Fractal lacunarity of trabecular bone and magnetic resonance imaging: New perspectives for osteoporotic fracture risk assessment

Osteoporosis represents one major health condition for our growing elderly population. It accounts for severe morbidity and increased mortality in postmenopausal women and it is becoming an emerging health concern even in aging men. Screening of the population at risk for bone degeneration and treatment assessment of osteoporotic patients to prevent bone fragility fractures represent useful tools to improve quality of life in the elderly and to lighten the related socio-economic impact. Bone mineral density (BMD) estimate by means of dual-energy X-ray absorptiometry is normally used in clinical practice for osteoporosis diagnosis. Nevertheless, BMD alone does not represent a good predictor of fracture risk. From a clinical point of view, bone microarchitecture seems to be an intriguing aspect to characterize bone alteration patterns in aging and pathology. The widening into clinical practice of medical imaging techniques and the impressive advances in information technologies together with enhanced capacity of power calculation have promoted proliferation of new methods to assess changes of trabecular bone architecture (TBA) during aging and osteoporosis. Magnetic resonance imaging (MRI) has recently arisen as a useful tool to measure bone structure in vivo. In particular, high-resolution MRI techniques have introduced new perspectives for TBA characterization by non-invasive non-ionizing methods. However, texture analysis methods have not found favor with clinicians as they produce quite a few parameters whose interpretation is difficult. The introduction in biomedical field of paradigms, such as theory of complexity, chaos, and fractals, suggests new approaches and provides innovative tools to develop computerized methods that, by producing a limited number of parameters sensitive to pathology onset and progression, would speed up their application into clinical practice. Complexity of living beings and fractality of several physio-anatomic structures suggest fractal analysis as a promising approach to quantify morpho-functional changes in both aging and pathology. In this particular context, fractal lacunarity seems to be the proper tool to characterize TBA texture as it is able to describe both discontinuity of bone network and sizes of bone marrow spaces, whose changes are an index of bone fracture risk. In this paper, an original method of MRI texture analysis, based on TBA fractal lacunarity is described and discussed in the light of new perspectives for early diagnosis of osteoporotic fractures.

Bone Microstructure in Response to Vitamin D3 Supplementation: A Randomized Placebo-Controlled Trial

Vitamin D supplementation is often used in the prevention and treatment of osteoporosis, but the role of vitamin D has lately been questioned. We aimed to investigate the effect of 3 months of daily vitamin D3 supplementation (70 µg [2800 IU] vs. placebo) initiated in winter months on bone health. This study is a double-blinded placebo-controlled randomized trial. Bone health was assessed by bone turnover markers, DXA, HRpQCT, and QCT scans. The participants were 81 healthy postmenopausal women with low 25(OH)D (< 50 nmol/l) and high PTH levels (> 6.9 pmol/l) at screening. Vitamin D3 supplementation significantly increased levels of 25(OH)D and 1,25(OH)₂D by 59 nmol/l and 19 pmol/l, respectively, whereas PTH was reduced by 0.7 pmol/l (all p < 0.0001). Compared with placebo, vitamin D3 did not affect bone turnover markers, aBMD by DXA or trabecular bone score. Vitamin D3 increased trabecular vBMD (QCT scans) in the trochanter region (0.4 vs. - 0.7 g/cm³) and the femoral neck (2.1 vs. - 1.8 g/cm³) p_all < 0.05. HRpQCT scans of the distal tibia showed reduced trabecular number (- 0.03 vs. 0.05 mm^-1) and increased trabecular thickness (0.001 vs. - 0.005 mm), as well as an improved estimated bone strength as assessed by failure load (0.1 vs. - 0.1 kN), and stiffness (2.3 vs. - 3.1 kN/mm p_all ≤ 0.01). Changes in 25(OH)D correlated significantly with changes in trabecular thickness, stiffness, and failure load. Three months of vitamin D3 supplementation improved bone strength and trabecular thickness in tibia, vBMD in the trochanter and femoral neck, but did not affect aBMD.

