Increased proportion of hypermineralized osteocyte lacunae in osteoporotic and osteoarthritic human trabecular bone: implications for bone remodeling

Subchondral Bone Osteocyte Lacunae Morphology in End-Stage Osteoarthritis of the Human Tibial Plateau

Subchondral bone remodeling, mediated by osteocytes within the lacuno-canalicular network, plays a crucial role in osteoarthritis (OA) progression. Following cell death, lacunae preserve integrity, offering insights into bone remodeling mechanisms. Limited and controversial data on osteocyte lacuna morphology in OA result from small sample sizes and two-dimensional (2D) techniques that have been used thus far. This study aimed to quantify three-dimensional (3D) osteocyte lacunar characteristics at well-defined tibial plateau locations, known to be differently affected by OA. Specifically, 11 tibial plateaus were obtained from end-stage knee-OA patients with varus deformity. Each plateau provided one sample from the less affected lateral compartment and two samples from the medial compartment, at minimum and maximum bone volume fraction (BV/TV) locations. High-resolution desktop micro-computed tomography (micro-CT) at 0.7 μm voxel resolution imaged the 33 samples. Lacuna number density (Lc.N/BV) and lacuna volume density (Lc.TV/BV) were significantly lower (p < 0.02) in samples from the medial side with maximum BV/TV compared to lateral side samples. In the medial compartment at maximum local BV/TV, mean lacuna volume (Lc.V), total lacuna volume (Lc.TV), and Lc.TV/BV were significantly (p < 0.001) lower than in the region with minimum BV/TV. Lc.N/BV was also significantly lower (p < 0.02) at the maximum local BV/TV location compared to the region with minimum BV/TV. Our findings suggest that subchondral bone lacunae adapt to the changing loads in end-stage OA.

Alterations in compositional and cellular properties of the subchondral bone are linked to cartilage degeneration in hip osteoarthritis

OBJECTIVE

The subchondral bone is an emerging regulator of osteoarthritis (OA). However, knowledge of how specific subchondral alterations relate to cartilage degeneration remains incomplete.

METHOD

Femoral heads were obtained from 44 patients with primary OA during total hip arthroplasty and from 30 non-OA controls during autopsy. A multiscale assessment of the central subchondral bone region comprising histomorphometry, quantitative backscattered electron imaging, nanoindentation, and osteocyte lacunocanalicular network characterization was employed.

RESULTS

In hip OA, thickening of the subchondral bone coincided with a higher number of osteoblasts (controls: 3.7 ± 4.5 mm-1, OA: 16.4 ± 10.2 mm-1, age-adjusted mean difference 10.5 mm-1 [95% CI 4.7 to 16.4], p < 0.001) but a similar number of osteoclasts compared to controls (p = 0.150). Furthermore, higher matrix mineralization heterogeneity (CaWidth, controls: 2.8 ± 0.2 wt%, OA: 3.1 ± 0.3 wt%, age-adjusted mean difference 0.2 wt% [95% CI 0.1 to 0.4], p = 0.011) and lower tissue hardness (controls: 0.69 ± 0.06 GPa, OA: 0.67 ± 0.06 GPa, age-adjusted mean difference -0.05 GPa [95% CI -0.09 to -0.01], p = 0.032) were detected. While no evidence of altered osteocytic perilacunar/canalicular remodeling in terms of fewer osteocyte canaliculi was found in OA, specimens with advanced cartilage degeneration showed a higher number of osteocyte canaliculi and larger lacunocanalicular network area compared to those with low-grade cartilage degeneration. Multiple linear regression models indicated that several subchondral bone properties, especially osteoblast and osteocyte parameters, were closely related to cartilage degeneration (R2 adjusted = 0.561, p < 0.001).

CONCLUSION

Subchondral bone properties in OA are affected at the compositional, mechanical, and cellular levels. Based on their strong interaction with cartilage degeneration, targeting osteoblasts/osteocytes may be a promising therapeutic OA approach.

DATA AND MATERIALS AVAILABILITY

All data are available in the main text or the supplementary materials.

Micropetrosis: Osteocyte Lacunar Mineralization in Aging and Disease

PURPOSE OF REVIEW

As the importance of osteocytes for bone mineral homeostasis is increasingly recognized, there is growing interest in osteocyte cell death as a relevant indicator in various physiological and pathological conditions. Micropetrosis is an established term used to describe osteocyte lacunae that are filled with minerals following osteocyte death. While the early reports of micropetrosis were purely descriptive, there is now an increasing body of literature showing quantitative data on micropetrosis in various conditions such as aging, osteoporosis, immobilization, and diabetes, and in osteoporosis treatment (denosumab and bisphosphonates). This review summarizes quantitative findings on micropetrosis, with a particular emphasis on the recent advances in the field.

RECENT FINDINGS

There is growing evidence that micropetrosis is more common in older, osteoporotic, and immobilized individuals, as well as in individuals with type 1 or type 2 diabetes. Denosumab and bisphosphonates seem to affect lacunar mineralization differently, where specifically bisphosphonates have been shown to prolong osteocyte viability and reduce micropetrosis. Despite continuous proceedings in the field of osteocyte-lacunar-network characteristics, more studies are necessary to further clarify the mechanisms of lacunar mineralization, the inter-site variability of micropetrosis accumulation, the relevance of micropetrosis in various diseases and conditions, and whether micropetrosis could be an indicator of bone fragility or a target for treatment.

Evaluating the Role of Canalicular Morphology and Perilacunar Region Properties on Local Mechanical Environment of Lacunar-Canalicular Network Using Finite Element Modeling

Physiological and pathological processes such as aging, diseases, treatments, and lactation can alter lacunar-canalicular network (LCN) morphology and perilacunar region properties. These modifications can impact the mechanical environment of osteocytes which in turn can influence osteocyte mechanosensitivity and the remodeling process. In this study, we aim to evaluate how the modifications in the canalicular morphology, lacunar density, and the perilacunar region properties influence the local mechanical environment of LCN and the apparent bone properties using three-dimensional finite element (FE) modeling. The simulation results showed that a 50% reduction in perilacunar elastic modulus led to about 7% decrease in apparent elastic modulus of the bone. The increase in canalicular density, length, and diameter did not influence the strain amplification in the models but they increased the amount of highly strained bone around LCN. Change in lacunar density did not influence the strain amplification and the amount of highly strained regions on LCN surfaces. Reduction in perilacunar elastic modulus increased both the strain amplification and the volume of highly strained tissue around and on the surface of LCN. The FE models of LCN in this study can be utilized to quantify the influence of modifications in canalicular morphology, lacunar density, and perilacunar region properties on the apparent bone properties and the local mechanical environment of LCN. Although this is a numerical study with idealized models, it provides important information on how mechanical environment of osteocytes is influenced by the modifications in LCN morphology and perilacunar region properties due to physiological and pathological processes.

The many facets of micropetrosis - Magnesium whitlockite deposition in bisphosphonate-exposed human alveolar bone with osteolytic metastasis

The lacuno-canalicular space of apoptotic osteocytes eventually becomes mineralised in vivo. This condition is known as micropetrosis and is a fundamental characteristic of ageing bone. Increased prevalence of such hypermineralised osteocyte lacunae is viewed as a structural marker of impaired bone function - both mechanical and biological. Within the lacuno-canalicular space, mineralised apoptotic debris typically occurs as micrometre-sized, spherical nodules of magnesium-rich, carbonated apatite. Moreover, characteristically facetted, rhomboidal nodules of magnesium whitlockite [Mg-whitlockite; Ca₁₈Mg₂(HPO₄)₂(PO₄)₁₂] have been reported in human alveolar bone exposed to the bisphosphonate alendronate. This work provides supporting evidence for Mg-whitlockite formation in the alveolar bone of a 70-year-old male exposed to the bisphosphonate zoledronic acid to suppress osteolytic changes in skeletal metastasis. Backscattered electron scanning electron microscopy (BSE-SEM) revealed spherical and rhomboidal nodules within the lacuno-canalicular space. A variant of spherical nodules exhibited a fuzzy surface layer comprising radially extending acicular crystallites. The rhomboidal nodules ranged between ∼200 nm to ∼2.4 µm across the widest dimension (652 ± 331 nm). Micro-Raman spectroscopy and energy dispersive X-ray spectroscopy confirmed that rhomboidal nodules are compositionally distinct from spherical nodules, exhibiting higher Mg content and lower Ca/P ratio. Formation of Mg-whitlockite within osteocyte lacunae is multifactorial in nature and suggests altered bone biomineralisation. Nevertheless, the underlying mechanism(s) and sequence of events remain poorly understood and warrant further investigation. The possibility to discriminate between carbonated apatite and Mg-whitlockite nodules within osteocyte lacunae, based on particle morphology, attests to the diagnostic potential of BSE-SEM with or without additional analyses of material composition.

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.

