Tibial or hip BMD predict clinical fracture risk equally well: results from a prospective study in 700 elderly Swiss women

Update of the fracture risk prediction tool FRAX: a systematic review of potential cohorts and analysis plan

We describe the collection of cohorts together with the analysis plan for an update of the fracture risk prediction tool FRAX with respect to current and novel risk factors. The resource comprises 2,138,428 participants with a follow-up of approximately 20 million person-years and 116,117 documented incident major osteoporotic fractures.

INTRODUCTION

The availability of the fracture risk assessment tool FRAX® has substantially enhanced the targeting of treatment to those at high risk of fracture with FRAX now incorporated into more than 100 clinical osteoporosis guidelines worldwide. The aim of this study is to determine whether the current algorithms can be further optimised with respect to current and novel risk factors.

METHODS

A computerised literature search was performed in PubMed from inception until May 17, 2019, to identify eligible cohorts for updating the FRAX coefficients. Additionally, we searched the abstracts of conference proceedings of the American Society for Bone and Mineral Research, European Calcified Tissue Society and World Congress of Osteoporosis. Prospective cohort studies with data on baseline clinical risk factors and incident fractures were eligible.

RESULTS

Of the 836 records retrieved, 53 were selected for full-text assessment after screening on title and abstract. Twelve cohorts were deemed eligible and of these, 4 novel cohorts were identified. These cohorts, together with 60 previously identified cohorts, will provide the resource for constructing an updated version of FRAX comprising 2,138,428 participants with a follow-up of approximately 20 million person-years and 116,117 documented incident major osteoporotic fractures. For each known and candidate risk factor, multivariate hazard functions for hip fracture, major osteoporotic fracture and death will be tested using extended Poisson regression. Sex- and/or ethnicity-specific differences in the weights of the risk factors will be investigated. After meta-analyses of the cohort-specific beta coefficients for each risk factor, models comprising 10-year probability of hip and major osteoporotic fracture, with or without femoral neck bone mineral density, will be computed.

CONCLUSIONS

These assembled cohorts and described models will provide the framework for an updated FRAX tool enabling enhanced assessment of fracture risk (PROSPERO (CRD42021227266)).

Predictors of Bone Mineral Density in Kidney Stone Formers

Introduction

Nephrolithiasis is associated with an increased fracture risk, but predictors of bone mineral density (BMD) in stone formers (SFs) remain poorly defined.

Methods

We conducted a retrospective analysis in the Bern Kidney Stone Registry (BKSR), an observational cohort of kidney SFs. Inclusion criteria were age ≥18 years and ≥1 past stone episode. Participants with non–calcium (Ca)-containing kidney stones, a history of primary hyperparathyroidism or antiresorptive or anabolic bone treatment were excluded. Multivariable linear regression analyses were used to assess the association of blood and 24-hours urine parameters and stone composition with BMD at the lumbar spine and femoral neck.

Results

In the analysis, 504 participants were included, mean age was 46 years, and 76% were male. In multivariable analyses, fasting (β: −0.031; P = 0.042), postload (β: −0.059; P = 0.0028) and Δ postload − fasting (β: −0.053; P = 0.0029) urine Ca-to-creatinine ratios after 1 week of a sodium- and Ca- restricted diet and Ca oxalate dihydrate stone content (β: −0.042; P = 0.011) were negatively associated with z scores at the lumbar spine. At the femoral neck, alkaline phosphatase (β: −0.035; P = 0.0034) and parathyroid hormone (PTH) (β: −0.035; P = 0.0026) were negatively associated with z scores, whereas 24-hours urine Ca (β: 0.033; P = 0.0085), magnesium (β: 0.043; P = 3.5 × 10⁻⁴), and potassium (β: 0.032; P = 0.012) correlated positively with z scores at the femoral neck.

Conclusion

Our study reveals distinct predictors of BMD in SFs. Commonly available clinical parameters, such as kidney stone composition results, can be used to identify SFs at risk for low BMD.

In vivo Measurement of Intraosseous Vascular Haemodynamic Markers in Human Bone Tissue Utilising Near Infrared Spectroscopy

Objective: Poor vascular health is associated with reduced bone strength and increased risk of fragility fracture. However, direct measurement of intraosseous vascular health is difficult due to the density and mineral content of bone. We investigated the feasibility of using a commercially available continuous wave near infrared spectroscopy (NIRS) system for the investigation of vascular haemodynamics in human bone in vivo.

