Impact microindentation assesses subperiosteal bone material properties in humans

Ten tips on how to assess bone health in patients with chronic kidney disease

Patients with chronic kidney disease (CKD) experience a several-fold increased risk of fracture. Despite the high incidence and the associated excess morbidity and premature mortality, bone fragility in CKD, or CKD-associated osteoporosis, remains a blind spot in nephrology with an immense treatment gap. Defining the bone phenotype is a prerequisite for the appropriate therapy of CKD-associated osteoporosis at the patient level. In the present review, we suggest 10 practical 'tips and tricks' for the assessment of bone health in patients with CKD. We describe the clinical, biochemical, and radiological evaluation of bone health, alongside the benefits and limitations of the available diagnostics. A bone biopsy, the gold standard for diagnosing renal bone disease, is invasive and not widely available; although useful in complex cases, we do not consider it an essential component of bone assessment in patients with CKD-associated osteoporosis. Furthermore, we advocate for the deployment of multidisciplinary expert teams at local, national, and potentially international level. Finally, we address the knowledge gaps in the diagnosis, particularly early detection, appropriate "real-time" monitoring of bone health in this highly vulnerable population, and emerging diagnostic tools, currently primarily used in research, that may be on the horizon of clinical practice.

Evaluating Osteoporosis in Chronic Kidney Disease: Both Bone Quantity and Quality Matter

Bone strength is determined not only by bone quantity [bone mineral density (BMD)] but also by bone quality, including matrix composition, collagen fiber arrangement, microarchitecture, geometry, mineralization, and bone turnover, among others. These aspects influence elasticity, the load-bearing and repair capacity of bone, and microcrack propagation and are thus key to fractures and their avoidance. In chronic kidney disease (CKD)-associated osteoporosis, factors traditionally associated with a lower bone mass (advanced age or hypogonadism) often coexist with non-traditional factors specific to CKD (uremic toxins or renal osteodystrophy, among others), which will have an impact on bone quality. The gold standard for measuring BMD is dual-energy X-ray absorptiometry, which is widely accepted in the general population and is also capable of predicting fracture risk in CKD. Nevertheless, a significant number of fractures occur in the absence of densitometric World Health Organization (WHO) criteria for osteoporosis, suggesting that methods that also evaluate bone quality need to be considered in order to achieve a comprehensive assessment of fracture risk. The techniques for measuring bone quality are limited by their high cost or invasive nature, which has prevented their implementation in clinical practice. A bone biopsy, high-resolution peripheral quantitative computed tomography, and impact microindentation are some of the methods established to assess bone quality. Herein, we review the current evidence in the literature with the aim of exploring the factors that affect both bone quality and bone quantity in CKD and describing available techniques to assess them.

Assessment of bovine cortical bone fracture behavior using impact microindentation as a surrogate of fracture toughness

The fracture behavior of bone is critically important for evaluating its mechanical competence and ability to resist fractures. Fracture toughness is an intrinsic material property that quantifies a material's ability to withstand crack propagation under controlled conditions. However, properly conducting fracture toughness testing requires the access to calibrated mechanical load frames and the destructive testing of bone samples, and therefore fracture toughness tests are clinically impractical. Impact microindentation mimicks certain aspects of fracture toughness measurements, but its relationship with fracture toughness remains unknown. In this study, we aimed to compare measurements of notched fracture toughness and impact microindentation in fresh and boiled bovine bone. Skeletally mature bovine bone specimens (n = 48) were prepared, and half of them were boiled to denature the organic matrix, while the other half remained preserved in frozen conditions. All samples underwent a notched fracture toughness test to determine their resistance to crack initiation (KIC) and an impact microindentation test using the OsteoProbe to obtain the Bone Material Strength index (BMSi). Boiling the bone samples increased the denatured collagen content, while mineral density and porosity remained unaffected. The boiled bones also showed significant reduction in both KIC (P < .0001) and the average BMSi (P < .0001), leading to impaired resistance of bone to crack propagation. Remarkably, the average BMSi exhibited a high correlation with KIC (r = 0.86; P < .001). A ranked order difference analysis confirmed the excellent agreement between the 2 measures. This study provides the first evidence that impact microindentation could serve as a surrogate measure for bone fracture behavior. The potential of impact microindentation to assess bone fracture resistance with minimal sample disruption could offer valuable insights into bone health without the need for cumbersome testing equipment and sample destruction.