Augmentation in fragility fractures, bone of contention: a systematic review

BACKGROUND

Osteoporosis is a complex multifactorial disease characterized by reduced bone mass and microarchitectural deterioration of bone tissue linked to an increase of fracture risk. Fragility fractures occur in osteoporotic subjects due to low-energy trauma. Osteoporotic patients are a challenge regarding the correct surgical planning, as it can include fixation augmentation techniques to reach a more stable anchorage of the implant, possibly lowering re-intervention rate and in-hospital stay.

METHODS

The PubMed database and the Google Scholar search engine were used to identify articles on all augmentation techniques and their association with fragility fractures until January 2022. In total, we selected 40 articles that included studies focusing on humerus, hip, spine, and tibia.

RESULTS

Literature review showed a quantity of materials that can be used for reconstruction of bone defects in fragility fractures in different anatomic locations, with good results over the stability and strength of the implant anchorage, when compared to non-augmented fractures.

CONCLUSION

Nowadays there are no recommendations and no consensus about the use of augmentation techniques in osteoporotic fractures. Our literature review points at implementing the use of bone augmentation techniques with a specific indication for elderly patients with comminuted fractures and poor bone quality.

Renal hyperparathyroidism

The number of the patients with chronic kidney disease is now increasing in the world. The pathophysiology of renal hyperparathyroidism is closely associated with Klotho-FGF-endocrine axes, which must be solved definitively as early as possible. It was revealed that the expression of fgf23 is activated by calciprotein particles, which induces vascular ossification. And it is well known that phosphorus overload directly increases parathyroid hormone and hyperparathyroid bone disease develops in those subjects. On the other hand, low turnover bone disease is often recently. Both the patients with chronic kidney disease suffering from hyperparathyroid bone disease or low turnover bone disease are associated with increased fracture risk. Micropetrosis may be one of the causes of increased fracture risk in the subjects with low turnover bone disease. In this chapter, we now describe the diagnosis, pathophysiology and treatments of renal hyperparathyroidism.

Structural role of osteocyte lacunae on mechanical properties of bone matrix: A cohesive finite element study

Despite the extensive studies on biological function of osteocytes, there are limited studies that evaluated the structural role of osteocyte lacunae on local mechanical properties of the bone matrix. As a result, the goal of this study was to elucidate the independent contribution of osteocyte lacunae structure on mechanical properties and fracture behavior of the bone matrix uncoupled from its biological effects and bone tissue composition variation. This study combined cohesive finite element modeling with experimental data from a lactation rat model to evaluate the influence of osteocyte lacunar area porosity, density, size, axis ratio, and orientation on the elastic modulus, ultimate strength, and ultimate strain of the bone matrix as well as on local crack formation and propagation. It also performed a parametric study to isolate the influence of a single osteocyte lacunae structural property on the mechanical properties of the bone matrix. The experimental measurements demonstrated statistically significant differences in lacunar size between ovariectomized rats with lactation history and virgin groups (both ovariectomized and intact) and in axis ratio between rats with lactation history and virgins. There were no differences in mechanical properties between virgin and lactation groups as determined by the finite element simulations. However, there were statistically significant linear relationships between the physiological range of osteocyte lacunar area porosity, density, size, and orientation and the elastic modulus and ultimate strength of the bone matrix in virgin and lactation rats. The parametric study also revealed similar but stronger relationships between elastic modulus and ultimate strength and lacunar density, size, and orientation. The simulations also demonstrated that the osteocyte lacunae guided the crack propagation through local stress concentrations. In summary, this study enhanced the limited knowledge on the structural role of osteocyte lacunae on local mechanical properties of the bone matrix. These data are important in gaining a better understanding of the mechanical implications of the local modifications due to osteocytes in the bone matrix.

Micropetrosis in hemodialysis patients

Micropetrosis develops as a result of stagnation of calcium, phosphorus and bone fluid, which appears as highly mineralized bone area in the osteocytic perilacunar/canalicular system regardless of bone turnover of the patients. And microcracks are predisposed to increase in these areas, which leads to increased bone fragility. However, micropetrosis of hemodialysis (HD) patients has not been discussed at all. Micropetrosis area per bone area (Mp.Ar/B·Ar) and osteocyte number per micropetrosis area (Ot.N/Mp.Ar) were measured in nine HD patients with renal hyperparathyroidism (Group I), twelve patients with hypoparathyroidism within 1 year after the treatment of renal hyperparathyroidism (Group II) and seven patients suffering from hypoparathyroidism for over two years (Group III). And bone mineral density (BMD) and tissue mineral density (TMD) were calculated using μCT to evaluate bone mineral content of iliac bone of the patients. These parameters were compared among the three groups. Only Mp.Ar/B·Ar was statistically greater in Group II and III compared to Group I in the parameters of bone mineral content and micropetrosis. However, the other parameters were not statistically different among the three groups. In long-term HD patients, BMD and TMD may be modified by the causes of renal insufficiency and the treatment of renal bone disease. We concluded that Mp.Ar/B·Ar was greater in patients with long-term hypoparathyroidism than both those with short-term hypoparathyroidism and with renal hyperparathyroidism. Special attention should be paid to avoid long-term hypoparathyroidism of the patients from the view point of increased fracture risk caused by increased micropetrosis area.

Sacral Insufficiency Fracture after Radiotherapy for Cervical Cancer: Appearance and Dynamic Changes on 18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography

Objective

With the increasing application of radiotherapy for cervical cancer, the incidence of sacral insufficiency fracture (SIF) is increasing gradually. Incorrect or untimely treatment caused by misdiagnosis may lead to serious adverse clinical consequences. This study retrospectively analyzed SIF caused by radiotherapy regarding the appearance and dynamic changes in 2-[fluorine-18]-fluoro-2-deoxy-D-glucose (18F-FDG) positive emission tomography (PET)/computed tomography (CT) images to improve the understanding of SIF.

Materials and Methods

We retrospectively examined cervical cancer patients who underwent pelvic radiotherapy and 18F-FDG PET/CT between January 2014 and January 2021. Comparative analysis of the imaging performance and follow-up data was conducted. In total, 38 patients with ages ranging from 28 to 81 years (mean age 59.2 ± 10.6 y, median age 56 y) participated in the study. The respective characteristics of the 38 patients were summarized, and diagnosis was confirmed by follow-up changes.

Results

Twenty-five (65.8%) of the 38 patients suffered from unilateral SIF, and 13 (34.2%) suffered from bilateral SIF. After receiving radiotherapy, SIF first appeared in 3–42 months (median, 13 months). The main 18F-FDG PET/CT manifestations of SIF were increased bone density (35/38, 92.1%), anterior sacral fracture line (28/38, 73.7%), and diffuse or linear uptake patterns parallel to the sacroiliac joint (37/38, 97.3%), with the maximum standard uptake value (SUVmax) ranging from 1.8 to 5.9 (average, 3.1). Follow-up lasted 3–59 months (mean, 14 months). The main changes in SIF were increases in the bone density and high-density range and decreases in the FDG uptake intensity and hypermetabolism range. Three patients had secondary sacral or sacroiliac joint infection (3/38, 7.9%), and 3 patients had secondary fracture and/or pelvic deformation (3/38, 7.9%).

Conclusions

18F-FDG PET/CT is an effective technique for diagnosing SIF. A small fracture line in the anterior sacrum and diffuse or linear areas of high density or metabolism parallel to the sacroiliac joint were the characteristic features of SIF. The main changes in SIF were increases in the bone density and high-density range and decreases in the FDG uptake intensity and hypermetabolism range.

Osteocyte Wnt/β-catenin pathway activation upon mechanical loading is altered in ovariectomized mice

Estrogen levels decline in both sexes with age, but more dramatically in females. Activation of the Wnt/β-catenin signaling pathway is central to the regulation of bone mass accrual and maintenance and in response to mechanical loading. Using the ovariectomized mouse model we examined the effect of estrogen loss on the osteocyte's ability to activate the Wnt/β-catenin pathway following mechanical loading. Female TOPGAL mice underwent ovariectomy (OVX) (n = 10) or sham surgery (n = 10) at 16 weeks of age. Four weeks post-surgery, a single loading session (global strain of 2200 με for 100 cycles at 2 Hz) was performed on the right forearm with the left as a non-loaded control. Mice (n = 5) were sacrificed at 1 or 24 hr post-load. Ulnae were stained for β-catenin activation, femurs were used for μCT and 3-pt bending/biomechanical testing, and tibiae were used for histology analysis and to determine osteocyte lacunar size using SEM and high resolution micro-XCT. A 2.2-fold increase in β-catenin signaling activation was observed 24 hr post-load in the Sham group but did not occur in the OVX group. The OVX group versus control had significant losses (p < 0.05) in trabecular BMD (−8%), BV/TV (−35%) and thickness (−23%), along with cortical thickness (−6%) and periosteal perimeter (−4%). The OVX group had significantly higher trabecular bone osteoclast numbers (63%), OCS/BS (77%) and N.OC/BPm (94%) and a significant decrease in osteoblast number (53%), OBS/BS (37%) and N.OB/BPm (40%) compared to the sham group (p < 0.05). Cortical bone lacunar number/lacunar volume and bone biomechanical properties did not change between groups. Given that the ulna is a cortical bone loading model and the lack of changes in osteocyte lacunar number/volume in cortical bone, which would alter strains experienced by osteocytes, these data suggest the absence of estrogen resulted in intrinsic changes in the ability of the osteocyte to respond to mechanical load, rather than changes in the biomechanical and architectural properties of bone.

