Modeling of Osteoprobe indentation on bone

Biologic therapies in stress fractures: Current concepts

Stress fractures, a common overuse injury in physically active individuals, present a significant challenge for athletes and military personnel. Patients who sustain stress fractures have demanding training regimes where periods of rest and immobilisation have unacceptable negative consequences on sports goals and finances. Aside from being an overuse injury, there are various contributing risk factors that put certain individuals at risk of a stress fracture. The main two being nutritional deficiencies and hormonal variations, which have significant effects on bone metabolism and turnover. Historically, treatment of stress fractures focused on conservative strategies such as rest and immobilisation. Calcium and vitamin D deficiencies have been closely linked to stress fractures and so over time supplementation has also played a role in treatment. With the introduction of biologics into orthopaedics, newer treatment strategies have been applied to accelerate fracture healing and perhaps improve fracture callus quality. If such therapies can reduce time spent away from sport and activity, it would be ideal for treating stress fractures. This article aims to offer insights into the evolving landscape of stress fracture management. It investigates the pre-clinical evidence and available published clinical applications. Though fracture healing is well understood, the role of biologics for fracture healing is still indeterminate. Available literature for the use of biologic therapies in stress fractures are restricted and most reports have used biologics as a supplement to surgical fixation in subjects in studies that lack control groups. Randomised control trials have been proposed and registered by a few groups, with results awaited. Assessing individuals for risk factors, addressing hormonal imbalances and nutritional deficiencies seems like an effective approach to addressing the burden of stress fractures. We await better designed trials and studies to accurately determine the clinical benefit of adding biologics to the management of these injuries.

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.

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).

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.

Characterization and comparison of hyper-viscoelastic properties of normal and osteoporotic bone using stress-relaxation experiment

Bone tissue behavior under various loads is nonlinear elastic due to irreversible energy absorption. Also, viscoelasticity is one of the most important properties of bone which is very important in dynamic analyses and helps a lot in making artificial bone. In this study, rat tibia bone specimens were subjected to compression stress-relaxation test for normal (n = 5) and osteoporotic (n = 5) groups in order to characterize their mechanical properties using finite element modeling coupled with an optimization algorithm. Using this method, the structural equation parameters for the Neo-Hookean model and the Prony series coefficients were used to describe the hyper-elastic and the viscoelastic behavior of specimens, respectively; moreover, the properties of materials including the bulk, shear and Young's moduli for both groups were obtained and compared. The shear modulus was also gained as a function of time. In addition, the percentage of stress reduction and its relation to the initial stress were investigated for specimens. Finally, the effect of changes in each of the parameters of the hyper-viscoelastic structural equation on the force response was determined. Results of this study can be used in predicting the transient response and dynamic analysis of the bone.

Significant correlation of bone material strength index as measured by the OsteoProbe with Vickers and Rockwell hardness

The bone material strength index (BMSi), as measured by the OsteoProbe, is significantly correlated with Vickers hardness and Rockwell (RW) hardness measurements on conventional materials. The Vickers and RW measurements were carried out according to American Society for Testing and Materials standard test methods, and OsteoProbe measurements followed published standardized testing methods. The correlations between the BMSi and RW hardness, r = 0.93, and between the BMSi and Vickers hardness, r = 0.94, are comparable with the correlation between RW and Vickers hardness, r = 0.87. The correlation between the BMSi and RW is significant at p < 0.01, and the correlation between the BMSi and Vickers hardness is significant at p < 0.01. These results show that the indentation measurement performed by the OsteoProbe may be considered as a type of hardness measurement comparable to widely used conventional methods, with specific applications targeted by its portable and narrow design.

In Vivo Assessment of Cortical Bone Fragility

PURPOSE OF REVIEW

This review updates readers on recent developments in the assessment of cortical bone fragility in vivo. The review explains the clinical need that motivated the development of Cortical Bone Mechanics Technology™ (CBMT) as a scientific instrument, its unique capabilities, and its necessary further development as a medical device.

RECENT FINDINGS

Clinical experience with dual-energy X-ray absorptiometry has led to calls for new clinical methods for assessing bone health. CBMT is a noninvasive, dynamic 3-point bending test that makes direct, functional measurements of the mechanical properties of cortical bone in ulnas of living people. Its technical validity in accurate measurements of ulna flexural rigidity and its clinical validity in accurate estimations of quasistatic ulna bending strength have been demonstrated. Because CBMT is a whole bone test, its measurements reflect the influences of bone quantity and bone quality at all hierarchical levels.

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.