Inter-site variability of the osteocyte lacunar network in the cortical bone underpins fracture susceptibility of the superolateral femoral neck

Research on the analysis of morphological characteristics in pediatric femoral neck fractures utilizing 3D CT mapping

Proximal femoral fractures in children are challenging in clinical treatment due to their unique anatomical and biomechanical characteristics. The distribution and characteristics of fracture lines directly affect the selection of treatment options and prognosis. Pediatric proximal femur fractures exhibit distinctive features, with the distribution and characteristics of the fracture line playing a crucial role in deciding optimal treatment. The study aims to investigate the morphological characteristics of pediatric femoral neck fracture (FNF) from clinical cases by fracture mapping technology and to analyze the relationship between fracture classifications and age. The CT data were collected from 46 consecutive pediatric inpatients' diagnoses of FNF from March 2009 to December 2022. The fracture imaging was reconstructed in three dimensions and performed the simulated anatomical reduction by Mimics and 3-matic. Both Delbet classification and Pauwels angle classification were documented according to the fracture line in each patient. Furthermore, all of the fracture lines in these patients were superimposed to form a fracture map and a heat map. This study included 24 boys and 22 girls (average age, 9.61 ± 3.17 years (4 to 16 years)). The fracture lines of the anterior and superior femoral neck were found to be mainly located in the middle and lower regions of the femoral neck, while fracture lines of the posterior and inferior neck were mainly concentrated in the middle region. Most children younger than 10 years had Delbet type III of fracture (69%), whereas those older than 10 years had Delbet type II of fracture (73%). Furthermore, most children had Pauwels angle type III of fracture (63%), especially in those over 10 years old (80%) (p = 0.0001). FNF in children is predominantly located in the middle and lower regions of the neck. Older children may be prone to be affected with higher fracture location of FNF or unstable type of fracture.

Automatic segmentation of cortical bone microstructure: Application and analysis of three proximal femur sites

Osteoporosis is the most common bone metabolic unbalance, leading to fragility fractures, which are known to be associated with structural changes in the bone. Cortical bone accounts for 80 % of the skeleton mass and undergoes remodeling throughout life, leading to changes in its thickness and microstructure. Although many studies quantified the different cortical bone structures using CT techniques (3D), they are often realised on a small number of samples. Therefore, the work presented here proposes a method to quantify cortical bone microstructure using 2D histology, shows its application on a set of 94 samples and compares to 3D methods. Fresh frozen human femur pairs from 47 donors aged between 57 and 96 years were obtained from the Medical University of Vienna. Bone samples were cut from 3 sites: proximal part of the diaphysis, inferior and superior segments of the neck. The samples were stained with toluidine blue and imaged under light microscopy. After manual segmentation of a few regions of interest by multiple operators, a convolutional neural network was trained in combination with a random forest for automatic segmentation. The segmentation analysis compares morphology and structure distribution of Haversian canals, osteocyte lacunae, and cement lines with literature, between anatomical sites, sex, left and right sides, and relation to ageing. Morphological analysis of the segmentation gives results similar to the literature. Comparison between male and female donors shows no significant differences. There is no significant difference between left and right femur on paired samples but significant differences are observed between anatomical locations. The structures' relative amounts do not present significant changes with age but only weak tendencies. Nevertheless, a strong correlation was observed between osteocyte lacunae density and bone areal fraction. This study presents a full process to stain and automatically segment digital cortical bone images. Its application to a large sample set of proximal femora provides strong statistics on the cortical bone structures morphology and distribution. Similarities observed between sides and sexes together with differences observed between sites could indicate that mechanical loading might be a main driver for bone microstructure. Additionally, the relationship between osteocyte lacunae density and bone areal fraction could suggest that bone porosity is regulated by osteocyte survival.

