Static histomorphometry of human iliac crest and vertebral trabecular bone: a comparative study

A comprehensive systematic review of marketed bone grafts for load-bearing critical-sized bone defects

Treatment of critical-sized bone defects typically involves implantation of a bone graft. Various types of bone grafts are nowadays marketed, categorized by their origin as allografts, xenografts, or synthetic grafts. Despite their widespread use, a comprehensive understanding of their morphology and mechanical response remains elusive. Controlling these characteristics for promoting bone growth and ensuring mechanical resistance remains challenging, especially in load-bearing districts. This study aims to systematically review existing literature to delineate the principal morpho-mechanical characteristics of marketed bone grafts designed for load-bearing applications. Furthermore, the obtained data are organized and deeply discussed to find out the relationship between different graft characteristics. Among 196 documents identified through PRISMA guidelines, encompassing scientific papers and 510(k) documents, it was observed that a majority of marketed bone grafts exhibited porosity akin to bone (>60%) and mechanical properties resembling those of low-bone volume fraction trabecular bone. The present review underscores the dearth of information regarding the morpho-mechanical characteristics of bone grafts and the incomparability of data derived from different studies, due to the absence of suitable standards and guidelines. The need for new standards and complete and transparent morpho-mechanical characterization of marketed bone grafts is finally emphasized. Such an approach would enhance the comparability of data, aiding surgeons in selecting the optimal device to meet patient's needs.

Interest of Bone Histomorphometry in Bone Pathophysiology Investigation: Foundation, Present, and Future

Despite the development of non-invasive methods, bone histomorphometry remains the only method to analyze bone at the tissue and cell levels. Quantitative analysis of transiliac bone sections requires strict methodologic conditions but since its foundation more 60 years ago, this methodology has progressed. Our purpose was to review the evolution of bone histomorphometry over the years and its contribution to the knowledge of bone tissue metabolism under normal and pathological conditions and the understanding of the action mechanisms of therapeutic drugs in humans. The two main applications of bone histomorphometry are the diagnosis of bone diseases and research. It is warranted for the diagnosis of mineralization defects as in osteomalacia, of other causes of osteoporosis as bone mastocytosis, or the classification of renal osteodystrophy. Bone biopsies are required in clinical trials to evaluate the safety and mechanism of action of new therapeutic agents and were applied to anti-osteoporotic agents such as bisphosphonates and denosumab, an anti-RANKL, which induces a marked reduction of the bone turnover with a consequent elongation of the mineralization period. In contrast, an increased bone turnover with an extension of the formation site is observed with teriparatide. Romosozumab, an anti-sclerostin, has a dual effect with an early increased formation and reduced resorption. Bone histomorphometric studies allow us to understand the mechanism of coupling between formation and resorption and to evaluate the respective role of bone modeling and remodeling. The adaptation of new image analysis techniques will help bone biopsy analysis in the future.

European Consensus Statement on the diagnosis and management of osteoporosis in chronic kidney disease stages G4-G5D

Controlling the excessive fracture burden in patients with chronic kidney disease (CKD) Stages G4-G5D remains an impressive challenge. The reasons are 2-fold. First, the pathophysiology of bone fragility in patients with CKD G4-G5D is complex and multifaceted, comprising a mixture of age-related (primary male/postmenopausal), drug-induced and CKD-related bone abnormalities. Second, our current armamentarium of osteoporosis medications has not been developed for, or adequately studied in patients with CKD G4-G5D, partly related to difficulties in diagnosing osteoporosis in this specific setting and fear of complications. Doubts about the optimal diagnostic and therapeutic approach fuel inertia in daily clinical practice. The scope of the present consensus paper is to review and update the assessment and diagnosis of osteoporosis in patients with CKD G4-G5D and to discuss the therapeutic interventions available and the manner in which these can be used to develop management strategies for the prevention of fragility fracture. As such, it aims to stimulate a cohesive approach to the management of osteoporosis in patients with CKD G4-G5D to replace current variations in care and treatment nihilism.

Regional variation in bone turnover at the iliac crest versus the greater trochanter

BACKGROUND

Iliac crest bone biopsy with histomorphometry is the gold standard for diagnosis of abnormalities in bone turnover, yet fractures more frequently occur at the greater trochanter of the hip. Whether bone turnover is similar at these two anatomic sites within individuals is uncertain.

METHODS

We collected bone biopsy samples from the ipsilateral iliac crest and greater trochanter in 9 deceased individuals undergoing autopsies at an academic medical center between March-August 2018. We measured 14 static bone histomorphometry parameters including osteoclast number (N.Oc/T.A), eroded surface (ES/BS), trabecular separation (Tb.Sp), osteoclast surface (Oc.S/BS) and osteoid volume (OV/BV) as markers of bone turnover, mineralization, and volume (TMV), and evaluated the correlation of these markers between the iliac crest and greater trochanter.

RESULTS

Average age at time of death was 58 ± 15 years, 2 were women, and average time from death to autopsy was 2.9 ± 1.8 days. Overall, correlations of the markers of bone turnover across the two sites were poor, ranging from as low as 0 for Tb.Sp (p = 1.0) to as high as 0.583 for Oc.S/BS (p = 0.102).

CONCLUSIONS

Static histomorphometric measures of bone turnover at the iliac crest may not provide reliable information about turnover at other anatomic sites.

Three-dimensional-printed replica models of bone for experimentally decoupling trabecular bone properties contribution to ultrasound propagation parameters

A detailed investigation of the relationship between ultrasonic (US) properties and trabecular bone microstructure is difficult because of the great variability in the bone loss process. The aim of this work was twofold. First, to verify by compressive tests that the three-dimensional (3D)-printer is able to produce precisely and repeatedly "bone replica models" of different size and density. Following, replicas of the original specimens with two different polymers and thinned trabeculae models were used to investigate US properties (speed of sound, SOS, and backscatter coefficient), aiming to deconvolute the influence of material properties on ultrasound characteristics. The results revealed that matrix material properties influence only the magnitude of the backscatter coefficient, whereas the characteristic undulated patterns are related to the trabecular structure. Simulation of perforation and thinning of cancellous bone, associated with bone loss, showed that SOS and mechanical properties were reduced perfectly linearly with apparent density when structure deteriorated. The 3D-printed bone replicas have the potential to enable systematic investigations of the influence of structure on both acoustical and mechanical properties and evaluate changes caused by bone loss. The development of replicas from materials with properties close to those of bone will permit quantitative conclusions for trabecular bone.

An overview of de novo bone generation in animal models

Some of the earliest success in de novo tissue generation was in bone tissue, and advances, facilitated by the use of endogenous and exogenous progenitor cells, continue unabated. The concept of one health promotes shared discoveries among medical disciplines to overcome health challenges that afflict numerous species. Carefully selected animal models are vital to development and translation of targeted therapies that improve the health and well-being of humans and animals alike. While inherent differences among species limit direct translation of scientific knowledge between them, rapid progress in ex vivo and in vivo de novo tissue generation is propelling revolutionary innovation to reality among all musculoskeletal specialties. This review contains a comparison of bone deposition among species and descriptions of animal models of bone restoration designed to replicate a multitude of bone injuries and pathology, including impaired osteogenic capacity.

Correspondence between bone mineral density and intervertebral disc degeneration across age and sex

The distribution of bone tissue within the vertebra can modulate vertebral strength independently of average density and may change with age and disc degeneration. Our results show that the age-associated decrease in bone density is spatially non-uniform and associated with disc health, suggesting a mechanistic interplay between disc and vertebra.

PURPOSE

While the decline of bone mineral density (BMD) in the aging spine is well established, the extent to which age influences BMD distribution within the vertebra is less clear. Measures of regional BMD (rBMD) may improve predictions of vertebral strength and suggest how vertebrae might adapt with intervertebral disc degeneration. Thus, we aimed to assess how rBMD values were associated with age, sex, and disc height loss (DHL).

METHODS

We measured rBMD in the L3 vertebra of 377 participants from the Framingham Heart Study (41-83 years, 181 M/196 F). Integral (Int.BMD) and trabecular BMD (Tb.BMD) were measured from QCT images. rBMD ratios (anterior/posterior, superior/mid-transverse, inferior/mid-transverse, and central/outer) were calculated from the centrum. A radiologist assigned a DHL severity score to adjacent intervertebral discs (L2-L3 and L3-L4).

