Cortical bone development in black and white South African children: iliac crest histomorphometry

Increased Osteocyte Lacunae Density in the Hypermineralized Bone Matrix of Children with Osteogenesis Imperfecta Type I

Osteocytes are terminally differentiated osteoblasts embedded within the bone matrix and key orchestrators of bone metabolism. However, they are generally not characterized by conventional bone histomorphometry because of their location and the limited resolution of light microscopy. OI is characterized by disturbed bone homeostasis, matrix abnormalities and elevated bone matrix mineralization density. To gain further insights into osteocyte characteristics and bone metabolism in OI, we evaluated 2D osteocyte lacunae sections (OLS) based on quantitative backscattered electron imaging in transiliac bone biopsy samples from children with OI type I (n = 19) and age-matched controls (n = 24). The OLS characteristics were related to previously obtained, re-visited histomorphometric parameters. Moreover, we present pediatric bone mineralization density distribution reference data in OI type I (n = 19) and controls (n = 50) obtained with a field emission scanning electron microscope. Compared to controls, OI has highly increased OLS density in cortical and trabecular bone (+50.66%, +61.73%; both p < 0.001), whereas OLS area is slightly decreased in trabecular bone (−10.28%; p = 0.015). Correlation analyses show a low to moderate, positive association of OLS density with surface-based bone formation parameters and negative association with indices of osteoblast function. In conclusion, hyperosteocytosis of the hypermineralized OI bone matrix associates with abnormal bone cell metabolism and might further impact the mechanical competence of the bone tissue.

Race and Ethnicity Predict Bone Markers and Fracture in Pediatric Patients With Chronic Kidney Disease

Studies in healthy children have shown racial-ethnic differences in bone markers and bone outcomes including fractures. At present, limited studies have evaluated the impact of race and ethnicity on bone markers and fractures within the pediatric chronic kidney disease (CKD) population. In a cohort study of 762 children between the ages of 1.5 years and 18 years, with CKD stages 1 to 4 from the CKD in children (CKiD) cohort, the relationship between racial-ethnic group and bone markers (parathyroid hormone [PTH], 25-hydroxyvitamin D [25-OHD], 1,25-dihydroxyvitamin D [1,25(OH)₂ D], and C-terminal fibroblast growth factor [FGF23]) was determined using linear mixed models. Additionally, logistic regression was used to evaluate racial-ethnic differences in prevalent fracture upon study entry. Black race was associated with 23% higher PTH levels (confidence interval [CI], 2.5% to 47.7%; p = .03), 33.1% lower 25-OHD levels (CI, -39.7% to -25.7%; p < .0001), and no difference in C-terminal FGF23 or 1,25(OH)₂ D levels when compared to whites. Hispanic ethnicity was associated with 15.9% lower C-terminal FGF23 levels (CI, -28.3% to -1.5%; p = .03) and 13.8% lower 25-OHD levels (CI, -22.2% to -4.5%; p = .005) when compared to whites. Black and Hispanic children had 74% (odds ratio [OR] 0.26; CI, 0.14 to 0.49; p = .001) and 66% (OR 0.34; CI, 0.17 to 0.65; p < .0001) lower odds of any fracture than white children at study entry, respectively. Race and ethnicity are associated with differences in bone markers and despite lower 25-OHD levels, both black and Hispanic children with CKD reported a lower prevalent fracture history than white children. The current findings in the CKD population are similar to racial-ethnic differences described in healthy children. Additional studies are needed to better understand how these differences might impact the management of pediatric CKD-MBD. © 2020 American Society for Bone and Mineral Research (ASBMR).

Racial differences in bone histomorphometry in children and young adults treated with dialysis

BACKGROUND

Healthy African-Americans are known to have greater bone mineral density and decreased risk of fracture when compared to Caucasians. In fact, comparisons of bone histomorphometry in healthy South African children and adults reveal greater cortical thickness in Black subjects as compared to White. How these differences are reflected in the bone of American children and young adults on dialysis is unknown.