Prediction of trabecular bone architectural features by deep learning models using simulated DXA images

Dual-energy X-ray absorptiometry (DXA) is widely used for clinical assessment of bone mineral density (BMD). Recent evidence shows that DXA images may also contain microstructural information of trabecular bones. However, no current image processing techniques could aptly extract the information. Inspired by the success of deep learning techniques in medical image analyses, we hypothesized in this study that DXA image-based deep learning models could predict the major microstructural features of trabecular bone with a reasonable accuracy. To test the hypothesis, 1249 trabecular cubes (6 mm × 6 mm × 6 mm) were digitally dissected out from the reconstruction of seven human cadaveric proximal femurs using microCT scans. From each cube, simulated DXA images in designated projections were generated, and the histomorphometric parameters (i.e., BV/TV, BS, Tb.Th, DA, Conn. D, and SMI) of the cube were determined using Image J. Convolutional neural network (CNN) models were trained using the simulated DXA images to predict the histomorphometric parameters of trabecular bone cubes. The results exhibited that the CNN models achieved high fidelity in predicting these histomorphometric parameters (from R = 0.80 to R = 0.985), showing that the DL models exhibited the capability of predicting the microstructural features using DXA images. This study also showed that the number and resolution of input simulated DXA images had considerable impacts on the prediction accuracy of the DL models. These findings support the hypothesis of this study and indicate a high potential of using DXA images in prediction of osteoporotic bone fracture risk.

Effect of low-magnitude different-frequency whole-body vibration on subchondral trabecular bone microarchitecture, cartilage degradation, bone/cartilage turnover, and joint pain in rabbits with knee osteoarthritis

Backgroud

Whole-body vibration(WBV) has been suggested for the prevention of subchondral bone loss of knee osteoarthritis (OA) . This study examined the effects of different frequency of whole-body vibration on subchondral trabecular bone microarchitecture, cartilage degradation and metabolism of the tibia and femoral condyle bone, and joint pain in an anterior cruciate ligament transection (ACLT)–induced knee osteoarthritisrabbit model.

Method

Ninety adult rabbits were divided into six groups: all groups received unilateral ACLT; Group 1, ACLT only; Group 2, 5 Hz WBV; Group 3, 10 Hz WBV; Group 4, 20 Hz WBV; Group 5, 30 Hz WBV; and Group 6, 40 Hz WBV. Pain was tested via weight-bearing asymmetry. Subchondral trabecular bone microarchitecture was examined using in vivo micro-computed tomography. Knee joint cartilage was evaluated by gross morphology, histology, and ECM gene expression level (aggrecan and type II collagen [CTX-II]). Serum bone-specific alkaline phosphatase, N-mid OC, cartilage oligometric protein, CPII, type I collagen, PIIANP, G1/G2 aggrecan levels, and urinary CTX-II were analyzed.

Results

After 8 weeks of low-magnitude WBV, the lower frequency (10 Hz and 20 Hz) WBV treatment decreased joint pain and cartilage resorption, accelerated cartilage formation, delayed cartilage degradation especially at the 20 Hz regimen. However, the higher frequencies (30 Hz and 40 Hz) had worse effects, with worse limb function and cartilage volume as well as higher histological scores and cartilage resorption. In contrast, both prevented loss of trabeculae and increased bone turnover. No significant change was observed in the 5 Hz WBV group.

Conclusion

Our data demonstrate that the lower frequencies (10 Hz and 20 Hz) of low-magnitude WBV increased bone turnover, delayed cartilage degeneration, and caused a significant functional change of the OA-affected limb in ACLT-induced OA rabbit model but did not reverse OA progression after 8 weeks of treatment.

Fractal lacunarity of trabecular bone in vertebral MRI to predict osteoporotic fracture risk in over-fifties women. The LOTO study

BACKGROUND

Osteoporotic fractures are a major cause of morbidity in the elderly. Menopausal women represent the population with the highest risk of early osteoporosis onset, often accompanied by vertebral fractures (VF). Bone mineral density (BMD) is commonly assessed by dual-energy X-ray absorptiometry (DXA) for osteoporosis diagnosis; however, BMD alone does not represent a significant predictor of fracture risk. Bone microarchitecture, instead, arises as a determinant of bone fragility independent of BMD. High-resolution magnetic resonance imaging (MRI) is an effective noninvasive/nonionizing tool for in vivo characterisation of trabecular bone microarchitecture (TBA). We have previously set up an MRI method able to characterise TBA changes in aging and osteoporosis by one parameter, trabecular bone lacunarity parameter β (TBLβ). Fractal lacunarity was used for TBA texture analysis as it describes discontinuity of bone network and size of bone marrow spaces, changes of which increase the risk of bone fracture. This study aims to assess the potential of TBLβ method as a tool for osteoporotic fracture risk.