For older individuals there is greater variance in low mean Bone Material Strength Index values obtained with the OsteoProbe

Purpose

Bone Material Strength Index (BMSi) quantifies the resistance of bone to a specified force in vivo at the mid tibia using impact microindentation (IMI). Anecdotal evidence suggests that within-participant variance in BMSi may be associated with the individual's mean BMSi. This study aimed to investigate associations between mean and variance of IMI measures in a population-based study.

Methods

Participants were men (n = 420) and women (n = 55) from the Geelong Osteoporosis Study who underwent BMSi measurement using the OsteoProbe at recent follow-up phases (men 2016-2022; women 2022-2023). Median age was 63.7 yr (IQR 53.0-71.8). BMSi standard deviation was skewed and therefore natural log transformed (referred to as ln-SD). Linear regression models were developed with ln-SD as the dependent variable and mean BMSi as the independent variable adjusting for sex, age, height and weight.

Results

In unadjusted models, greater BMSi was associated with lower ln-SD (β = -1.58, p = 0.042). This association was sustained after adjustment (p = 0.013), and an interaction between BMSi and age was observed (p = 0.004). In those aged 63.7 yr and over (median age), mean BMSi was inversely associated with ln-SD (β = -3.22, p = 0.002). Sex was not identified as an effect modifier. In younger participants, no BMSi*ln-SD association was observed.

Conclusion

In older men and women, there was greater variance in low BMSi values. This suggests that standard deviation of the BMSi measure may provide additional information in the assessment of bone health and is worthy of further investigation.

Mini abstract

In older men and women, greater variance is observed when BMSi values are low, reflecting potential variation in the bone surface.

Assessment of bovine cortical bone fracture behavior using impact microindentation as a surrogate of fracture toughness

The fracture behavior of bone is critically important for assessing its mechanical competence and ability to resist fractures. Fracture toughness, which quantifies a material's resistance to crack propagation under controlled geometry, is regarded as the gold standard for evaluating a material's resistance to fracture. However properly conducting this test requires access to calibrated mechanical load frames the destruction of the bone samples, making it impractical for obtaining clinical measurement of bone fracture. Impact microindentation offers a potential alternative by mimicking certain aspects of fracture toughness measurements, but its relationship with mechanistic fracture toughness remains unknown. In this study, we aimed to compare measurements of notched fracture toughness and impact microindentation in fresh and boiled bovine bone. Skeletally mature bovine bone specimens (n=48) were prepared, and half of them were boiled to denature the organic matrix, while the other half remained preserved in frozen conditions. Notched fracture toughness tests were conducted on all samples to determine Initiation toughness (KIC), and an impact microindentation test using the OsteoProbe was performed to obtain the Bone Material Strength index. Boiling the bone samples resulted increased the denatured collagen without affecting mineral density or porosity. The boiled bones also showed significant reduction in both KIC (p < 0.0001) and the average Bone Material Strength index (p < 0.0001), leading to impaired resistance of bone to crack propagation. Remarkably, the average Bone Material Strength index exhibited a high correlation with KIC (r = 0.86; p < 0.001). The ranked order difference analysis confirmed excellent agreement between the two measures. This study provides the first evidence that impact microindentation could serve as a surrogate measure for bone fracture behavior. The potential of impact microindentation to non-destructively assess bone fracture resistance could offer valuable insights into bone health without the need for elaborate testing equipment and sample destruction.

Increased Bone Material Strength Index Is Positively Associated With the Risk of Incident Osteoporotic Fractures in Older Swedish Women