RESULTS

Int.BMD and Tb.BMD were both associated with age, though the decrease across age was greater in women (Int.BMD, - 2.6 mg/cm3 per year; Tb.BMD, - 2.6 mg/cm3 per year) than men (Int.BMD, - 0.5 mg/cm3 per year; Tb.BMD, - 1.2 mg/cm3 per year). The central/outer (- 0.027/decade) and superior/mid-transverse (- 0.018/decade) rBMD ratios were negatively associated with age, with similar trends in men and women. Higher Int.BMD or Tb.BMD was associated with increased odds of DHL after adjusting for age and sex. Low central/outer ratio and high anterior/poster and superior/mid-transverse ratios were also associated with increased odds of DHL.

CONCLUSIONS

Our results indicate that the distribution of bone within the L3 vertebra is different across age, but not between sexes, and is associated with disc degeneration.

Aberrant miR-145-5p/β-catenin signal impairs osteocyte function in adolescent idiopathic scoliosis

Recently, noncoding RNAs have been thought to play important roles in the sporadic occurrence of spinal deformity of adolescent idiopathic scoliosis (AIS). As a prognostic factor for curve progression, low bone mass has been hypothesized to crosstalk with AIS pathogenesis. Abnormal osteoblasts activities are reported in AIS without a clear mechanism. In this study, bone biopsies from patients with AIS and control subjects and the primary osteoblasts derived from those samples were used to identify the potential microRNA (miRNA) candidates that interfere with osteoblasts and osteocytes function. Microarray analysis identified miRNA-145-5p (miR-145) as a potential upstream regulator. miR-145 and β-catenin mRNA ( CTNNB1) were overexpressed in AIS bone tissues and primary osteoblasts, and their expression correlated positively in AIS. Knockdown of miR-145 restored impaired osteocyte activity through the down-regulation of active β-catenin expression and its transcriptional activity. Significant negative correlations between circulating miR-145 and serum sclerostin, osteopontin, and osteoprotegerin were noted in patients with AIS, which was in line with our cellular findings. This is the first study to demonstrate the effect of aberrant miRNA expression and its effect on osteocyte function in AIS, which may contribute to the low bone mass. Our findings also provide insight into the development of circulating microRNAs as a bone quality biomarker or even a prognostic biomarker for AIS.-Zhang, J., Chen, H., Leung, R. K. K., Choy, K. W., Lam, T. P., Ng, B. K. W., Qiu,Y., Feng, J. Q., Cheng, J. C. Y., Lee, W. Y. W. Aberrant miR-145-5p/β-catenin signal impairs osteocyte function in adolescent idiopathic scoliosis.

Bone histomorphometry in transiliac biopsies from 48 normal, healthy men

Investigators and clinicians use bone histomorphometry data from iliac bone biopsies to study bone abnormalities in diseased patients, and to understand the safety and effectiveness of pharmaceutical interventions. This requires access to a high quality normal data-set to be used for comparisons, a resource that has not been adequate to date. The objective of this work is to present static and dynamic bone histomorphometry data from transilial bone biopsies performed on 48 healthy males, evenly distributed between ages 45 and 75. In addition, we compared these results with results from our earlier study in normal postmenopausal women (Recker et al., 1988 [1]). The data include bone density and anthropometric measurements, micro-CT, and a collection of serum biochemical measurements. We found that several of the histomorphometry variables were correlated with serum measurements, i.e. serum testosterone and sex hormone-binding globulin (SHBG). Micro-CT variables were correlated with the static histomorphometry variables, and were very similar. Age-related changes were observed for both histomorphometry and Micro-CT, but were surprisingly small in most cases. Comparisons with our previously reported histomorphometry data from normal women were surprisingly similar, but there was a significant age by gender interaction in the wall thickness (W.Th) measurements, i.e. there was a small increase in this variable with age in men, and a significant decline with age in women. The population selected for this study, and the prior study in normal women, were carefully chosen so as to rule out the presence of clinical, life-style or other confounding factors. While the cohort chosen herein was a convenience sample, and not a population-based sample, we believe it can be used as a reference standard with proper precautions in its interpretation and in its comparisons with diseased populations.

A comparative study of bone biopsies from the iliac crest, the tibial bone, and the lumbar spine

BACKGROUND

Patients with an impaired renal function show a high incidence of bone and mineral disturbances. These 'chronic kidney disease - mineral and bone disorders' (CKD-MBD) range from high turnover osteoporosis to adynamic bone disease. Currently, the histomorphometric analysis of a bone biopsy taken from the iliac crest is viewed as the gold standard for CKD-MBD subtype differentiation. However, the clinical relevance of such a biopsy is questionable since iliac crest fractures are an extremely rare finding. Therefore, we aimed to elucidate if the histomorphometric parameter 'trabecular bone volume (BV/TV)' from the iliac crest is representative for other biopsy locations. We chose two skeletal sites of higher fracture risk for testing, namely, the tibial bone and the lumbar spine, to examine if the current gold standard of bone biopsy is indeed golden.

METHODS

Bone biopsies were taken from 12 embalmed body donors at the iliac crest, the proximal tibia, and the lumbar vertebral body, respectively. Masson-Goldner stained sections of methyl methacrylate embedded biopsies were used for trabecular bone volume calculation. Furthermore, exemplary μ-computed tomography (XtremeCT) scans with subsequent analysis were performed.

RESULTS

Median values of trabecular bone volume were comparable between all body donors with median (interquartile range, IQR) 18.3% (10.9-22.9%) at the iliac crest, 21.5% (9.5-40.1%) at the proximal tibia, and 16.3% (11.4-25.0%) at the lumbar spine. However, single values showed extensive intra-individual variation, which were also confirmed by XtremeCT imaging.

CONCLUSIONS

Distinct intra-individual heterogeneity of trabecular bone volume elucidate why a bone biopsy from one site does not necessarily predict patient relevant endpoints like hip or spine fractures. Physicians interpreting bone biopsy results should know this limitation of the current gold standard for CKD-MBD diagnostic, especially, when systemic therapeutic decisions should be based on it.

Unique local bone tissue characteristics in iliac crest bone biopsy from adolescent idiopathic scoliosis with severe spinal deformity

Adolescent idiopathic scoliosis is a complex disease with unclear etiopathogenesis. Systemic and persistent low bone mineral density is an independent prognostic factor for curve progression. The fundamental question of how bone quality is affected in AIS remains controversy because there is lack of site-matched control for detailed analysis on bone-related parameters. In this case-control study, trabecular bone biopsies from iliac crest were collected intra-operatively from 28 severe AIS patients and 10 matched controls with similar skeletal and sexual maturity, anthropometry and femoral neck BMD Z-score to control confounding effects. In addition to static histomorphometry, micro-computed tomography (μCT) and real time-PCR (qPCR) analyses, individual trabecula segmentation (ITS)-based analysis, finite element analysis (FEA), energy dispersive X-ray spectroscopy (EDX) were conducted to provide advanced analysis of structural, mechanical and mineralization features. μCT and histomorphometry showed consistently reduced trabecular number and connectivity. ITS revealed predominant change in trabecular rods, and EDX confirmed less mineralization. The structural and mineralization abnormality led to slight reduction in apparent modulus, which could be attributed to differential down-regulation of Runx2, and up-regulation of Spp1 and TRAP. In conclusion, this is the first comprehensive study providing direct evidence of undefined unique pathological changes at different bone hierarchical levels in AIS.

Limited Trabecular Bone Density Heterogeneity in the Human Skeleton

There is evidence for variation in trabecular bone density and volume within an individual skeleton, albeit in a few anatomical sites, which is partly dependent on mechanical loading. However, little is known regarding the basic variation in trabecular bone density throughout the skeleton in healthy human adults. This is because research on bone density has been confined to a few skeletal elements, which can be readily measured using available imaging technology particularly in clinical settings. This study comprehensively investigates the distribution of trabecular bone density within the human skeleton in nine skeletal sites (femur, proximal and distal tibia, third metatarsal, humerus, ulna, radius, third metacarpal, and axis) in a sample of N = 20 individuals (11 males and 9 females). pQCT results showed that the proximal ulna (mean = 231.3 mg/cm³) and axis vertebra (mean = 234.3 mg/cm³) displayed significantly greater (p < 0.01) trabecular bone density than other elements, whereas there was no significant variation among the rest of the elements (p > 0.01). The homogeneity of the majority of elements suggests that these sites are potentially responsive to site-specific genetic factors. Secondly, the lack of correlation between elements (p > 0.05) suggests that density measurements of one anatomical region are not necessarily accurate measures of other anatomical regions.

