The ratio of osteocytic incorporation to bone matrix formation in femoral neck cancellous bone: an enhanced osteoblast work rate in the vicinity of hip osteoarthritis

Quantification of the bone lacunocanalicular network from 3D X-ray phase nanotomography images

There is a growing interest in developing 3D microscopy for the exploration of thick biological tissues. Recently, 3D X-ray nanocomputerised tomography has proven to be a suitable technique for imaging the bone lacunocanalicular network. This interconnected structure is hosting the osteocytes which play a major role in maintaining bone quality through remodelling processes. 3D images have the potential to reveal the architecture of cellular networks, but their quantitative analysis remains a challenge due to the density and complexity of nanometre sized structures and the need to handle and process large datasets, for example, 2048³ voxels corresponding to 32 GB per individual image in our case. In this work, we propose an efficient image processing approach for the segmentation of the network and the extraction of characteristic parameters describing the 3D structure. These parameters include the density of lacunae, the porosity of lacunae and canaliculi, and morphological features of lacunae (volume, surface area, lengths, anisotropy etc.). We also introduce additional parameters describing the local environment of each lacuna and its canaliculi. The method is applied to analyse eight human femoral cortical bone samples imaged by magnified X-ray phase nanotomography with a voxel size of 120 nm, which was found to be a good compromise to resolve canaliculi while keeping a sufficiently large field of view of 246 μm in 3D. The analysis was performed on a total of 2077 lacunae showing an average length, width and depth of 17.1 μm × 9.2 μm × 4.4 μm, with an average number of 58.2 canaliculi per lacuna and a total lacuno-canalicular porosity of 1.12%. The reported descriptive parameters provide information on the 3D organisation of the lacuno-canalicular network in human bones.

Requirement of TGFβ Signaling for Effect of Fluoride on Osteoblastic Differentiation

Research focused on transforming growth factor β (TGFβ) signaling in osteoblast is gradually increasing, whereas literature is rare in terms of fluorosis. This work aimed to investigate how TGFβ signaling participated in regulation of the osteoblast by different doses of fluoride treatment. Bone marrow stem cells (BMSCs) were developed into osteoblastic cells and exposed to 1, 4, and 16 mg/L F^- with and without 10 ng/mL of TGFβ. Cell viability and differentiation state of osteoblast under different settings were measured by means of cell counting kit and analysis of alkaline phosphatase (ALP) activity as well as formation of mineral nodules. Real-time PCR was utilized to test expression of ALP and Runt-related transcription factor 2 (Runx2) at gene level. The gene expression of TGFβ signaling effectors was also investigated, such as TGFβ receptors (TβRs), smad3, and mitogen-activated protein kinases (MAPK). Results demonstrated that fluoride treatment exhibited action on osteoblast viability and osteogenic differentiation and upregulated expression of TβR2, smad3, and MAPK in this process. Administration of TGFβ strengthened ALP activity but attenuated formation of mineral nodules. Co-treatment of TGFβ and low-dose fluoride increased ALP activity compared to same dose of single fluoride treatment, whereas it inhibited mineral nodule formation. Administration of TGFβ reversed the suppression of high-dose fluoride on osteogenic differentiation of BMSCs. Taken together, studies revealed that TβR2 acted as a target for fluoride and TGFβ treatment on BMSCs, and smad3 and MAPK were involved in the mechanism of fluoride regulating osteogenic differentiation. Together, our data indicated that TGFβ receptor-mediated signaling through smad3 and MAPK was required for modulation of fluoride on osteoblast viability and differentiation, and activating TβR2-smad3 signaling pathway reversed suppression of osteoblasts differentiation by high dose of fluoride treatment.

Increased detection of genetic loci associated with risk predictors of osteoporotic fracture using a pleiotropic cFDR method

Although GWAS have been successful in identifying some osteoporosis associated loci, the findings explain only a small fraction of the total genetic variance. In this study we use a recently developed novel pleiotropic conditional false discovery rate (cFDR) method to identify novel genetic loci associated with two risk traits for osteoporotic fracture (the clinical outcome and end result of osteoporosis), Height (HT) and Femoral Neck (FNK) BMD. The cFDR method allows us to improve the detection of associated variants by incorporating any potentially shared genetic mechanisms between the two associated traits. We analyzed the summary statistics from two GWAS meta-analyses for single nucleotide polymorphisms (SNPs) that are associated with HT and FNK BMD. Using the cFDR method, we show enrichment in the identification of SNPs associated with each trait conditioned on their strength of association with the second trait. The findings revealed 18 SNPs that are associated with both HT and FNK BMD, 4 of which had not previously been reported to play a role in bone health. The novel SNPs located at KIF1B and the intergenic region between FERD3L and TWISTNB are noteworthy as these genes may be associated with processes that are functionally important in bone metabolism. By leveraging GWAS results from related phenotypes we identified several novel loci that may contribute to the proportion of variability explained for each trait, although we cannot speculate about these potential contributions to heritability based on this analysis alone.