No previous studies have investigated the association between the bone material strength index (BMSi; an indicator of bone material properties obtained by microindentation) and the risk of incident fracture. The primary purpose of this prospective cohort study was to evaluate if BMSi is associated with incident osteoporotic fracture in older women and, secondarily, with prevalent fractures, anthropometric traits, or measurements of bone mineral density (BMD) by dual-energy X-ray absorptiometry (DXA). In a population-based cohort, 647 women aged 75 to 80 years underwent bone microindentation using the OsteoProbe device. Data on clinical risk factors (CRFs), prevalent fractures, and incident fractures were collected using questionnaires, medical records, and a regional X-ray archive. BMD and vertebral fracture assessment (VFA) were assessed by DXA (Hologic, Discovery A). Associations between BMSi, anthropometrics, BMD, and prevalent fractures were investigated using correlation and linear and logistic regression. Cox proportional hazards and competing risks analysis by Fine and Gray were used to study the association between BMSi and the risk of fracture and mortality. BMSi was weakly associated with age (r = -0.13, p < 0.001) and BMI (r = -0.21, p < 0.001) and with BMD of lumbar spine (β = 0.09, p = 0.02) and total hip (β = 0.08, p = 0.05), but only after adjustments. No significant associations were found between BMSi and prevalent fractures (self-reported and/or VFA identified, n = 332). During a median follow-up time of 6.0 years, 121 major osteoporotic fractures (MOF), 151 any fractures, and 50 deaths occurred. Increasing BMSi (per SD) was associated with increased risk of MOF (hazard ratio [HR] = 1.29, 95% confidence interval [CI] 1.07-1.56), any fracture (HR = 1.29, 95% CI 1.09-1.53), and mortality (HR = 1.44, 95% CI 1.07-1.93). The risk of fracture did not materially change with adjustment for confounders, CRFs, femoral neck BMD, or when considering the competing risk of death. In conclusion, unexpectedly increasing BMSi was associated with greater fracture risk. The clinical relevance and potential mechanisms of this finding require further study. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Reference Intervals for Bone Impact Microindentation in Healthy Adults: A Multi-Centre International Study

Impact microindentation (IMI) is a novel technique for assessing bone material strength index (BMSi) in vivo, by measuring the depth of a micron-sized, spherical tip into cortical bone that is then indexed to the depth of the tip into a reference material. The aim of this study was to define the reference intervals for men and women by evaluating healthy adults from the United States of America, Europe and Australia. Participants included community-based volunteers and participants drawn from clinical and population-based studies. BMSi was measured on the tibial diaphysis using an OsteoProbe in 479 healthy adults (197 male and 282 female, ages 25 to 98 years) across seven research centres, between 2011 and 2018. Associations between BMSi, age, sex and areal bone mineral density (BMD) were examined following an a posteriori method. Unitless BMSi values ranged from 48 to 101. The mean (± standard deviation) BMSi for men was 84.4 ± 6.9 and for women, 79.0 ± 9.1. Healthy reference intervals for BMSi were identified as 71.0 to 97.9 for men and 59.8 to 95.2 for women. This study provides healthy reference data that can be used to calculate T- and Z-scores for BMSi and assist in determining the utility of BMSi in fracture prediction. These data will be useful for positioning individuals within the population and for identifying those with BMSi at the extremes of the population.

Bone material strength index as measured by in vivo impact microindentation is normal in subjects with high-energy trauma fractures

Bone material properties were assessed using impact microindentation in patients with high-energy trauma fractures. Compared to patients with low-energy trauma fractures, bone material strength index was significantly higher in patients with high-energy trauma fractures, and did not differ between patients with osteopenia and those with osteoporosis within each trauma group.

INTRODUCTION

Impact microindentation (IMI) is a technique to assess tissue-level properties of bone at the tibia. Bone material strength index (BMSi), measured by IMI, is decreased in patients with low-energy trauma fractures, independently of areal bone mineral density (aBMD), but there is no information about BMSi in patients with high-energy trauma fractures. In the present study, we evaluated tissue-level properties of bone with IMI in patients with high-energy trauma fractures.

METHODS

BMSi was measured 3.0 months (IQR 2.0-5.8) after the fracture in 40 patients with high-energy trauma and 40 age- and gender-matched controls with low-energy trauma fractures using the OsteoProbe® device.

RESULTS

Mean age of high- and low-energy trauma patients was 57.7 ± 9.1 and 57.2 ± 7.7 years, respectively (p = 0.78). Fracture types were comparable in high- vs low-energy trauma patients. Lumbar spine (LS)-aBMD, but not femoral neck (FN)-aBMD, was higher in high- than in low-energy trauma patients (LS 0.96 ± 0.13 vs 0.89 ± 0.13 g/cm², p = 0.02; FN 0.75 ± 0.09 vs 0.72 ± 0.09 g/cm², p = 0.09). BMSi was significantly higher in high- than in low-energy trauma patients (84.4 ± 5.0 vs 78.0 ± 4.6, p = 0.001), also after adjusting for aBMD (p = 0.003). In addition, BMSi did not differ between patients with osteopenia and those with osteoporosis within each trauma group.