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In vivo mechanical loading activates β-catenin signaling in osteocytes.

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Ovariectomy induced estrogen loss attenuates in vivo loading induced β-catenin signaling in osteocytes.

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Changes in bone material and architectural properties do not appear to explain attenuated pathway activation.

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Our data suggests estrogen loss alters the intrinsic ability of the osteocyte to respond to mechanical load.

Rethinking Fragility Fractures in Type 2 Diabetes: The Link between Hyperinsulinaemia and Osteofragilitas

Patients with type 2 diabetes mellitus (T2DM) and/or cardiovascular disease (CVD), conditions of hyperinsulinaemia, have lower levels of osteocalcin and bone remodelling, and increased rates of fragility fractures. Unlike osteoporosis with lower bone mineral density (BMD), T2DM bone fragility "hyperinsulinaemia-osteofragilitas" phenotype presents with normal to increased BMD. Hyperinsulinaemia and insulin resistance positively associate with increased BMD and fragility fractures. Hyperinsulinaemia enforces glucose fuelling, which decreases NAD+-dependent antioxidant activity. This increases reactive oxygen species and mitochondrial fission, and decreases oxidative phosphorylation high-energy production capacity, required for osteoblasto/cytogenesis. Osteocytes directly mineralise and resorb bone, and inhibit mineralisation of their lacunocanalicular space via pyrophosphate. Hyperinsulinaemia decreases vitamin D availability via adipocyte sequestration, reducing dendrite connectivity, and compromising osteocyte viability. Decreased bone remodelling and micropetrosis ensues. Trapped/entombed magnesium within micropetrosis fossilisation spaces propagates magnesium deficiency (MgD), potentiating hyperinsulinaemia and decreases vitamin D transport. Vitamin D deficiency reduces osteocalcin synthesis and favours osteocyte apoptosis. Carbohydrate restriction/fasting/ketosis increases beta-oxidation, ketolysis, NAD+-dependent antioxidant activity, osteocyte viability and osteocalcin, and decreases excess insulin exposure. Osteocalcin is required for hydroxyapatite alignment, conferring bone structural integrity, decreasing fracture risk and improving metabolic/endocrine homeodynamics. Patients presenting with fracture and normal BMD should be investigated for T2DM and hyperinsulinaemia.

Greater heterogeneity of the bone mineralisation density distribution and low bone matrix mineralisation characterise tibial subchondral bone marrow lesions in knee osteoarthritis patients

Tibial subchondral bone marrow lesions (BMLs) identified by MRI have been recognised as potential disease predictors in knee osteoarthritis (KOA), and may associate with abnormal bone matrix mineralisation and reduced bone quality. However, these tissue-level changes of BMLs have not been extensively investigated. Thus, the aim of this study was to quantify the degree of subchondral bone matrix mineralisation (both plate and trabeculae) in relation to histomorphometric parameters of bone remodelling and osteocyte lacunae (OL) characteristics in the tibial plateau (TP) of KOA patients with and without BMLs (OA-BML and OA No-BML, respectively) in comparison to nonOA cadaveric controls (CTL). Osteochondral (cartilage-bone) tissue was sampled from the BML signal region within the medial compartment for each OA-BML TP, and from a corresponding medial region for OA No-BML and CTL TPs. The tissue samples were embedded in resin, and sections stained with Von-Kossa Haematoxylin and Eosin (H&E) for quantitation of static indices of bone remodelling. Resin blocks were then further polished, and carbon-coated for quantitative backscattered electron imaging (qBEI) to determine the bone mineralisation density distribution (BMDD), as well as OL characteristics. It was found that OA-BML contained higher osteoid volume per tissue volume (OV/TV; %) and per bone volume (OV/BV; %) in both subchondral plate and trabecular bone compared to OA No-BML and CTL. The BMDD of OA-BML in both subchondral plate and trabecular bone was shifted toward a lower degree of mineralisation. Typically, an increase in both the heterogeneity of mineralisation density (Ca Width; wt%Ca) and the percentage of lower calcium (Ca Low; % B.Ar) in trabecular bone with OA-BML versus CTL was observed. Further, unmineralised OL density (#/mm²) in subchondral plate was distinctly higher in OA-BML samples compared to CTL. The KOA patients with and without BMLs had significantly decreased density of mineralised OL (#/mm²) in trabecular bone compared to CTL. Taken together, these findings indicate that tibial BMLs in advanced KOA patients are characterised by significantly hypo-mineralised subchondral bone compared with CTL. These differences associated with evidence of increased bone remodelling in OA-BML, and may influence the mechanical properties of the subchondral bone, with implications for the overlying cartilage.

Risk Factors Associated With Foot and Ankle Insufficiency Fractures in Postmenopausal Sedentary Women

BACKGROUND

Insufficiency fractures occur in bones with low elastic resistance. In contrast to stress fractures, which affect normal bones and have been extensively studied, insufficiency fractures of the foot and ankle have been the subject of little research. The objective of this study was to identify risk factors associated with the development of foot and ankle insufficiency fractures.

METHODS

The study included 55 postmenopausal sedentary women with foot and ankle insufficiency fractures and 51 women in the control group. The data collected were the fracture site, body mass index, use of corticosteroids, T scores of the femur and lumbar spine measured by bone densitometry, and serum 25-OH vitamin D level. The calcaneal pitch (CP), talar-first metatarsal, and metatarsus adductus (MA) angles were measured on radiographs.

RESULTS

In 49 patients (89%), fractures occurred in the metatarsals. All metatarsals were affected, and the most common fracture site was the base of the fifth metatarsal, with 21 cases (33%). Twenty patients (36%) in the study group reported chronic use of corticosteroids and had lower bone mineral density levels than controls (P < .05). The factors associated with fracture development (P < .05) were the CP and MA angles and low lumbar bone mineral density.

CONCLUSION

Insufficiency fractures in this population were associated with low bone mineral density and unfavorable biomechanical characteristics such as pes cavus and metatarsus adductus.

LEVEL OF EVIDENCE

Level IIIB, case-control study.

Study on the morphological and metabolic changes of femur in laying hens with hypophosphatemia

Layer fatigue syndrome caused by the lack of calcium and phosphorus can cause fracture in laying hens. The effect of phosphorus deficiency on the femur of laying hens with layer fatigue syndrome has not been studied. In this study, sixty 22-week-old Roman white layers were randomly divided into control group (group C) and low phosphorus group (group P), 30 individuals in each group. The available phosphorus content of group P was 0.18%. At the age of 26, 30 and 34 weeks, the production performance, biomechanical index, protein expression, histopathological change of femur and serological index were detected. The results showed that the laying rate, egg quality and body weight of laying hens, bone density, cortical bone thickness, rigidity, flexural modulus, flexural rigidity, the maximum load of femur and expression of osteocalcin (OCN), receptor activator of nuclear factor kappa-Β (RANK) and receptor activator of nuclear factor kappa-Β ligand (RANKL) decreased of group P. The number of osteocytes was decreased, and the voids was increased. However, cell lacunae were not obvious. The levels of phosphorus, calcium and OCN were increased, and the content of estradiol (E₂), OPG and calcitonin (CT) were decreased in serum. In conclusion, the low phosphorus diet can induce layer fatigue syndrome and affect the content of OPG and E₂ in serum and the expression of OCN, OPG, RANK and RANKL in femur protein, which leads to the imbalance of bone homeostasis, the thinning of femur cortex bone and the decrease of bone density.

Reference Intervals for Bone Histomorphometric Measurements Based on Data from Healthy Premenopausal Women

This study has established the normal reference intervals for bone histomorphometric measurements derived from healthy premenopausal women, which is rarely available. We presented the static and dynamic bone histomorphometric data from trans-iliac bone biopsies in 62 healthy premenopausal women (19 blacks and 43 whites, ages 20-53 years). There were no significant differences in age and BMI between black and white women. Since there was no significant difference in bone remodeling between the two ethnic groups, we pooled data of all 62 premenopausal women to establish normal reference intervals for bone histomorphometry. The results provide normal reference intervals for both static and dynamic histomorphometric variables in cancellous and cortical bone of the ilium. None of the bone remodeling-related variables correlated with age or BMI. This study provides reference intervals for bone histomorphometric measurements in both cancellous and cortical bone of the ilium, which would be helpful in the evaluation of bone health in women.