METHODS

Using tetracycline-labeled, iliac crest bone biopsies obtained in prior research protocols in pediatric and young adult dialysis patients, we compared trabecular and cortical parameters between non-Hispanic African-American subjects and non-Hispanic Caucasian subjects matched by age and gender. A linear regression model controlled for trabecular turnover and mineralization was used to further investigate the association of race with cortical thickness.

RESULTS

The matched cohort consisted of 52 subjects-26 African-American and 26 Caucasian. Turnover, mineralization and volume parameters in trabecular bone did not show significant differences between racial groups. Characterizing subjects by renal osteodystrophy type did not show a statistically significant difference although Caucasian patients had double the prevalence of mineralization defects. Consistent with this was a trend toward better mineralization parameters in African-Americans including shorter osteoid maturation time and lower osteoid volume. A sub-cohort of patients with cortical measures demonstrated greater median (IQR) cortical thickness in African-Americans (541 μm [354, 694]) than in Caucasians (371 μm [336, 446], p = 0.08). In a linear regression model controlling for trabecular turnover and mineralization, African-American subjects had 36.2% (95% CI 0.28 to 85.1%, p = 0.048) greater cortical thickness as compared to White subjects. There was no significant difference in cortical porosity.

CONCLUSIONS

Although likely limited by sample size, our findings suggest that, similar to findings in populations of normal children, African-American race in pediatric and young adults on dialysis is associated with greater cortical thickness. Additionally, there was a trend toward greater mineralization defects in Caucasian children. Both findings require further exploration with larger patient samples in order to thoroughly explore these racial differences and the implications on CKD-MBD treatment.

Calcium Deficiency Rickets in African Adolescents: Cortical Bone Histomorphometry

Rickets due to dietary calcium deficiency has been well described in black African children, but less is known about this condition in black adolescents. We investigated 26 black adolescents (19 males aged 11 to 19 years and 7 females aged 12 to 15 years) with rachitic leg deformities and 20 controls by routine iliac crest undecalcified cortical bone histomorphometry for disturbances of bone turnover and for mineralization defects, including severity of osteocytic osteolysis (Ot.Olysis) and periosteocytic osteolysis (Peri.Ot.Olysis) of the lacunar‐canalicular space. Serum levels of calcium (sCa), 25‐hydroxyvitamin D (25OHD), 1,25‐dihydroxyvitamin D (1,25(OH)₂D), and total alkaline phosphatase (ALP) were measured. Histomorphometry showed varying degrees of severity of secondary hyperparathyroidism (2⁰ HPT) characterized by hyperosteoidosis, increased erosion, and porosis. Because osteoid was neither being mineralized nor eroded (osteoclasts cannot erode osteoid), it increasingly blocked bone surface needed for osteoclastic resorption. Where osteoid covered >50% of bone surface, osteoid thickness, severity of Ot.Olysis, and extent of Peri.Ot.Olysis increased, sCa and 25OHD declined, and 1,25(OH)₂D and ALP increased. At 80% osteoid cover, bone remodeling had all but ceased, secondary HPT had changed to osteomalacia, and serum biochemical results had deteriorated further. Disease severity was greater in males than in females, likely because males grow faster and for longer than females. In conclusion, this cross‐sectional clinical case study presents cortical bone histomorphometric data of secondary HPT and its transition to osteomalacia in black adolescents with rickets attributable to dietary calcium deficiency. The bone disease was most severe in older adolescent males. Importantly, bone pathology of calcium deficiency rickets in adolescents was not confined to bone surfaces but also manifested at osteocyte level as Ot.Olysis and Peri.Ot.Olysis. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Abnormally High and Heterogeneous Bone Matrix Mineralization After Childhood Solid Organ Transplantation: A Complex Pathology of Low Bone Turnover and Local Defects in Mineralization