CONCLUSION

Our data demonstrate that BMSi and LS-aBMD, but not FN-aBMD, are significantly higher in high-energy trauma patients compared to matched controls with similar fractures from low-energy trauma. Further studies of non-osteoporotic patients with high-energy trauma fracture with measurements of BMSi are warranted to determine whether IMI might help in identifying those with reduced bone strength.

Associations between parameters of peripheral quantitative computed tomography and bone material strength index

BACKGROUND

Bone material strength index (BMSi) is measured in vivo using impact microindentation (IMI). However, the associations between BMSi and other bone measures are not clear. This study investigated whether bone parameters derived by peripheral quantitative computed tomography (pQCT) are associated with BMSi.

METHODS

Participants were men (n = 373, ages 34-96 yr) from the Geelong Osteoporosis Study. BMSi was measured using an OsteoProbe (Active Life Scientific, USA). Bone measures were obtained at both the radius (n = 348) and tibia (n = 342) using pQCT (XCT 2000 Stratec Medizintechnik, Germany). Images were obtained at 4% and 66% of radial and tibial length. Associations between pQCT parameters and BMSi were tested using Spearman's correlation and multivariable regression used to determine independent associations after adjustment for potential confounders. Models were checked for interaction terms.

RESULTS

Weak associations were observed between total bone density (radius 4%; r = +0.108, p = 0.046, tibia 4%; r = +0.115, p = 0.035), cortical density (tibia 4%; r = +0.123, p = 0.023) and BMSi. The associations were independent of weight, height, and glucocorticoid use (total bone density: radius 4%; β = 0.020, p = 0.006, tibia 4%; β = 0.020, p = 0.027 and cortical density: radius 4%; β = 4.160, p = 0.006, tibia 4%; β = 0.038, p = 0.010). Associations with bone mass were also observed at the 66% radial and tibial site, independent of age, weight, and glucocorticoid use (β = 4.160, p = 0.053, β = 1.458, p = 0.027 respectively). Total area at the 66% tibial site was also associated with BMSi (β = 0.010, p = 0.012), independent of weight and glucocorticoid use. No interaction terms were identified.

CONCLUSION

There were weak associations detected between some pQCT-derived bone parameters and BMSi.

Bone Material Strength Index as Measured by Impact Microindentation is Low in Patients with Primary Hyperparathyroidism

CONTEXT

In primary hyperparathyroidism (PHPT) bone mineral density (BMD) is typically decreased in cortical bone and relatively preserved in trabecular bone. An increased fracture rate is observed however not only at peripheral sites but also at the spine, and fractures occur at higher BMD values than expected. We hypothesized that components of bone quality other than BMD are affected in PHPT as well.

OBJECTIVE

To evaluate bone material properties using impact microindentation (IMI) in PHPT patients.

METHODS

In this cross-sectional study, the Bone Material Strength index (BMSi) was measured by IMI at the midshaft of the tibia in 37 patients with PHPT (28 women), 11 of whom had prevalent fragility fractures, and 37 euparathyroid controls (28 women) matched for age, gender, and fragility fracture status.

RESULTS

Mean age of PHPT patients and controls was 61.8 ± 13.3 and 61.0 ± 11.8 years, respectively, P = .77. Calcium and PTH levels were significantly higher in PHPT patients but BMD at the lumbar spine (0.92 ± 0.15 vs 0.89 ± 0.11, P = .37) and the femoral neck (0.70 ± 0.11 vs 0.67 ± 0.07, P = .15) were comparable between groups. BMSi however was significantly lower in PHPT patients than in controls (78.2 ± 5.7 vs 82.8 ± 4.5, P < .001). In addition, BMSi was significantly lower in 11 PHPT patients with fragility fractures than in the 26 PHPT patients without fragility fractures (74.7 ± 6.0 vs 79.6 ± 5.0, P = .015).

CONCLUSION

Our data indicate that bone material properties are altered in PHPT patients and most affected in those with prevalent fractures. IMI might be a valuable additional tool in the evaluation of bone fragility in patients with PHPT.