Long-Term Immobilization in Elderly Females Causes a Specific Pattern of Cortical Bone and Osteocyte Deterioration Different From Postmenopausal Osteoporosis

Immobilization as a result of long-term bed rest can lead to gradual bone loss. Because of their distribution throughout the bone matrix and remarkable interconnectivity, osteocytes represent the major mechanosensors in bone and translate mechanical into biochemical signals controlling bone remodeling. To test whether immobilization affects the characteristics of the osteocyte network in human cortical bone, femoral diaphyseal bone specimens were analyzed in immobilized female individuals and compared with age-matched postmenopausal individuals with primary osteoporosis. Premenopausal and postmenopausal healthy individuals served as control groups. Cortical porosity, osteocyte number and lacunar area, the frequency of hypermineralized lacunae, as well as cortical bone calcium content (CaMean) were assessed using bone histomorphometry and quantitative backscattered electron imaging (qBEI). Bone matrix properties were further analyzed by Fourier transform infrared spectroscopy (FTIR). In the immobilization group, cortical porosity was significantly higher, and qBEI revealed a trend toward higher matrix mineralization compared with osteoporotic individuals. Osteocyte density and canalicular density showed a declining rate from premenopausal toward healthy postmenopausal and osteoporotic individuals with peculiar reductions in the immobilization group, whereas the number of hypermineralized lacunae accumulated inversely. In conclusion, reduced osteocyte density and impaired connectivity during immobilization are associated with a specific bone loss pattern, reflecting a phenotype clearly distinguishable from postmenopausal osteoporosis. Immobilization periods may lead to a loss of survival signals for osteocytes, provoking bone loss that is even higher than in osteoporosis states, whereas osteocytic osteolysis remains absent. © 2020 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research.

Co-aligned chondrocytes: Zonal morphological variation and structured arrangement of cell lacunae in tessellated cartilage

In most vertebrates the embryonic cartilaginous skeleton is replaced by bone during development. During this process, cartilage cells (chondrocytes) mineralize the extracellular matrix and undergo apoptosis, giving way to bone cells (osteocytes). In contrast, sharks and rays (elasmobranchs) have cartilaginous skeletons throughout life, where only the surface mineralizes, forming a layer of tiles (tesserae). Elasmobranch chondrocytes, unlike those of other vertebrates, survive cartilage mineralization and are maintained alive in spaces (lacunae) within tesserae. However, the functions of the chondrocytes in the mineralized tissue remain unknown. Applying a custom analysis workflow to high-resolution synchrotron microCT scans of tesserae, we characterize the morphologies and arrangements of stingray chondrocyte lacunae, using lacunar morphology as a proxy for chondrocyte morphology. We show that the cell density is comparable in unmineralized and mineralized tissue and that cells maintain similar volume even when they have been incorporated into tesserae. Our findings support previous hypotheses that elasmobranch chondrocytes, unlike those of other taxa, do not proliferate, hypertrophy or undergo apoptosis during mineralization. Tessera lacunae show zonal variation in their shapes, being flatter further from and more spherical closer to the unmineralized cartilage matrix, and larger in the center of tesserae. The lacunae show pronounced organization into parallel layers and strong orientation toward neighboring tesserae. Tesserae also exhibit local variation in lacunar density, with the density considerably higher near pores passing through the tesseral layer, suggesting pores and cells interact, and that pores may contain a nutrient source. We propose that the different lacunar types reflect the stages of the tesserae formation process, while also representing local variation in tissue architecture and cell function. Lacunae are linked by small passages (canaliculi) in the matrix to form elongated series at the tesseral periphery and tight clusters in the center of tesserae, creating a rich connectivity among cells. The network arrangement and the shape variation of chondrocytes in tesserae indicate that cells may interact within and between tesserae and manage mineralization differently from chondrocytes in other vertebrates, perhaps performing analogous roles to osteocytes in bone.

Age related changes in the bone microstructure in patients with femoral neck fractures

BACKGROUND

The risk of femoral neck fracture progressively increases with age. However, the reasons behind this consistent increase in the fracture risk can't be completely justified by the decrease in the bone mineral density. The objective of this study was to analyze the correlation between various bone structural features and age.

STUDY DESIGN & METHODS

A total of 29 consecutive patients who suffered an intracapsular hip fracture and underwent joint replacement surgery between May 2012 and March 2013 were included in this study. A 2 cm × 1 cm Ø cylindrical trabecular bone sample was collected from the femoral heads and preserved in formaldehyde. Bone mineral density (BMD), microarchitecture, organic content and crystallography were analyzed using a Dual-energy X-ray absorptiometry scan, micro-CT scan, and high resolution magic-angle-spinning-nuclear magnetic resonance (MAS-NMR), respectively. Statistical correlations were made using Spearman´s or Pearson´s correlation tests depending on the distribution of the continuous variables.

RESULTS

The mean patient age was 79.83 ± 9.31 years. A moderate negative correlation was observed between age and the hydrogen content in bone (¹H), which is an indirect estimate to quantify the organic matrix (r = -0.512, p = 0.005). No correlations were observed between BMD, trabecular number, trabecular thickness, phosphorous content, apatite crystal size, and age (r = 0.06, p = 0.755; r = -0.008, p = 0.967; r = -0.046, p = 0.812; r = -0.152, p = 0.430, respectively). A weak positive correlation was observed between Charlson´s comorbidity index (CCI) and c-axis of the hydroxiapatite (HA) crystals (r = -0.400, p = 0.035).

CONCLUSION

The femoral head relative protein content progressively decreases with age. BMD was not correlated with other structural bone parameters and age. Patients with higher comorbidity scores had larger HA crystals. The present results suggest that the progressive increase in the hip fracture risk in elderly patients could be partially explained by the lower bone protein content in this age group.

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.

Is the bone tissue of the femoral neck demineralised in patients with hip fracture?

The aim of this study is to establish the falsifiability of the "osteoporotic hypothesis" for hip fracture, according to which the bone density and mineral composition of bone tissue in patients with hip fracture is poorer than when no such fracture is present, and that this circumstance is relevant to the occurrence of a fracture. The study population consisted of forty patients treated with arthroplasty. Twenty patients with femoral neck fracture and another twenty with hip osteoarthritis received the same diagnostic protocol and the same antibiotic, anaesthetic, surgical and antithrombotic prophylaxis. Levels of calcium (Ca), phosphorus (P) and vitamin D in blood, amongst other values, were determined, and five samples of bone tissue from the proximal femoral metaphysis were obtained and characterised by optical microscopy and microanalytical analysis. No statistically significant differences were observed between the two groups with respect to the trabecular number, area or thickness, or inter-trabecular distance. However, there were differences in the length of the trabeculae, which was greater in the patients with hip osteoarthritis (p = 0.002), but not when the groups were compared by gender. When compared by age, a greater inter-trabecular distance was observed in the patients aged over 75 years (p = 0.036) but there were no differences in the remaining parameters. Serum levels of Ca (p = 0.03), P (p < 0.01) and vitamin D (p < 0.01) were lower in the fracture group. In the quantitative microanalytical analysis, no significant differences were observed in bone levels of Ca or P or in the Ca/P index, nor was there any correlation between serum and levels of bone Ca or P (Ca-0.197:p = 0.314;P-0.274:p = 0.158).Multiple linear regression revealed no correlation between the diagnoses, vitamin D and bone levels of Ca or P. Despite the reduced serum levels of Ca and P in the patients with hip fracture, no correlation was observed with bone levels of Ca and P,which were similar in both groups. There were differences in the organic bone structure, in terms of length and inter-trabecular distance. For patients with osteoporosis, treatment should be aimed at increasing the synthesis of bone trabeculae to reinforce their structure. Nevertheless, no such treatment can prevent falls, and therefore no reduction in hip fractures amongst this population can be assured.

Bone Mineral Is More Heterogeneously Distributed in the Femoral Heads of Osteoporotic and Diabetic Patients: A Pilot Study

Osteoporosis is associated with systemic bone loss, leading to a significant deterioration of bone microarchitecture and an increased fracture risk. Although recent studies have shown that the distribution of bone mineral becomes more heterogeneous because of estrogen deficiency in animal models of osteoporosis, it is not known whether osteoporosis alters mineral distribution in human bone. Type 2 diabetes mellitus (T2DM) can also increase bone fracture risk and is associated with impaired bone cell function, compromised collagen structure, and reduced mechanical properties. However, it is not known whether alterations in mineral distribution arise in diabetic (DB) patients’ bone. In this study, we quantify mineral content distribution and tissue microarchitecture (by μCT) and mechanical properties (by compression testing) of cancellous bone from femoral heads of osteoporotic (OP; n = 10), DB (n = 7), and osteoarthritic (OA; n = 7) patients. We report that though OP cancellous bone has significantly deteriorated compressive mechanical properties and significantly compromised microarchitecture compared with OA controls, there is also a significant increase in the mean mineral content. Moreover, the heterogeneity of the mineral content in OP bone is significantly higher than controls (+25%) and is explained by a significant increase in bone volume at high mineral levels. We propose that these mineral alterations act to exacerbate the already reduced bone quality caused by reduced cancellous bone volume during osteoporosis. We show for the first time that cancellous bone mineralization is significantly more heterogeneous (+26%) in patients presenting with T2DM compared with OA (non‐DB) controls, and that this heterogeneity is characterized by a significant increase in bone volume at low mineral levels. Despite these mineralization changes, bone microarchitecture and mechanical properties are not significantly different between OA groups with and without T2DM. Nonetheless, the observed alterations in mineral heterogeneity may play an important tissue‐level role in bone fragility associated with OP and DB bone. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Can we enhance osteoporotic metaphyseal fracture healing through enhancing ultrastructural and functional changes of osteocytes in cortical bone with low-magnitude high-frequency vibration?