Bone quality analysis of the mandible in alcoholic liver cirrhosis: Anatomical, microstructural, and microhardness evaluation

OBJECTIVES

Alcoholic bone disease has been recognized in contemporary literature as a systemic effect of chronic ethanol consumption. However, evidence about the specific influence of alcoholic liver cirrhosis (ALC) on mandible bone quality is scarce. The aim of this study was to explore microstructural, compositional, cellular, and mechanical properties of the mandible in ALC individuals compared with a healthy control group.

MATERIALS AND METHODS

Mandible bone cores of mаle individuаls with ALC (n = 6; age: 70.8 ± 2.5 yeаrs) and age-matched healthy controls (n = 11; age: 71.5 ± 3.8 yeаrs) were obtаined postmortem during аutopsy from the edentulous аlveolаr bone in the mandibular first molаr region аnd the mаndibulаr аngulus region of each individual. Micro-computed tomogrаphy wаs used to аssess bone microstructure. Analyses based on quаntitаtive bаckscаttered electron microscopy included the characterization of osteon morphology, osteocyte lаcunаr properties, and bone mаtrix minerаlizаtion. Composition of bone minerаl аnd collаgen phаses was assessed by Rаmаn spectroscopy. Histomorphometry wаs used to determine cellulаr аnd tissue chаrаcteristics of bone specimens. Vickers microhardness test was used to evaluate cortical bone mechanical properties.

RESULTS

The ALC group showed higher closed cortical porosity (volume of pores thаt do not communicаte with the sаmple surfаce) (p = 0.003) and smaller lacunar area in the trabecular bone of the molar region (p = 0.002) compared with the Control group. The trabecular bone of the angulus region showed lower osteoclast number (p = 0.032) in the ALC group. There were higher carbonate content in the buccal cortex of the molar region (p = 0.008) and lower calcium content in the trabecular bone of the angulus region (p = 0.042) in the ALC group. The cortical bone showed inferior mechanical properties in the ALC cortical bony sites (p < 0.001), except for the buccal cortex of the molar region (p = 0.063). There was no significant difference in cortical thickness between the groups.

CONCLUSIONS

Bone quality is differentially altered in ALC in two bony sites and compartments of the mandible, which leads to impaired mechanical properties.

CLINICAL RELEVANCE

Altered mandible bone tissue characteristics in patients with ALC should be considered by dental medicine professionals prior to oral interventions in these patients. Knowledge about mandible bone quality alterations in ALC is valuable for determining diagnosis, treatment plan, indications for oral rehabilitation procedures, and follow-up procedures for this group of patients.

Osteocyte lacunae in transiliac bone biopsy samples across life span

Osteocytes act as bone mechanosensors, regulators of osteoblast/osteoclast activity and mineral homeostasis, however, knowledge about their functional/morphological changes throughout life is limited. We used quantitative backscattered electron imaging (qBEI) to investigate osteocyte lacunae sections (OLS) as a 2D-surrogate characterizing the osteocytes. OLS characteristics, the density of mineralized osteocyte lacunae (i.e., micropetrotic osteocytes, md.OLS-Density in nb/mm²) and the average degree of mineralization (Ca_Mean in weight% calcium) of cortex and spongiosa were analyzed in transiliac biopsy samples from healthy individuals under 30 (n=59) and over 30 years (n=50) (i.e., before and after the age of peak bone mass, respectively). We found several differences in OLS-characteristics: 1). Inter-individually between the age groups: OLS-Density and OLS-Porosity were reduced by about 20% in older individuals in spongiosa and in cortex versus younger probands (both, p < 0.001). 2). Intra-individually between bone compartments: OLS-Density was higher in the cortex, +18.4%, p < 0.001 for younger and +7.6%, p < 0.05 for older individuals. Strikingly, the most frequent OLS nearest-neighbor distance was about 30 µm in both age groups and at both bone sites revealing a preferential organization of osteocytes in clusters. OLS-Density was negatively correlated with Ca_Mean in both spongiosa and cortex (both, p < 0.001). Few mineralized OLS were found in young individuals along with an increase of md.OLS-Density with age. In summary, this transiliac bone sample analysis of 200000 OLS from 109 healthy individuals throughout lifespan reveals several age-related differences in OLS characteristics. Moreover, our study provides reference data from healthy individuals for different ages to be used for diagnosis of bone abnormalities in diseases. STATEMENT OF SIGNIFICANCE: Osteocytes are bone cells embedded in lacunae within the mineralized bone matrix and have a key role in the bone metabolism and the mineral homeostasis. Not easily accessible, we used quantitative backscattered electron imaging to determine precisely number and shape descriptors of the osteocyte lacunae in 2D. We analyzed transiliac biopsy samples from 109 individuals with age distributed from 2 to 95 years. Compact cortical bone showed constantly higher lacunar density than cancellous bone but the lacunar density in both bone tissue decreased with age before the peak bone mass age at 30 years and stabilized or even increased after this age. This extensive study provides osteocyte lacunae reference data from healthy individuals usable for bone pathology diagnosis.