Histological and molecular characterisation of feline humeral condylar osteoarthritis

Background

Osteoarthritis (OA) is a clinically important and common disease of older cats. The pathological changes and molecular mechanisms which underpin the disease have yet to be described. In this study we evaluated selected histological and transcriptomic measures in the articular cartilage and subchondral bone (SCB) of the humeral condyle of cats with or without OA.

Results

The histomorphometric changes in humeral condyle were concentrated in the medial aspect of the condyle. Cats with OA had a reduction in articular chondrocyte density, an increase in the histopathological score of the articular cartilage and a decrease in the SCB porosity of the medial part of the humeral condyle. An increase in LUM gene expression was observed in OA cartilage from the medial part of the humeral condyle.

Conclusions

Histopathological changes identified in OA of the feline humeral condyle appear to primarily affect the medial aspect of the joint. Histological changes suggest that SCB is involved in the OA process in cats. Differentiating which changes represent OA rather than the aging process, or the effects of obesity and or bodyweight requires further investigation.

Variation in osteocyte lacunar morphology and density in the human femur--a synchrotron radiation micro-CT study

In recent years there has been growing interest in the spatial properties of osteocytes (including density and morphology) and how these potentially relate to adaptation, disease and aging. This interest has, in part, arisen from the availability of increasingly high-resolution 3D imaging modalities such as synchrotron radiation (SR) micro-CT. As resolution increases, field of view generally decreases. Thus, while increasingly detailed spatial information is obtained, it is unclear how representative this information is of the skeleton or even the isolated bone. The purpose of this research was to describe the variation in osteocyte lacunar density, morphology and orientation within the femur from a healthy young male human. Multiple anterior, posterior, medial and lateral blocks (2 mm × 2 mm) were prepared from the proximal femoral shaft and SR micro-CT imaged at the Advanced Photon Source. Average lacunar densities (± standard deviation) from the anterior, posterior, medial and lateral regions were 27,169 ± 1935, 26,3643 ± 1262, 37,521 ± 6416 and 33,972 ± 2513 lacunae per mm(3) of bone tissue, respectively. These values were significantly different between the medial and both the anterior and posterior regions (p<0.05). The density of the combined anterior and posterior regions was also significantly lower (p=0.001) than the density of the combined medial and lateral regions. Although no difference was found in predominant orientation, shape differences were found; with the combined anterior and posterior regions having more elongated (p=0.004) and flattened (p=0.045) lacunae, than those of the medial and lateral regions. This study reveals variation in osteocyte lacunar density and morphology within the cross-section of a single bone and that this variation can be considerable (up to 30% difference in density between regions). The underlying functional significance of the observed variation in lacunar density likely relates to localized variations in loading conditions as the pattern corresponds well with mechanical axes. Lower density and more elongate shapes being associated with the antero-posterior oriented neutral axis. Our findings demonstrate that the functional and pathological interpretations that are increasingly being drawn from high resolution imaging of osteocyte lacunae need to be better situated within the broader context of normal variation, including that which occurs even within a single skeletal element.

Osteocyte recruitment declines as the osteon fills in: interacting effects of osteocytic sclerostin and previous hip fracture on the size of cortical canals in the femoral neck