Fragility fractures are related to the loss of bone integrity and deteriorated morphology of osteocytes. Our previous studies have reported that low-magnitude high-frequency vibration (LMHFV) promoted osteoporotic fracture healing. As osteocytes are known for mechanosensing and initiating bone repair, we hypothesized that LMHFV could enhance osteoporotic fracture healing through enhancing morphological changes in the osteocyte lacuna-canalicular network (LCN) and mineralization. A metaphyseal fracture model was established in female Sprague-Dawley rats to investigate changes in osteocytes and healing outcomes from early to late phase post-fracture. Our results showed that the LCN exhibited an exuberant outgrowth of canaliculi in the osteoporotic fractured bone at day 14 after LMHFV. LMHFV upregulated the E11, dentin matrix protein 1 (DMP1), and fibroblast growth factor 23 (FGF23), but downregulated sclerostin (Sost) in osteocytes. Moreover, LMHFV promoted mineralization with significant enhancements of Ca/P ratio, mineral apposition rate (MAR), mineralizing surface (MS/BS), and bone mineral density (BMD) in the osteoporotic group. Consistently, better healing was confirmed by microarchitecture and mechanical properties, whereas the enhancement in osteoporotic group was comparable or even greater than the normal group. This is the first report to reveal the enhancement effect of LMHFV on the osteocytes' morphology and functions in osteoporotic fracture healing.

Abnormal lacuno-canalicular network and negative correlation between serum osteocalcin and Cobb angle indicate abnormal osteocyte function in adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis (AIS) is a prevalent spinal deformity occurring during peripubertal growth period that affects 1-4% of adolescents globally without clear etiopathogenetic mechanism. Low bone mineral density is an independent and significant prognostic factor for curve progression. Currently, the cause underlying low bone mass in AIS remains elusive. Osteocytes play an important role in bone metabolism and mineral homeostasis, but its role in AIS has not been studied. In the present study, iliac bone tissues were harvested from 21 patients with AIS (mean age of 14.3 ± 2.20 yr old) with a mean Cobb angle of 55.6 ± 10.61° and 13 non-AIS controls (mean age of 16.5 ± 4.79 yr old) intraoperatively. Acid-etched scanning electron microscopy (SEM) images of AIS demonstrated abnormal osteocytes that were more rounded and cobblestone-like in shape and were aligned in irregular clusters with shorter and disorganized canaliculi. Further quantitative analysis with FITC-Imaris technique showed a significant reduction in the canalicular number and length as well as an increase in lacunar volume and area in AIS. SEM with energy-dispersive X-ray spectroscopy analysis demonstrated a lower calcium-to-phosphorus ratio at the perilacunar/canalicular region. Moreover, microindentaion results revealed lower values of Vickers hardness and elastic modulus in AIS when compared with controls. In addition, in the parallel study of 99 AIS (27 with severe Cobb angle of 65.8 ± 14.1° and 72 with mild Cobb angle of 26.6 ± 9.1°) with different curve severity, the serum osteocalcin level was found to be significantly and negatively associated with the Cobb angle. In summary, the findings in this series of studies demonstrated the potential link of abnormal osteocyte lacuno-canalicular network structure and function to the observed abnormal bone mineralization in AIS, which may shed light on etiopathogenesis of AIS.-Chen, H., Zhang, J., Wang, Y., Cheuk, K.-Y., Hung, A. L. H., Lam, T.-P., Qiu, Y., Feng, J. Q., Lee, W. Y. W., Cheng, J. C. Y. Abnormal lacuno-canalicular network and negative correlation between serum osteocalcin and Cobb angle indicate abnormal osteocyte function in adolescent idiopathic scoliosis.

Extracellular matrix composition during bone regeneration in the human dental alveolar socket

Within the dental alveolar socket, the sequence of events following tooth extraction involves deposition of a provisional connective tissue matrix that is later replaced by woven bone and eventually by lamellar bone. Bone regeneration within the dental alveolar socket is unique since the space occupied by the root(s) of a tooth does not originally contain any bone. However, extracellular matrix composition of the healing alveolar socket has not previously been investigated. Here, alveolar bone biopsies representing early (7-46 months, < 4y) and late (48-60 months; 4-5y) healing periods were investigated using Raman spectroscopy, X-ray micro-computed tomography and backscattered electron scanning electron microscopy. Partially or completely edentulous individuals and those with a smoking habit were not excluded. Between < 4y and 4-5y, mineral crystallinity and bone mineral density increase, phenylalanine, proline/hydroxyproline, and bone surface-to-volume ratio decrease, while the carbonate-to-phosphate ratio, the mineral-to-matrix ratio, and the collagen crosslink ratio remain relatively unchanged. Observed exclusively at 4-5y, hypermineralised osteocyte lacunae contain spherical and rhomboidal mineral nodules. Spearman correlation analysis reveals several significant, high (ρ = 0.7-0.9; p ≤ 0.01) and moderate (ρ = 0.5-0.7; p ≤ 0.01) correlations. Mineral crystallinity and proline/hydroxyproline, the carbonate-to-phosphate ratio and phenylalanine, mineral crystallinity and bone surface-to-volume ratio, the carbonate-to-phosphate ratio and bone surface-to-volume ratio, proline/hydroxyproline and bone mineral density, and bone mineral density and bone surface-to-volume ratio are negatively correlated. Mineral crystallinity and bone mineral density, and proline/hydroxyproline and bone surface-to-volume ratio are positively correlated. Although bone regeneration in the dental alveolar socket follows typical bone healing patterns, the compositional and microstructural patterns reveal mature bone at <4y with indications of better mechanical competence at 4-5y.

New insights into the process of osteogenesis of anosteocytic bone

The bone material of almost all vertebrates contains the same cellular components. These comprise osteoblasts that produce bone, osteoclasts that resorb bone and osteocytes, which are the master regulators of bone metabolism, particularly bone modeling and remodeling. It is thus surprising that the largest group of extant vertebrates, neoteleost fish, lacks osteocytes entirely (anosteocytic bone). Osteocytes are the progeny of osteoblasts, which become entrapped in the osteoid they secrete, then undergo several morphologic and functional changes, to finally form an intricate network of living cells in the bone matrix. While the process of osteogenesis of osteocytic bone has been thoroughly studied, osteogenesis of anosteocytic bone is less well understood. The current paradigm for formation of anosteocytic bone suggests that osteoblasts remain always on the external surface of the formed bone, and do not become entrapped in the osteoid. Such a process requires the osteoblasts to function in a fundamentally-different way from osteoblasts of all other bony vertebrates. Here we present a comparative structural study of the osteocytic bones of zebrafish and anosteocytic bones of medaka and show that they are remarkably similar in structure at several hierarchical levels. Scanning electron microscopy and phase contrast-enhanced μCT reveal the presence of numerous mineralized objects in the matrix of anosteocytic bone. These objects resemble osteocytic lacunae in zebrafish bone, and their locations and distribution are similar to those of osteocytes in zebrafish bone. Our findings provide support for the occurrence of a process of anosteocytic bone osteogenesis that has so far been rejected. In this process osteoblasts become entrapped in the bone matrix (as occurs in osteogenesis of osteocytic bone), but then undergo apoptosis, become mineralized and end up as part of the mineralized bone matrix.

50 years of scanning electron microscopy of bone-a comprehensive overview of the important discoveries made and insights gained into bone material properties in health, disease, and taphonomy

Bone is an architecturally complex system that constantly undergoes structural and functional optimisation through renewal and repair. The scanning electron microscope (SEM) is among the most frequently used instruments for examining bone. It offers the key advantage of very high spatial resolution coupled with a large depth of field and wide field of view. Interactions between incident electrons and atoms on the sample surface generate backscattered electrons, secondary electrons, and various other signals including X-rays that relay compositional and topographical information. Through selective removal or preservation of specific tissue components (organic, inorganic, cellular, vascular), their individual contribution(s) to the overall functional competence can be elucidated. With few restrictions on sample geometry and a variety of applicable sample-processing routes, a given sample may be conveniently adapted for multiple analytical methods. While a conventional SEM operates at high vacuum conditions that demand clean, dry, and electrically conductive samples, non-conductive materials (e.g., bone) can be imaged without significant modification from the natural state using an environmental scanning electron microscope. This review highlights important insights gained into bone microstructure and pathophysiology, bone response to implanted biomaterials, elemental analysis, SEM in paleoarchaeology, 3D imaging using focused ion beam techniques, correlative microscopy and in situ experiments. The capacity to image seamlessly across multiple length scales within the meso-micro-nano-continuum, the SEM lends itself to many unique and diverse applications, which attest to the versatility and user-friendly nature of this instrument for studying bone. Significant technological developments are anticipated for analysing bone using the SEM.