Approach: An arterial occlusion (AO) protocol was developed for obtaining haemodynamic measurements of the proximal tibia and lateral calf, including assessment of the protocol’s intra operator reproducibility. For 36 participants, intraosseous haemodynamics derived by NIRS were compared to alternative tests of bone health based on dual x-ray absorptiometry (DXA) testing and MRI.

Main Results: Near infrared spectroscopy markers of haemodynamics of the proximal tibia demonstrated acceptable reproducibility, comparable with reproducibility assessments of alternative modalities measuring intraosseous haemodynamics, and the use of NIRS for measuring muscle. Novel associations have been demonstrated between haemodynamic markers of bone measured with NIRS and body composition and bone mineral density (BMD) measurements obtained with both DXA and MRI.

Significance: Near infrared spectroscopy provides inexpensive, non-invasive, safe, and real time data on changes in oxygenated and deoxygenated haemoglobin concentration in bone at the proximal tibia. This study has demonstrated the potential for NIRS to contribute to research investigating the pathophysiological role of vascular dysfunction within bone tissue, but also the limitations and need for further development of NIRS technology.

Cortical parameters predict bone strength at the tibial diaphysis, but are underestimated by HR-pQCT and μCT compared to histomorphometry

Cortical bone and its microstructure are crucial for bone strength, especially at the long bone diaphysis. However, it is still not well‐defined how imaging procedures can be used as predictive tools for mechanical bone properties. This study evaluated the capability of several high‐resolution imaging techniques to capture cortical bone morphology and assessed the correlation with the bone's mechanical properties. The microstructural properties (cortical thickness [Ct.Th], porosity [Ct.Po], area [Ct.Ar]) of 11 female tibial diaphysis (40–90 years) were evaluated by dual‐energy X‐ray absorptiometry (DXA), high‐resolution peripheral‐quantitative‐computed‐tomography (HR‐pQCT), micro‐CT (μCT) and histomorphometry. Stiffness and maximal torque to failure were determined by mechanical testing. T‐Scores determined by DXA ranged from 0.6 to −5.6 and a lower T‐Score was associated with a decrease in Ct.Th (p ≤ 0.001) while the Ct.Po (p ≤ 0.007) increased, and this relationship was independent of the imaging method. With decreasing T‐Score, histology showed an increase in Ct.Po from the endosteal to the periosteal side (p = 0.001) and an exponential increase in the ratio of osteons at rest to those after remodelling. However, compared to histomorphometry, HR‐pQCT and μCT underestimated Ct.Po and Ct.Th. A lower T‐Score was also associated with significantly reduced stiffness (p = 0.031) and maximal torque (p = 0.006). Improving the accuracy of Ct.Po and Ct.Th did not improve prediction of the mechanical properties, which was most closely related to geometry (Ct.Ar). The ex‐vivo evaluation of mechanical properties correlated with all imaging modalities, with Ct.Th and Ct.Po highly correlated with the T‐Score of the tibial diaphysis. Cortical microstructural changes were underestimated with the lower resolution of HR‐pQCT and μCT compared to the histological ‘gold standard’. The increased accuracy did not result in an improved prediction for local bone strength in this study, which however might be related to the limited number of specimens and thus needs to be evaluated in a larger collective.

Biomechanical analysis of proximal tibia bone grafting and the effect of the size of osteotomy using a validated finite element model

Harvesting bone graft from the proximal tibia is gaining popularity, with lower complication rates and adequate quantity of cancellous bone. The amount of harvested bone is dependent on the size of the cortical window introduced via osteotomy onto the proximal tibia, and its mechanical strength after surgery could be compromised. The aim of the study was to investigate the proximal tibia's mechanical stability after bone harvesting and the effect of varying window sizes using a validated finite element model. Two cadaveric tibiae were tested with bone strains measured for different circular cortical window diameters (10-25 mm). Sixteen finite element models of the intact and harvested tibia were simulated and validated with experimental data. The experimental and predicted max/min principal bone strains were fitted into regression models and showed good correlations. It was predicted the maximum principal bone stresses were greatest and concentrated at postero-inferior and antero-superior regions of the cortical window. A stress line progressed from the edge of the window to the posterior side of the tibia, which became more prominent with the increase of size of the cortical window. It was found that large circular osteotomies for bone harvesting at the proximal tibia induced stress concentrations and stress lines which could lead to eventual failure. Graphical abstract The formation of a stress line in the harvested tibia initiated from the postero-inferior edge of the window and progressed to the medial side. The stress line became more prominent with the increase of the size of the cortical window from 10 to 25 mm in diameter.