Three-dimensional mapping of cortical porosity and thickness along the superolateral femoral neck in older women

Although several studies have analyzed inter-individual differences in the femoral neck cortical microstructure, intra-individual variations have not been comprehensively evaluated. By using microCT, we mapped cortical pore volume fraction (Ct.Po) and thickness (Ct.Th) along the superolateral femoral neck in 14 older women (age: 77.1 ± 9.8 years) to identify subregions and segments with high porosity and/or low thickness-potential "critical" spots where a fracture could start. We showed that Ct.Po and Ct.Th significantly differed between basicervical, midcervical, and subcapital subregions of the femoral neck (p < 0.001), where the subcapital subregion showed the lowest mean Ct.Th and the highest mean Ct.Po. These cortical parameters also varied substantially with age and with the location of the analyzed microsegments along the individual's neck (p < 0.001), showing multiple microsegments with high porosity and/or low thickness. Although the highest ratio of these microsegments was found in the subcapital subregion, they were also present at other examined subregions, which may provide an anatomical basis for explaining the fracture initiation at various sites of the superolateral neck. Given that fractures likely start at structurally and mechanically weaker spots, intra-individual variability in Ct.Po and Ct.Th should be considered and the average values for the entire femoral neck should be interpreted with caution.

The altered osteocytic expression of connexin 43 and sclerostin in human cadaveric donors with alcoholic liver cirrhosis: Potential treatment targets

Previous studies suggested that osteocyte lacunar network disruption could play a role in the complex pathophysiology of bone changes in aging and disease. Considering that particular research interest is lacking, we aimed to assess alcoholic liver cirrhosis (ALC)-induced changes in osteocyte lacunar network and bone marrow adiposity. Immunohistochemistry was conducted to assess changes in the micro-morphology of osteocyte lacunar network and bone marrow adiposity, and expression of connexin 43 and sclerostin in vertebral and femoral samples collected from 40 cadaveric men (age range between 44 and 70 years) divided into ALC group (n = 20) and control group (n = 20). Furthermore, the assessment of the potential association between bone changes and the severity of the hepatic disorder (given by Knodell's pathohistologic scoring) was conducted. Our data revealed fewer connexin 43-positive osteocytes per vertebral and femoral bone area (p < 0.01), suggesting defective signal transduction among osteocytes in ALC individuals. Moreover, we found an ALC-induced increase in the number of adipocytes in the vertebral bone marrow (p = 0.038). Considering significant associations between the severity of liver tissue disturbances and impaired functionality of osteocyte lacunar network (Pearson's correlation analyses, p < 0.05), we may assume that timely treatment of the liver disease may delay bone impairment. ALC induced an increase in osteocytic sclerostin expression (p < 0.001), suggesting its role in mediating low bone formation among ALC individuals. Hence, medicaments targeting low bone formation may be beneficial to attenuate the bone changes among ALC patients. However, future clinical studies are required to verify the therapeutic utility of these findings.

