchitecture and macroarchitecture (including length, width and curvature of the tibia) were measured using microtomography. Paralysis occurred as soon as day 2. At the left hind limb, muscle surface area, cortical thickness, cross sectional total area and growth in length significantly increased during the time study. At the right hind limb, muscle surface area, bone trabecular volume, and cortical thickness decreased as soon as day 14 associated with an increased cortical porosity. Growth in length did not differ from left side; cross sectional total area did not increase and the diaphyseal cross section acquired a more rounded shape. There was no modification of the curvature between right and left hind limbs during the time study. In this murine model of unilateral muscle paralysis in growing animals, we showed a rapid muscle loss leading to a decreased growth in width; however growth in length and curvature were unaltered.

The role of remodeling and asymmetric growth in vertebral wedging

BACKGROUND

Scoliosis with vertebral wedging is thought to be caused by asymmetric growth (Hueter-Volkmann law), but vertebral diaphyseal remodeling (Wolff's law) may also contribute to the deformity. We investigated whether vertebral wedging in scoliosis might involve both mechanisms.

METHODS

An external fixator was used to impose a 30 degrees scoliosis and compression of 0.1 or 0.2 MPa to the tails of 10 5-week-old and 20 14-week-old Sprague-Dawley rats for 6 weeks. The rats were divided into three groups of 10 animals each: Group 1: 5-week-old animals with 0.1 MPa compression; Group 2: 14-week-old animals with 0.1 MPa compression; Group 3: 14-week-old animals with 0.2 MPa compression. Vertebral wedging and diaphyseal curvature were measured from micro CT scans performed at weeks 1, 3, and 6. Wedging due to asymmetrical growth and remodeling was calculated from a Calcein label administered at week 3 and a Xylenol label at week 6.

RESULTS

The growth rate of the loaded vertebrae as a per cent of control vertebrae was 60% in Group 1, 40% in Group 2, and 30% in Group 3. The growth rate of control vertebrae in 14-week-old animals was 16% that of 5-week-old animals. The animals in all 3 groups developed a scoliosis with vertebral wedging that averaged 18.7 degrees in Group 1, 8.2 degrees in Group 2, and 10.1 degrees in Group 3. Asymmetric growth was much greater in Group 1 (5-week-old) animals. The ossified epiphyses became wedged and diaphyseal remodeling occurred in all groups.

CONCLUSIONS

The major contribution to the vertebral wedging was asymmetric growth in the 5-week-old animals and diaphyseal remodeling in the 14-week-old animals. The results support the concept that if appropriate loads can be applied to human vertebrae through minimally invasive techniques, scoliosis and vertebral wedging can be corrected without a spinal fusion in both adolescents and adults.

Biomechanical performance of diaphyseal shafts and bone tissue of femurs from hypothyroid rats

The bone changes in hypothyroidism are characterized by a low bone turnover with a reduced osteoid apposition and bone mineralization rate, and a decreased osteoclastic resorption in cortical bone. These changes could affect the mechanical performance of bone. The evaluation of such changes was the object of the present investigation. Hypothyroidism was induced in female rats aged 21 days through administration of propylthiouracil in the drinking water for 70 days (HT group). Controls were untreated rats (C group). Right femur mechanical properties were tested in 3-point bending. Structural (load bearing capacity and stiffness), geometric (cross-sectional area and moment of inertia) and material (modulus of elasticity) properties were evaluated. The left femur was ashed for calcium content determination. Plasma T(4) concentration was significantly decreased in HT rats. Body and femur weight and length in HT rats were also reduced. Femoral calcium concentration in ash was higher in HT than in C rats. However, the femoral calcium mass was significantly lower in HT than in C rats because of the reduced femoral size seen in the former. The stiffness of bone material was higher in HT than in C rats, while the bone geometric properties were significantly lower. The "load capacity" was between 30 and 50% reduced in the HT group, although, the differences disappeared when the values were normalized per 100-g body weight. The lowered biomechanical ability observed in the femoral shafts of HT rats seems to be the expression of a diminished rate of growth. Qualitative alterations in the intrinsic mechanical properties of bone tissue were observed in HT rats, probably because the mineral content and the modulus of elasticity were positively affected. The cortical bone of the HT rat thus appears as a bone with a higher than normal strength and stiffness relative to body weight, probably due to improvement of bone material quality due to an increased matrix calcification.

Formation of tethers linking the epiphysis and metaphysis is regulated by vitamin d receptor-mediated signaling

Rat tibial growth plates have X-ray opaque tethers that link the epiphysis and metaphysis and increase with age as the growth plate (GP) becomes thinner. To determine if tether formation is a regulated process of GP maturation, we tested the hypotheses that tether properties and distribution can be quantified by micro-computed tomography (microCT), that rachitic GPs typical of vitamin D receptor knockout (VDR(-/-)) mice have fewer tethers and altered tether distribution, and that tether formation is regulated by signaling via the VDR. Distal femoral GPs from VDR(+/+) and VDR(-/-) 8-week-old mice were analyzed with microCT and then processed for decalcified and undecalcified histomorphometry. A wide range of parameters that assessed GP and tether geometry and morphology, along with tether distribution, were measured using both microCT and histology. Growth plates of 10-week-old VDR(+/+) and VDR(-/-) mice on a high-calcium, phosphorus, lactose, and vitamin D(3) rescue diet were also analyzed. Both microCT and histology showed tethers present throughout normal mice GPs, while reduction in tether number and volume percentage occurred in VDR(-/-) GPs with localization to the central region. Decreased shrinkage in the axial direction during decalcified histological processing correlated with tether formation, suggesting mechanical stability due to tethers. Tether formation increased greatly between 8 and 10 weeks. Rescue diets restored VDR(-/-) GP size but not tether volume percentage. Overall, these results demonstrate microCT imaging's utility for analyzing tether formation and suggest that signaling via the VDR plays a pivotal role in tether formation.

