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

A Machine Learning-Based Image Segmentation Method to Quantify In Vitro Osteoclast Culture Endpoints

Quantification of in vitro osteoclast cultures (e.g. cell number) often relies on manual counting methods. These approaches are labour intensive, time consuming and result in substantial inter- and intra-user variability. This study aimed to develop and validate an automated workflow to robustly quantify in vitro osteoclast cultures. Using ilastik, a machine learning-based image analysis software, images of tartrate resistant acid phosphatase-stained mouse osteoclasts cultured on dentine discs were used to train the ilastik-based algorithm. Assessment of algorithm training showed that osteoclast numbers strongly correlated between manual- and automatically quantified values (r = 0.87). Osteoclasts were consistently faithfully segmented by the model when visually compared to the original reflective light images. The ability of this method to detect changes in osteoclast number in response to different treatments was validated using zoledronate, ticagrelor, and co-culture with MCF7 breast cancer cells. Manual and automated counting methods detected a 70% reduction (p < 0.05) in osteoclast number, when cultured with 10 nM zoledronate and a dose-dependent decrease with 1-10 μM ticagrelor (p < 0.05). Co-culture with MCF7 cells increased osteoclast number by ≥ 50% irrespective of quantification method. Overall, an automated image segmentation and analysis workflow, which consistently and sensitively identified in vitro osteoclasts, was developed. Advantages of this workflow are (1) significantly reduction in user variability of endpoint measurements (93%) and analysis time (80%); (2) detection of osteoclasts cultured on different substrates from different species; and (3) easy to use and freely available to use along with tutorial resources.

Weekly teriparatide treatment increases vertebral body strength by improving cortical shell architecture in ovariectomized cynomolgus monkeys

Weekly teriparatide treatment is reported to reduce the incidence of osteoporotic vertebral fractures. However, the effect of weekly teriparatide on cortical bone has not been clarified. This study aimed to examine the effects of weekly teriparatide treatment on bone mass, intracortical structure, and remodeling of the lumbar vertebral cortical shell and its relation to mechanical properties in ovariectomized cynomolgus monkeys. Female monkeys, aged 9 to 15 years, were divided into four groups: (1) SHAM group, (2) ovariectomized group (OVX group), (3) OVX with 1.2 μg/kg once-weekly teriparatide group (LOW group), (4) OVX with 6.0 μg/kg once-weekly teriparatide group (HIGH group). After 18 months, all animals were double-labeled with calcein, and lumbar vertebrae were analyzed with histomorphometry and compressive mechanical tests. Following ovariectomy, we found reductions in the anterior cortical shell area of the vertebrae and reductions in nearly all of the tested vertebral mechanical properties. Weekly teriparatide significantly preserved the anterior cortical shell area and the energy absorption capacity of the lumbar vertebrae in a dose-dependent manner. Multiple regression analyses indicated that improved mechanical properties were more associated with the increased anterior cortical shell area rather than the cancellous bone volume. The intracortical structure of the Haversian canals was also preserved following teriparatide treatment after ovariectomy. These findings suggest the importance of the cortical shell as a therapeutic target in the treatment of osteoporosis. Weekly teriparatide treatment increases the compressive mechanical strength of the lumbar vertebrae by thickening the anterior cortical shell.

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.

Open source software for semi-automated histomorphometry of bone resorption and formation parameters

Micro-CT analysis has become the standard method for assessing bone volume and architecture in small animals. However, micro-CT does not allow the assessment of bone turnover parameters such as bone formation rate and osteoclast (OC) number and surface. For these crucial variables histomorphometric analysis is still an essential technique. Histomorphometry however, is time consuming and, especially in mouse bones, OCs can be difficult to detect. The main purpose of this study was to develop and validate a relatively easy and rapid method to measure static and dynamic bone histomorphometry parameters. Here we present the adaptation of established staining protocols and three novel open source image analysis packages: TrapHisto, OsteoidHisto and CalceinHisto that allow rapid, semi-automated analysis of histomorphometric bone resorption, osteoid, and calcein double labelling parameters respectively. These three programs are based on ImageJ, but use a relatively simple user interface that hides the underlying complexity of the image analysis.

Iliac crest histomorphometry and skeletal heterogeneity in men

Purpose

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

Methods

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

Results

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

Conclusions

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

•

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

•

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

•

The cortical microarchitecture is highly variable between different skeletal sites.

•

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

Cortical bone histomorphometry in male femoral neck: the investigation of age-association and regional differences

Low bone volume and changes in bone quality or microarchitecture may predispose individuals to fragility fractures. As the dominant component of the human skeleton, cortical bone plays a key role in protecting bones from fracture. However, histological investigations of the underlying structural changes, which might predispose to fracture, have been largely limited to the cancellous bone. The aim of this study was to investigate the age-association and regional differences of histomorphometric properties in the femoral neck cortical bone. Undecalcified histological sections of the femoral neck (n = 20, aged 18-82 years, males) were cut (15 μm) and stained using modified Masson-Goldner stain. Complete femoral neck images were scanned, and cortical bone boundaries were defined using our previously established method. Cortical bone histomorphometry was performed with low (×50) and high magnification (×100). Most parameters related to cortical width (Mean Ct.Wi, Inferior Ct.Wi, Superior Ct.Wi) were negatively associated with age both before and after adjustment for height. The inferior cortex was the thickest (P < 0.001) and the superior cortex was the thinnest (P < 0.008) of all cortical regions. Both osteonal size and pores area were negatively associated with age. Osteonal area and number were higher in the antero-inferior area (P < 0.002) and infero-posterior area (P = 0.002) compared to the postero-superior area. The Haversian canal area was higher in the infero-posterior area compared to the postero-superior area (P = 0.002). Moreover, porosity was higher in the antero-superior area (P < 0.002), supero-anterior area (P < 0.002) and supero-posterior area (P < 0.002) compared to the infero-anterior area. Eroded endocortical perimeter (E.Pm/Ec.Pm) correlated positively with superior cortical width. This study describes the changes in cortical bone during ageing in healthy males. Further studies are needed to investigate whether these changes explain the increased susceptibility to femoral neck fractures.