Influence of age and gender on microarchitecture and bone remodeling in subchondral bone of the osteoarthritic femoral head

INTRODUCTION

Age and gender have been reported to have a remarkable impact on bone homeostasis. However, subchondral bone, which plays a pivotal role in the initiation and progression of OA, has been poorly investigated. This study was to investigate age- and gender-related changes of microarchitecture and bone remodeling in subchondral bone in OA.

METHODS

Subchondral trabecular bone (STB) and deeper trabecular bone (DTB) specimens were extracted in the load-bearing region of femoral heads from 110 patients with OA. Micro-CT and histomorphometry were performed to analyze microarchitectural and bone remodeling changes of all specimens.

RESULTS

Compared to DTB, STB showed more sclerotic microarchitecture, more active bone remodeling and higher frequency of bone cysts. There were no gender differences for both microarchitecture and bone remodeling in STB. However, gender differences were found in DTB, with thinner Tb.Th, higher Tb.N, higher OS/BV and ES/BV in males. In both STB and DTB, no correlation between microarchitecture and age was found in both genders. However, bone remodeling of STB increased significantly with age in males, while bone remodeling of DTB increased significantly with age in females. No age or gender preference was found in subchondral bone cyst (SBC) frequency. The cyst volume fraction was correlated with neither age nor gender.

CONCLUSIONS

There were differences in microarchitecture and bone remodeling between STB and DTB, which may be due to the distinct biomechanical and biochemical functions of these two bone structures in maintaining joint homeostasis. OA changed the normal age- and gender-dependence of bone homeostasis in joints, in a site-specific manner.

Age-related changes in vertebral and iliac crest 3D bone microstructure--differences and similarities

Age-related changes of vertebra and iliac crest 3D microstructure were investigated, and we showed that they were in general similar. The 95th percentile of vertebral trabecular thickness distribution increased with age for women. Surprisingly, vertebral and iliac crest bone microstructure was only weakly correlated (r = 0.38 to 0.75), despite the overall similar age-related changes.

INTRODUCTION

The purposes of the study were to determine the age-related changes in iliac and vertebral bone microstructure for women and men over a large age range and to investigate the relationship between the bone microstructure at these skeletal sites.

METHODS

Matched sets of transiliac crest bone biopsies and lumbar vertebral body (L2) specimens from 41 women (19-96 years) and 39 men (23-95 years) were micro-computed tomography (μCT) scanned, and the 3D microstructure was quantified.

RESULTS

For both women and men, bone volume per total volume (BV/TV), connectivity density (CD), and trabecular number (Tb.N) decreased significantly, while structure model index (SMI) and trabecular separation (Tb.Sp) increased significantly with age at either skeletal site. Vertebral trabecular thickness (Tb.Th) was independent of age for both women and men, while iliac Tb.Th decreased significantly with age for men, but not for women. In general, the vertebral and iliac age-related changes were similar. The 95th percentile of the Tb.Th distribution increased significantly with age for women but was independent of age for men at the vertebral body, while it was independent of age for either sex at the iliac crest. The Tb.Th probability density functions at the two skeletal sites became significantly more similar with age for women, but not for men. The microstructural parameters at the iliac crest and the vertebral bodies were only moderately correlated from r = 0.38 for SMI in women to r = 0.75 for Tb.Sp in men.

CONCLUSION

Age-related changes in vertebral and iliac bone microstructure were in general similar. The iliac and vertebral Tb.Th distributions became more similar with age for women. Despite the overall similar age-related changes in trabecular bone microstructure, the vertebral and iliac bone microstructural measures were only weakly correlated (r = 0.38 to 0.75).

Early Trabecular Development in Human Vertebrae: Overproduction, Constructive Regression, and Refinement

Early bone development may have a significant impact upon bone health in adulthood. Bone mineral density (BMD) and bone mass are important determinants of adult bone strength. However, several studies have shown that BMD and bone mass decrease after birth. If early development is important for strength, why does this reduction occur? To investigate this, more data characterizing gestational, infant, and childhood bone development are needed in order to compare with adults. The aim of this study is to document early vertebral trabecular bone development, a key fragility fracture site, and infer whether this period is important for adult bone mass and structure. A series of 120 vertebrae aged between 6 months gestation and 2.5 years were visualized using microcomputed tomography. Spherical volumes of interest were defined, thresholded, and measured using 3D bone analysis software (BoneJ, Quant3D). The findings showed that gestation was characterized by increasing bone volume fraction whilst infancy was defined by significant bone loss (≈2/3rds) and the appearance of a highly anisotropic trabecular structure with a predominantly inferior-superior direction. Childhood development progressed via selective thickening of some trabeculae and the loss of others; maintaining bone volume whilst creating a more anisotropic structure. Overall, the pattern of vertebral development is one of gestational overproduction followed by infant "sculpting" of bone tissue during the first year of life (perhaps in order to regulate mineral homeostasis or to adapt to loading environment) and then subsequent refinement during early childhood. Comparison of early bone developmental data in this study with adult bone volume values taken from the literature shows that the loss in bone mass that occurs during the first year of life is never fully recovered. Early development could therefore be important for developing bone strength, but through structural changes in trabecular microarchitecture rather than bone mass.

Age-related changes of vertical and horizontal lumbar vertebral trabecular 3D bone microstructure is different in women and men

The study presents a 3D method for subdividing a trabecular network into horizontal and vertical oriented bone. This method was used to investigate the age related changes of the bone volume fraction and thickness of horizontal and vertical trabeculae in human lumbar vertebral bone estimated with unbiased 3D methods in women and men over a large age-range. The study comprised second lumbar vertebral body bone samples from 40 women (aged 21.7-96.4years, median 56.6years) and 39 men (aged 22.6-94.6years, median 55.6years). The bone samples were μCT scanned and the 3D microstructure was quantified. A voxel based algorithm inspecting the local neighborhood is presented and used to segment the trabecular network into horizontal and vertical oriented bone. For both women and men BV/TV decreased significantly with age, Tb.Th* was independent of age, while SMI increased significantly with age. Vertical (BV.vert/TV) and horizontal (BV.horz/TV) bone volume fraction decreased significantly with age for both sexes. BV.vert/TV decreased significantly faster with age for women than for men. Vertical (Tb.Th*.vert) and horizontal (Tb.Th*.horz) trabecular thickness were independent of age, while Tb.Th*.horz/Tb.Th*.vert decreased significantly with age for both sexes. Additionally, the 95th percentile of the trabecular thickness distribution increased significantly with age for vertical trabeculae in women, whereas it was independent of age in men. In conclusion, we have shown that vertical and horizontal oriented bone density decreases with age in both women and men, and that vertical oriented bone is lost more quickly in women than in men. Furthermore, vertical and horizontal trabecular thickness were independent of age, whereas the horizontal to vertical trabecular thickness ratio decreased significantly with age indicating a relatively more pronounced thinning of horizontal trabeculae. Finally, the age-related loss of trabecular elements appeared to result in a compensatory hypertrophy of vertical trabeculae in women, but not in men.

Increased osteoblast and osteoclast indices in individuals with systemic mastocytosis

Indolent systemic mastocytosis (ISM) can trigger bone loss. However, the clinical relevance of different mast cell infiltration patterns for bone remains to be clarified. Here, we report increased bone turnover in individuals with ISM, and its extent is rather related to the type of mast cell distribution within the bone marrow than to the presence or absence of cutaneous manifestations.

INTRODUCTION

It is well established that ISM can trigger osteopenia or osteoporosis. However, neither the clinical relevance of the infiltration pattern of mast cells within the bone marrow nor the impact of the presence or absence of cutaneous mast cell infiltration has been elucidated.

METHODS

We retrospectively analysed 300 cases with histologically proven ISM of the bone marrow and performed quantitative histomorphometry for a subgroup of 159 patients that did not receive any treatment before the biopsies were taken. Most importantly, since 66 % of the patients displayed ISM without the characteristic skin lesions, we were able to compare ISM with or without cutaneous manifestation.

RESULTS

We found that both forms of ISM were not only characterized by a decreased trabecular bone mass but also by an increased number of osteoclasts and osteoblasts. Interestingly, when we analysed these data in relation to mast cell distribution, we found that the bone cell numbers in cases with mast cell granulomas were significantly increased compared to cases with diffuse mast cell distribution. Moreover, evidence of increased bone turnover was also found in 16 patients displaying osteosclerosis.