Genetic selection for fast growth generates bone architecture characterised by enhanced periosteal expansion and limited consolidation of the cortices but a diminution in the early responses to mechanical loading

Bone strength is, in part, dependent on a mechanical input that regulates the (re)modelling of skeletal elements to an appropriate size and architecture to resist fracture during habitual use. The rate of longitudinal bone growth in juveniles can also affect fracture incidence in adulthood, suggesting an influence of growth rate on later bone quality. We have compared the effects of fast and slow growth on bone strength and architecture in the tibiotarsi of embryonic and juvenile birds. The loading-related biochemical responses (intracellular G6PD activity and NO release) to mechanical load were also determined. Further, we have analysed the proliferation and differentiation characteristics of primary tibiotarsal osteoblasts from fast and slow-growing strains. We found that bones from chicks with divergent growth rates display equal resistance to applied loads, but weight-correction revealed that the bones from juvenile fast growth birds are weaker, with reduced stiffness and lower resistance to fracture. Primary osteoblasts from slow-growing juvenile birds proliferated more rapidly and had lower alkaline phosphatase activity. Bones from fast-growing embryonic chicks display rapid radial expansion and incomplete osteonal infilling but, importantly, lack mechanical responsiveness. These findings are further evidence that the ability to respond to mechanical inputs is crucial to adapt skeletal architecture to generate a functionally appropriate bone structure and that fast embryonic and juvenile growth rates may predispose bone to particular architectures with increased fragility in the adult.

Bone growth and turnover in progesterone receptor knockout mice

The role of progesterone receptor (PR) signaling in skeletal metabolism is controversial. To address whether signaling through the PR is necessary for normal bone growth and turnover, we performed histomorphometric and microcomputed tomography analyses of bone from homozygous female PR knockout (PRKO) mice at 6, 12, and 26 wk of age. These mice possess a null mutation of the PR locus, which blocks the gene expression of A and B isoforms of PR. Body weight gain, uterine weight gain, and tibia longitudinal bone growth were normal in PRKO mice. In contrast, total, cancellous, and cortical bone mass were increased in the humerus of 12-wk-old PRKO mice, whereas cortical and cancellous bone mass in the tibia was normal. At 26 wk of age, cancellous bone area in the proximal tibia metaphysis of PRKO mice was 153% greater than age matched wild-type mice. The improved cancellous bone balance in 6-month-old PRKO mice was associated with elevated bone formation and a tendency toward reduced osteoclast perimeter. Taken together, these findings suggest that PR signaling in mice is not essential for bone growth and turnover. However, at some skeletal sites, PR signaling attenuates the accumulation of cortical and cancellous bone mass during adolescence.

[Formation of ossification nucleus in the femoral head in hamsters exposed to laser radiation]

The purpose of the study was to detect the relation between the formation of ossification nucleus in the epiphysis and the ingrowth of vessels into it, using laser radiation of femoral heads. The study was performed in 30 golden hamsters, 20 of them starting at 10 days after birth were exposed to daily irradiation of the right hip joint (during 3-80 days). The left joint was used as control. The radiation was performed with Agnis laser device (radiation power--2 mW, impulse frequency--2500 Hz, exposure duration--8 min, optical fiber diameter--4 mm). Femoral bones of experimental and control animals were histologically studied at days 13 till 90. Laser radiation was found could delay vessel growth from diaphysis into epiphysis for up to 13 days, and the beginning of ossification nucleus formation in the femoral head--for up to 5 days. This suggests the direct relation of the development of bone ossification nucleus in the epiphysis and growing of vessels into its cartilage, since no other factors retarding the vessel growth and formation of bone nucleus were used.

Morbidity, rickets and long-bone growth in post-medieval Britain--a cross-population analysis

BACKGROUND

Vitamin D deficiency rickets is associated with skeletal deformities including swollen rib junctions, bowing of the legs, and the flaring and fraying of the wrist and long-bone metaphyses. There is, however, scarce information on the direct effect of rickets on skeletal growth in either present or past populations.

AIM

The study investigated the effect of vitamin D deficiency rickets on long-bone growth in two post-medieval skeletal populations from East London (Broadgate and Christ Church Spitalfields). Subsequently, inter-population growth variations in relation to non-specific environmental stress (dental enamel defects), industrialization, urbanization and socio-economic status during infancy (birth to 3 years) and early childhood (3-7 years) were examined.

SUBJECTS AND METHODS

Data on long-bone diaphyseal length dimensions and stress indicators of 234 subadults from Anglo-Saxon, late medieval and post-medieval archaeological skeletal samples were analysed using both linear and non-linear growth models.

RESULTS

Rickets had no effect on the growth curves for any of the long bones studied. However, pronounced variations in growth between the four populations were noted, mainly during infancy. The diaphyseal length of long bones of Broadgate were significantly smaller-per-age than those of Spitalfields and the other samples up to the age of 4 years, and were associated with a high prevalence of enamel defects during early infancy.

CONCLUSION

Socio-economic status, rather than urbanization, industrialization or rickets, was the central factor behind the observed differences in growth among the post-medieval populations. The observed inter-population growth variations were only significant during infancy.

Evidence for overgrowth after midfemoral fracture via increased RNA for mitosis

Middiaphyseal femoral fractures in children and young rats stimulate linear femoral growth, a phenomenon commonly attributed to increased vascularity. To test for changes in mRNA expression of genes related to blood vessels, nerve fibers, cartilage, bone, and cell metabolism, we measured mRNA gene expression for all known rat genes in the physis at various times after diaphyseal fracture. Female Sprague-Dawley rats, 4 weeks of age at surgery, were subjected to a unilateral, simple, transverse, middiaphyseal femoral fracture stabilized with an intramedullary rod. At 0 (intact), 0.1, 0.4, 1, 2, 3, 4, and 6 weeks after fracture, the femoral head with the proximal physis was collected from fractured and intact femora. The RNA was extracted, processed to biotinlabeled cRNA, and hybridized to Affymetrix Rat 230 2.0 GeneChip microarrays. Transcripts from fracture-induced lengthening of the injured femora were compared to those of the intact contralateral femur. In the proximal physis, transcripts related to blood vessels and cartilage formation were down-regulated by fracture. Transcripts related to bone remodeling, nerve axon elongation, cell division, and protein synthesis were up-regulated by fracture. The data support increased mitotic activity in the physis after a midshaft fracture and not increased vascularity.

Multiple forearm diaphyseal fracture: reduction and plaster cast control at the end of growth

The authors followed up 20 patients with multiple diaphyseal fractures of the radius and ulna who were treated nonoperatively and who healed with axial deviation >5 degrees in at least one plane 20.4+/-6.7 years after radiographic evidence of fracture union. Mean age at follow-up was 28.6+/-6.4 years. Radiographs were measured soon after reduction, at 10 days from reduction, at the end of treatment, and at follow-up (17/20). Both elbow and forearm range of motion (ROM) were compared with those of the contralateral side. At follow-up, ROM was normal and radiographs showed angular deviations <5 degrees .