Chronic renal, liver, and heart failure in children associates with multiple skeletal complications. Increased fracture incidence often persists after transplantation and could be related to alterations in bone material properties. In the present cohort study we evaluated bone mineralization density distribution (BMDD) by quantitative backscattered electron imaging (qBEI) in 23 pediatric solid organ allograft recipients with suspected osteoporosis. We measured BMDD in the entire cross-sectional area of transiliac bone biopsies obtained from kidney (n = 9), liver (n = 9), and heart (n = 5) transplant recipients (aged 7.6 to 19.7 years; 6.0 ± 5.6 years posttransplantation, patients with a history of clinical fractures: n = 14). The BMDD findings were compared with age-appropriate references and with a previously presented cohort of children with chronic kidney disease on dialysis (CKD5D, n = 18). Furthermore, we related the BMDD parameters with patients' clinical and bone histomorphometric outcomes. Compared to healthy children, qBEI results for cancellous and cortical bone in transplant recipients revealed an increase in the most frequently occurring calcium concentration (+2.9%, p = 0.001; +3.5%, p = 0.014), in the portion of fully mineralized bone (fivefold; 10-fold, both p < 0.0001) and in heterogeneity of mineralization (+26,5% and +27.8%, both p < 0.0001), respectively. Moreover, the BMDD parameters were nonsignificantly distinct from CKD5D cohort except that the heterogeneity in mineralization was higher posttransplantation. There was a strong inverse correlation between the average calcium content of the bone matrix and patients' biochemical ALP levels, histomorphometric indices of bone formation and resorption. The abnormally high bone matrix mineralization in transplant recipients, consistent with serum and histomorphometric outcomes, suggests a history of low bone turnover with accumulation of fully mineralized bone packets. Additionally, the increased heterogeneity of mineralization suggests local alterations in mineralization kinetics, which may be linked to dysfunctional osteocytes that were recently shown to accumulate within the bone matrix during organ failure and concomitant glucocorticoid and immunosuppressive medication. © 2017 American Society for Bone and Mineral Research.

Iliac crest histomorphometry and skeletal heterogeneity in men

Purpose

The cortical characteristics of the iliac crest in male have rarely been investigated with quantitative histomorphometry. Also it is still unknown how cortical microarchitecture may vary between the iliac crest and fractures related sites at the proximal femur. We studied the microarchitecture of both external and internal cortices within the iliac crest, and compared the results with femoral neck and subtrochanteric femoral shaft sites.

Methods

Undecalcified histological sections of the iliac crest were obtained bicortically from cadavers (n = 20, aged 18–82 years, males). They were cut (7 μm) and stained using modified Masson-Goldner stain. Histomorphometric parameters of cortical bone were analysed with low (× 50) and high (× 100) magnification, after identifying cortical bone boundaries using our previously validated method. Within cortical bone area, only complete osteons with typical concentric lamellae and cement line were selected and measured.

Results

At the iliac crest, the mean cortical width of external cortex was higher than at the internal cortex (p < 0.001). Also, osteon structural parameters, e.g. mean osteonal perimeter, were higher in the external cortex (p < 0.05). In both external and internal cortices, pore number per cortical bone area was higher in young subjects (≤ 50 years) (p < 0.05) while mean pore perimeter was higher in the old subjects (> 50 years) (p < 0.05). Several cortical parameters (e.g. osteon area per cortical bone area, pore number per cortical area) were the lowest in the femoral neck (p < 0.05). The maximal osteonal diameter and mean wall width were the highest in the external cortex of the iliac crest (p < 0.05), and the mean cortical width, osteon number per cortical area were the highest in the subtrochanteric femoral shaft (p < 0.05). Some osteonal structural parameters (e.g. min osteonal diameter) were significantly positively correlated (0.29 ≤ R² ≤ 0.45, p < 0.05) between the external iliac crest and the femoral neck.