There is little information on the distribution of osteocytes within the individual cortical osteon, but using direct 3-D imaging in a single subject, Hannah et al. found a gradient with a two-fold higher density of cells adjacent to the cement line compared to near the canal. Since a limiting factor for bone formation might be the availability of osteoblasts due to their recruitment as osteocytes, we studied distributions of osteonal osteocytes in frozen sections of the femoral neck cortex. Osteocytes were stained with an anti-sclerostin antibody and counter-stained with toluidine blue. Adjacent sections were stained for alkaline phosphatase (ALP). Each osteonal osteocyte was categorised as being sclerostin-positive (scl+) or negative (scl-). ImageJ was used to measure the perimeter and area of each osteon and canal, while special purpose routines were used to measure the minimum distances of each osteocyte from the cement line and the canal. Canal area was strongly correlated with osteon area. Osteocytes were most dense close to the cement line; and their areal density within the matrix declined up to three-fold between the cement line and the canal, depending on osteon diameter. Large and small osteons had similar densities of osteocytes close to the cement line, but fractured neck of femur cases had significantly lower densities of osteocytes close to the canal. Higher osteocyte density close to the canal was associated with ALP expression. It is concluded that entombment of osteocytes newly drawn from the osteoblast pool into the mineralising matrix is independent of preceding bone resorption depth. As osteonal infilling proceeds, osteocyte formation declines more rapidly than matrix formation, leading to a progressive reduction in osteocyte density. A shrinking supply of precursor osteoblasts due to previous osteocyte recruitment, apoptosis, or both could produce this effect. In a statistically significant contrast, sclerostin negative osteocytes adjacent to the canal had the expected effect of reducing canal size in controls but this was not seen in hip fracture. This demonstrated the failure of osteonal osteoblasts to sustain bone formation through a complete remodelling cycle in osteoporosis, perhaps due to insufficient osteoblasts remaining capable of mineralized matrix formation. The failure of osteocytic sclerostin suppression to associate with bone formation in these osteons might alternatively be explained by downstream interference with sclerostin's effect on wnt signalling.

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

Hypermineralized osteocyte lacunae (micropetrosis) have received little research attention. While they are a known aspect of the aging human skeleton, no data are available for pathological bone. In this study, intertrochanteric trabecular bone cores were obtained from patients at surgery for osteoporotic (OP) femoral neck fracture (10F, 4M, 65-94 years), for hip osteoarthritis (OA; 7F, 8M, 62-87 years), and femora at autopsy (CTL; 5F, 11M, 60-84 years). Vertebral trabecular bone cores were also obtained from the vertebra of autopsy cases (CVB; 3F, 6M, 53-83 years). Specimens were resin-embedded, polished, and carbon coated for quantitative backscattered electron imaging (qBEI), energy dispersive X-ray (EDX) spectrometry, and imaging analysis. Bone mineralization (Wt %Ca) was not different between OP, OA, and CTL; but was greater in femoral CTL than in CVB. The percent of hypermineralized osteocyte lacunae relative to the total number (HL/TL) was greater in OP and OA than in CTL. However, relative to bone mineral area, OP was characterised by increased hypermineralized osteocyte lacunar number density (Hd.Lc.Dn), whereas OA was characterised by decreased osteocyte lacunar number density (Lc.Dn) and total osteocyte lacunar number density (Tt.Lc.Dn). Lc.Dn was higher in CVB than in femoral CTL. The calcium-phosphorus ratio (R(Ca/P)) was not different between hypermineralized osteocyte lacunae and bone matrix in each group. In addition, this study focused on the phenomenon of osteocyte lacunae hypermineralization using qBEI. Seven morphological types of osteocyte lacunae hypermineralization were described according to the presence of one or several hypermineralized spherites, associated or not with a hypermineralized lacunar ring. This study has described, for the first time, the morphology of hypermineralized osteocyte lacunae in OP and OA human bone. Further studies are suggested to investigate the functional influence of hypermineralized osteocyte lacunae on bone remodeling and bone biomechanical properties.

Ultrastructural properties in cortical bone vary greatly in two inbred strains of mice as assessed by synchrotron light based micro- and nano-CT

Nondestructive SR-based microCT and nano-CT methods have been designed for 3D quantification and morphometric analysis of ultrastructural phenotypes within murine cortical bone, namely the canal network and the osteocyte lacunar system. Results in two different mouse strains, C57BL/6J-Ghrhr(lit)/J and C3.B6-Ghrhr(lit)/J, showed that the cannular and lacunar morphometry and their bone mechanics were fundamentally different.

INTRODUCTION

To describe the different aspects of bone quality, we followed a hierarchical approach and assessed bone tissue properties in different regimens of spatial resolution, beginning at the organ level and going down to cellular dimensions. For these purposes, we developed different synchrotron radiation (SR)-based CT methods to assess ultrastructural phenotypes of murine bone.