Factors associated with acute-phase response of bisphosphonate-naïve or pretreated women with osteoporosis receiving an intravenous first dose of zoledronate or ibandronate

A first intravenous dose of bisphosphonates may be associated with an acute-phase response (APR). In bisphosphonate-naïve women with postmenopausal osteoporosis, the characteristics and frequency of APR may differ by compound. Prior bisphosphonate exposure was predictive of APR risk and severity.

INTRODUCTION

Intravenous (IV) administration of bisphosphonates (BP), such as zoledronate (ZOL) and ibandronate (IBN), may be associated with an APR. The characteristics of APR may differ by compound. The aim of the present study was to evaluate the characteristics of APR (rates, signs and symptoms, severity), in the absence of any preventive measure, after a first IV application of ZOL or IBN in patients naïve or previously exposed to BP in a real-world clinical setting.

METHODS

This is an open-label prospective exploratory study with two cohorts of consecutive postmenopausal women with osteoporosis treated with either IV ZOL or IBN at the Department of Osteoporosis of the University Hospital of Berne, Switzerland.

RESULTS

Intravenous BP was administered to 725 women (411 ZOL and 314 IBN). Prior oral or IV BP use was less frequent in the ZOL group (61.8 vs. 71.7%, p = 0.005). In total, 301 women (41.5%) reported the presence of one or more signs or symptoms of APR with rates for ZOL and IBN of 47.7 and 33.4%, respectively (p < 0.001). Corresponding APR rates in the subgroup of BP-naïve patients were 55.6 and 32.4%, respectively (p < 0.001). The leading APR clinical sign was the presence of post-dose myalgia or arthralgia (68.1%). Prior BP exposure was predictive of both APR risk and severity, and lower serum 25-hydroxy vitamin D (25(OH)D) levels were possibly predictive of severity.

CONCLUSIONS

In a real-world setting, APR rates with ZOL and IBN may be higher than reported in randomised controlled trials and may differ by compound, prior BP exposure, and serum 25(OH)D levels.

Bone Mass Distribution of the Distal Tibia in Normal, Osteopenic, and Osteoporotic Conditions: An Ex Vivo Assessment Using HR-pQCT, DXA, and Computational Modelling

Osteoporosis leads to bone loss and structural deterioration, which increase the risk of fractures. The aim of this study was to characterize the three-dimensional (3D) bone mass distributions of the distal tibia in normal, osteopenic, and osteoporotic conditions. High-resolution peripheral quantitative computed tomography (HR-pQCT) of the 33 % of the distal tibia and local dual-energy X-ray absorptiometry were applied to 53 intact, fresh-frozen tibiae. The HR-pQCTs were graded to assign local T-scores and merged into three equally sized average normal, osteopenic, and osteoporotic surface models. Volumetric bone mineral density (vBMD) was determined using categorized T-scores, volumetric visualization, and virtual bore probes at the dia-, meta-, and epiphyseal sites (T-DIA, T-META, and T-EPI). We observed a distinct 3D bone mass distribution that was gradually uninfluenced by T-score categories. T-DIA was characterized by the lowest bone mass located in the medullary cavity and a wide homogenous cortex containing the maximum vBMD. The T-META showed decreased cortical thickness and maximal vBMD. At the T-EPI, the relatively low vBMD of the mostly trabecular bone was similar to the maximal cortical vBMD in this sub-region. Four trabecular regions of low bone mass were identified in the recesses. The bone content gradually decreased at all sites, whereas the pattern of bone mass distribution remained essentially unchanged, with the exception of disproportionate losses at T-DIA, T-META, and T-EPI that consistently showed increased endocortical, intracortical, and trabecular bone loss. Extra information can be obtained from the specific pattern of bone mass distribution, potential disproportionate bone losses, and method used.