Ontogeny of Femur Subtrochanteric Shape in Native Americans and American Blacks and Whites

Femur subtrochanteric size and shape can be used to differentiate between adult Native Americans and American Blacks and Whites, but little is known about when shape differences are established during growth and development. Ontological changes in subtrochanteric shape were examined using 74 Native American and 61 American Black/White subadult femora. At birth, the proximal femur diaphysis is relatively circular in both groups. Between birth and 5 years, the diaphysis becomes more mediolaterally broad, especially in Native Americans, due to differential growth between the mediolateral and anteroposterior planes. This change may be due to biomechanical stresses associated with developing a mature gait pattern. After the age of 5, growth occurs more equally in the two planes and shape does not change significantly. The adult shape of the proximal femur is established by c. 5 years of age and can be used to discriminate between Native American and American Black/White femora in older subadults.

Involvement of Neuronal Cannabinoid Receptor CB1 in Regulation of Bone Mass and Bone Remodeling

The CB1 cannabinoid receptor has been implicated in the regulation of bone remodeling and bone mass. A high bone mass (HBM) phenotype was reported in CB1-null mice generated on a CD1 background (CD1(CB1-/-) mice). By contrast, our preliminary studies in cb1-/- mice, backcrossed to C57BL/6J mice (C57(CB1-/-) mice), revealed low bone mass (LBM). We therefore analyzed CB1 expression in bone and compared the skeletons of sexually mature C57(CB1-/-) and CD1(CB1-/-) mice in the same experimental setting. CB1 mRNA is weakly expressed in osteoclasts and immunoreactive CB1 is present in sympathetic neurons, close to osteoblasts. In addition to their LBM, male and female C57(CB1-/-) mice exhibit decreased bone formation rate and increased osteoclast number. The skeletal phenotype of the CD1(CB1-/-) mice shows a gender disparity. Female mice have normal trabecular bone with a slight cortical expansion, whereas male CD1(CB1-/-) animals display an HBM phenotype. We were surprised to find that bone formation and resorption are within normal limits. These findings, at least the consistent set of data obtained in the C57(CB1-/-) line, suggest an important role for CB1 signaling in the regulation of bone remodeling and bone mass. Because sympathetic CB1 signaling inhibits norepinephrine (NE) release in peripheral tissues, part of the endocannabinoid activity in bone may be attributed to the regulation of NE release from sympathetic nerve fibers. Several phenotypic discrepancies have been reported between C57(CB1-/-) and CD1(CB1-/-) mice that could result from genetic differences between the background strains. Unraveling these differences can provide useful information on the physiologic functional milieu of CB1 in bone.

Genetic variation in bone growth patterns defines adult mouse bone fragility

Femoral morphology and composition were determined for three inbred mouse strains between ages E18.5 and 1 year. Genotype-specific variation in postnatal, pubertal, and postpubertal growth patterns and mineral accrual explained differences in adult bone trait combinations and thus bone fragility.

INTRODUCTION

Fracture risk is strongly regulated by genetic factors. However, this regulation is generally considered complex and polygenic. Therefore, the development of effective genetic-based diagnostic and treatment tools hinges on understanding how multiple genes and multiple cell types interact to create mechanically functional structures. The goal of this study was to connect variability in whole bone mechanical function, including measures of fragility, to variability in the biological processes underlying skeletal development. We accomplished this by testing for variation in bone morphology and composition among three inbred mouse strains from E18.5 to 1 year of age.

MATERIALS AND METHODS

Mid-diaphyseal cross-sectional areas, diameters, moments of inertia, and ash content were determined for three strains of mice with widely differing adult whole bone femoral mechanical properties (A/J, C57BL/6J, and C3H/HeJ) at E18.5 and postnatal days 1, 7, 14, 28, 56, 112, 182, and 365 (n = 5-15 mice/strain/age).

RESULTS

Significant differences in the magnitude and rate of change in morphological and compositional bone traits were observed among the three strains at each phase of growth, including prenatal, postnatal, pubertal, and adult ages. These genotype-specific variations in growth patterns mathematically determined how variation in adult bone trait combinations and mechanical properties arose. Furthermore, six bone traits were identified that characterize phenotypic variability in femoral growth. These include (1) bone size and shape at postnatal day 1, (2) periosteal and (3) endosteal expansion during early growth, (4) periosteal expansion and (5) endosteal contraction in later growth, and (6) ash content. These results show that genetic variability in adult bone traits arises from variation in biological processes at each phase of growth.

CONCLUSIONS

Inbred mice achieve different combinations of adult bone traits through genotype-specific regulation of bone surface activity, growth patterns, and whole bone mineral accrual throughout femoral development. This study provides a systematic approach, which can be applied to the human skeleton, to uncover genetic control mechanisms influencing bone fragility.

Transient disturbance in physeal morphology is associated with long-term effects of nitrogen-containing bisphosphonates in growing rabbits

Bisphosphonates have clinical benefit in children with severe osteogenesis imperfecta or osteoporosis and potential benefit in children with Perthes disease or undergoing distraction osteogenesis. However, there is concern about the effects of bisphosphonates on the physis and bone length. In 44 growing rabbits, zoledronic acid caused a transient disruption of physeal morphology, retention of cartilaginous matrix in trabeculae and cortical bone of the metaphysis, and a minor decrement in tibial bone length at maturity.

INTRODUCTION

Data from growing animal models suggest that bisphosphonates cause retention of longitudinal cartilaginous septa at the chondro-osseous junction, extension of trabeculae to the metaphyseal-diaphyseal junction, and varying dose-dependent effects on longitudinal growth. However, there is a lack of data regarding effects of intermittent use of nitrogen-containing bisphosphonates on the physis and on tibial length in models reaching maturity.

MATERIALS AND METHODS

Contralateral tibias of juvenile rabbits were examined after right tibial distraction osteogenesis from two previous studies. Animals were randomized to receive 0.1 mg/kg zoledronic acid (ZA) IV at 8 weeks of age (ZA*1) or 8 and 10 weeks of age (ZA*2) or saline. Body mass was analyzed from 5 to 44 weeks of age; tibial length and proximal physeal-metaphyseal histology and histomorphometry were analyzed at 8-52 weeks of age.