Conclusions

This study reveals heterogeneity in cortical microarchitecture between the external and internal iliac crest cortices, as well as between the iliac crest, the femoral neck and the subtrochanteric femoral shaft. Standard iliac crest biopsy does not reflect accurately cortical microarchitecture of other skeletal sites.

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The structural asymmetry between cortices of the ilium remains after childhood.

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In both cortices of the ilium, cortical pore perimeter was higher in the old subjects.

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The cortical microarchitecture is highly variable between different skeletal sites.

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Positive correlation is revealed between the external iliac crest and the femoral neck in osteonal characteristics.

Racial Differences in Bone Microarchitecture and Estimated Strength at the Distal Radius and Distal Tibia in Older Adolescent Girls: a Cross-Sectional Study

BACKGROUND

Previous studies have demonstrated that an individual's race and ethnicity are important determinants of their areal bone mineral density (aBMD), assessed by dual-energy X-ray absorptiometry. However, there are few data assessing the impact of race on bone microarchitecture and strength estimates, particularly in older adolescent girls and young adults. We hypothesized that bone microarchitecture and strength estimates would be superior in Blacks compared to White and Asian American adolescent girls and young adults of similar age based on reports of higher aBMD in Blacks.

METHODS

We assessed BMD using dual-energy X-ray absoptiometry (DXA), bone microarchitecture at the distal radius and distal tibia using high-resolution peripheral quantitative computed tomography (HRpQCT) and estimated measures of bone strength using micro-finite element analysis (FEA) in 35 White, 15 Asian American, and 10 Black girls 14-21 years.

RESULTS

After controlling for height, most DXA measures of aBMD and aBMD Z scores were higher in Black girls compared with Whites and Asian Americans. HRpQCT and FEA showed that at the distal radius, Blacks had greater cortical perimeter, cortical area, trabecular thickness, trabecular BMD, estimated failure load, and stiffness than the other two groups. For the distal tibia, trabecular number and BMD were higher in Blacks than Asian Americans.

CONCLUSIONS

Particularly at the distal radius, adolescent and young adult White and Asian American girls have less favorable bone microarchitecture and lower bone strength than Blacks, possibly explaining the lower risk of fracture seen in Blacks.

LEVEL OF EVIDENCE

Level II.

Role of cortical bone in bone fragility

PURPOSE OF REVIEW

Trabecular bone loss and vertebral fractures are historical hallmarks of osteoporosis. During the past 70 years, this view has dominated research aiming to understand the structural basis of bone fragility. We suggest this notion needs to be revised to recognize and include the role of cortical bone deterioration as an important determinant of bone strength throughout life.

RECENT FINDINGS

About 80% of the fragility fractures involve the appendicular skeleton, at regions comprising large amounts of cortical bone. Up to 70% of the age-related bone loss at these locations is the result of intracortical remodeling that cavitates cortical bone producing porosity. It is now possible to accurately quantify cortical porosity in vivo and use this information to understand the pathogenesis of bone fragility throughout life, assist in identifying patients at risk for fracture, and use this as a potential marker to monitor the effects of treatment on bone structure and strength.

SUMMARY

Cortical bone has an important role in determining bone strength. The loss of strength is the result of intracortical and endocortical remodeling imbalance that produces cortical porosity and thinning. Studies are needed to determine whether porosity is an independent predictor of fracture risk and whether a reduction in porosity serves as a surrogate of antifracture efficacy.