A biomechanical study of proximal tibia bone grafting through the lateral approach

BACKGROUND

Autologous bone graft remains the gold standard source of bone graft. Iliac crest has traditionally been the most popular source for autologous bone graft. However, iliac crest bone graft harvesting is associated with high donor site morbidity. Bone graft harvesting from the proximal tibia has shown great potential with reported low complication rates. However, there is a paucity of biomechanical studies concerning the safety as well as yield of proximal bone graft harvesting.

PURPOSE

This biomechanical study was designed to investigate (1) the stability of the harvested proximal tibial during physiological loading, and (2) the maximum size of the cortical window that can be safely created and (3) volume of accessible bone graft.

METHODS

Bone grafts were harvested from eleven cadaveric tibiae using a circular cortical window along the lateral proximal tibia. These harvested proximal tibiae were then loaded under physiological conditions (mean 2320N, range 1650-3120N) using a customized test fixture. Strain rosettes were mounted at 7 locations in the harvested proximal tibia to record the changes in strain at the harvested proximal tibia. The change in strain with increasing cortical window size (10-25mm diameter) was also studied. Bone principal strains as well as volume of bone harvested were recorded.

RESULTS

A repeated measures ANOVA was used to analyze the change in bone strains with the cortical window size. Statistically significant (p<0.05) increases in bone strains at the anterior and medial aspects of the tibia were observed with increasing size of osteotomies (-328.85με, SD=232.21 to -964.78με, SD=535.89 and 361.64με, SD=229.90 to -486.08με, SD=270.40 respectively), and marginally significant changes in strain at the lateral and posterior aspects. None of the tibiae failed under normal walking loads even with increasing osteotomies size of 10-25 mm diameter. A smaller osteotomy of 10mm diameter yielded an average volume of 7.15ml of compressed bone graft, while a larger osteotomy of 25mm diameter yielded on average an additional 3.64ml of bone graft. Bone grafting of the proximal tibia through the lateral approach with a circular osteotomy is a feasible option even with osteotomies of 25mm diameter. Even though increased bone strains were observed, the strains did not exceed the yield strain of cortical bone when loaded under normal walking conditions. The quantity of bone harvested from the proximal tibia is comparable to that harvested from the iliac crest.

CONCLUSIONS

This biomechanical study demonstrated the stability of the harvested proximal tibia under conditions of full weight bearing ambulation. It has also refined the technique of proximal bone graft harvesting by determining the maximum size of the cortical window. The findings of this study add to the overall understanding of proximal tibial bone graft harvesting, providing objective data regarding stability as well as yield. This information would be useful during selection of source of autologous bone graft.

Microstructural parameters of bone evaluated using HR-pQCT correlate with the DXA-derived cortical index and the trabecular bone score in a cohort of randomly selected premenopausal women

Background

Areal bone mineral density is predictive for fracture risk. Microstructural bone parameters evaluated at the appendicular skeleton by high-resolution peripheral quantitative computed tomography (HR-pQCT) display differences between healthy patients and fracture patients. With the simple geometry of the cortex at the distal tibial diaphysis, a cortical index of the tibia combining material and mechanical properties correlated highly with bone strength ex vivo. The trabecular bone score derived from the scan of the lumbar spine by dual-energy X-ray absorptiometry (DXA) correlated ex vivo with the micro architectural parameters. It is unknown if these microstructural correlations could be made in healthy premenopausal women.

Methods

Randomly selected women between 20–40 years of age were examined by DXA and HR-pQCT at the standard regions of interest and at customized sub regions to focus on cortical and trabecular parameters of strength separately. For cortical strength, at the distal tibia the volumetric cortical index was calculated directly from HR-pQCT and the areal cortical index was derived from the DXA scan using a Canny threshold-based tool. For trabecular strength, the trabecular bone score was calculated based on the DXA scan of the lumbar spine and was compared with the corresponding parameters derived from the HR-pQCT measurements at radius and tibia.

Results

Seventy-two healthy women were included (average age 33.8 years, average BMI 23.2 kg/m²). The areal cortical index correlated highly with the volumetric cortical index at the distal tibia (R  =  0.798). The trabecular bone score correlated moderately with the microstructural parameters of the trabecular bone.