CONCLUSION

Based on the largest cohort of bone biopsies from patients with ISM analysed so far, we could demonstrate high bone turnover, more specifically increased osteoblast and osteoclast numbers and surface indices, as a cause of the skeletal changes. Moreover, the severity of the bone disease is presumably rather dependent on the amount of mast cells and their distribution within the bone marrow irrespective of the presence or absence of cutaneous involvement.

Changes in 3-dimensional bone structure indices in hypoparathyroid patients treated with PTH(1-84): a randomized controlled study

Hypoparathyroidism (hypoPT) is characterized by a state of low bone turnover and high bone mineral density (BMD) despite conventional treatment with calcium supplements and active vitamin D analogues. To assess effects of PTH substitution therapy on 3-dimensional bone structure, we randomized 62 patients with hypoPT into 24 weeks of treatment with either PTH(1-84) 100 µg/day subcutaneously or similar placebo as an add-on therapy. Micro-computed tomography was performed on 44 iliac crest bone biopsies (23 on PTH treatment) obtained after 24 weeks of treatment. Compared with placebo, PTH caused a 27% lower trabecular thickness (p < 0.01) and 4% lower trabecular bone tissue density (p < 0.01), whereas connectivity density was 34% higher (p < 0.05). Trabecular tunneling was evident in 11 (48%) of the biopsies from the PTH group. Patients with tunneling had significantly higher levels of biochemical markers of bone resorption and formation. At cortical bone, number of Haversian canals per area was 139% higher (p = 0.01) in the PTH group, causing a tendency toward an increased cortical porosity (p = 0.09). At different subregions of the hip, areal BMD (aBMD) and volumetric BMD (vBMD), as assessed by dual-energy X-ray absorptiometry (DXA) and quantitative computed tomography (QCT), decreased significantly by 1% to 4% in the PTH group. However, at the lumbar spine, aBMD decreased by 1.8% (p < 0.05), whereas vBMD increased by 12.8% (p = 0.02) in the PTH compared with the placebo group.

Osteoporotic characteristics persist in the spine of ovariectomized sheep after withdrawal of corticosteroid administration

A validated ovine model of osteoporosis achieves severe bone loss in a relatively short period. This study investigated if osteoporotic features persist in this model after cessation of corticosteroid administration. Methods. Osteoporosis was induced in nine ewes by chronic corticosteroid injection, ovariectomy, and low calcium diet. Six ewes were used as controls. Bone mineral density (BMD) of the lumbar spine (LS) and body weight were assessed at regular intervals. After five months, corticosteroid treatment was withdrawn systematically over one month. Three months later, all animals were euthanised, and the LS was collected for histomorphometric analysis. Results. BMD in the LS of osteoporotic sheep was 25% lower than control sheep. Body weight of osteoporotic sheep was reduced in the first month of the corticosteroid withdrawal period but returned to baseline level thereafter. Trabecular bone volume of LS in osteoporotic sheep was 27% lower than controls and showed a heterogeneous structure. Conclusions. Osteoporotic characteristics remain in the vertebra after ceasing corticosteroid administration providing an opportunity to evaluate potential systemic or local treatments in vivo under realistic physiological conditions. The microstructural arrangement of vertebral trabecular bone in sheep is similar to humans demonstrating further relevance of this model for preclinical investigations.

Variability of trabecular microstructure is age-, gender-, race- and anatomic site-dependent and affects stiffness and stress distribution properties of human vertebral cancellous bone

Cancellous bone microstructure is an important determinant of the mechanical integrity of vertebrae. The numerous microstructural parameters that have been studied extensively are generally represented as a single value obtained as an average over a sample. The range of the intra-sample variability of cancellous microstructure and its effect on the mechanical properties of bone are less well-understood. The objectives of this study were to investigate the extent to which human cancellous bone microstructure within a vertebra i) is related to bone modulus and stress distribution properties and ii) changes along with age, gender and locations thoracic 12 (T12) vs lumbar 1 (L1). Vertebrae were collected from 15 male (66±15 years) and 25 female (54±16 years) cadavers. Three dimensional finite element models were constructed using microcomputed tomography images of cylindrical specimens. Linear finite element models were used to estimate apparent modulus and stress in the cylinders during uniaxial compression. The intra-specimen mean, standard deviation (SD) and coefficient of variation (CV) of microstructural variables were calculated. Mixed model statistical analysis of the results demonstrated that increases in the intra-specimen variability of the microstructure contribute to increases in the variability of trabecular stresses and decreases in bone stiffness. These effects were independent from the contribution from intra-specimen average of the microstructure. Further, the effects of microstructural variability on bone stiffness and stress variability were not accounted for by connectivity and anisotropy. Microstructural variability properties (SD, CV) generally increased with age, were greater in females than in males and in T12 than in L1. Significant interactions were found between age, gender, vertebra and race. These interactions suggest that microstructural variability properties varied with age differently between genders, races and vertebral levels. The current results collectively demonstrate that microstructural variability has a significant effect on mechanical properties and tissue stress of human vertebral cancellous bone. Considering microstructural variability could improve the understanding of bone fragility and improve assessment of vertebral fracture risk.

Gender aspects of osteoporosis and bone strength

Although postmenopausal and elderly women are more frequently affected by osteoporosis, men are not protected from the disease. Age-related osteoporosis involves several gender-specific clinical aspects such as disease onset time and different dynamics of bone loss. Men benefit from larger bones and a time-delay of age-related changes in bone density and quality. Moreover, secondary osteoporosis is more common in males than in females. High-resolution peripheral quantitative computed tomography (HR-pQCT) and high-resolution magnetic resonance imaging (HR-MRI) represent novel research tools for a noninvasive quantification of bone microstructure which is of interest for musculoskeletal gender studies. For optimal design of such studies, researchers should be aware of technical pitfalls and site-specificity of bone microstructure.

Increased calcium content and inhomogeneity of mineralization render bone toughness in osteoporosis: mineralization, morphology and biomechanics of human single trabeculae

The differentiation and degree of the effects of mineral content and/or morphology on bone quality remain, to a large extent, unanswered due to several microarchitectural particularities in spatial measuring fields (e.g., force transfer, trajectories, microcalli). Therefore, as the smallest basic component of cancellous bone, we focused on single trabeculae to investigate the effects of mineralization and structure, both independently and in superposition. Transiliac Bordier bone cores and T12 vertebrae were obtained from 20 females at autopsy for specimen preparation, enabling radiographical analyses, histomorphometry, Bone Mineral Density Distribution (BMDD) analyses, and trabecular singularization to be performed. Evaluated contact X-rays and histomorphometric limits from cases with osteoporotic vertebral fractures generated two subdivisions, osteoporotic (n=12, Ø 78 years) and non-osteoporotic (n=8, Ø 49 years) cases, based on fracture appearance and bone volume (BV/TV). Measurements of trabecular number (Tb.N.), trabecular separation (Tb.Sp.), trabecular thickness (Tb.Th.), trabecular bone pattern factor (TBPf) and eroded surface (ES/BS) were carried out to provide detailed structural properties of the investigated groups. The mechanical properties of 400 rod-like single vertebral trabeculae, assessed by three-point bending, were matched with mineral properties as quantified by BMDD analyses of cross-sectioned rod-like and plate-like trabeculae, both in superposition and independently. Non-osteoporotic iliac crests and vertebrae displayed linear dependency on structure parameters, whereas osteoporotic compartments proved to be non-correlated with bone structure. Independent of trabecular thickness, osteoporotic rod-like trabeculae showed decreases in Young's modulus, fracture load, yield strength, ultimate stress, work to failure and bending stiffness, along with significantly increased mean calcium content and calcium width. Non-osteoporotic trabeculae showed biomechanically beneficial properties due to a homogeneous mineralization configuration, whereas osteoporotic trabeculae predominantly demonstrated various mineralized bone packets, eroded surfaces, highly mineralized cement lines and microcracks. The Young's moduli of single trabeculae exhibited significantly negative linear correlations with trabecular thickness. Because of increased, but inhomogeneously distributed, calcium content, osteoporotic trabeculae may be subject to shear stresses that render bone fragile beyond structure impairment due to cracks and lacunae.