Growth and Age-Related Abnormalities in Cortical Structure and Fracture Risk

Vertebral fractures and trabecular bone loss have dominated thinking and research into the pathogenesis and the structural basis of bone fragility during the last 70 years. However, 80% of all fractures are non-vertebral and occur at regions assembled using large amounts of cortical bone; only 20% of fractures are vertebral. Moreover, ~80% of the skeleton is cortical and ~70% of all bone loss is cortical even though trabecular bone is lost more rapidly than cortical bone. Bone is lost because remodelling becomes unbalanced after midlife. Most cortical bone loss occurs by intracortical, not endocortical remodelling. Each remodelling event removes more bone than deposited enlarging existing canals which eventually coalesce eroding and thinning the cortex from 'within.' Thus, there is a need to study the decay of cortical as well as trabecular bone, and to develop drugs that restore the strength of both types of bone. It is now possible to accurately quantify cortical porosity and trabecular decay in vivo. The challenges still to be met are to determine whether measurement of porosity identifies persons at risk for fracture, whether this approach is compliments information obtained using bone densitometry, and whether changes in cortical porosity and other microstructural traits have the sensitivity to serve as surrogates of treatment success or failure.

Cortical and trabecular bone in pediatric end-stage kidney disease

BACKGROUND

Cortical bone represents nearly 80 % of human bone mass and is the major determinant of bone strength; however, cortical bone parameters and their relationship to trabecular bone in the pediatric chronic kidney disease (CKD) population have not been evaluated.

METHODS

Biochemical values and cortical and trabecular bone parameters were assessed in 22 pediatric dialysis patients: 12 with high and 10 with normal to low trabecular bone turnover.

RESULTS

Trabecular bone turnover and osteoid volume correlated with parathyroid hormone (PTH) levels (r = 0.86, p < 0.01 and r = 0.93, p < 0.01, respectively). Internal cortical osteonal bone formation rate was directly related to alkaline phosphatase (r = 0.45, p < 0.05) and inversely related to insulin-like growth factor (IGF)-1 values (r = -0.55, p < 0.01), and internal cortical porosity was also related to serum alkaline phosphatase levels (r = 0.57, p < 0.01). A similar relationship was not found between external cortical bone formation rate and parameters of bone turnover and porosity, however. No relationship was found between trabecular and cortical bone formation rates.

CONCLUSIONS

Secondary hyperparathyroidism was associated with increased external cortical, relative to internal cortical, osteonal activity in pediatric dialysis patients. The clinical consequences of these changes and their response to therapy for secondary hyperparathyroidism remain to be defined.

Development of new criteria for cortical bone histomorphometry in femoral neck: intra- and inter-observer reproducibility

Histomorphometry is commonly applied to study bone remodeling. Histological definitions of cortical bone boundaries have not been consistent. In this study, new criteria for specific definition of the transitional zone between the cortical and cancellous bone in the femoral neck were developed. The intra- and inter-observer reproducibility of this method was determined by quantitative histomorphometry and areal overlapping analysis. The undecalcified histological sections of femoral neck specimens (n = 6; from men aged 17-59 years) were processed and scanned to acquire histological images of complete bone sections. Specific criteria were applied to define histological boundaries. "Absolute cortex area" consisted of pure cortical bone tissue only, and was defined mainly based on the size of composite canals and their distance to an additional "guide" boundary (so-called "preliminary cortex boundary," the clear demarcation line of density between compact cortex and sparse trabeculae). Endocortical bone area was defined by recognizing characteristic endocortical structures adjacent to the preliminary cortical boundary. The present results suggested moderate to high reproducibility for low-magnification parameters (e.g., cortical bone area). The coefficient of variation (CV %) ranged from 0.02 to 5.61 in the intra-observer study and from 0.09 to 16.41 in the inter-observer study. However, the intra-observer reproducibility of some high-magnification parameters (e.g., osteoid perimeter/endocortical perimeter) was lower (CV %, 0.33-87.9). The overlapping of three histological areas in repeated analyses revealed highest intra- and inter-observer reproducibility for the absolute cortex area. This study provides specific criteria for the definition of histological boundaries for femoral neck bone specimens, which may aid more precise cortical bone histomorphometry.