MATERIALS AND METHODS

The femoral mid-diaphyses of 12 C57BL/6J-Ghrhr(lit)/J (B6-lit/lit) and 12 homozygous mutants C3.B6-Ghrhr(lit)/J (C3.B6-lit/lit) were measured with global SR microCT and local SR nano-CT (nCT) at nominal resolutions ranging from 3.5 microm to 700 nm, respectively. For volumetric quantification, morphometric indices were determined for the cortical bone, the canal network, and the osteocyte lacunar system using negative imaging. Moreover, the biomechanics of B6-lit/lit and C3.B6-lit/lit mice was determined by three-point bending.

RESULTS

The femoral mid-diaphysis of C3.B6-lit/lit was larger compared with B6-lit/lit mice. On an ultrastructural level, the cannular indices for C3.B6-lit/lit were generally bigger in comparison with B6-lit/lit mice. Accordingly, we derived and showed a scaling rule, saying that overall cannular indices scaled with bone size, whereas indices describing basic elements of cannular and lacunar morphometry did not. Although in C3.B6-lit/lit, the mean canal volume was larger than in B6-lit/lit, canal number density was proportionally smaller in C3.B6-lit/lit, so that lacuna volume density was found to be constant and therefore independent of mouse strain and sex. The mechanical properties in C3.B6-lit/lit were generally improved compared with B6-lit/lit specimens. For C3.B6-lit/lit, we observed a sex specificity of the mechanical parameters, which could not be explained by bone morphometry on an organ level. However, there is evidence that for C3.B6-lit/lit, the larger cortical bone mass is counterbalanced or even outweighed by the larger canal network in the female mice.

CONCLUSIONS

We established a strategy to subdivide murine intracortical porosity into ultrastructural phenotypes, namely the canal network and the osteocyte lacunar system. Nondestructive global and local SR-based CT methods have been designed for 3D quantification and subsequent morphometric analysis of these phenotypes. Results in the two different mouse strains C57BL/6J-Ghrhr(lit)/J and C3.B6-Ghrhr(lit)/J showed that the cannular and lacunar morphometry and the biomechanical properties were fundamentally different.

Differences in osteocyte density and bone histomorphometry between men and women and between healthy and osteoporotic subjects

Bone defects related to osteoporosis develop with increasing age and differ between males and females. It is currently thought that the bone remodeling process is supervised by osteocytes in a strain-dependent manner. We have shown an altered response of osteocytes from osteoporotic patients to mechanical loading, and osteocyte density is reduced in osteoporotic patients, which might relate to imperfect bone remodeling, leading to lack of bone mass and strength. Hence, information on osteocyte density will contribute to a better understanding of bone biology in males and females and to the assessment of osteoporosis. Osteocyte density as well as conventional histomorphometric parameters of trabecular bone were determined in cancellous iliac crest bone of healthy postmenopausal women and men and of osteoporotic women and men. Osteocyte density was higher in healthy females than in healthy males and lower in osteoporotic females than in healthy females. Bone mass was reduced in osteoporotic patients, both male and female. In females, trabecular number was reduced, whereas in males, trabecular thickness was reduced and eroded surface was increased. There were no correlations between the parameter groups bone architecture, bone formation, bone resorption, and osteocyte density. These results are consistent with impaired osteoblast function in osteoporotic patients and with a different mechanism of bone loss between men and women, in which osteocyte density might play a role. The reduced osteocyte numbers in female osteoporotic patients might relate to imperfect bone remodeling leading to lack of bone mass and strength.

Osteoclastic cortical erosion as a determinant of subperiosteal osteoblastic bone formation in the femoral neck's response to BMU imbalance. Effects of stance-related loading and hip fracture

Femoral neck fractures have previously been shown to be associated with increased cortical and endocortical remodeling, reduced wall thickness of endocortical packets and cortical porosity. Femoral neck width is associated positively with history of lifetime physical activity; so we hypothesized that exposure to mechanical loading may influence the subperiosteal osteoblastic response to the weakening effect of intracortical bone resorption. In 21 femoral neck biopsies from female subjects (13 with hip fracture), there was a positive association between osteoblastic periosteal alkaline phosphatase expression shown in frozen sections and the percentage of cortical canals internal to the subperiosteal surface showing evidence of osteoclastic erosion (Goldner's stain; p =0.03). This was stronger in the plane of locomotor loading and particularly strong in the inferior (compression) cortex ( p =0.002). In 35 cases and 23 age/gender-matched postmortem controls, osteoid-bearing cortical canals (%) were significantly elevated in the fracture cases compared with the controls within the anterior region. There was also a significant correlation between cortical and endocortical %OS/BS (percentage osteoid surface to bone surface) (fracture, n =12; control, n =12) over the whole biopsy ( p =0.041). Generally, these associations of intracortical with endocortical remodeling were consistent with both envelopes being regulated by common processes. These results support the concept that the slow growth of femoral neck width by subperiosteal apposition of bone occurs directly or, otherwise, in response to the weakening of the cortex as it is "trabecularized" by imbalance of bone multicellular units (BMU). This process, in turn, depends on cortical thinning and enlargement of canals with the formation of giant, composite osteons, the whole being more marked in cases of future hip fracture.