Anticipating bipedalism: trabecular organization in the newborn ilium

Trabecular bone structural organization is considered to be predominantly influenced by localized temporal forces which act to maintain and remodel the trabecular architecture into a biomechanically optimal configuration. In the adult pelvis, the most significant remodelling forces are believed to be those generated during bipedal locomotion. However, during the fetal and neonatal period the pelvic complex is non-weight bearing and, as such, structural organization of iliac trabecular bone cannot reflect direct stance-related forces. In this study, micro-computed tomography scans from 28 neonatal ilia were analysed, using a whole bone approach, to investigate the trabecular characteristics present within specific volumes of interest relevant to density gradients highlighted in a previous radiographic study. Analysis of the structural indices bone volume fraction, trabecular thickness, trabecular spacing and trabecular number was carried out to quantitatively investigate structural composition. Quantification of the neonatal trabecular structure reinforced radiographic observations by highlighting regions of significant architectural form which grossly parallel architectural differences in the adult pattern but which have previously been attributed to stance-related forces. It is suggested that the seemingly organized rudimentary scaffold observed in the neonatal ilium may be attributable to other non-weight bearing anatomical interactions or even to a predetermined genetic blueprint. It must also be postulated that whilst the observed patterning may be indicative of a predetermined inherent template, early non-weight bearing and late stance-related locomotive influences may subsequently be superimposed upon this scaffolding and perhaps reinforced and likely remodelled at a later age. Ultimately, the analysis of this fundamental primary pattern has core implications for understanding the earliest changes in pelvic trabecular architecture and provides a baseline insight into future ontogenetic development and bipedal capabilities.

Three-dimensional quantification of structures in trabecular bone using measures of complexity

The study of pathological changes of bone is an important task in diagnostic procedures of patients with metabolic bone diseases such as osteoporosis as well as in monitoring the health state of astronauts during long-term space flights. The recent availability of high-resolution three-dimensional (3D) imaging of bone challenges the development of data analysis techniques able to assess changes of the 3D microarchitecture of trabecular bone. We introduce an approach based on spatial geometrical properties and define structural measures of complexity for 3D image analysis. These measures evaluate different aspects of organization and complexity of 3D structures, such as complexity of its surface or shape variability. We apply these measures to 3D data acquired by high-resolution microcomputed tomography (microCT) from human proximal tibiae and lumbar vertebrae at different stages of osteoporotic bone loss. The outcome is compared to the results of conventional static histomorphometry and exhibits clear relationships between the analyzed geometrical features of trabecular bone and loss of bone density, but also indicate that the measures reveal additional information about the structural composition of bone, which were not revealed by the static histomorphometry. Finally, we have studied the dependency of the developed measures of complexity on the spatial resolution of the microCT data sets.

Site-specific deterioration of trabecular bone architecture in men and women with advancing age

We tested the hypothesis that the age dependence of trabecular bone microstructure differs between men and women and is specific to skeletal site. Furthermore, we aimed to investigate the microstructural pattern of bone loss in aging. Microstructural properties of trabecular bone were measured in vitro in 75 men and 75 age-matched women (age, 52-99 yr) using microCT. Trabecular bone samples were scanned at a 26-microm isotropic resolution at seven anatomical sites (i.e., distal radius, T(10) and L(2) vertebrae, iliac crest, femoral neck and trochanter, and calcaneus). DXA measurements were obtained at the distal radius and proximal femur and QCT was used at T(12). No significant decrease in bone density or structure with age was found in men using microCT, DXA, or QCT at any of the anatomical sites. In women, a significant age-dependent decrease in BV/TV was observed at most sites, which was strongest at the iliac crest and weakest at the distal radius. At most sites, the reduction in BV/TV was associated with an increase in structure model index, decrease in Tb.N, and an increase in Tb.Sp. Only in the calcaneus was it associated with a significant decrease in Tb.Th. In conclusion, a significant, site-specific correlation of trabecular bone microstructure with age was found in women but not in men of advanced age. The microstructural basis by which a loss of BV/TV occurs with age can vary between anatomical sites.

Effects of high bone turnover on the biomechanical properties of the L3 vertebra in an ovine model of early stage osteoporosis

STUDY DESIGN

Investigations of the effects of high bone turnover on the L3 vertebra were carried out, using an ovariectomized (OVX) ovine model of early stage osteoporosis.

OBJECTIVE

To assess the contribution of bone turnover to the biomechanics of L3.

SUMMARY OF BACKGROUND DATA

Clinically, dual energy x-ray absorptiometry (DEXA) is used to measure bone mineral density (BMD). However, this can only predict 60% to 70% of bone strength; the remainder is due to bone quality. There is currently little information available on how strength is affected by changes in bone quality parameters, particularly bone turnover. Turnover can be assessed clinically using biochemical markers; however, this provides systemic values, whereas localized values are required to predict site-specific fracture risk.

METHODS

Thirty-eight sheep were assigned to 2 groups (control, n = 19; OVX, n = 19). Both groups were intravenously administered a fluorochrome dye on the day of surgery and 3, 6, 9, and 12 months thereafter, to label sites of bone turnover. After 12 months, animals were killed and the spinal columns harvested. L3 vertebrae were scanned using DEXA. Bone turnover was quantified using epifluorescence microscopy, and microarchitecture was assessed by microCT scanning. Compressive testing was used to characterize the mechanical properties of the vertebrae.

RESULTS

BMD and microarchitecture were unchanged in OVX compared with controls. However, bone turnover, as measured by fluorochrome labeled sites, was significantly increased in the OVX group in cortical and trabecular compartments. As a consequence, the biomechanical properties were significantly reduced in that group.

CONCLUSION

These findings show that OVX resulted in changes in bone turnover, which reduced biomechanical properties in a model of early stage osteoporosis. These differences were present despite microarchitecture or BMD remaining unchanged. In the future, the ability to assess site-specific bone turnover would greatly enhance the accuracy with which fracture risk could be predicted.

Regional variations of vertebral trabecular bone microstructure with age and gender

The vertebral trabecular bone has a complex three-dimensional (3D) microstructure, with inhomogeneous morphology. A thorough understanding of regional variations in the microstructural properties is crucial for evaluating age- and gender-related bone loss of the vertebra, and may help us to gain more insight into the mechanism of the occurrence of vertebral osteoporosis and the related fracture risks.

INTRODUCTION

The aim of this study was to identify regional differences in 3D microstructure of vertebral trabecular bone with age and gender, using micro-computed tomography (micro-CT) and scanning electron microscopy (SEM).

METHODS

We used 56 fourth lumbar vertebral bodies from 28 women and men (57-98 years of age) cadaver donors. The subjects were chosen to give an even age and gender distribution. Both women and men were divided into three age groups, 62-, 77- and 92-year-old groups. Five cubic specimens were prepared from anterosuperior, anteroinferior, central, posterosuperior and posteroinferior regions at sagittal section. Bone specimens were examined by using micro-CT and SEM.

RESULTS

Reduced bone volume (BV/TV), trabecular number (Tb.N) and connectivity density (Conn.D), and increased structure model index (SMI) were found between ages 62 and 77 years, and between ages 77 and 92 years. As compared with women, men had higher Tb.N in the 77-year-old group and higher Conn.D in the 62- and 77-year-old groups. The central and anterosuperior regions had lower BV/TV and Conn.D than their corresponding posteroinferior region. Increased resorbing surfaces, perforated or disconnected trabeculae and microcallus formations were found with age.

CONCLUSION

Vertebral trabeculae are microstructurally heterogeneous. Decreases in BV/TV and Conn.D with age are similar in women and men. Significant differences between women and men are observed at some microstructural parameters. Age-related vertebral trabecular bone loss may be caused by increased activity of resorption. These findings illustrate potential mechanisms underlying vertebral fractures.

Characterization of dense bovine cancellous bone tissue microstructure by ultrasonic backscattering using weak scattering models

A weak scattering model was proposed for the ultrasonic frequency-dependent backscatter in dense bovine cancellous bone, using two autocorrelation functions to describe the medium: one with discrete homogeneities (spherical distribution of equal spheres) and another, which considers tissue as an inhomogeneous continuum (densely populated medium). The inverse problem to estimate trabecular thickness of bone tissue has been addressed. A combination of the two autocorrelation functions was required to closely approximate the backscatter from bovine bone with various microarchitecture, given that the shape of trabeculae ranges from a rodlike to a platelike shape. Because of the large variation in trabecular thickness, both at an intraspecimen and an interspecimen level, thickness distributions for individual trabeculae for each bone specimen were obtained, and dominant trabecular sizes were determined. Comparison of backscatter measurements to theoretical predictions indicated that there were more than one dominant trabecular sizes that scatter sound for most specimens. Linear regression, performed between dominant trabecular thickness and estimated correlation length, showed significant linear correlation (R(2)=0.81). Attenuation due to scattering by a continuous distribution of scatterers was predicted to be linear over a frequency range from 0.3 to 0.9 MHz, suggesting a possibility that scattering may be a significant source of attenuation.