RESULTS

Tibial length was 3% less at 14 weeks of age in the ZA*2-treated versus saline group (p<0.05) in both studies, and this difference persisted at maturity in the long-term study group (26 weeks of age, p<0.05). Total body mass gain from 5 to 26 weeks of age was 14% less in ZA*2-treated than saline animals (p<0.05). Rate of weight gain from 8 to 10 weeks of age was 76% less in ZA*2 compared with saline animals (p<0.05). Radiographs showed radiodense lines in the metaphyses of ZA-treated bones, corresponding to the number of doses. Histologically, lines resulting from the first dose of ZA contained longitudinal cartilaginous matrix cores surrounded by bone, whereas those from the second dose contained spherical cores of matrix caused by transient disruption of physeal morphology after the first dose of ZA. Resorption of these lines at later times was radiographically and histologically evident, but remnants of cartilaginous matrix remained in the cortical bone of ZA-treated animals.

CONCLUSIONS

ZA treatment within the final 13.5% of the rabbit tibial growth period caused a transient disruption in physeal morphology and resorption associated with retention of cartilaginous matrix and coinciding with a persistent 3% decrement in tibial length. Disruption of physeal morphology and potential loss of bone length should be considered when administering nitrogen-containing bisphosphonates to children before closure of the major physes.

Mandibular pubertal growth spurt prediction. Part one: Method based on the hand-wrist radiographs

Many orthodontic treatment modalities will yield a better result in less time if properly correlated with the unique facial growth patterns of the patients. The pubertal growth spurt depends on gender and varies in relationship to the chronologic age. General skeletal maturity usually is used as an indicator to predict timing of mandibular growth velocity peak. Hand-wrist radiographic evaluation is one of the diagnostic tools currently available to determine whether the pubertal growth has started, is occurring or has finished. The overview of topic related literature and skeletal maturity assessment (SMA) system developed by L. Fishman are presented. The SMA system is based on eleven discrete adolescence skeletal maturational indicators of hand-wrist bones, covering the entire period of adolescent development. Maturational stage and level demonstrated close correlation with maxillary and mandibular growth velocity, amount of incremental growth and timing. Clinical indications for the use of hand-wrist radiographs to assess skeletal maturity are provided.

Interstitial growth of bone revisited

The distance between two or more metallic implants placed within the same flat bones (mandible, nasal, frontal, hyoplastron, hypoplastron) of young pigs, rabbits, and turtles followed by means of serial radiographs, remained the same for periods as long as 546 days. Thus, it is concluded that there is no interstitial growth. In 1743, Duhamel demonstrated that long bones grow at their ends and that there is no interstitial growth. This report is unique in that it demonstrates by use of radiopaque implants and serial radiographs that there is no interstitial growth of flat bones, which grow by apposition and resorption, and not endochondrally, such as occurs in long bones.

Age determination on long bones in a skeletal subadults sample (b-12 years)

The skeletal age on the basis of the diaphyseal length of long bones was assessed. To this aim a sample of subadults skeleton, dated to last century, coming from the cemetery of Bologna was studied. The sample is composed by 79 males and 70 females between 0 and 12 years, whose chronological age and sex are known. Some information can be obtained by the means, standard deviation and graphs of the specimens grouped in age classes. The comparison with other studies confirms the interest of using standards based on direct measurements on long bones of known age and similar to the skeletal populations under study.

Age-Related Vascular Changes in the Epiphysis, Physis, and Metaphysis:Normal Findings on Gadolinium-Enhanced MRI of Piglets

OBJECTIVE

We sought to study the normal enhancement patterns seen on MRIs of the epiphysis, physis, and metaphysis and age-related vascular changes in piglets using gadoteridol, a nonionic gadolinium chelate.

MATERIALS AND METHODS

We quantitatively and qualitatively analyzed the normal changes on sequential T1-weighted images after the IV administration of gadoteridol. In an investigation approved by the research animal care committee at our hospital, we studied the proximal and distal femurs of 26 piglets 1-6 weeks old and correlated the enhanced images with findings on intermediate-weighted, T2-weighted, and gradient-recalled echo images and at histologic examination.

RESULTS

We observed early enhancement of the epiphyseal vascular canals, the main physis, the physis of the secondary ossification center, and a metaphyseal band adjacent to the physis. Enhancement of the epiphyseal and metaphyseal marrow and of the epiphyseal cartilage was slower. In the epiphyseal cartilage, we saw three phases of enhancement: vascular, canalicular, and cartilaginous. As the piglets matured, enhancement of the epiphyseal cartilage decreased, and the epiphyseal vascular canals were less conspicuous. Physeal enhancement was greatest during the first week of life, declined at 3 weeks, and subsequently increased again as the physis came to lie adjacent to a larger segment of the epiphyseal ossification center.

CONCLUSION

Gadoteridol-enhanced MRIs showed multiple cartilaginous and vascular structures of the growing skeleton. With maturity and progressive epiphyseal ossification, epiphyseal cartilage enhancement decreased, and physeal cartilage enhancement increased.

An assessment of ADAMs in bone cells: absence of TACE activity prevents osteoclast recruitment and the formation of the marrow cavity in developing long bones

ADAMs (A Disintegrin And Metalloprotease domain) are metalloprotease-disintegrin proteins that have been implicated in cell adhesion, protein ectodomain shedding, matrix protein degradation and cell fusion. Since such events are critical for bone resorption and osteoclast recruitment, we investigated whether they require ADAMs. We report here which ADAMs we have identified in bone cells, as well as our analysis of the generation, migration and resorptive activity of osteoclasts in developing metatarsals of mouse embryos lacking catalytically active ADAM 17 [TNFalpha converting enzyme (TACE)]. The absence of TACE activity still allowed the generation of cells showing an osteoclastic phenotype, but prevented their migration into the core of the diaphysis and the subsequent formation of marrow cavity. This suggests a role of TACE in the recruitment of osteoclasts to future resorption sites.

Ontogenetic adaptation to bipedalism: age changes in femoral to humeral length and strength proportions in humans, with a comparison to baboons

The increase in lower/upper limb bone length and strength proportions in adult humans compared to most other anthropoid primates is commonly viewed as an adaptation to bipedalism. The ontogenetic development of femoral to humeral proportions is examined here using a longitudinal sample of 20 individuals measured radiographically at semiannual or annual intervals from 6 months of age to late adolescence (a subset of the Denver Growth Study sample). Anthropometric data (body weights, muscle breadths) were also available at each examination age. Results show that while femoral/humeral length proportions close to those of adults are already present in human infants, characteristically human femoral/humeral diaphyseal strength proportions only develop after the adoption of bipedalism at about 1 year of age. A rapid increase in femoral/humeral strength occurs between 1 and 3 years, followed by a slow increase until mid-late adolescence, when adult proportions are reached. When age changes in material properties are factored in, femoral strength shows an almost constant relationship to body size (body mass.bone length) after 5 years of age, while humeral strength shows a progressive decline relative to body size. Femoral/humeral length proportions increase slightly throughout growth, with no apparent change in growth trajectory at the initiation of walking, and with a small decline in late adolescence due to later growth in length of the humerus. A sex difference in femoral/humeral strength proportions (females greater) but not length proportions, develops early in childhood. Thus, growth trajectories in length and strength proportions are largely independent, with strength proportions more responsive to actual changes in mechanical loading. A cross-sectional ontogenetic sample of baboons (n=30) illustrates contrasting patterns of growth, with much smaller age changes in proportions, particularly strength proportions, although there is some indication of an adaptation to altered limb loadings early in baboon development.