Sexual dimorphism and age dependence of osteocyte lacunar density for human vertebral cancellous bone

The sexual dimorphism in age-related loss of human vertebral cancellous bone is not fully understood and could be related to dimorphism in the bone cell populations. The objective of this study was to investigate age- and gender-related differences in the osteocyte population and its relationship with bone volume fraction for human vertebral cancellous bone. Histomorphometric techniques were used to quantify osteocyte lacunae (a measure of osteocyte population) and bone volume fraction in male and female human T12 vertebrae, the most common site of vertebral fracture. Two measures of osteocyte population [number of osteocytes per bone area (OtLcDn) and number of osteocytes per total area (OtLcN/TA)] and their relationships with age and bone volume fraction were found to be sexually dimorphic. Dimorphism in osteocyte density may explain the dimorphic patterns of bone loss in human vertebrae due to the sensory and signal communication functions that osteocytes perform.

Buried alive: How osteoblasts become osteocytes

During osteogenesis, osteoblasts lay down osteoid and transform into osteocytes embedded in mineralized bone matrix. Despite the fact that osteocytes are the most abundant cellular component of bone, little is known about the process of osteoblast-to-osteocyte transformation. What is known is that osteoblasts undergo a number of changes during this transformation, yet retain their connections to preosteoblasts and osteocytes. This review explores the osteoblast-to-osteocyte transformation during intramembranous ossification from both morphological and molecular perspectives. We investigate how these data support five schemes that describe how an osteoblast could become entrapped in the bone matrix (in mammals) and suggest one of the five scenarios that best fits as a model. Those osteoblasts on the bone surface that are destined for burial and destined to become osteocytes slow down matrix production compared to neighbouring osteoblasts, which continue to produce bone matrix. That is, cells that continue to produce matrix actively bury cells producing less or no new bone matrix (passive burial). We summarize which morphological and molecular changes could be used as characters (or markers) to follow the transformation process.

Matrix metalloproteinases (MMPs) safeguard osteoblasts from apoptosis during transdifferentiation into osteocytes: MT1-MMP maintains osteocyte viability

Osteoblasts undergo apoptosis or differentiate into either osteocytes or bone-lining cells after termination of bone matrix synthesis. In this study, we investigated the role of matrix metalloproteinases (MMPs) in differentiation of osteoblasts, bone formation, transdifferentiation into osteocytes, and osteocyte apoptosis. This was accomplished by using calvarial sections from the MT1-MMP-deficient mouse and by culture of the mouse osteoblast cell line MC3T3-E1 and primary mouse calvarial osteoblasts. We found that a synthetic matrix metalloprotease inhibitor, GM6001, strongly inhibited bone formation in vitro of both primary osteoblasts and MC3T3 cells by approximately 75%. To further investigate at which level of osteoblast differentiation MMP inhibition was attenuating osteoblast function, we found that neither preosteoblast nor mature osteoblast activity was affected. In contrast, cell survival of osteoblasts forced to transdifferentiate into osteocytes in 3D type I collagen gels were inhibited by more than 50% when exposed to 10 microM GM6001 and to Tissue Inhibitor of Metalloproteinase-2 (TIMP-2), a natural MT1-MMP inhibitor. This shows the importance of MMPs in safeguarding osteoblasts from apoptosis when transdifferentiating into osteocytes. By examination of osteoblasts and osteocytes embedded in calvarial bone in the MT1-MMP deficient mice, we found that MT1-MMP deficient mice had 10-fold higher levels of apoptotic osteocytes than wild-type controls. We have previously shown that MT1-MMP activates latent Transforming Growth Factorbeta (TGF-beta). These findings strongly suggest that MT1-MMP-activated TGF-beta maintains osteoblast survival during transdifferentiation into osteocytes, and maintains mature osteocyte viability. Thus, the interrelationship of MMPs and TGF-beta may play an important role in bone formation and maintenance.