Impaired bone quality in the superolateral femoral neck occurs independent of hip geometry and bone mineral density

Skeletal adaptation is substantially influenced by mechanical loads. Osteocytes and their lacuno-canalicular network have been identified as a key player in load sensation and bone quality regulation. In the femoral neck, one of the most common fracture sites, a complex loading pattern with lower habitual loading in the superolateral neck and higher compressive stresses in the inferomedial neck is present. Variations in the femoral neck-shaft angle (NSA), i.e., coxa vara or coxa valga, provide the opportunity to examine the influence of loading patterns on bone quality. We obtained femoral neck specimens of 28 osteoarthritic human subjects with coxa vara, coxa norma and coxa valga during total hip arthroplasty. Bone mineral density (BMD) was assessed preoperatively by dual energy X-ray absorptiometry (DXA). Cortical and trabecular microstructure and three-dimensional osteocyte lacunar characteristics were assessed in the superolateral and inferomedial neck using ex vivo high resolution micro-computed tomography. Additionally, BMD distribution and osteocyte lacunar characteristics were analyzed by quantitative backscattered electron imaging (qBEI). All groups presented thicker inferomedial than superolateral cortices. Furthermore, the superolateral site exhibited a lower osteocyte lacunar density along with lower lacunar sphericity than the inferomedial site, independent of NSA. Importantly, BMD and corresponding T-scores correlated with microstructural parameters at the inferomedial but not superolateral neck. In conclusion, we provide micromorphological evidence for fracture vulnerability of the superolateral neck, which is independent of NSA and BMD. The presented bone qualitative data provide an explanation why DXA may be insufficient to predict a substantial proportion of femoral neck fractures. STATEMENT OF SIGNIFICANCE: The femoral neck, one of the most common fracture sites, is subject to a complex loading pattern. Site-specific differences (i.e., superolateral vs. inferomedial) in bone quality influence fracture risk, but it is unclear how this relates to hip geometry and bone mineral density (BMD) measurements in vivo. Here, we examine femoral neck specimens using a variety of high-resolution imaging techniques and demonstrate impaired bone quality in the superolateral compared to the inferomedial neck. Specifically, we found impaired cortical and trabecular microarchitecture, mineralization, and osteocyte properties, regardless of neck-shaft angle. Since BMD correlated with bone quality of the inferomedial but not the superolateral neck, our results illustrate why bone densitometry may not predict a substantial proportion of femoral neck fractures.

Bone microarchitecture of the distal fibula assessed by HR-pQCT

The distal fibula represents one of the most common fracture sites, and its epidemiology is characterized by a high incidence in both adolescence and the elderly. While fracture occurrence is influenced by trauma mechanism, a possible underlying skeletal microarchitectural deterioration in certain patient groups remains elusive. The purpose of this study was to determine the influence of age, sex, and overall skeletal status on fibular microarchitecture. We analyzed the microarchitecture of the distal fibula in 300 people by high-resolution peripheral quantitative computed tomography (HR-pQCT). Three areal bone mineral density (aBMD) groups (normal, osteopenia, osteoporosis; n = 100 per group) based on the concurrent assessment of aBMD by dual-energy X-ray absorptiometry (DXA) at the lumbar spine and total hip were established. Next to group comparisons, linear and non-linear regression analyses were carried out to assess the association between age, sex, BMI, tibial and fibular microarchitecture. While women had lower values for both trabecular bone volume fraction (BV/TV^d, p < 0.001) and cortical thickness (Ct.Th^d, p < 0.001) than men, osteoporosis by DXA negatively affected these parameters in both sexes. Remarkably, cortical but not trabecular microarchitecture declined with age, with a stronger decrease in females compared to males (Ct.Th^d female -10.0 μm/year (95% CI: -12.2 to -7.7 μm/year), male -4.0 μm/year (95% CI: -6.3 to -1.7 μm/year)). Moderate positive associations between distal tibial and fibular microarchitecture were noted (e.g., BV/TV^d R² = 0.54, Ct.Th^d R² = 0.58). In summary, we here demonstrate the severe negative effects of age, female sex and osteoporosis on distal fibula bone mineralization and microarchitecture. The presented findings are likely to explain the higher susceptibility to distal fibula fractures in elderly women (independent of trauma mechanism). These alterations in fibular bone quality must be taken into account in the context of fracture prevention and treatment (e.g., osteosynthesis planning).