Childhood cortical porosity is related to microstructural properties of the bone-muscle junction

Childhood cortical porosity is attributable to giant asymmetrical drifting osteonal canals that arise predominantly along the primary-secondary bone interface (PSBI). Bone from the external iliac crest cortex of 92 subjects aged 0 to 25 years was examined histomorphometrically for differences in microstructural properties between primary and secondary bone that might account for features of drifting osteonal canals. Primary compared with secondary bone showed greater numbers of osteocyte lacunae, thinner collagen lamellae, and a scaffold of elastic perforating fibers (PFs). The greater number of osteocyte lacunae compounded by known perilacunar strain amplification and the presence of elastic PFs are expected to be associated with greater bone tissue strain in primary than in secondary bone and thus with strain gradients at the PSBI. Strain gradients may lead local osteocytes to originate resorption canals and to promote transverse drift of the resorption front into lower-strain secondary bone, thus creating giant asymmetrical drifting osteonal canals that remodel primary to secondary bone. PFs extended from muscle fibers through periosteum and primary bone to the PSBI, where they were resorbed by origination of drifting canals. Growth modeling by periosteal osteoblasts proceeds in the gaps between PFs. Through the direct connection between muscle and the PSBI via PFs, muscle forces may influence not only modeling by raising strain but also remodeling of primary to secondary bone by increasing strain gradients at the PSBI. With reduction in primary bone width after the mid-teens, numbers of drifting canals and porosity declined. Differences in microstructural properties between primary and secondary bone are expected to generate strain gradients at the PSBI that contribute to site, transverse drift, asymmetry and large size of drifting canals, and, hence, to cortical porosity. Cortical porosity in children is a physiological feature of bone growth in width. Advisability of therapeutic intervention remains to be defined.

Increased intra-cortical porosity reduces bone stiffness and strength in pediatric patients with osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a heritable disease occurring in one out of every 20,000 births. Although it is known that Type I collagen mutation in OI leads to increased bone fragility, the mechanism of this increased susceptibility to fracture is not clear. The aim of this study was to assess the microstructure of cortical bone fragments from patients with osteogenesis imperfecta (OI) using polarized light microscopy, and to correlate microstructural observations with the results of previously performed mechanical compression tests on bone from the same source. Specimens of cortical bone were harvested from the lower limbs of three (3) OI patients at the time of surgery, and were divided into two groups. Group 1 had been subjected to previous micro-mechanical compression testing, while Group 2 had not been subjected to any prior testing. Polarized light microscopy revealed disorganized bone collagen architecture as has been previously observed, as well as a large increase in the areal porosity of the bone compared to typical values for healthy cortical bone, with large (several hundred micron sized), asymmetrical pores. Importantly, the areal porosity of the OI bone samples in Group 1 appears to correlate strongly with their previously measured apparent Young's modulus and compressive strength. Taken together with prior nanoindentation studies on OI bone tissue, the results of this study suggest that increased intra-cortical porosity is responsible for the reduction in macroscopic mechanical properties of OI cortical bone, and therefore that in vivo imaging modalities with resolutions of ~100 μm or less could potentially be used to non-invasively assess bone strength in OI patients. Although the number of subjects in this study is small, these results highlight the importance of further studies in OI bone by groups with access to human OI tissue in order to clarify the relationship between increased porosity and reduced macroscopic mechanical integrity.

Bone Mineral Density in Children From Anthropological and Clinical Sciences: A Review

Bone mineral density (BMD) is a frequent topic of discussion in the clinical literature in relation to the bone health of both adults and children. However, in archaeological and/ or anthropological studies the role of BMD is often cited as a possible factor in the poor skeletal preservation which can lead to an under-representation of juvenile skeletal remains. During skeletal development and growth throughout childhood and adolescence changes take place in both the size and shape of bones and these changes also result in the increasing of mineral content. BMD can be affected by many factors, which include, age, genetics, sexual maturation, amount of physical activity and dietary calcium. This paper aims to review the clinical and anthropological literature on BMD and discuss the numerous methods of measurement and how the availability of certain methods such as Dual-energy x-ray absorptiometry (DEXA) and quantitative computed tomography (QCT) can influence the study of bone density in archaeological skeletal collections and also the future potential for forensic anthropological studies.