Osteoarthritis and osteoporosis: clinical and research evidence of inverse relationship

The etiology of osteoporosis (OP) and osteoarthritis (OA) is multifactorial: both constitutional and environmental factors, ranging from genetic susceptibility, endocrine and metabolic status, to mechanical and traumatic injury, are thought to be involved. When interpreting research data, one must bear in mind that pathophysiologic factors, especially in disorders associated with aging, must be regarded as either primary or secondary. Therefore, findings in end-stage pathology are not necessarily the evidence or explanation of the primary cause or event in the diseased tissue. Both aspects of research are important for potentially curative or preventive measures. These considerations, in the case of our topic--the inverse relationship of OP and OA--are of particular importance. Although the inverse relationship between two frequent diseases associated with aging, OA and OP, has been observed and studied for more than 30 years, the topic remains controversial for some and stimulating for many. The anthropometric differences of patients suffering from OA compared with OP are well established. OA cases have stronger body build and are more obese. There is overwhelming evidence that OA cases have increased BMD or BMC at all sites. This increased BMD is related to high peak bone mass, as shown in mother-daughter and twin studies. With aging, the bone loss in OA is lower, except when measured near an affected joint (hand, hip, knee). The lower degree of bone loss with aging is explained by lower bone turnover as measured by bone resorption-formation parameters. OA cases not only have higher apparent and real bone density, but also wider geometrical measures of the skeleton, diameters of long bones and trabeculae, both contributing positively to better strength and fewer fragility fractures. Not only is bone quantity in OA different but also bone quality, compared with controls and OP cases, with increased content of growth factors such as IGF and TGFbeta, factors required for bone repair. Furthermore, in vitro studies of osteoblasts recruited from OA bone have different differentiation patterns and phenotypes. These general bone characteristics of OA bone may explain the inverse relationship OA-OP and why OA cases have fewer fragility fractures. The role of bone, in particular subchondral bone, in the pathophysiology, initiation and progression of OA is not fully elucidated and is still controversial. In 1970, it was hypothesized that an increased number of microfractures lead to an increase in subchondral bone stiffness, which impairs its ability to act as a shock absorber, so that cartilage suffers more. Although subchondral bone is slightly hypomineralized because of local increased turnover, the increase in trabecular number and volume compensates for this, resulting in a stiffer structure. There is also some experimental evidence that osteoblasts themselves release factors such as metalloproteinases directly or indirectly from the matrix, which predispose cartilage to deterioration. Instead, the osteoblast regenerative capacity of bone in OP is compromised compared with OA, as suggested by early cell adhesion differences. The proposition that drugs which suppress bone turnover in OP, such as bisphosphonates, may be beneficial for OA is speculative. Although bone turnover in the subchondral region of established OA is increased, the general bone turnover is reduced. Further reduction of bone turnover, however, may lead to overmineralized (aged) osteons and loss of bone quality, resulting in increased fragility.

Increased cancellous bone in the femoral neck of patients with coxarthrosis (hip osteoarthritis): a positive remodeling imbalance favoring bone formation

Osteoporosis is caused by an imbalance between bone resorption and formation which results in an absolute reduction in bone mass. In a previous study we highlighted a condition, osteoarthritis of the hip (coxarthrosis, cOA), where an imbalance between resorption and formation provided beneficial effects in the form of an absolute increase in bone mass. We demonstrated that the femoral neck in patients with cOA had increased cancellous bone area, connectivity and trabecular thickness which might contribute to the protection against fracture associated with the condition. The aim of the present study was to analyze forming and resorbing surfaces in coxarthritic cancellous bone to assess whether increased formation or reduced resorption could be responsible for these structural changes. Whole cross-sectional femoral neck biopsies were obtained from 11 patients with cOA and histomorphometric parameters compared with 14 age- and sex-matched cadaveric controls. The ratio of osteoid surface to bone surface was 121% ( p<0.001) higher in the cases but there was no significant difference in resorptive surface. The percentage osteoid volume to bone volume (%OV/BV; +270%, p<0.001) and osteoid width (O.Wi; +127%, p<0.001) were also higher in the cases. This study suggests that the increased cancellous bone mass seen in cases of cOA is due to increased bone formation rather than decreased bone resorption. Investigation of the cellular and biochemical basis for these changes might provide new insights into the pathogenesis of osteoarthritis and highlight novel biological mechanisms regulating bone multicellular unit (BMU) balance that could be relevant to developing new interventions against hip and other osteoporotic fractures.