Changes in the osteocyte lacunocanalicular network with aging

Osteoporosis is an aging-related disease of reduced bone mass that is particularly prevalent in post-menopausal women, but also affects the aged male population and is associated with increased fracture risk. Osteoporosis is the result of an imbalance whereby bone formation by osteoblasts no longer keeps pace with resorption of bone by osteoclasts. Osteocytes are the most abundant cells in bone and, although previously thought to be quiescent, they are now known to be active, multifunctional cells that play a key role in the maintenance of bone mass by regulating both osteoblast and osteoclast activity. They are also thought to regulate bone mass through their role as mechanoresponsive cells in bone that coordinate adaptive responses to mechanical loading. Osteocytes form an extensive interconnected network throughout the mineralized bone matrix and receive their nutrients as well as hormones and signaling factors through the lacunocanalicular system. Several studies have shown that the extent and connectivity of the lacunocanalicular system and osteocyte networks degenerates in aged humans as well as in animal models of aging. It is also known that the bone anabolic response to loading is decreased with aging. This review summarizes recent research on the degenerative changes that occur in osteocytes and their lacunocanalicular system as a result of aging and discusses the implications for skeletal health and homeostasis as well as potential mechanisms that may underlie these degenerative changes. Since osteocytes are such key regulators of skeletal homeostasis, maintaining the health of the osteocyte network would seem critical for maintenance of bone health. Therefore, a more complete understanding of the structure and function of the osteocyte network, its lacunocanalicular system, and the degenerative changes that occur with aging should lead to advances in our understanding of age related bone loss and potentially lead to improved therapies.

Dense cancellous bone as evidenced by a high HU value is predictive of late implant failure: a preliminary study

OBJECTIVES

The mechanism of late implant failure is unclear. This study examined the association between sclerosing cancellous bone images and the risk of late implant failures using multi-detector row computed tomography (CT) imaging data.

METHODS

We performed a case-control study. The study group consisted of consecutive patients with implant failures treated at Kyushu Dental University between 2001 and 2016. CT data for late failure of 36 implants in 16 patients were available. The study cohort consisted of 16 patients with 36 late failed implants and 28 patients with 113 successful implants.

RESULTS

The mean survival rate was 6.9 months for early implant failure, 76.6 months for late failure with marginal bone resorption, inflammation symptoms, and so-called peri-implantitis, and 95.0 months for late failure caused by implant fracture. The mean HU value for cases in the control group was 507 compared with 1231 for cases with late failure implants. Logistic regression was used for analysis. There were signs of high radiodensity of peri-implant cancellous bone when comparing adjusted radiodensity per 100 HU using CT data (OR 2.35; 95% CI 1.73-3.20; p < 0.001).

CONCLUSIONS

Within the limits of our study, the presence of high radiodensity and cancellous bone consolidation on imaging may be related to risk factors for late implant failure. Therefore, CT images of the host cancellous bone status for observation of visible sclerosis could be a useful diagnostic indicator for late implant failure.

Bone tissue aging affects mineralization of cement lines

Cement lines are known as thin peripheral boundaries of the osteons. With a thickness below 5 μm their composition of inorganic and organic compounds has been a matter of debate. Here, we hypothesized that cement lines become hypermineralized and their degree of mineralization is not constant but related to the tissue age of the osteon. Therefore, we analyzed the calcium content of osteons and their corresponding cement lines in a range of different tissue ages reflected by osteonal mineralization levels in femoral cortical bone of both postmenopausal women with osteoporosis and bisphosphonate-treated cases. Quantitative backscattered electron imaging (qBEI) showed that cement lines are hypermineralized entities with consistently higher calcium content than their corresponding osteons (mean calcium content: 29.46 ± 0.80 vs. 26.62 ± 1.11 wt%; p < 0.001). Micro-Raman spectroscopy complemented the qBEI data by showing a significantly higher phosphate/amide I ratio in the cement lines compared to the osteonal bone (8.78 ± 0.66 vs. 6.33 ± 0.58, p < 0.001), which was both due to an increased phosphate peak and a reduced amide I peak in cement lines. A clear positive correlation of cement line mineralization and the mineralization of the osteon was observed (r = 0.839, p = 0.003). However, the magnitude of the difference between cement line and osteonal calcium content decreased with increased osteonal calcium content (r = -0.709, p < 0.001), suggesting diverging mineralization dynamics in these osseous entities. The number of mineralized osteocyte lacunae per osteon bone area correlated positively with both osteonal and cement line calcium content (p < 0.01). The degree of mineralization of cement lines may represent another tissue-age related phenomenon, given that it strongly relates to the osteonal mineralization level. Understanding of the cement lines' mineralization and their changes in aging and disease states is important for predicting crack propagation pathways and fracture resistance mechanisms in human cortical bone.

Bone matrix microdamage and vascular changes characterize bone marrow lesions in the subchondral bone of knee osteoarthritis

INTRODUCTION

Bone marrow lesions (BMLs) in the subchondral bone in osteoarthritis (OA) are suggested to be multifactorial, although the pathogenic mechanisms are unknown. Bone metabolism and cardiovascular risk factors associate with BML in epidemiologic studies. However, there are no studies at the tissue level investigating the relationship between these processes and BML. The aim of this study was to investigate the relationship between BMLs in the tibial plateau (TP) of knee OA and bone matrix microdamage, osteocyte density and vascular changes.

METHODS

TP were obtained from 73 patients at total knee replacement surgery and BMLs were identified ex vivo in TP tissue using MRI. Comparator 'No BML' tissue was from matched anatomical sites to the BMLs. Quantitative assessment was made of subchondral bone microdamage, bone resorption indices, osteocyte cellularity, and vascular features.

RESULTS

Several key parameters were different between BML and No BML tissue. These included increased microcrack burden (p = .01, p = .0001), which associated positively with bone resorption and negatively with cartilage volume, and greater osteocyte numerical density (p = .02, p = .01), in the subchondral bone plate and subchondral trabeculae, respectively. The marrow tissue within BML zones contained increased arteriolar density (p = .04, p = .0006), and altered vascular characteristics, in particular increased wall thickness (p = .007) and wall:lumen ratio (wall thickness over internal lumen area) (p = .001), compared with No BML bone.

CONCLUSIONS

Increased bone matrix microdamage and altered vasculature in the subchondral bone of BMLs is consistent with overloading and vascular contributions to the formation of these lesions. Given the important role of BMLs in knee OA, these contributing factors offer potential targets for the treatment and prevention of knee OA.

Early bone tissue aging in human auditory ossicles is accompanied by excessive hypermineralization, osteocyte death and micropetrosis

Within the mineralized bone, osteocytes form a multifunctional mechanosensitive network orchestrating bone remodelling. A preserved osteocyte population is a crucial determinant of bone quality. In human auditory ossicles, the early decrease in osteocyte numbers but maintained integrity remains an unexplained phenomenon that might serve for sound transmission from air to the labyrinth. Here we analysed the frequency, size and composition of osteocyte lacunae in the auditory ossicles of 22 individuals from early postnatal period to old age. Mineralization of the bone matrix was determined using backscattered electron imaging. No signs of bone remodelling were observed above the age of 1 year. We detected characteristics of early bone tissue aging, such as decrease in osteocytes, lower total lacunar density and lacunar area, as well as high matrix mineralization accompanied by distinct accumulation of micropetrotic lacunae and decreased indentation depths. The majority of these changes took place in the first months and years of life, while afterwards only minor reorganization was present. With osteocyte apoptosis potentially being a consequence of low mechanical stimuli, the early loss of osteocytes without initiation of bone remodelling indicates an adaptive response conserving the architecture of the auditory ossicles and ensuring stable sound transmission throughout life.

Extracellular Vesicles from Adipose-Derived Mesenchymal Stem Cells Downregulate Senescence Features in Osteoarthritic Osteoblasts

Osteoarthritis (OA) affects all articular tissues leading to pain and disability. The dysregulation of bone metabolism may contribute to the progression of this condition. Adipose-derived mesenchymal stem cells (ASC) are attractive candidates in the search of novel strategies for OA treatment and exert anti-inflammatory and cytoprotective effects on cartilage. Chronic inflammation in OA is a relevant factor in the development of cellular senescence and joint degradation. In this study, we extend our previous observations of ASC paracrine effects to study the influence of conditioned medium and extracellular vesicles from ASC on senescence induced by inflammatory stress in OA osteoblasts. Our results in cells stimulated with interleukin- (IL-) 1β indicate that conditioned medium, microvesicles, and exosomes from ASC downregulate senescence-associated β-galactosidase activity and the accumulation of γH2AX foci. In addition, they reduced the production of inflammatory mediators, with the highest effect on IL-6 and prostaglandin E₂. The control of mitochondrial membrane alterations and oxidative stress may provide a mechanism for the protective effects of ASC in OA osteoblasts. We have also shown that microvesicles and exosomes mediate the paracrine effects of ASC. Our study suggests that correction of abnormal osteoblast metabolism by ASC products may contribute to their protective effects.