Bone development and age-related bone loss in male C57BL/6J mice

The objective of this study was to examine changes in the long bones of male C57BL/6J mice with growth and aging, and to consider the applicability of this animal for use in studying Type II osteoporosis. Male C57BL/6J mice were aged in our colony between 4 and 104 weeks (n=9-15/group). The right femur and humeri were measured for length and subjected to mechanical testing (3-point flexure) and compositional analysis. The left femurs were embedded and thick slices at the mid-diaphysis were assessed for morphology, formation indices, and bone structure. In young mice, rapid growth was marked by substantial increases in bone size, mineral mass, and mechanical properties. Maturity occurred between 12 and 42 weeks of age with the maintenance of bone mass and mechanical properties. From peak levels, mice aged for 104 weeks experienced decreased whole femur mass (12.1 and 18.6% for dry and ash mass, respectively), percentage mineralization (7.4%), diminished whole bone stiffness (29.2%), energy to fracture (51.8%), and decreased cortical thickness (20.1%). Indices of surface-based formation decreased rapidly from the onset of the study. However, the periosteal perimeter and, consequently, the cross-sectional moments of inertia continued to increase through 104 weeks, thus maintaining structural properties. This compensated for cortical thinning and increased brittleness due to decreased mineralization and stiffness. The shape of the mid-diaphysis became increasingly less elliptical in aged mice, and endocortical resorption and evidence of subsequent formation were present in 20-50% of femurs aged > or =78 weeks. This, combined with the appearance of excessive endocortical resorption after 52 weeks, indicated a shift in normal mechanisms regulating bone shape and location, and was suggestive of remodeling. The pattern of bone loss at the femoral mid-diaphysis in this study is markedly similar to that seen in cortical bone in the human femoral neck in Type II osteoporosis. This study has thus demonstrated that the male C57BL/6J mouse is a novel and appropriate model for use in studying endogenous, aging-related osteopenia and may be a useful model for the study of Type II osteoporosis.

Immunohistochemical localization of matrix metalloproteinase 13 (MMP-13) in mouse mandibular condylar cartilage

MMP-13 appears to be one of the most important MMPs in cartilage remodeling and mineralization, because it exhibits a substrate preference for the cartilage-specific type II collagen. The condylar process is constructed by rapid accumulation of hypertrophic chondrocytes during development, but its mechanism is still unclear. To investigate the role of MMP-13 in developing condylar cartilage, we immunohistochemically examined the localization of MMP-13 in the endochondral ossification of the mandibular condyle and tibiae of newborn mice. In the tibiae, the MMP-13 expression was detected only in the deepest layer of the terminal hypertrophic chondrocytes through every examined stage (day 1 to day 10 after birth). On the other hand, in the condylar cartilage at days 1 and 5, MMP-13 was expressed throughout the proliferating and the hypertrophic chondrocytes, and at day 10, MMP-13 was mainly localized in the deepest edge of the hypertrophic layer. A zymographical study showed that the activity of MMP-13 in the condyle was observed at day 1, earlier than in the tibia, and increased until day 7. The time-dependent and cell-specific expression of MMP-13 and its enzymatic property suggest that in the mandibular condylar cartilage, MMP-13 plays a role in making the space for cell enlargement by degradation of the cartilage matrix and in onset of mineralization during the early stage of development.

Ontogenetic and regional morphologic variations in the turkey ulna diaphysis: implications for functional adaptation of cortical bone

This study examines relationships between bone morphology and mechanically mediated strain/fluid-flow patterns in an avian species. Using mid-diaphyseal transverse sections of domestic turkey ulnae (from 11 subadults and 11 adults), we quantified developmental changes in predominant collagen fiber orientation (CFO), mineral content (%ash), and microstructure in cortical octants or quadrants (i.e., %ash). Geometric parameters were examined using whole mid-diaphyseal cross-sections. The ulna undergoes habitual bending and torsion, and demonstrates nonuniform matrix fluid-flow patterns, and high circumferential strain gradients along the neutral axis (cranial-caudal) region at mid-diaphysis. The current results showed significant porosity differences: 1) greater osteocyte lacuna densities (N.Lac/Ar) (i.e., "non-vascular porosity") in the caudal and cranial cortices in both groups, 2) greater N.Lac/Ar in the pericortex vs. endocortex in mature bones, and 3) greater nonlacunar porosity (i.e., "vascular porosity") in the endocortex vs. pericortex in mature bones. Vascular and nonvascular porosities were not correlated. There were no secondary osteons in subadults. In adults, the highest secondary osteon population densities and lowest %ash occurred in the ventral-caudal, caudal, and cranial cortices, where shear strains, circumferential strain gradients, and fluid displacements are highest. Changes in thickness of the caudal cortex explained the largest proportion of the age-related increase in cranial-caudal breadth; the thickness of other cortices (dorsal, ventral, and cranial) exhibited smaller changes. Only subadult bones exhibited CFO patterns corresponding to habitual tension (ventral) and compression (dorsal). These CFO variations may be adaptations for differential mechanical requirements in "strain-mode-specific" loading. The more uniform oblique-to-transverse CFO patterns in adult bones may represent adaptations for shear strains produced by torsional loading, which is presumably more prevalent in adults. The micro- and ultrastructural heterogeneities may influence strain and fluid-flow dynamics, which are considered proximate signals in bone adaptation.