METHODS

An observational, cross-sectional, and prospective study on over-50s women at risk for VF was designed. TBLβ, our index of osteoporotic fracture risk, is the main outcome measure. It was calculated on lumbar vertebra axial images, acquired by 1.5 T MRI spin-echo technique, from 279 osteopenic/osteoporotic women with/without prior VF. Diagnostic power of TBLβ method, by Receiver Operating Characteristics (ROC) curve and other diagnostic accuracy measurements were compared with lumbar spine DXA-BMD.

RESULTS

Baseline results show that TBLβ is able to discriminate patients with/without prevalent VF (p = 0.003). AUC (area under the curve from ROC) is 0.63 for TBLβ, statistically higher (p = 0.012) than BMD one (0.53). Contribution of TBLβ to prevalent VF is statistically higher (p < 0.001) than BMD (sensitivity: 66% vs. 52% respectively; OR: 3.20, p < 0.0001 for TBLβ vs. 1.31, p = 0.297 for BMD). Preliminary 1-year prospective results suggest that TBA contribution to incident VF is even higher (sensitivity: 73% for TBLβ vs. 55% for BMD; RR: 3.00, p = 0.002 for TBLβ vs. 1.31, p = 0.380 for BMD).

CONCLUSION

Results from this study further highlight the usefulness of TBLβ as a biomarker of TBA degeneration and an index of osteoporotic fracture risk.

Trabecular bone microarchitecture analysis, a way for an early detection of genetic dwarfism? Case study of a dwarf mother's offspring

A 66 year-old woman with a disproportionate dwarfism and who bore seven children was discovered at the Middenbeemster archaeological site (The Netherlands). Three are perinates and show no macroscopic or radiological evidence for a FGFR3 mutation causing hypo-or achondroplasia. This mutation induces dysfunction of the growth cartilage, leading to abnormalities in the development of trabecular bone. Because the mutation is autosomal dominant, these perinates have a 50% risk of having been affected. This study determines whether trabecular bone microarchitecture (TBMA) analysis is useful for detecting genetic dwarfism. Proximal metaphyses of humeri were μCT-scanned with a resolution of 7-12 μm. Three volumes of interest were segmented from each bone with TIVMI© software. The TBMA was quantified in BoneJ© using six parameters on which a multivariate analysis was then performed. Two of the Middenbeemster perinates show a quantitatively different TBMA organization. These results and the family's medical history suggest a diagnosis of genetic dwarfism for this two perinates. This study provides evidence to support the efficacy of μCT for diagnosing early-stage bone disease.

Automated micro-CT morphometry of femoral biopsies from hip arthroplasties: adaptive local thresholding, volume of interest wrapping and removal of debris

Bone biopsies are an important biological tool for investigating bone microarchitecture, which can be non-destructively imaged in 3D via micro-computed tomography (micro-CT). Image thresholding and delineation of a region of interest (ROI) are prerequisites for quantifying bone parameters. Validated automatic protocols enable quantification of biopsies that contain trabecular and cortical bone. However, irregularly shaped trabecular bone biopsies with peripheral and internal debris have required manual ROI delineation, which is time-intensive and subject to inter and intra-observer variance. We hypothesise that an automated workflow will be a suitable alternative to overcome these issues and objectively determine bone microarchitecture in surgical biopsies, at higher throughput suitable for clinical studies. Hence, the aim of this study was to develop an objective, reproducible and automated workflow to analyse microarchitecture of trabecular bone biopsies. To accomplish this aim, we tested six different methods of ROI delineation: a whole biopsy ROI, and both manual (slow) and automatically delineated (fast) reduced ROIs to remove peripheral debris, each with (adaptive thresholding and a set of morphological operations to remove debris) and without (global thresholding) processing in a subset (n = 8) of intertrochanteric femoral biopsies obtained from patients undergoing hip arthroplasty. Number of objects, bone volume to tissue volume (BV/TV), trabecular separation (Tb.Sp), structure model index (SMI) and Euler number and trabecular pattern factor (Tb.Pf) were compared between the six workflows using Friedman's test and post-hoc pairwise comparisons with Bonferroni correction was performed. The two most reproducible techniques were tested for validation in a larger cohort of arthroplasty patients (n = 60) and results were compared with appropriate t-test. Subset analysis indicated that the manual and automated ROI with processing increased the ability to resolve real differences between these groups in parameters BV/TV, Tb.Sp and Euler number compared to with no processing and whole biopsy ROI approach. A validation cohort consisted of thirty osteoarthritis patients with a mean age 68.25 ± 8.64 and thirty neck of femur fracture with a mean age 82.4 ± 8.9. The manual technique failed to detect differences in BV/TV, SMI and Tb.Pf between the two patient groups (p > 0.05, for all) while the automated workflow demonstrated significant differences in these parameters between the OA and the NOF patients (p < 0.05). This is probably due to irregularity in the reference VOI volume introduced by manual ROI delineation reducing morphometric precision, compared to the automated method. In conclusion, our automated workflow performed better than customary practice; it represents a user-independent, high throughput technique to measure bone microarchitecture accurately in surgical biopsies.

