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

Bone properties in persons with type 1 diabetes and healthy controls - A cross-sectional study

BACKGROUND

The risk of fractures is increased in persons with type 1 diabetes (T1D) and assessment of bone health has been included in the 2024 updated Standards of Care by The American Diabetes Association (ADA). Previous studies have found that in T1D bone metabolism, mineral content, microstructure, and strength diverge from that of persons without diabetes. However, a clear description of a T1D bone phenotype has not yet been established. We investigated bone mechanical properties and microstructure in T1D compared with healthy controls. For the potential future introduction of additional bone measures in the clinical fracture risk assessment, we aimed to assess any potential associations between various measures related to bone indices in subjects with T1D.

METHODS

We studied human bone indices in a clinical cross-sectional setup including 111 persons with early-onset T1D and 37 sex- and age-matched control persons. Participants underwent hip and spine DXA scans for bone mineral density (BMD) of the femoral neck (FN), total hip (TH), and lumbar spine (LS), and TBS evaluation, microindentation of the tibial shaft for Bone Material Strength index (BMSi), and high-resolution periphery quantitative computed tomography (HRpQCT) of the distal radius and tibia for volumetric BMD (vBMD) and structural measures of trabecular and cortical bone. Results are reported as means with (standard deviation) or (95 % confidence intervals (CI)), medians with [interquartile range], and differences are reported with (95 % CI).

RESULTS

The study included 148 persons aged 20 to 75 years with a median age of 43.2 years. The T1D group who had all been diagnosed with T1D before the age of 18 years demonstrated values of HbA1c ranging from 39 to 107 mmol/mol and a median HbA1c of 57 mmol/mol. The BMD did not differ between groups (the mean difference in FN-BMD was 0.026 g/cm2 (-0.026; 0.079), p = 0.319) and the median BMSi was comparable in the two groups (79.2 [73.6; 83.8] in the T1D group compared with 77.9 [70.5, 86.1] in the control group). Total and trabecular vBMD (Tb.vBMD), cortical thickness (Ct.Th), and trabecular thickness (Tb.Th) of both radius and tibia were lower in participants with T1D. The mean Tb.vBMD at the radius was 143.6 (38.5) mg/cm3 in the T1D group and 171.5 (37.7) mg/cm3 in the control group, p < 0.001. The mean Ct. Thd of the radius was 0.739 mm (0.172) in the T1D group and 0.813 (0.188) in the control group, p = 0.044. Crude linear regressions revealed limited agreement between BMSi and Tb.vBMD (p = 0.010, r2 = 0.040 at the radius and p = 0.008, r2 = 0.040 at the tibia and between BMSi and the estimated failure load (FL) at the tibia (p < 0.001, r2 = 0.090). There were no significant correlations between BMSi and Ct.Th. TBS correlated with Tb.vBMD at the radius (p = 0.008, r2 = 0.044) and the tibia (p = 0.001, r2 = 0.069), and with the estimated FL at the distal tibia (p = 0.038, r2 = 0.026).

CONCLUSION

In this study, we examined the bones of persons with well-controlled, early-onset T1D. Compared with sex- and age-matched healthy control persons, we found reduced total and trabecular vBMD, as well as decreased trabecular and cortical thickness. These results suggest that a debut of T1D before reaching peak bone mass negatively impacts bone microarchitecture. No differences in areal BMD or BMSi were observed. Although the variations in total hip BMD reflect some variation in the vBMD, the reduction in trabecular bone mineral density was not captured by the DXA scan. Consequently, fracture risk may be underestimated when relying on DXA, and further research into fracture risk assessment in T1D is warranted.

Type 2 Diabetes and Fracture Risk in Older Women

Importance

The reasons for the increased fracture risk in type 2 diabetes (T2D) are not fully understood.

Objective

To determine if poorer skeletal characteristics or worse physical function explain the increased fracture risk in T2D.

Design, Setting, and Participants

This prospective observational study is based on the population-based Sahlgrenska University Hospital Prospective Evaluation of Risk of Bone Fractures study cohort of older women, performed in the Gothenburg area between March 2013 and May 2016. Follow-up of incident fracture data was completed in March 2023. Data analysis was performed between June and December 2023.

Exposures

Data were collected from questionnaires and through examination of anthropometrics, physical function, and bone measurements using bone densitometry (dual-energy x-ray absorptiometry), and high-resolution peripheral computed tomography. A subsample underwent bone microindentation to assess bone material strength index (BMSi).