Cortical porosity in children is determined by age-dependent osteonal morphology

INTRODUCTION

Fracture rates in children are high. Cortical bone makes a major contribution to bone strength, determined by cortical geometry, mineralization and porosity. Of these, porosity remains least well explored. Since most cortical canals are part of an osteon, we examined osteons and their canals for age-related changes in numbers, size and shape in 87 iliac crest bone samples of subjects aged 0-25 years, using histomorphometry.

RESULTS

Three types of secondary osteons were identified: drifting, eccentric and concentric. 1. Drifting osteons predominated to the mid-teens, were large, asymmetrical, and had giant canals (remodeling space) with the resorption front drifting towards the marrow. The cause of drift remains unclear. Onset of formation appeared delayed, and commenced on the periosteum-facing surface. From the mid-teens numerical density of drifting osteons decreased, and so did porosity. 2. Eccentric osteons were smaller, more circular and had a small excentric canal; their numerical density gradually increased with age. 3. Concentric osteons (adult bone) were the smallest, most symmetrical osteons, had a small central canal, and markedly increased in numerical density from the mid-teens. Boys showed greater overall porosity and greater numerical density of drifting osteons, and later change to concentric osteons than girls. Whites had greater numerical density and greater areal density of resorption cavities than blacks.

CONCLUSIONS

Structure of osteons and canals varied during growth. Large asymmetrical drifting osteons with giant active canals (remodeling space) predominated until the mid-teens and accounted for > 70% of childhood cortical porosity. Thereafter smaller concentric (adult type) osteons increasingly predominated. Gender differences may relate to greater fracture rates in boys, and race differences to greater fracture rates in whites. The role of osteocyte-mediated mechanotransduction in osteonal structure and cortical porosity during growth warrants further exploration.

Comparative effects of teriparatide and strontium ranelate in the periosteum of iliac crest biopsies in postmenopausal women with osteoporosis

The periosteum contains osteogenic cells that regulate the outer shape of bone and contribute to determine its cortical thickness, size and position. We assessed the effects of subcutaneous injections of teriparatide (TPTD, 20μg/day) or oral strontium ranelate (SrR, 2g/day) in postmenopausal women with osteoporosis on new bone formation activity at the periosteal and endosteal bone surfaces using dynamic histomorphometric measurements. Evaluable tetracycline-labeled transiliac crest bone biopsies were analyzed from 27 patients in the TPTD group, and 22 in the SrR group after six months of treatment. Measurements were conducted on the thicker and thinner cortices separately, and comparisons between the thicker, thinner and combined cortices were carried out. At the combined periosteal cortex, the mineralization surface as a percent of bone surface (MS/BS%) was greater for TPTD (mean±SE: 8.08±1.22%) than SrR (3.22±1.05%) (p<0.005). The difference in mineral apposition rate (MAR) between TPTD (0.35±0.06μm/day) and SrR (0.14±0.06μm/day) was also significant (p<0.05), while that of bone formation rate per bone surface (BFR/BS) between TPTD (0.014±0.004 mm(3)/mm(2)/year) and SrR (0.004±0.003 mm(3)/mm(2)/year) was not (p=0.057). Statistically significant differences between the two treatments were also observed for MS/BS%, BFR/BS, MAR and the double-labeled perimeter in the periosteum of the thicker, but not thinner, iliac crest cortices. The comparison between the thicker and thinner cortices of both periosteal and endosteal surfaces showed statistically significant differences for MAR and the double-labeled perimeter for TPTD treated women. There were no statistically significant differences in any bone formation dynamic measurements between the two cortices in the SrR group. In conclusion, most of the bone formation and mineralization variables were significantly higher for TPTD- than SrR-treated women at both the periosteal and endosteal combined cortices. The response to TPTD for dynamic bone formation measurements in the periosteal surface was greater for the thicker than thinner cortex, but this difference was not significant in SrR treated patients. This may reflect a greater ability of TPTD to enhance responsiveness of bone to the mechanical loading environment. These effects on bone formation may underlie the improvement in bone quality in patients with osteoporosis treated with TPTD.