Bone quality analysis of jaw bones in individuals with type 2 diabetes mellitus-post mortem anatomical and microstructural evaluation

OBJECTIVES

With the higher risk of dental implant failure with type 2 diabetes mellitus (T2DM), there is a need to characterize the jaw bones in those individuals. The aim of this post mortem study was to compare jaw bone quality of individuals with T2DM to healthy controls.

MATERIAL AND METHODS

Bone cores from the edentulous lower first molar region and the region of mandibular angle were collected from male individuals with T2DM (n = 10, 70.6 ± 4.5 years) and healthy controls (n = 11, 71.5 ± 3.8 years) during autopsy. Within the T2DM, a subgroup treated with oral antidiabetics (OAD) and one on insulin were identified. Bone quality assessment encompassed evaluation of bone microstructure, matrix composition, and cellular activity, using microcomputed tomography (micro-CT), quantitative backscattered electron imaging (qBEI), Raman spectroscopy, and bone histomorphometry.

RESULTS

In the mandibular angle, T2DM showed 51% lower porosity of the lingual cortex (p = 0.004) and 21% higher trabecular thickness (p = 0.008) compared to control. More highly mineralized bone packets were found in the buccal cortex of the mandibular angle in insulin-treated compared to OAD-treated T2DM group (p = 0.034). In the molar region, we found higher heterogeneity of trabecular calcium content in T2DM insulin compared to controls (p = 0.015) and T2DM OAD (p = 0.019). T2DM was associated with lower osteocyte lacunar size in the trabecular bone of the molar region (vs. control p = 0.03).

CONCLUSIONS

Alterations in microstructure, mineralization, and osteocyte morphology were determined in jaw bone of individuals with T2DM compared to controls.

CLINICAL RELEVANCE

Future studies will have to verify if the mild changes determined in this study will translate to potential contraindications for dental implant placements.

Three-Dimensional Microstructural Basis for Differential Occurrence of Subcapital versus Basicervical Hip Fractures in Men

We analyzed the bone microarchitecture of the subcapital and basicervical subregions of the femoral neck in men, to determine whether microarchitectural differences of cortical or trabecular bone can explain differential frequency of subcapital vs. basicervical fractures, especially in aged persons. The study sample encompassed twenty male proximal femora obtained during autopsy. They were divided in two age groups: young (< 40 years, n = 10) and aged (> 60 years, n = 10). Micro-computed tomography was used to evaluate cortical and trabecular microarchitecture of the subcapital and basicervical regions of the superolateral femoral neck-typical fracture initiation site. Basicervical region showed significantly thicker and less porous cortex than subcapital region (p = 0.02, p < 0.001, respectively), along with increased distance between cortical pores (p = 0.004) and smaller pore diameters (p = 0.069). Higher trabecular number (Tb.N: p = 0.042), lower trabecular thickness (Tb.Th: p < 0.001), and lower trabecular separation (p = 0.003) were also hallmarks of the basicervical compared to subcapital region, although BV/TV was similar in both regions (p = 0.133). Age-related deterioration was mostly visible in trabecular bone (for BV/TV, Tb.Th, Tb.N and fractal dimension: p = 0.026, p = 0.049, p = 0.059, p = 0.009, respectively). Moreover, there were tendencies to age-specific patterns of trabecular separation (more pronounced inter-site differences in aged) and cortical thickness (more pronounced inter-site differences in young). Trabecular microarchitecture corresponded to cortical characteristics of each region. Our study revealed the microarchitectural basis for higher incidence of subcapital than basicervical fractures of the femoral neck. This is essential for better understanding of the fracture risk, as well as for future strategies to prevent hip fractures and their complications.