Primary components of MCT ketogenic diet are detrimental to bone loss associated with accelerated aging and age-related neurotoxicity in mice

Medium chained triglycerides (MCT) ketogenic diet is being extensively investigated for its neuroprotective effects against adverse effects associated with aging and neurodegenerative disorders. Aging is a common risk factor for the development of both osteoporosis and neurological disorders. Hence, suppression of aging and age-related neurodegeneration might contribute to delaying skeletal aging. The present study was designed to investigate the effects of the primary components of the MCT diet, against bone resorption associated with D-gal-induced accelerated aging and D-gal /AlCl3-induced age-related toxicity. We report bone loss in accelerated aged mice and age-related neurotoxic mice through declined Sirtuin1 (SIRT1) expression, depleted bone turnover markers, (P1NP and β-CTX-1), low bone mineral density (BMD), and deterioration of trabecular bone microarchitecture in both the distal femur and proximal tibia bones. Administration of MCT dietary components decanoic acid and octanoic acid, led to a decrease in body weight and only octanoic acid increased serum levels of ketone body, β-hydroxybutyrate (β-HB), but both of them failed to reverse the diminishing effects on bone health associated with aging and age-related neurotoxicity. Surprisingly, decanoic acid, octanoic acid, and their combination also exhibited negative effects on trabecular bone microarchitecture and BMD in the distal femur and proximal tibia bones of healthy mice. The findings from this study provide supporting evidence on the deterioration of bone health associated with aging and age-related neurotoxicity, and the bone resorption potential of MCT dietary supplements that are being prescribed in healthy older populations and elderly persons diagnosed with neurological disorders.

Long-Term Intake of Green Tea Extract Causes Mal-Conformation of Trabecular Bone Microarchitecture in Growing Rats

The purpose of this study was to examine the effects of green tea extract (GTE) intake on bone structural and physiological properties, such as bone mass, trabecular bone microarchitecture, cortical bone geometry, and bone mechanical strength, in growing rats. Four-week-old male Wistar rats were divided into the following four groups: standard diet feeding for 85 days (S-CON) or 170 days (L-CON), and GTE diet feeding for 85 days (S-GTE) or 170 days (L-GTE). At the end of the experiment, in addition to measurement of circulating bone formation/resorption markers, bone mass, trabecular bone microarchitecture, and cortical bone geometry were analyzed in the left femur, and bone mechanical strength of the right femur was measured. There was no difference in all bone parameters between the S-CON and S-GTE groups. On the other hand, the L-GTE group showed the decrease in some trabecular bone mass/microarchitecture parameters and no change in cortical bone mass/geometry parameters compared with the L-CON group, and consequently the reduction in bone weight corrected by body weight. There was no difference in bone formation/resorption markers and bone mechanical strength between the S-CON and S-GTE groups and also between the L-CON and L-GTE groups. However, serum leptin levels were significantly lower in the L-GTE group than in the L-CON group. Thus, the long-term GTE intake had negative effects on bone, especially trabecular bone loss and microarchitecture mal-conformation, in growing rats.