Preferred collagen fiber orientation in the human mid-shaft femur

Collagen fiber orientation is one aspect of the microstructure of bone that influences its mechanical properties. While the spatial distribution of preferentially oriented collagen is hypothesized to reflect the effects of loading during the process of aging, its variability in a modern human sample is essentially unknown. In a large sample (n = 67) of autopsied adults, the variability of collagen fiber orientation in the mid-shaft femur was examined in relation to age and sex. Montaged images of entire 100 microm thick cross-sections were obtained using circularly polarized light microscopy (CPLM) under standardized illuminating conditions. An automated image-analyzing routine divided images into 48 segments according to anatomical position. Average gray values (varying with orientation) were quantified for each segment, and one-way ANOVA with Tukey HSD post hoc tests were applied to assess differences between segments. Collagen fiber orientation appeared to be nonrandomly distributed across the mid-shaft femur sample; however, no single "human" pattern was identified. Individual variation, unexplainable by age, sex, or body size, exceeded population-level trends. Differences between age and sex groups suggest there is a strong correspondence between collagen fiber orientation and tissue-type distributions. The minimal consistencies demonstrated here may reflect mechanical forces induced at the femoral mid-shaft. However, the myriad of other factors that may influence collagen fiber orientation patterning, including growth trajectories, metabolic and nutritional status, and disease states, must be explored further. Only then, in conjunction with studies of other structural and material properties of bone, will we be able to elucidate the linkages between microstructure and functional adaptation in the human mid-shaft femur.

Three dimensional ultrastructure of transverse (Harris) lines in the long bone

To investigate the occurrence of transverse lines in long bones of adults, we studied 27 cadavers (14 males and 13 females). After confirming the presence of a transverse line, a cross-sectional sample was examined macroscopically, and by soft X-ray and scanning electron microscopy. The following results were obtained: 1. According to roentgenograms, transverse (Harris') lines were observed in 40.7% of the distal half of the femur and in 29.6% of the proximal half of the tibia. 2. Macroscopic examination of the bone cross-sections at the level of the transverse line showed various membranous structures. 3. In scanning electron micrographs, no marked difference in structure was observed between the transverse line trabeculae and the compact bone.

[Ultrasonic anatomy of pediatric joints]

The radiological work-up of joint injuries in young children can be very tedious due to the absent ossification of secondary ossification centers, which cannot be seen directly on plain X-ray images in this age group. Cartilaginous joint structures therefore cannot be distinguished from joint gaps using X-ray images in young children. High-resolution ultrasound scanning probes facilitate ultrasound studies of cartilaginous joint structures and growth plates in young children, thus providing a new and rewarding option for imaging of traumatic alterations of growing joints, especially in children whose secondary ossification centers have not yet undergone calcification processes. The use of ultrasound for evaluation of joint injuries avoids the shortcomings of ionizing radiation, contralateral joints can be examined for comparison, and functional dynamic studies can be obtained easily.

Stimulatory effect of zinc on insulin-like growth factor-I and transforming growth factor-beta1 production with bone growth of newborn rats

The effect of zinc, an essential trace element, on insulin-like growth factor-I (IGF-I) and transforming growth factor-beta1 production was investigated to determine the role of this metal in bone growth of newborn rats. Femoral-diaphyseal and metaphyseal tissues were obtained between 1 and 28 days after birth of newborn rats, and cultured for 24 h in a serum-free Dulbecco's modified Eagle's medium containing either vehicle or zinc sulfate (10(-6) - 10(-4) M). Protein concentration in the medium was significantly increased by culture with bone tissues of newborn rats with increasing age (14 and 21 days). Medium IGF-I and TGF-beta1 concentration was gradually reduced with increasing age after birth. The presence of zinc (10(-5) and 10(-4) M) caused a significant increase in protein, IGF-I, and TGF-beta1 concentrations in the medium cultured with the diaphyseal or metaphyseal tissues obtained at 7 and 14 days after birth. The expression of IGF-I and TGF-beta1 mRNA was demonstrated by reverse transcription-polymerase chain reaction (RT-PCR) analysis in the diaphyseal and metaphyseal tissues cultured for 24 h using rat IGF-I or TGF-beta1-specific primers. These expressions were significantly raised in the presence of zinc (10(-4) M) in culture medium. The present study demonstrates that zinc has a stimulatory effect on IGF-I and TGF-beta1 production in the femoral tissues with bone growth of newborn rats.

Stimulatory effect of zinc on deoxyribonucleic acid synthesis in bone growth of newborn rats: enhancement with zinc and insulin-like growth factor-I

The effect of zinc on in vitro deoxyribonucleic acid (DNA) synthesis activity in the femoral-diaphyseal and metaphyseal tissues of newborn rats was investigated to determine a role of zinc in bone growth. In vitro DNA synthesis was assayed in a reaction mixture containing the 100 g centrifugation supernatant, which includes the nucleus of bone cells, of bone issue homogenate with incorporation of [3H]-deoxythymidine 5'-triphosphate (dTTP). DNA synthesis activity in the femoral-diaphyseal and metaphyseal tissues of newborn rats was significantly raised with increasing age (1-21 days) after birth. The presence of dipicolinate (10(-3) M), a chelator of zinc, in the reaction mixture caused a significant decrease in DNA synthesis activity in the diaphyseal and metaphyseal tissues of newborn rats at 7 and 14 days after birth. The addition of zinc sulfate (10(-6) - 10(-4) M) resulted in a significant increase in DNA synthesis activity in the diaphyseal and metaphyseal tissues. When the diaphyseal and metaphyseal tissues of newborn rats at 7 days after birth were cultured for 24 hours in a serum-free medium containing either vehicle, zinc sulfate (10(-4) M), insulin-like growth factor-I (IGF-I; 10(-8) M) or transforming growth factor-beta (TGF-beta; 10(-10) M), bone DNA synthesis activity was significantly elevated. Culture with both zinc and IGF-I enhanced additively bone DNA synthesis activity. Such an effect was not seen in the case of zinc and TGF-beta. The effect of zinc, IGF-I, or zinc plus IGF-I in increasing bone DNA synthesis activity was completely prevented by culture with PD98059 (10(-5) M), an inhibitor of mitogen-activated protein (MAP) kinase. Also, the effect of zinc, TGF-beta. or zinc plus TGF-beta in elevating bone DNA synthesis activity was significantly inhibited by culture with staurosporine (10(-6) M), an inhibitor of protein kinase C. The present study demonstrates that zinc, like bone growth factors, has a stimulatory effect on bone DNA synthesis in newborn rats.