Main Outcomes and Measures

Baseline assessment of bone characteristics and physical function and radiograph verified incident fractures.

Results

Of 3008 women aged 75 to 80 years, 294 women with T2D (mean [SD] age, 77.8 [1.7] years) were compared with 2714 women without diabetes (mean [SD] age, 77.8 [1.6] years). Women with T2D had higher bone mineral density (BMD) at all sites (total hip, 4.4% higher; femoral neck (FN), 4.9% higher; and lumbar spine, 5.2% higher) than women without. At the tibia, women with T2D had 7.4% greater cortical area and 1.3% greater density, as well as 8.7% higher trabecular bone volume fraction. There was no difference in BMSi (T2D mean [SD], 78.0 [8.3] vs controls, 78.1 [7.3]). Women with T2D had lower performance on all physical function tests. The study found 9.7% lower grip strength, 9.9% slower gait speed, and 13.9% slower timed up-and-go time than women without diabetes. During a median (IQR) follow-up of 7.3 (4.4-8.4) years, 1071 incident fractures, 853 major osteoporotic fractures (MOF), and 232 hip fractures occurred. In adjusted (for age, body mass index, clinical risk factors, and FN BMD) Cox regression models, T2D was associated with an increased risk of any fracture (HR, 1.26; 95% CI, 1.04-1.54) and MOF (HR, 1.25; 95% CI, 1.00-1.56).

Conclusions and Relevance

In this cohort study of older women, T2D was associated with higher BMD, better bone microarchitecture, and no different BMSi but poorer physical function, suggesting that poor physical function is the main reason for the increased fracture risk in T2D women.

The practicality of using bone impact microindentation in a population-based study of women: A Geelong-Osteoporosis Study

Impact microindentation (IMI) is a minimally invasive technique that allows the assessment of 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. In this study, we aimed to assess the practicality of its application in 99 women aged 42-84 yr from the Geelong Osteoporosis Study. Impact microindentation was performed in the mid-shaft of the right tibia using the OsteoProbe. Immediately following measurement, each participant was requested to rate on a Visual Analogue Scale [0-10] the level of discomfort anticipated and experienced, any initial reluctance towards the measurement and whether they were willing to repeat the measurement. Of 99 potential participants who attended this assessment phase, 55 underwent IMI measurement. Reasons for non-measurement in 44 women were existing skin conditions (n = 8, 18.2 %) and excessive soft tissue around mid-tibial region (n = 32, 72.2 %). An additional four (9.1 %) participants did not provide any reasons for declining. For 55 participants who had underwent IMI, the expectation for pain when briefed about the procedure was low (2.28 ± 2.39), as was pain experienced during the measurement (0.72 ± 1.58). Participants were not reluctant to undergo the measurement (0.83 ± 1.67), and all indicated a willingness to repeat the measurement. Results of this study showed that the IMI technique is well tolerated and accepted by women participating in the Geelong Osteoporosis Study, suggesting that the technique shows promise in a research or clinical setting.

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.

Mean Bone Material Strength Index Values for Women are Lower Than Those for Men: Data from a Single Geographical Location

Bone material strength index (BMSi) values are obtained using impact microindentation, which assesses the ability of bone to resist indentation. Differences in BMSi between men and women are unclear, and to date, BMSi sex differences have not been compared for individuals from the same population. Therefore, we compared BMSi values for men and women drawn from the same geographical location in Australia. Participants (n = 220) were from the Geelong Osteoporosis Study. BMSi was measured, following international published guidelines, using an OsteoProbe for participants at recent follow-up phases (women 2022-2023 and men 2016-2022). Women (n = 55) were age matched to men (n = 165) in a 1:3 ratio. A two-sample t test was used to determine the intergroup difference in mean BMSi. Linear regression was also performed, adjusting for weight and height. Median (IQR) ages for men and women were 67.0 (61.7-71.5) and 67.4 (62.0-71.2) years (p = 0.998). Men were heavier (81.0 ± 10.9 vs 71.0 ± 13.9 kg, p < 0.001) and taller (173.9 ± 6.4 vs 161.5 ± 7.5 cm, p < 0.001) than women. Mean (± SD) BMSi for women (75.7 ± 7.4) was lower than for men (82.8 ± 6.8) (p < 0.001). The difference persisted after adjustment for weight and height (mean ± SE: 76.5 ± 1.1 vs 82.5 ± 0.6, p < 0.001). Given the higher fracture risk observed for women, the higher mean BMSi values in men are consistent with cross sectional data suggesting this measure may be useful in fracture prediction.

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.