Sex differences of human trabecular bone microstructure in aging are site-dependent

In this study, we characterize bone microstructure, specifically sex differences, at multiple skeletal sites in 165 subjects >52 yr of age, using microCT technology in vitro. Significant sex differences are observed at the distal radius, femoral neck, and femoral trochanter, but not at the iliac crest, calcaneus, and lumbar vertebral body. Correlations in BV/TV between sites ranged from r = 0.13 to 0.56.

INTRODUCTION

The goals of this study were (1) to assess potential sex differences of bone microstructure and their difference between skeletal sites and (2) to explore the relationship of trabecular microstructural properties between relevant skeletal sites.

MATERIALS AND METHODS

Trabecular bone microstructural properties were measured in vitro in 165 subjects 52-99 yr of age using microCT. Defined volumes of interest (cylinders with 6 mm diameter and 6 mm length) were scanned at a resolution of 26 microm (isotropic) in six different anatomical sites: distal radius, femoral neck and trochanter, iliac crest, calcaneus, and second lumbar vertebral body.

RESULTS

At the radius and femoral neck, trabecular bone displayed a more plate-like structure, thicker trabeculae, smaller separation/higher trabecular number, higher connectivity, and a higher degree of anisotropy in men than in women (p < 0.05). At the trochanter, men displayed more plate-like structure and thicker trabeculae (p < 0.05), but no differences in trabecular separation or other parameters compared with the women. At the calcaneus, iliac crest, and second lumbar vertebra none of the bone parameters displayed significant differences between sexes. The BV/TV at one site explained a range of only 2-32% of the variability at other sites.

CONCLUSIONS

These results suggest that trabecular bone microstructural properties are remarkably heterogeneous throughout the skeleton. Significant differences between men and women are observed at some, but not at all, sites. The magnitude of sex differences in trabecular microstructure coincides with that of fracture incidence observed for some of the sites in epidemiological studies.

Comparative study of axial and femoral bone mineral density and parameters of mandibular bone quality in patients receiving dental implants

INTRODUCTION

In view of the increase in the life expectancy of humans and in edentulism of the population above 50 years of age, in which the prevalence of osteoporosis is also higher, it is fundamental to better understand the effects of systemic bone mass loss on the healing process of dental implants and to determine the quality of the bone that surrounds them. The objective of the present study was to compare systemic osteoporosis (axial and femoral) and parameters of mandibular bone quality, and to evaluate osseointegration in postmenopausal women receiving dental implants.

METHODS

The sample consisted of 39 women aged 48-70 years, 19 with a densitometric diagnosis of osteoporosis in the lumbar spine and femoral neck and 20 controls with a normal densitometric diagnosis. Bone mineral density was measured in the patients and controls by dual-energy X-ray absorptiometry. Eighty-two osseointegrated dental implants were placed in the mandible, 39 of them in the osteoporosis group and 43 in the control group. Mandibular bone quality was evaluated by classifying mandibular inferior cortical and trabecular bone on panoramic radiographs and by histomorphometric analysis of a mandibular bone biopsy. Osseointegration was analyzed after 9 months.

RESULTS

No significant difference was observed between patients with osteoporosis and controls when comparing individuals with a normal cortex and those with a severely or moderately eroded cortex determined on panoramic radiographs, although patients with MEC/SEC had lower femoral neck BMD than those with NC (0.688 +/- 0.17 vs. 0.814+/- 0.144 g/cm2, P<0.012). Histomorphometric analysis also revealed no difference in the parameters of bone formation or resorption between the two groups. Implant failure was observed in only one case.

CONCLUSION

We conclude that there is an association between low femoral neck BMD and poor mandibular bone quality as assessed by panoramic radiography. The loss of one implant (1.2%) is compatible with the literature and cannot be attributed to systemic osteoporosis.

Trabecular bone microarchitecture is related to the number of risk factors and etiology in osteoporotic men

Microarchitecture of trabecular bone is a very important component of bone quality in osteoporosis and a determinant of vertebral fracture in men with low bone mineral density (BMD). In contrast to women, male osteoporosis is, in most cases, secondary. The relationships between microarchitecture and different risk factors have never been evaluated in men. About 152 men with low BMD at the lumbar spine or hip (BMD, T-score < -2.5) were included in this study. Risk factors were: age, BMI, alcohol intake, corticosteroid therapy, hypogonadism, and chronic diseases. Transiliac bone biopsies were obtained and histomorphometry was done on an image analyzer; the following parameters were measured: cortical thickness (Ct.Th), trabecular bone volume (BV/TV), trabecular thickness (Tb.Th), separation (Tb.Sp) and number (Tb.N), interconnectivity Index (ICI), star volume of the bone marrow, and strut analysis with node and free-end count. The 50 men with two risk factors had a lower BMD, lower Ct.Th and a significant higher star volume than those with one factor or idiopathic osteoporosis. The 26 men with at least three risk factors, had a lower BMD, a reduction of BV/TV and Ct.Th and a marked disorganization of the trabecular network (increased Tb.Sp, ICI, star volume, and free-end to free-end struts). The prevalence of vertebral fractures was higher in these patients. When the main risk factor was considered, a marked decrease in trabecular bone connectivity was observed in hypogonadic men. In osteoporotic men, higher the number of risk factors, lower the connectivity of trabecular network and higher the vertebral fracture risk.

Independent and combined contributions of cancellous and cortical bone deficits to vertebral fracture risk in postmenopausal women

Using iliac bone histomorphometry on 78 patients with vertebral fracture and 66 healthy postmenopausal women, cortical thickness discriminated at least as well as any cancellous bone structural index between the two groups. Subjects with a deficit in both cortical and cancellous bone had much greater likelihood of fracture.

INTRODUCTION

Vertebral fracture is often attributed to disproportional loss of cancellous bone, but fracture patients may have deficits in cortical and cancellous bone. Accordingly, we examined the contribution of cortical and cancellous bone deficits, separately and together, to the likelihood of vertebral fracture.

MATERIALS AND METHODS

Iliac bone histomorphometry was performed in 78 white woman with clinically apparent vertebral fracture, 66 healthy postmenopausal women, and 38 healthy premenopausal women. We measured cancellous bone volume (Cn.BV/TV), trabecular number (Tb.N), trabecular thickness (Tb.Th), cortical bone volume (Ct.BV/TV), and cortical thickness (Ct.Th). For each variable, a value of >1 SD below the mean in premenopausal women was treated as a putative risk factor, and its association with the presence or absence of fracture was determined by OR calculated by logistic regression and by receiver operating characteristic (ROC) curve analysis. Subsets of fracture and control subjects were separately matched for Cn.BV/TV and Ct.Th.

RESULTS

All structural indices differed between fracture patients and controls except Ct.BV/TV. There was a weak but highly significant correlation between Cn.BV/TV and Ct.Th in the entire group (r = 0.389, r(2) = 0.151 p < 0.001). Many control subjects had a high value for one of these variables and a low value for the other. Ct.Th., Cn.BV/TV, and Tb.N were all significantly associated with vertebral fracture (ORs, 4.4-5.8; ROC area under the curve [AUC], 0.74-0.85). In subjects matched for Cn.BV/TV, Ct.Th was reduced by 29% (OR, 5.0), and in subjects matched for Ct.Th, Cn.BV/TV was reduced by 27% (OR, 5.0). In patients with deficits in both cortical and cancellous bone, the ORs ( 28-35 ) were much higher.

CONCLUSIONS

Deficits in cortical bone (reduced value for Ct.Th) and in cancellous bone (reduced values for Cn.BV/TV or Tb.N) were equally effective in discriminating between subjects with and without vertebral fracture. With a deficit in both cortical and cancellous bone, the association with vertebral fracture was much stronger. Vertebral fracture is not the result of disproportionate loss of cancellous bone in the patients as a whole, although individual patients may have relatively greater deficits in either cancellous or cortical bone.