Effects of loading frequency on mechanically induced bone formation

The anabolic effect of mechanical loading on bone tissue is modulated by loading frequency. The objective of this study was to characterize the new bone formation on the periosteal and endocortical surfaces of the ulnar diaphysis in adult, female rats in response to controlled dynamic loading and to examine the interactions between strain magnitude, loading frequency, and bone formation rate (BFR/BS) for frequencies ranging from 1 to 10 Hz. Cyclic, compressive loading was applied to the ulnas of 60 adult, female rats divided into 12 loading groups. Loading was applied for 360 cycles/day with peak loads ranging from 4.3 to 18N at frequencies of 1, 5, and 10 Hz. After 2 weeks of loading, bone formation on the periosteal and endocortical surfaces of the ulna was quantified using double-label histomorphometry on transverse sections obtained at the middiaphysis. Periosteal bone formation increased in a dose-response manner with peak load at each of the three loading frequencies tested. Loading frequency significantly affected the x intercepts and slopes of the peak strain versus BFR/BS (p < 0.001) and peak strain versus mineralizing surface (MS/BS; p < 0.001) curves. Periosteal osteogenesis was best predicted by a mathematical model that assumed: (1) bone cells are activated by fluid shear stresses and (2) that stiffness of the bone cells and the extracellular matrix near the cells increases at higher loading frequencies because of viscoelasticity. Consequently, mechanotransduction appears to involve a complex interaction between extracellular fluid forces and cellular mechanics.

Bone morphogenetic protein (BMP) localization in developing human and rat growth plate, metaphysis, epiphysis, and articular cartilage

We assessed the distribution and relative staining intensity of bone morphogenetic protein (BMP)-1-7 by immunohistochemistry in tibial growth plates, epiphyses, metaphyses, and articular cartilage in one 21-week and one 22-week human fetus and in five 10-week-old Sprague-Dawley rats. In the rats, articular cartilage was also examined. BMP proteins were mostly cytoplasmic, with negligible matrix staining. Highest BMP levels were seen in (a) hypertrophic and calcifying zone chondrocytes of growth plate (BMP-1-7), (b) osteoblasts and/or osteoprogenitor fibroblasts and vascular cells of the metaphyseal cortex and medulla (BMP-1-6), (c) osteoclasts of the metaphysis and epiphysis (BMP-1,-4,-5, and -6), and (d) mid to deep zone articular chondrocytes of weanling rats (BMP-1-7). BMP staining in osteoclasts, an unexpected finding, was consistently strong with BMP-4, -5, and -6 but was variable and dependent on osteoclast location with BMP-2,-3, and -7. BMP-1-7 were moderately to intensely stained in vascular canals of human fetal epiphyseal cartilage by endothelial cells and pericytes. BMP-1,-3,-5,-6, and -7 were localized in hypertrophic chondrocytes adjacent to cartilage canals. We conclude that BMP expression is associated with maturing chondrocytes of growth plate and articular cartilage, and may play a role in chondrocyte differentiation and/or apoptosis. BMP appears to be expressed by osteoclasts and might be involved in the intercellular "cross-talk" between osteoclasts and neighboring osteoprogenitor cells at sites of bone remodeling.

Does the mechanical milieu associated with high-speed running lead to adaptive changes in diaphyseal growing bone?

Exercise during growth can be important for attaining optimal bone mass. High-intensity long-duration protocols, however, can have detrimental effects on immature bone morphology and mechanics. The underlying mechanisms are poorly understood. Here, we quantified the mechanical environment of the middiaphyseal rooster tarsometatarsus during high-speed running and examined whether short bouts of this exercise-related mechanical milieu can induce positive changes in cortical bone morphology, mechanics, and mineral ash content. At 9 weeks of age, roosters were assigned to controls (n = 9) and runners (n = 8). Treadmill running was applied in loading sessions of 5 min, three times per day (approximately 2600 cycles/day) for 8 weeks. Both controls and runners received double-fluorochrome labels during weeks 3 and 8 of the protocol. Middiaphyseal distributions of tarsometatarsal longitudinal normal strain, strain rate, and strain gradients engendered by walking and running were determined via in vivo strain gauges. Compared with walking, running elevated mean peak strain magnitude by 19%, peak strain rates by 136%, and peak strain gradients by approximately 18%. After 8 weeks of running, middiaphyseal areal and mechanical properties and normalized ash weight were no different between runners and controls. Transient and focal reductions in periosteal mineral apposition rates occurred during the exercise protocol. Our current data suggest that reducing the number of loading cycles can mitigate the adverse response previously observed in this model with long-duration running. This study also supports the tenet that the exercise-generated mechanical milieu must differ substantially from the habitual milieu to induce significant adaptations.

Mechanics of avian fibrous periosteum: tensile and adhesion properties during growth

We report the results of direct mechanical tests of the fibrous periosteum from the tibiotarsi of white leghorn chicks at 4, 6, 8, 9, 10, 11, 12, and 14 weeks of age using a newly developed sample isolation technique. Additionally, this technique allows the determination of the apparent in vivo load on the fibrous periosteum. The periosteum has a highly nonlinear stress-strain relationship at all ages. For loading below the in vivo level, the periosteum is pliant and mean tensile modulus is 3.35 MPa (+/- 1.84 SD, n = 75). For loading above the in vivo level, tensile stiffness is nearly two orders of magnitude greater. In the region of high stiffness, mean modulus is 229.5 MPa (+/- 89.6, n = 72). In vivo, the periosteum is loaded at the transition between these two stiffness regions. We interpret this as indicating that, in vivo, the collagen fibers of the periosteum are aligned, but subject to minimal loading. Stress levels in the periosteum corresponding to in vivo conditions indicate modest loading, and mean apparent in vivo stress levels are 0.92 MPa (+/- 0.37 SD, n = 67). A second technique demonstrated that the adhesion of the periosteum in the diaphyseal region (1-6 weeks of age) is minimal, but is substantial in the metaphyseal region. The metaphyseal adhesion will affect the transmission of load between the physes. These studies suggest that growth of the fibrous periosteum follows the longitudinal growth of the bone, rather than the periosteum having a direct mechanical influence on growth plate activity. Comparison of tensile properties over the course of growth indicates a substantial increase in periosteal stiffness in the early portion of the growth period, which reaches a maximum at approximately 9 weeks posthatching. There is also a marked decline in periosteal stiffness as growth rate declines in the latest stages of growth (14 weeks). This suggests that the basic properties of periosteal collagen may undergo a transition during the course of this tissue's brief functional lifetime; that is, during long bone growth.