The Effect of an Exercise Intervention Program on Bone Health After Bariatric Surgery: A Randomized Controlled Trial

Exercise has been suggested as a therapeutic approach to attenuate bone loss induced by bariatric surgery (BS), but its effectiveness remains unclear. Our aim was to determine if an exercise-training program could induce benefits on bone mass after BS. Eighty-four patients, submitted to gastric bypass or sleeve gastrectomy, were randomized to either exercise (EG) or control group (CG). One month post-BS, EG underwent a 11-month supervised multicomponent exercise program, while CG received only standard medical care. Patients were assessed before BS and at 1, 6, and 12 months post-BS for body composition, areal bone mineral density (BMD), bone turnover markers, calciotropic hormones, sclerostin, bone material strength index, muscle strength, and daily physical activity. A primary analysis was conducted according to intention-to-treat principles and the primary outcome was the between-group difference on lumbar spine BMD at 12 months post-BS. A secondary analysis was also performed to analyze if the exercise effect depended on training attendance. Twelve months post-BS, primary analysis results revealed that EG had a higher BMD at lumbar spine (+0.024 g∙cm^-2 [95% confidence interval (CI) 0.004, 0.044]; p = .015) compared with CG. Among total hip, femoral neck, and 1/3 radius secondary outcomes, only 1/3 radius BMD improved in EG compared with CG (+0.013 g∙cm^-2 [95% CI 0.003, 0.023]; p = .020). No significant exercise effects were observed on bone biochemical markers or bone material strength index. EG also had a higher lean mass (+1.5 kg [95% CI 0.1, 2.9]; p = .037) and higher number of high impacts (+51.4 [95% CI 6.6, 96.1]; p = .026) compared with CG. In addition, secondary analysis results suggest that exercise-induced benefits may be obtained on femoral neck BMD but only on those participants with ≥50% exercise attendance compared with CG (+5.3% [95% CI 2.0, 8.6]; p = .006). Our findings suggest that an exercise program is an effective strategy to ameliorate bone health in post-BS patients. © 2020 American Society for Bone and Mineral Research (ASBMR).

Breaking new ground in mineralized tissue: Assessing tissue quality in clinical and laboratory studies

Mineralized tissues, such as bone and teeth, have extraordinary mechanical properties of both strength and toughness. This mechanical behavior originates from deformation and fracture resistance mechanisms in their multi-scale structure. The term quality describes the matrix composition, multi-scale structure, remodeling dynamics, water content, and micro-damage accumulation in the tissue. Aging and disease result in changes in the tissue quality that may reduce strength and toughness and lead to elevated fracture risk. Therefore, the capability to measure the quality of mineralized tissues provides critical information on disease progression and mechanical integrity. Here, we provide an overview of clinical and laboratory-based techniques to assess the quality of mineralized tissues in health and disease. Current techniques used in clinical settings include radiography-based (radiographs, dual energy x-ray absorptiometry, EOS) and x-ray tomography-based methods (high resolution peripheral quantitative computed tomography, cone beam computed tomography). In the laboratory, tissue quality can be investigated in ex vivo samples with x-ray imaging (micro and nano-computed tomography, x-ray microscopy), electron microscopy (scanning/transmission electron imaging (SEM/STEM), backscattered scanning electron microscopy, Focused Ion Beam-SEM), light microscopy, spectroscopy (Raman spectroscopy and Fourier transform infrared spectroscopy) and assessment of mechanical behavior (mechanical testing, fracture mechanics and reference point indentation). It is important for clinicians and basic science researchers to be aware of the techniques available in different types of research. While x-ray imaging techniques translated to the clinic have provided exceptional advancements in patient care, the future challenge will be to incorporate high-resolution laboratory-based bone quality measurements into clinical settings to broaden the depth of information available to clinicians during diagnostics, treatment and management of mineralized tissue pathologies.

Treatments of osteoporosis increase bone material strength index in patients with low bone mass

Effects on bone material properties of two-year antiosteoporotic treatment were assessed using in vivo impact microindentation (IMI) in patients with low bone mineral density (BMD) values. Antiresorptive treatment, in contrast to vitamin D ± calcium treatment alone, induced BMD-independent increases in bone material strength index, measured by IMI, the magnitude of which depended on pretreatment values.

INTRODUCTION

Bone material strength index (BMSi), measured by IMI in vivo, is reduced in patients with fragility fractures, but there is no information about changes in values during long-term therapy. In the present study, we assessed changes in BMSi in patients receiving antiosteoporotic treatments for periods longer than 12 months.

METHODS

We included treatment-naive patients with low bone mass who had a BMSi measurement with OsteoProbe® at presentation and consented to a repeat measurement after treatment.