Automated method to measure trabecular thickness from microcomputed tomographic scans and its application

Trabeculae form the internal bony mesh work and provide strength to the bone; interconnectivity, overall density, and trabecular thickness are important measures of the integrity of the internal architecture. Such strength is achieved only gradually during ontogeny, whereby an increase in trabecular thickness precedes an increase in mineralization. Loss of bone mass later in life may be compensated for by thickening of the remaining trabeculae. These facts, and the role of trabeculae in mineral homeostasis, highlight the importance of investigating trabecular thickness within and between species. While nondestructive imaging techniques (i.e., muCT and MRI) are becoming increasingly popular, quantification of trabecular thickness using nondestructive techniques has proved difficult owing to limitations imposed by scanning parameters, uniform thresholding, and partial volume averaging. Here we present a computer application, which aims to overcome these problems. Validation is carried out against a phantom and against trabecular thickness measured in corresponding histological sections. Good agreement was found between these measurements. Furthermore, when trabecular thickness is recorded for modern human fetal ilia, a trend toward trabecular thickness increase is found and is in line with reports of ontogenetic morphometric changes using histological sections. However, there are discrepancies. These may in part be due to partial volume effects of obliquely oriented structures. More crucial, however, are problems inherent in histological sections, e.g., shrinkage and distortion, especially where differences in mineralization are concerned; this may affect biological interpretations.

Comparative study of axial and femoral bone mineral density and parameters of mandibular bone quality in patients receiving dental implants

INTRODUCTION

In view of the increase in the life expectancy of humans and in edentulism of the population above 50 years of age, in which the prevalence of osteoporosis is also higher, it is fundamental to better understand the effects of systemic bone mass loss on the healing process of dental implants and to determine the quality of the bone that surrounds them. The objective of the present study was to compare systemic osteoporosis (axial and femoral) and parameters of mandibular bone quality, and to evaluate osseointegration in postmenopausal women receiving dental implants.

METHODS

The sample consisted of 39 women aged 48-70 years, 19 with a densitometric diagnosis of osteoporosis in the lumbar spine and femoral neck and 20 controls with a normal densitometric diagnosis. Bone mineral density was measured in the patients and controls by dual-energy X-ray absorptiometry. Eighty-two osseointegrated dental implants were placed in the mandible, 39 of them in the osteoporosis group and 43 in the control group. Mandibular bone quality was evaluated by classifying mandibular inferior cortical and trabecular bone on panoramic radiographs and by histomorphometric analysis of a mandibular bone biopsy. Osseointegration was analyzed after 9 months.

RESULTS

No significant difference was observed between patients with osteoporosis and controls when comparing individuals with a normal cortex and those with a severely or moderately eroded cortex determined on panoramic radiographs. Histomorphometric analysis also revealed no difference in the parameters of bone formation or resorption between the two groups. Implant failure was observed in only one case.

CONCLUSION

We conclude that there is no association between systemic osteoporosis (axial and femur) and parameters of poor mandibular bone quality. The loss of one implant (1.2%) is compatible with the literature and cannot be attributed to systemic osteoporosis.

Bone loss dynamics result in trabecular alignment in aging and ovariectomized rats

Because of the destructive nature of techniques used to measure bone morphometry, studies of architectural changes and bone loss have utilized cross-sectional study designs, with all its inherent limitations in nuances. Here, the results of a longitudinal study using in vivo micro-CT are presented elucidating the dynamics of bone loss and architectural adaptation in rat models of aging and postmenopausal bone loss. Using 3-D methodology, we observed the changes in bone architecture in the proximal tibia of normally aging and ovariectomized rats for 54 weeks. Spatial patterns in bone resorption were observed that were similar for both groups. Remaining trabeculae increased in thickness or were remodeled into new trabecular structures, especially in the ovariectomized animals. The combination of bone loss and bone formation resulted in alignment of trabeculae across the growth plate. Cortical modeling that was associated with growth continued after cessation of longitudinal growth in the ovariectomized animals, resulting in shape changes of the proximal tibia. The organized nature of the changes in bone architecture that occurred after ovariectomy and the high similarity with the changes observed in the normally aging animals, suggest that estrogen depletion resulted in an acceleration of a normal bone adaptation process. The observed aligning of trabeculae suggests regulation through mechanical loading.

Texture analysis of X-ray radiographs of iliac bone is correlated with bone micro-CT

INTRODUCTION

Alteration of bone trabecular architecture is a predictor of fracture risk in osteoporosis. Until now, microarchitecture can only be measured on a bone biopsy, thus limiting microarchitecture analysis in routine clinical practice for osteoporosis. Texture analysis on X-ray images has been advocated to be a suitable means to assess two-dimensional (2-D) microarchitecture in the research field. But little is known about the relationships between three-dimensional (3-D) architecture and texture analysis, particularly in clinical practice. The purposes of the study were: (1) to explore the relationship between 3-D histomorphometric parameters and 2-D texture analysis, and (2) to see if cortical assessment may influence results.

METHODS

In this study, the anterosuperior part of the iliac bone was removed from 24 cadavers. Large samples were prepared and comprised of the crest and a strip of bone approximately 3 cm wide and 5 cm long. These large specimens were used in order to preserve bone architecture; they also corresponded to the location used by histomorphometrists for the diagnosis of metabolic bone diseases on iliac crest biopsies. Bone samples were examined with a microcomputed tomograph for 3-D microarchitecture [BV/TV, C.BV/C.TV, Tb.P(f), structure model index (SMI), Tb.Th, Tb.N, Tb.Sp]. Texture analysis was done by several methods (skeletonization, run lengths, fractal techniques) from X-ray projection images. No correlation was found between bone mass parameters (BV/TV and C.BV/C.TV, which take into account both cortical and trabecular bone) and texture parameters.

RESULTS

However, when specific descriptors of trabecular bone microarchitecture were used, several relationships with texture parameters were found [(Tb.N)/BOUND, r=0.628;/VGLN, r=0.596;/Fractal D, r=0.569].

CONCLUSION

When multiple correlations were used, the correlation coefficients were markedly improved with trabecular characteristics. X-ray texture analysis seemed to be a suitable approach for 2-D bone microarchitecture assessment. Furthermore, there is a good correlation between texture analysis of X-ray radiographs and 3-D bone microarchitecture assessed by microcomputed tomography.

Bone remodeling at the iliac crest can predict the changes in remodeling dynamics, microdamage accumulation, and mechanical properties in the lumbar vertebrae of dogs

We previously demonstrated that suppression of bone remodeling allows microdamage to accumulate, thereby leading to reduced bone toughness in dog bone. In this study we evaluated the relationships between bone remodeling at the iliac crest and skeletal activation frequency, microdamage accumulation, or biomechanical properties of lumbar vertebrae using the same dogs to determine whether bone remodeling at the iliac crest can predict damage accumulation and mechanical parameters of the lumbar spine following treatment with antiresorptive agents. Thirty-six female beagles, 1 to 2 years old, were divided into three groups. The control group was treated daily for 12 months with saline vehicle. The remaining two groups were treated daily with oral risedronate at a dose of 0.5 mg/kg/day, or alendronate at 1.0 mg/kg/day orally. The doses of these bisphosphonates were 5 to 6 times the clinical doses approved for treatment of osteoporosis in humans. After sacrifice, the right ilium and L2 vertebra were assigned to histomorphometry. The left ilium and L3 vertebra were used for microdamage analysis. The L4 vertebra was mechanically tested to failure in compression, and bone toughness calculated from the stress-strain curve. There was a strong positive relationship for activation frequency (Ac.f) between ilium and lumbar vertebrae (r2 = 0.82; P < 0.0001). Iliac crest Ac.f underestimates Ac.f in L2, but L2 Ac.f reaches a minimum threshold and does not decline further when iliac crest Ac.f is below 0.10/yr. Microdamage (Cr.S.Dn) accumulation at the ilium was significantly associated with increased microdamage accumulation in the L3 lumbar vertebra (r2 = 0.43, P < 0.0001). The data also show that bisphosphonate treatment increased Cr.S.Dn at a faster rate in L3 than in the iliac crest. Although bisphosphonate treatment decreased bone toughness in L4, this decrease demonstrated no relationship to decreased Ac.f in the ilium. These results clearly indicate that bone remodeling data obtained from iliac crest biopsy could be used to estimate the activation frequency and microdamage burden in the vertebral column.

Comparison insight bone measurements by histomorphometry and microCT

Morphometric analysis of 70 bone biopsies was done in parallel by microCT and histomorphometry. microCT provided higher results for trabecular thickness and separation because of the 3D shape of these anatomical objects.