[Comparison of the histologic structure of the compact bone of the long hollow bones of mouse, hamster, rat, guinea pig, rabbit, cat, and dog during development]

This paper reports on histological examinations of the diaphyseal structure of the long bones (humerus, radius, ulna, os femoris and tibia) of mouse, hamster, rat, guinea pig, rabbit, cat, and dog using six animals in three different age groups. There are considerable differences in structure between the species. The results show that with increasing height in the evolution of the species and period of life, as well as advancing age, the differentiation and complexity of bone structures increases. The differences in structure between the localization of bones within the individual species are not considerable. The species comparison results in great similarities between the bone structures of each of mouse and hamster, of rat and guinea pig, as well as of cat and dog. The bone structure of the animals examined becomes more similar to the human structure from mouse, hamster, rat, guinea pig, rabbit, and cat to dog.

Single-column high-performance liquid chromatographic-fluorescence detection of immature, mature, and senescent cross-links of collagen

A high-performance liquid chromatographic-fluorescence detection method of reducible (immature) and nonreducible (mature and senescent) cross-links of collagen was established without the use of a radioisotope and preliminary fractionation step. This method used a gradient elution procedure of sodium citrate buffer containing 7% ethanol. The reducible cross-links (dihydroxylysinonorleucine, hydroxylysinonorleucine, and lysinonorleucine) and nonreducible cross-link (histidinohydroxylysinonorleucine) were detected by O-phthalaldehyde derivatization with the postcolumn method, whereas other nonreducible cross-links (pyridinoline, deoxypyridinoline, and pentosidine) were detected by natural fluorescence. The linear ranges of contents of the O-phthalaldehyde derivative cross-links and the natural fluorescent nonreducible cross-links were 20-600, 5-500 (pyridinoline, deoxypyridinoline), and 0.2-20 pmol (pentosidine), respectively. Tissue containing 1-2 mg dry wt of collagen was adequate for duplicate analyses of the reducible and nonreducible cross-links. An equivalent of 0.25 mg of hydrolyzed collagen could be analyzed by this HPLC system. Using this system, age-related changes in the cross-links of collagen from human connective tissues were also investigated.

Ossification of the distal phalanx of the first digit as a maturity indicator for initiation of orthodontic treatment of Class III malocclusion in Japanese women

The influence of mandibular growth on the stability of orthodontic treatment has been well established. A particular problem is late mandibular growth in patients with Class III malocclusions, because of skeletal jaw discrepancies that may influence the timing and course of treatment, as well as the stability of posttreatment. We have used the ossification of the distal phalanx of the first digit as an indicator of the skeletal maturity of the patient and of their potential for further growth. Our previous studies have shown that fusion of the epiphysis and the diaphysis of the distal phalanx of the first digit occurs from 1 to 3 years after the pubertal growth maximum in Japanese women. In these case reports, the orthodontic treatment of two female patients with mild Class III skeletal malocclusions is presented to show the possible clinical application of the ossification of the first digit as an indicator of the completion or near cessation of mandibular growth in the timing of treatment of Class III malocclusions. The case reports show that, although both patients experienced some mild degree of mandibular growth after treatment, this method can be helpful in determining residual mandibular growth potential in Japanese female patients with Class III malocclusions and mild skeletal discrepancies.

Comparison of diaphyseal growth between the Libben Population and the Hamann-Todd chimpanzee sample

The differences in limb lengths and proportions between humans and chimpanzees are widely known. Humans have relatively shorter forelimbs and longer hind limbs than chimpanzees. Humans have a longer period of long bone formation than chimpanzees. Recent advances in estimating age-at-death in chimpanzees from their dentition have allowed us to reexamine long bone growth in chimpanzees using their skeletal remains and compare it with similar data for humans. A chronological normalization procedure allowing direct interspecific comparison of long bone growth is presented. The preadult chimpanzee sample (n = 43) is from the Hamann-Todd Osteological Collection from the Cleveland Museum of Natural History. All human specimens (n = 202) are from the late Woodland Libben Population currently housed at Kent State University. Relying on these cross-sectional data, we conclude that both species elongate their femora at similar absolute (length per unit time) but different relative (length relative to normalized dental age) rates. The species differ in the absolute growth rate of the humerus but share a common normalized rate of growth. Forelimb segment proportion differences between species are due to differential elongation rates of the segments. Hind limb diaphyseal proportions are the same in both species, which suggests that changes in segment length are proportional. Therefore, alternative developmental mechanisms exist in these closely related species which can produce changes in limb length.

Monophasic dose-response curves of betamethasone on geometric and mechanical properties of femur diaphyses in growing rats

The biomechanical repercussion of the corticoid-induced osteopenia (a severe consequence of long-term glucocorticoid therapy) was studied in cortical bone of small rodents. Growing rats receiving 12.5-3200 micrograms/kg/d of betamethasone (BMS) s.c. for 20 days suffered a log-dose related impairment in body weight gain and in mechanical (fracture load, bending stiffness) and cross-sectional properties (area, moment of inertia) of femur diaphyses. No changes in bone material properties (ability to stand stress, elastic modulus, energy absorption per unit volume) were observed. At variance with the biphasic dose-response curves (positive effects at low-medium doses, negative at high doses) previously obtained with cortisol in a similar model, only negative effects on every variable studied were observed in this experiment. Results suggest that BMS effects on cortical bone biomechanics derived mainly or completely from those induced on bone geometry (biomechanical correlate of corticoid-induced osteopenia) in the assayed conditions. Data are compatible with a BMS-induced change in the setpoint of bone mechanostat. Correlation of bone geometric and biomechanical data with body weight gain showed that the anti-anabolic effects of BMS on bone were proportionally less intense than those exerted on the whole biomass.

[Morphogenesis of the femoral diaphysis in humans: significance of function and evolution]

The obliquity of the femoral diaphysis, measured by the bicondylar angle, permits the adducted position of the knee in humans. The presence of a high femoral bicondylar angle has been a hallmark of hominid bipedality, but its pattern of development has not been documented. We have observed radiographic and skeletal data on the development of this angle. The two samples exhibit a pattern of a bicondylar angle of 0 degrees at birth and then a steady average increase in the angle through infancy and into the juvenile years. These data establish a high degree of potential for plasticity in the development of this angle and the direct association of a bipedal locomotion with the developmental emergence of a human femoral bicondylar angle. We show that the obliquity angle, which occasionally appears in some non-human primates, is not homologous to the human condition. As this angle is an epigenetic functional feature in modern humans, we suggest that it developed following a change in infantile locomotor behaviour of the early australopithecines and was not the result of a genomic change.