Protective effect of low-dose risedronate against osteocyte apoptosis and bone loss in ovariectomized rats

Osteocyte apoptosis is the first reaction to estrogen depletion, thereby stimulating osteoclastic bone resorption resulting in bone loss. We investigated the effects of two different risedronate (RIS) doses (high and low) on osteocyte apoptosis, osteoclast activity and bone loss in ovariectomized rats. Forty rats with ovariectomy (OVX) and sham ovariectomy (SHAM) were divided into 4 groups: 1) SHAM rats treated with saline (SHAM); 2) OVX rats treated with saline (OVX); 3) OVX rats treated with low-dose RIS (OVX-LR, 0.08 μg/kg/day); 4) OVX rats treated with high-dose RIS (OVX-HR, 0.8 μg/kg/day). All animals were sacrificed 90 days after surgery for the examinations of osteocyte apoptosis by caspase-3 staining, osteoclast activity by TRAP staining and bone volume by micro-CT scanning in lumbar vertebral cancellous bone. Both low and high dose RIS significantly reduced caspase-3 positive osteocytes, empty lacunae and TRAP positive osteoclasts in OVX rats. Although the difference in caspase-3 positive osteocytes was not significant between the OVX-LR and OVX-HR groups, numerically these cells were significantly more prevalent in OVX-HR (not OVX-LR) group than in SHAM group. TRAP positive osteoclasts were significantly higher in OVX-LR group than in SHAM or OVX-HR group. There was no significant difference in bone volume among the OVX-LR, OVX-HR and SHAM groups, but lower in OVX group alone. However, significant increase in trabecular thickness only occurred in OVX-LR group. We conclude that both low and high dose RIS significantly inhibit osteocyte apoptosis and osteoclast activity in OVX rats, but the low-dose RIS has weaker effect on osteoclast activity. However, low-dose RIS preserves cancellous bone mass and microarchitecture as well as high-dose RIS after estrogen depletion.

Micrometer-Sized Magnesium Whitlockite Crystals in Micropetrosis of Bisphosphonate-Exposed Human Alveolar Bone

Osteocytes are contained within spaces called lacunae and play a central role in bone remodelling. Administered frequently to prevent osteoporotic fractures, antiresorptive agents such as bisphosphonates suppress osteocyte apoptosis and may be localized within osteocyte lacunae. Bisphosphonates also reduce osteoclast viability and thereby hinder the repair of damaged tissue. Osteocyte lacunae contribute to toughening mechanisms. Following osteocyte apoptosis, the lacunar space undergoes mineralization, termed "micropetrosis". Hypermineralized lacunae are believed to increase bone fragility. Using nanoanalytical electron microscopy with complementary spectroscopic and crystallographic experiments, postapoptotic mineralization of osteocyte lacunae in bisphosphonate-exposed human bone was investigated. We report an unprecedented presence of ∼80 nm to ∼3 μm wide, distinctly faceted, magnesium whitlockite [Ca₁₈Mg₂(HPO₄)₂(PO₄)₁₂] crystals and consequently altered local nanomechanical properties. These findings have broad implications on the role of therapeutic agents in driving biomineralization and shed new insights into a possible relationship between bisphosphonate exposure, availability of intracellular magnesium, and pathological calcification inside lacunae.

Histomorphometric and osteocytic characteristics of cortical bone in male subtrochanteric femoral shaft

The histomorphometric properties of the subtrochanteric femoral region have rarely been investigated. The aim of this study was to investigate the age-associated variations and regional differences of histomorphometric and osteocytic properties in the cortical bone of the subtrochanteric femoral shaft, and the association between osteocytic and histological cortical bone parameters. Undecalcified histological sections of the subtrochanteric femoral shaft were obtained from cadavers (n = 20, aged 18-82 years, males). They were cut and stained using modified Masson-Goldner stain. Histomorphometric parameters of cortical bone were analysed with ×50 and ×100 magnification after identifying cortical bone boundaries using our previously validated method. Within cortical bone areas, only complete osteons with typical concentric lamellae and cement line were selected and measured. Osteocytic parameters of cortical bone were analyzed under phase contrast microscopy and epifluorescence within microscopic fields (0.55 mm² for each). The cortical widths of the medial and lateral quadrants were significantly higher than other quadrants (P < 0.01). Osteonal area per cortical bone area was lower and cortical porosities were higher in the posterior quadrant than in the other quadrants (P < 0.05). Osteocyte lacunar number per cortical bone area was found higher in the young subjects (≤ 50 years) than in the older ones (> 50 years) both before and after adjustments for body height and weight (P < 0.05). Moreover, significant but low correlations were found between the cortical bone and osteocytic parameters (0.20 ≤ R²  ≤ 0.35, P < 0.05). It can be concluded that in healthy males, the cortical histomorphometric parameters differ between the anatomical regions of the subtrochanteric femoral shaft, and are correlated with the osteocytic parameters from the same site. These findings may be of use when discussing mechanisms that predispose patients to decreasing bone strength.

Role of osteocytes in mediating bone mineralization during hyperhomocysteinemia

Hyperhomocysteinemia (HHCY) is a risk factor for osteoporosis but whether HHCY affects bone mineralization or not is still ambiguous. Herein we evaluated whether homocysteine affects tissue mineral density (TMD) of cortical bone and if so the role of osteocytes. CD1 mice administered with homocysteine (5 mg/100 g body weight, i.p.) for 7, 15 and 30 days showed temporal changes in TMD and osteocyte lacunar density in femoral cortices. Short-term administration of homocysteine (day 7) increased osteocyte lacunar density and reduced TMD evidenced by microCT50 while prolonged administration of homocysteine (day 30) reinstated TMD and lacunar density to baseline values. Major differences were decreased number of nucleated osteocyte lacunae, increased number of empty lacunae and cleaved caspase 3-positive osteocyte lacunae in day 30 HHCY bone evidenced by H&E staining and immunohistochemistry. Other differences were induction in mineralization genes like Dmp1, Phex and Sost in cortical bone by real-time PCR and increased number of Dmp1- and Sost-positive osteocyte lacunae in day 30 HHCY bone evidenced by immunohistochemistry. Both HHCY day 7 and day 30 samples showed reduced Young's modulus demonstrating that biomechanical property of bone was lost during early HHCY itself, which did not improve with recovery of TMD. Our results thus demonstrate occurrence of two phases in cortical bone upon HHCY: the early phase that involved loss of TMD and increase in osteocyte numbers and a late phase that involved osteocyte reprogramming, apoptosis and mineralization, which reinstated TMD but compromised biomechanical property. To conclude, osteocytes have a potential role in arbitrating bone pathogenesis during HHCY.

Spatial heterogeneity in the canalicular density of the osteocyte network in human osteons

Osteocytes interconnect with each other forming an intricate cell network within the mineralized bone matrix. One important function of the osteocyte network is the mechano-regulation of bone remodeling, where a possible mechanism includes the fluid flow through the porosity housing the cell network - the osteocyte lacuno-canalicular network (OLCN). In our study the OLCN in human osteons was three-dimensionally imaged with the aim to obtain a quantitative description of the canalicular density and spatial variations of this quantity within osteons. The topology of the OLCN was determined by first staining the bone samples with rhodamine, then imaging the OLCN with confocal laser scanning microscopy and finally using image analysis to obtain a skeletonized version of the network for further analysis. In total 49 osteons were studied from the femoral cortical bone of four different middle-aged healthy women. The mean canalicular density given as length of the canaliculi in a unit volume was 0.074 ± 0.015 μm/μm³ (corresponding to 74 km/cm³). No correlation was found between the canalicular density and neither the size of the osteon nor the volume fraction occupied by osteocyte lacunae. Within osteons the canalicular density varied substantially with larger regions without any network. On average the canalicular density decreases when moving from the Haversian canal outwards towards the cement line. We hypothesize that a decrease in accessible canaliculi with tissue age as a result of micropetrosis can reduce the local mechanosensitivity of the bone. Systematic future studies on age- and disease-related changes on the topology of the OLCN have to demonstrate the diagnostic potential of the presented characterization method.

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accurate three-dimensional representation of the canalicular network topology using confocal microscopy and image analysis

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quantitative network description with an average canalicular density of 74 km per cubic centimeter in healthy human osteons

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substantial variability of the canalicular density within osteons with 10% of the bone having a density twice the average

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in osteons large regions lacking an accessible network were found

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radial decrease of the canalicular density from the Haversian canal towards the cement line

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.