INTRODUCTION

Bone histomorphometry is used to explore the various metabolic bone diseases. The technique is done on microscopic 2D sections, and several methods have been proposed to extrapolate 2D measurements to the 3D dimension. X-ray microCT is a recently developed imaging tool to appreciate 3D architecture. Recently the use of 2D histomorphometric measurements have been shown to provide discordant results compared with 3D values obtained directly.

MATERIAL AND METHODS

Seventy human bone biopsies were removed from patients presenting with metabolic bone diseases. Complete bone biopsies were examined by microCT. Bone volume (BV/TV), Tb.Th, and Tb.Sp were measured on the 3D models. Tb.Th and Tb.Sp were measured by a method based on the sphere algorithm. In addition, six images were resliced and transferred to an image analyzer: bone volume and trabecular characteristics were measured after thresholding of the images. Bone cores were embedded undecalcified; histological sections were prepared and measured by routine histomorphometric methods providing another set of values for bone volume and trabecular characteristics. Comparison between the different methods was done by using regression analysis, Bland-Altman, Passing-Bablock, and Mountain plots.

RESULTS

Correlations between all parameters were highly significant, but microCT overestimated bone volume. The osteoid volume had no influence in this series. Overestimation may have been caused by a double threshold used in microCT, giving trabecular boundaries less well defined than on histological sections. Correlations between Tb.Th and Tb.Sp values obtained by 3D or 2D measurements were lower, and 3D analysis always overestimated thickness by approximately 50%. These increases could be attributed to the 3D shape of the object because the number of nodes and the size of the marrow cavities were correlated with 3D values.

CONCLUSION

In clinical practice, microCT seems to be an interesting method providing reliable morphometric results in less time than conventional histomorphometry. The correlation coefficient is not sufficient to study the agreement between techniques in histomorphometry. The architectural descriptors are influenced by the algorithms used in 3D.

Age-Related Changes of Bone Mineral Density and Microarchitecture in Miniature Pigs

Bone mineral density (BMD), distribution of its density and bone histomorphometric parameters were evaluated in lumbar vertebra of normally growing miniature pigs. The fourth lumbar vertebra (L4) of the Göttingen miniature pig were used in this cross-sectional study in vitro. The BMD of the miniature pig was similar to that of humans in tendency of gender differences and some growth patterns during puberty. In these regards this animal appears useful as a model for human bone study. However, the trabecular and cortical BMDs of lumbar spine were extremely high value (399.43 +/- 26.36 mg/cm(3) in female trabeculae; 973.06 +/- 69.55 mg/cm(3) in female cortical bone; 419.04 +/- 34.84 mg/cm(3) in male trabeculae; 1038.81 +/- 125.72 mg/cm(3) in male cortical bone in pigs 30 months or more). Furthermore, histomorphometric analysis yielded values that were remarkably different from those found in humans. From these results, it was revealed that miniature pig had a higher bone mass and denser trabecular network than human, indicating that its bone is probably stronger. Therefore, care should be taken in choosing the miniature pig as a bone study model.

Age-related differences between thinning of horizontal and vertical trabeculae in human lumbar bone as assessed by a new computerized method

To investigate whether vertical trabeculae undergo compensatory thickening with age in the human vertebral body, a new computerized method was developed that is able to distinguish between horizontal and vertical trabeculae on normal histological sections. Study subjects included 48 individuals (24 women aged 19-97 years, and 24 men aged 23-95 years). From each L-2, thick frontal sections of half of the vertebra were embedded undecalcified in methylmetacrylate and cut into 10-microm-thick sections. A simple method able to classify image pixels as belonging to either vertical or horizontal trabeculae was developed and implemented in a computer program. The parallel-plate model was modified so that it was able to determine trabecular thickness, number, and separation (Tb.Th, Tb.N, and Tb.Sp) for horizontal and vertical trabeculae separately. The histomorphometric parameters were measured in three different regions: whole section, mid-third, and sub-endplate, for both horizontal and vertical trabeculae. It was found that the trabecular thickness of vertical trabeculae was independent of age in all investigated regions. The thickness of the horizontal trabeculae, in contrast, decreased significantly with age in all these regions. Tb.N decreased significantly with age for both horizontal and vertical trabeculae in all regions. However, the relative loss of trabeculae per unit length was largest for the horizontal trabeculae, whereas the absolute loss of trabeculae per unit length was largest for the vertical trabeculae. Tb.Sp was found to increase significantly with age for both vertical and horizontal trabeculae in all regions. No significant gender-related differences were found. In conclusion, in this study we describe a new, simple method for separation of horizontal and vertical bone tissue. This method has been applied on frontal vertebral sections. Trabecular bone thickness measured with the parallel-plate model showed that the thickness of horizontal trabeculae decreases significantly with age, whereas the thickness of vertical trabeculae did not decrease significantly with age. Furthermore, although the relative loss of trabeculae was larger for horizontal trabeculae than for vertical trabeculae, the absolute loss of vertical trabeculae was higher than that of horizontal trabeculae.

Zone-dependent changes in human vertebral trabecular bone: clinical implications

We have previously shown that there are pronounced age-related changes in human vertebral cancellous bone density and microarchitecture. However, the magnitude of these changes seemed to be dependent on zone location in the vertebral body-the central third vs. the areas adjacent to the endplates. The aim of the present study was, therefore, to investigate whether such zone-specific differences could be identified by static histomorphometric measures. The material comprised 48 individuals (24 women aged 19-97 years, and 24 men aged 23-95 years). Three of the women had a known fracture of the L-2. From each L-2, thick frontal sections of half of the vertebra were embedded undecalcified in methylmethacrylate, cut into 10-microm-thick sections, and stained with aniline blue. The sections were scanned into a computer, and classic static histomorphometry was performed on the images. The histomorphometry was performed on both the whole section and on the separate zones (central and sub-endplate zone). The results showed that trabecular bone volume, trabecular number, and connectivity density decreased significantly faster with age, whereas marrow space star volume increased significantly faster with age in the zones adjacent to the endplates than in the central zone. The other histomorphometric measures showed no zone specificity in relation to aging. However, trabecular thickness and trabecular separation were both higher at all ages in the central zone than in the sub-endplate zone, although this was significant only for trabecular separation. The described differences might have significant clinical implications concerning quantitative computed tomography (QCT) scanning, X-ray analyses, and assessment of fracture liability in the human spine, but the underlying pathogenesis is still not known. This study shows that the human vertebral body can be described as two distinct zones with very specific age-related changes in density and microstructure. This zone-specificity is important for the correct interpretation of clinical data.

Predicting human vertebral bone strength by vertebral static histomorphometry

The study investigates the relationship between static histomorphometry and bone strength of human lumbar vertebral bone. The ability of vertebral histomorphometry to predict vertebral bone strength was compared with that of vertebral densitometry, and also with histomorphometry and bone strength of iliac crest bone biopsies. The material comprised matched sets of second lumbar vertebrae, third lumbar vertebrae, and two iliac crest bone biopsies from each of 21 women (19--96 years) and 24 men (23--95 years). One of the iliac crest biopsies and 9-mm-thick mediolateral slices of half of each of the entire vertebral bodies (L-2) were used for histomorphometry. The other iliac crest biopsies and the L-3 were destructively tested by compression. High correlation was found between BV/TV or Tb.Sp and vertebral bone strength (absolute value of r = 0.86 in both cases). Addition of Tb.Th significantly improved the correlation between BV/TV and bone strength, and the addition of bone space star volume significantly improved the correlation between Tb.Sp and bone strength (from absolute value of r = 0.86 to absolute value of r = 0.89 in both cases). Bone structure (connectivity density) was not capable of improving the prediction of bone strength of the vertebral body. The correlations between BV/TV of L-2 and bone strength of L-3 were comparable with the correlation obtained by quantitative computed tomography (QCT), peripheral QCT (pQCT), and dual-energy X-ray absorptrometry (DEXA) of L-3 and bone strength of L-3. The iliac crest was found to have low predictive power of vertebral bone strength (iliac BV/TV: r = 0.62; iliac bone strength: r = 0.67). No gender-related differences were found in any of the relationships. It was shown that trabecular bone volume BV/TV and mean trabecular plate separation Tb.Sp are good predictors of vertebral bone strength. The ability of histomorphometry to predict vertebral bone strength was comparable to that of densitometry. Bone structure assessed by connectivity density did not improve the correlation between static histomorphometric measures and vertebral bone strength. No gender-related differences were found in any of the relationships. Neither static histomorphometry nor biomechanical testing of iliac crest bone biopsies is a good predictor of vertebral bone strength.