Large osteocyte lacunae in iliac crest infantile bone are not associated with impaired mineral distribution or signs of osteocytic osteolysis

The enlargement of osteocyte lacunae via osteocytic osteolysis was previously detected in situations of increased calcium demand (e.g., lactation, vitamin D deficiency). However, it is unclear whether similar processes occur also in the growing infantile skeleton and how this is linked to the mineral distribution within the bone matrix. Human iliac crest biopsies of 30 subjects (0-6 months, n = 14; 2-8 years, n = 6 and 18-25 years, n = 10) were acquired. Bone microarchitecture was assessed by micro-CT, while cellular bone histomorphometry was performed on undecalcified histological sections. Quantitative backscattered electron imaging (qBEI) was conducted to determine the bone mineral density distribution (BMDD) as well as osteocyte lacunar size and density. We additionally evaluated cathepsin K positive osteocytes using immunohistochemistry. Infantile bone was characterized by various signs of ongoing bone development such as higher bone (re)modeling, lower cortical and trabecular thickness compared to young adults. Importantly, a significantly higher osteocyte lacunar density and increased lacunar area were detected. Large osteocyte lacunae were associated with a more heterogeneous bone mineral density distribution of the trabecular bone matrix due to the presence of hypermineralized cartilage remnants, whereas the mean mineralization (i.e., CaMean) was not different in infantile bone. Absence of cathepsin K expression in osteocyte lacunae indicated nonexistent osteocytic osteolysis. Taken together, we demonstrated that the overall mineralization distribution in infantile bone is not altered compared to young adults besides high trabecular mineralization heterogeneity. Our study also provides important reference values for bone microstructure, BMDD and osteocyte characteristics in infants, children and young adults. Infantile bone displays large osteocyte lacunae indicating a developmental phenomenon rather than osteocytic osteolysis. Larger osteocytes may have superior mechanosensory abilities to enable bone adaption during growth.

Phenomenon of osteocyte lacunar mineralization: indicator of former osteocyte death and a novel marker of impaired bone quality?

An increasing number of patients worldwide suffer from bone fractures that occur after low intensity trauma. Such fragility fractures are usually associated with advanced age and osteoporosis but also with long-term immobilization, corticosteroid therapy, diabetes mellitus, and other endocrine disorders. It is important to understand the skeletal origins of increased bone fragility in these conditions for preventive and therapeutic strategies to combat one of the most common health problems of the aged population. This review summarizes current knowledge pertaining to the phenomenon of micropetrosis (osteocyte lacunar mineralization). As an indicator of former osteocyte death, micropetrosis is more common in aged bone and osteoporotic bone. Considering that the number of mineralized osteocyte lacunae per bone area can distinguish healthy, untreated osteoporotic and bisphosphonate-treated osteoporotic patients, it could be regarded as a novel structural marker of impaired bone quality. Further research is needed to clarify the mechanism of lacunar mineralization and to explore whether it could be an additional target for preventing or treating bone fragility related to aging and various endocrine diseases.

Inter-site Variability of the Human Osteocyte Lacunar Network: Implications for Bone Quality

PURPOSE OF REVIEW

This article provides a review on the variability of the osteocyte lacunar network in the human skeleton. It highlights characteristics of the osteocyte lacunar network in relation to different skeletal sites and fracture susceptibility.

RECENT FINDINGS

Application of 2D analyses (quantitative backscattered electron microscopy, histology, confocal laser scanning microscopy) and 3D reconstructions (microcomputed tomography and synchrotron radiation microcomputed tomography) provides extended high-resolution information on osteocyte lacunar properties in individuals of various age (fetal, children's growth, elderly), sex, and disease states with increased fracture risk. Recent findings on the distribution of osteocytes in the human skeleton are reviewed. Quantitative data highlighting the variability of the osteocyte lacunar network is presented with special emphasis on site specificity and maintenance of bone health. The causes and consequences of heterogeneous distribution of osteocyte lacunae both within specific regions of interest and on the skeletal level are reviewed and linked to differential bone quality factors and fracture susceptibility.