The Formation of Calcified Nanospherites during Micropetrosis Represents a Unique Mineralization Mechanism in Aged Human Bone

Osteocytes-the central regulators of bone remodeling-are enclosed in a network of microcavities (lacunae) and nanocanals (canaliculi) pervading the mineralized bone. In a hitherto obscure process related to aging and disease, local plugs in the lacuno-canalicular network disrupt cellular communication and impede bone homeostasis. By utilizing a suite of high-resolution imaging and physics-based techniques, it is shown here that the local plugs develop by accumulation and fusion of calcified nanospherites in lacunae and canaliculi (micropetrosis). Two distinctive nanospherites phenotypes are found to originate from different osteocytic elements. A substantial deviation in the spherites' composition in comparison to mineralized bone further suggests a mineralization process unlike regular bone mineralization. Clearly, mineralization of osteocyte lacunae qualifies as a strong marker for degrading bone material quality in skeletal aging. The understanding of micropetrosis may guide future therapeutics toward preserving osteocyte viability to maintain mechanical competence and fracture resistance of bone in elderly individuals.

Calcification during bone healing in a standardised rat calvarial defect assessed by micro-CT and SEM-EDX

OBJECTIVE

The study was designed to investigate the process of calcification during bone healing in a standardized rat calvarial bone defect model, measured by bone mineral density and the concentrations and distributions of calcium, phosphorus and carbon in the bone matrix.

MATERIALS AND METHODS

A standard defect was made on the parietal bone of 12-week-old rats under anaesthesia. The rats were fixed in weeks 1, 2, 4 and 8,and the calvaria were resected and examined with microcomputed tomography, then frozen and sectioned for histology and analysed with energy-dispersive X-ray spectroscopy (EDX). Parietal bone of 12-week-old control rats was processed similarly.

RESULTS

The mineral density of healing bone increased with time. The healing bone became thicker and denser with time in histology. The distributions of Ca and P expanded over the bone matrix, whereas that of C became localised and complemented that of C and P. The Ca/P concentration ratio increased, whereas the C/Ca and C/P ratios decreased in the healing bone matrix.

CONCLUSION

Healing bone is immaturely calcified initially and proceeds calcification gradually, that is, as the bone volume increases, mineral increases in density and matures in quality, while organic components decrease.

The effects of implant topography on osseointegration under estrogen deficiency induced osteoporotic conditions: Histomorphometric, transcriptional and ultrastructural analysis

Compromised bone quality and/or healing in osteoporosis are recognised risk factors for impaired dental implant osseointegration. This study examined the effects of (1) experimentally induced osteoporosis on titanium implant osseointegration and (2) the effect of modified implant surface topography on osseointegration under osteoporosis-like conditions. Machined and micro-roughened surface implants were placed into the maxillary first molar root socket of 64 ovariectomised and sham-operated Sprague-Dawley rats. Subsequent histological and SEM observations showed tissue maturation on the micro-rough surfaced implants in ovariectomised animals as early as 3days post-implantation. The degree of osseointegration was also significantly higher around the micro-rough implants in ovariectomised animals after 14days of healing although by day 28, similar levels of osseointegration were found for all test groups. The micro-rough implants significantly increased the early (day 3) gene expression of alkaline phosphatase, osteocalcin, receptor activator of nuclear factor kappa-B ligand and dentin matrix protein 1 in implant adherent cells. By day 7, the expression of inflammatory genes decreased while the expression of the osteogenic markers increased further although there were few statistically significant differences between the micro-rough and machined surfaces. Osteocyte morphology was also affected by estrogen deficiency with the size of the cells being reduced in trabecular bone. In conclusion, estrogen deficiency induced osteoporotic conditions negatively influenced the early osseointegration of machined implants while micro-rough implants compensated for these deleterious effects by enhancing osteogenic cell differentiation on the implant surface.

STATEMENT OF SIGNIFICANCE

Lower bone density, poor bone quality and osseous microstructural changes are all features characteristic of osteoporosis that may impair the osseointegration of dental implants. Using a clinically relevant trabecular bone model in the rat maxilla, we demonstrated histologically that the negative effects of surgically-induced osteoporosis on osseointegration could be ameliorated by the biomaterial's surface topography. Furthermore, gene expression analysis suggests this may be a result of enhanced osteogenic cell differentiation on the implant surface.

Ultrastructural and developmental features of the tessellated endoskeleton of elasmobranchs (sharks and rays)

The endoskeleton of elasmobranchs (sharks and rays) is comprised largely of unmineralized cartilage, differing fundamentally from the bony skeletons of other vertebrates. Elasmobranch skeletons are further distinguished by a tessellated surface mineralization, a layer of minute, polygonal, mineralized tiles called tesserae. This 'tessellation' has defined the elasmobranch group for more than 400 million years, yet the limited data on development and ultrastructure of elasmobranch skeletons (e.g. how tesserae change in shape and mineral density with age) have restricted our abilities to develop hypotheses for tessellated cartilage growth. Using high-resolution, two-dimensional and three-dimensional materials and structural characterization techniques, we investigate an ontogenetic series of tessellated cartilage from round stingray Urobatis halleri, allowing us to define a series of distinct phases for skeletal mineralization and previously unrecognized features of tesseral anatomy. We show that the distinct tiled morphology of elasmobranch calcified cartilage is established early in U. halleri development, with tesserae forming first in histotroph embryos as isolated, globular islets of mineralized tissue. By the sub-adult stage, tesserae have increased in size and grown into contact with one another. The intertesseral contact results in the formation of more geometric (straight-edged) tesseral shapes and the development of two important features of tesseral anatomy, which we describe here for the first time. The first, the intertesseral joint, where neighboring tesserae abut without appreciable overlapping or interlocking, is far more complex than previously realized, comprised of a convoluted bearing surface surrounded by areas of fibrous attachment. The second, tesseral spokes, are lamellated, high-mineral density features radiating outward, like spokes on a wheel, from the center of each tessera to its joints with its neighbors, likely acting as structural reinforcements of the articulations between tesserae. As tesserae increase in size during ontogeny, spokes are lengthened via the addition of new lamellae, resulting in a visually striking mineralization pattern in the larger tesserae of older adult skeletons when viewed with scanning electron microscopy (SEM) in backscatter mode. Backscatter SEM also revealed that the cell lacunae in the center of larger tesserae are often filled with high mineral density material, suggesting that when intratesseral cells die, cell-regulated inhibition of mineralization is interrupted. Many of the defining ultrastructural details we describe relate to local variation in tissue mineral density and support previously proposed accretive growth mechanisms for tesserae. High-resolution micro-computed tomography data indicate that some tesseral anatomical features we describe for U. halleri are common among species of all major elasmobranch groups despite large variation in tesseral shape and size. We discuss hypotheses about how these features develop, and compare them with other vertebrate skeletal tissue types and their growth mechanisms.

Tissue-Level Mechanical Properties of Bone Contributing to Fracture Risk

Tissue-level mechanical properties characterize mechanical behavior independently of microscopic porosity. Specifically, quasi-static nanoindentation provides measurements of modulus (stiffness) and hardness (resistance to yielding) of tissue at the length scale of the lamella, while dynamic nanoindentation assesses time-dependent behavior in the form of storage modulus (stiffness), loss modulus (dampening), and loss factor (ratio of the two). While these properties are useful in establishing how a gene, signaling pathway, or disease of interest affects bone tissue, they generally do not vary with aging after skeletal maturation or with osteoporosis. Heterogeneity in tissue-level mechanical properties or in compositional properties may contribute to fracture risk, but a consensus on whether the contribution is negative or positive has not emerged. In vivo indentation of bone tissue is now possible, and the mechanical resistance to microindentation has the potential for improving fracture risk assessment, though determinants are currently unknown.

Understanding the pathogenesis of hip fracture in the elderly, osteoporotic theory is not reflected in the outcome of prevention programmes

Hip fractures are an acute and worsening public health problem. They mainly affect elderly people, a population group that is highly vulnerable to disease and accidents, and to falls in particular. Although it has been suggested that osteoporosis is the cause of hip fractures, they mainly occur after a fall has been suffered. The underlying causes of a fall are not related to osteoporosis, although pharmaceutical companies have coined the term “osteoporotic fracture” for hip fractures in the elderly. Drug treatments for osteoporosis have not diminished the frequency of these injuries, nor have they prevented the occurrence of a subsequent fracture. Since pharmaceutical interests require osteoporosis to be considered a disease, rather than a normal condition of senescence, they go further by assuming that treatment for osteoporosis is essential, and that this policy will diminish the incidence of hip fractures. On the other hand, the origin and treatment of conditions that may be conducive to provoking falls are very difficult to elucidate. In this paper, we consider some of the medical and social problems that arise in this area, as well as conflicts of interest regarding the aetiopathogenesis and prevention of hip fracture, and propose a new paradigm for the prevention of falls.