Bone mass and bone size in pre- or early pubertal 10-year-old black and white South African children and their parents

Genetic factors are thought to maintain bone mass in socioeconomically disadvantaged black South Africans. We compared bone mass between environmentally disadvantaged black and advantaged white children and their parents, after determining the most appropriate method by which to correct bone mineral content (BMC) for size. We collected data from 419 healthy black and white children of mean age 10.6 years (range 10.0-10.9), 406 biological mothers, and 100 biological fathers. Whole-body, femoral neck, lumbar spine, and mid- and distal one-third of radius bone area (BA) and BMC were measured by dual-energy X-ray absorptiometry. Power coefficients (PCs) were calculated from the linear-regression analyses of ln(BMC) on ln(BA) and used to correct site-specific BMC for bone size differences. Heritability (½h(2), %) by maternal and paternal descent was estimated by regressing children's Z scores on parents' Z scores. Correcting BMC for height, weight, and BA(PC) accounted for the greatest variance of BMC at all skeletal sites. In so doing, BMC in blacks was up to 2.6 times greater at the femoral neck and lumbar spine. Maternal and paternal heritability was estimated to be ~30% in both black and white subjects. These results may in part explain the lower prevalence of fragility fractures at the hip in black South African children when compared to whites. Heritability was comparable between environmentally disadvantaged black and advantaged white South African children and similar to that reported for Caucasians in other parts of the world.

Three-dimensional cortical bone microstructure in a rat model of hypoxia-induced growth retardation

Little is known about hypoxia-induced modification of the canal network in the cortical bone despite its involvement in intracortical vascularity and bone blood supply. In this study, we examined the effect of chronic hypoxia on the canal network in postnatal bone. Tibiae were harvested from 4- and 8-week-old rats (hyp-4 and -8, n = 8 each), whose growth was retarded owing to postnatal exposure to hypoxia (12-14% O₂), and from 3- and 4-week-old normoxic rats (cnt-4 and -5, n = 8 each), which were similar in tibial length and cortical cross-sectional area to hyp-4 and -8, respectively. The diaphyseal canals were detected by monochromatic synchrotron radiation CT with a 3.1-μm voxel resolution. The anatomical properties of the canal network were compared between age- or size-matched hypoxic and normoxic groups. The canals were larger in diameter, were more densely distributed and connected, and opened into the marrow cavity with a higher density in hyp-4 than in cnt-4. The canal density and connectivity were also higher in hyp-4 than in cnt-3. The canal diameter, density, and connectivity were smaller in hyp-8 than in cnt-4; however, the densities of endocortical and periosteal canal openings did not differ between hyp-8 and cnt-4. We concluded that chronic hypoxia enhanced the formation of cortical canal networks at the postnatal developmental stage, probably facilitating intra- and transcortical vascularization and bone perfusion accordingly.

Iliac cortical thickness in the neonate - the gradient effect

Recent studies of the neonatal ilium are beginning to reveal that a recognizable structural patterning of trabecular bone is present in the absence of any direct stance-related weight transfer. However, little is known about the organization of compact bone in the ilium and the way in which it is laid down during the earliest stages of development. This study investigates cortical bone thickness across both gluteal and pelvic iliac shells in the human neonatal ilium. Measurements of specific regions of interest on the iliac cortices were recorded using reconstructed micro-computed tomography scans from 30 neonatal ilia. Analysis of gluteal and pelvic cortical thicknesses revealed a distinctive patterning consistent with the expected bone distribution achieved through early bone modelling and remodelling. The analysis of this pattern is important for understanding the relationship between trabecular bone patterning and cortical bone structure in the earliest stages of pelvic development prior to locomotive influences and its response to the specific functional forces acting during this period.