RESULTS

We studied 54 patients (34 women), median age 58 years, of whom 30 were treated with bisphosphonates or denosumab (treatment group) and 24 with vitamin D ± calcium alone (control group). There were no differences in clinical characteristics between the two groups with the exception of a higher number of previous fragility fractures in the treatment group. Baseline hip BMD and BMSi values were lower in the treatment group. After 23.1 ± 6.6 months, BMSi increased significantly in the treatment group (82.4 ± 4.3 vs 79.3 ± 4.1; p < 0.001), but did not change in the control group (81.5 ± 5.2 vs 82.2 ± 4.1; p = 0.35). Changes in BMSi with antiresorptives were inversely related with baseline values (r = - 0.43; p = 0.02) but not with changes in BMD. Two patients in the control group with large decreases in BMSi values sustained incident fractures.

CONCLUSION

In patients at increased fracture risk, antiresorptive treatments induced BMD-independent increases in BMSi values, the magnitude of which depended on pretreatment values.

Impact microindentation measurements correlate with cortical bone material properties measured by Fourier transform infrared imaging in humans

Bone Material Strength index (BMSi) measured by Impact Microindentation is generally lower in subjects with fragility fractures independently of BMD values. We recently reported that in humans, BMSi values are strongly associated with material properties of subperiosteal mineralized bone surface (local mineral content, nanoporosity, pyridinoline content). In the present study we investigated the relationship of BMSi with material properties of the whole bone cortex, by analyzing thin sections of iliac crest biopsies (N = 12) from patients with different skeletal disorders and a wide range of BMD with or without fractures, by Fourier transform infrared imaging (FTIRI). The calculated parameters were: i) mineral and organic matrix content and their ratio (MM), ii) mineral maturity/crystallinity (MMC) and iii) the ratio of pyridinoline (Pyd) and divalent collagen cross-links (XLR). Results were expressed as images, which were converted to histogram distributions. For each histogram the characteristics recorded were: mean value, mode (most often occurring value), skewness, and kurtosis and their association with BMSi values was examined by correlation analysis. BMSi values were significantly correlated only with MM mean and mode values (r = 0.736, p = 0.0063, and r = 0.855, p = 0.0004, respectively), and with XLR mode values (r = -0.632, p = 0.0274). The results of the present study demonstrate that BMSi values are strongly associated with MM, a metric that corrects the mineral content for the organic matrix content, and may also depend on organic matrix quality. These and our previous observations strongly suggest that BMSi assesses material properties of cortical bone.

Added Value of Impact Microindentation in the Evaluation of Bone Fragility: A Systematic Review of the Literature

The current gold standard for the diagnosis of osteoporosis and the prediction of fracture risk is the measurement of bone mineral density (BMD) using dual energy x-ray absorptiometry (DXA). A low BMD is clearly associated with increased fracture risk, but BMD is not the only determinant of bone strength, particularly in secondary osteoporosis and metabolic bone disorders in which components other than BMD are affected and DXA often underestimates true fracture risk. Material properties of bone which significantly contribute to bone strength have become evaluable in vivo with the impact microindentation (IMI) technique using the OsteoProbe® device. The question arises whether this new tool is of added value in the evaluation of bone fragility. To this effect, we conducted a systematic review of all clinical studies using IMI in vivo in humans also addressing practical aspects of the technique and differences in study design, which may impact outcome. Search data generated 38 studies showing that IMI can identify patients with primary osteoporosis and fractures, patients with secondary osteoporosis due to various underlying systemic disorders, and scarce longitudinal data also show that this tool can detect changes in bone material strength index (BMSi), following bone-modifying therapy including use of corticosteroids. However, this main outcome parameter was not always concordant between studies. This systematic review also identified a number of factors that impact on BMSi outcome. These include subject- and disease-related factors such as the relationship between BMSi and age, geographical region and the presence of fractures, and technique- and operator-related factors. Taken together, findings from this systematic review confirm the added value of IMI for the evaluation and follow-up of elements of bone fragility, particularly in secondary osteoporosis. Notwithstanding, the high variability of BMSi outcome between studies calls for age-dependent reference values, and for the harmonization of study protocols. Prospective multicenter trials using standard operating procedures are required to establish the value of IMI in the prediction of future fracture risk, before this technique is introduced in routine clinical practice.