Conclusion

This study in randomly selected premenopausal women demonstrated that microstructural parameters of the bone evaluated by HR-pQCT correlated with the DXA derived parameters of skeletal regions containing predominantly cortical or cancellous bone. Whether these indexes are suitable for better predictions of the fracture risk deserves further investigation.

Cortical bone loss at the tibia in postmenopausal women with osteoporosis is associated with incident non-vertebral fractures: results of a randomized controlled ancillary study of HORIZON

BACKGROUND

In postmenopausal women, yearly intravenous zoledronate (ZOL) compared to placebo (PLB) significantly increased bone mineral density (BMD) at lumbar spine (LS), femoral neck (FN), and total hip (TH) and decreased fracture risk. The effects of ZOL on BMD at the tibial epiphysis (T-EPI) and diaphysis (T-DIA) are unknown.

METHODS

A randomized controlled ancillary study of the HORIZON trial was conducted at the Department of Osteoporosis of the University Hospital of Berne, Switzerland. Women with ≥1 follow-up DXA measurement who had received ≥1 dose of either ZOL (n=55) or PLB (n=55) were included. BMD was measured at LS, FN, TH, T-EPI, and T-DIA at baseline, 6, 12, 24, and 36 months. Morphometric vertebral fractures were assessed. Incident clinical fractures were recorded as adverse events.

RESULTS

Baseline characteristics were comparable with those in HORIZON and between groups. After 36 months, BMD was significantly higher in women treated with ZOL vs. PLB at LS, FN, TH, and T-EPI (+7.6%, +3.7%, +5.6%, and +5.5%, respectively, p<0.01 for all) but not T-DIA (+1.1%). The number of patients with ≥1 incident non-vertebral or morphometric fracture did not differ between groups (9 ZOL/11 PLB). Mean changes in BMD did not differ between groups with and without incident fracture, except that women with an incident non-vertebral fracture had significantly higher bone loss at predominantly cortical T-DIA (p=0.005).

CONCLUSION

ZOL was significantly superior to PLB at T-EPI but not at T-DIA. Women with an incident non-vertebral fracture experienced bone loss at T-DIA.

Automated, foot-bone registration using subdivision-embedded atlases for spatial mapping of bone mineral density

We present an atlas-based registration method for bones segmented from quantitative computed tomography (QCT) scans, with the goal of mapping their interior bone mineral densities (BMDs) volumetrically. We introduce a new type of deformable atlas, called subdivision-embedded atlas, which consists of a control grid represented as a tetrahedral subdivision mesh and a template bone surface embedded within the grid. Compared to a typical lattice-based deformation grid, the subdivision control grid possesses a relatively small degree of freedom tailored to the shape of the bone, which allows efficient fitting onto subjects. Compared with previous subdivision atlases, the novelty of our atlas lies in the addition of the embedded template surface, which further increases the accuracy of the fitting. Using this new atlas representation, we developed an efficient and fully automated pipeline for registering atlases of 12 tarsal and metatarsal bones to a segmented QCT scan of a human foot. Our evaluation shows that the mapping of BMD enabled by the registration is consistent for bones in repeated scans, and the regional BMD automatically computed from the mapping is not significantly different from expert annotations. The results suggest that our improved subdivision-based registration method is a reliable, efficient way to replace manual labor for measuring regional BMD in foot bones in QCT scans.

Fragility fractures in the elderly: Evolving approaches in the NHS

Fragility fractures account for a significant proportion of trauma admissions and clinic attendances in the UK. Hip fractures constitute a major part of these fractures followed by wrist, spine and humerus. With the increasing elderly population and increasing life expectancy, incidences of these fractures have increased proportionately. Hip fractures cause significant morbidity and mortality because of existing medical co-morbidities or perioperative complications. In order to decrease the overall incidence of osteoporotic fractures and improve outcome of surgical treatment, different approaches to prevention and treatment are currently evolving throughout the NHS. These include primary prevention through management of osteoporosis and secondary prevention aimed at treating osteoporosis and reducing further fractures. In this article, we highlight the different care pathways that could effectively decrease the incidence of fragility fractures as well as the morbidity and mortality in these patients.

Prediction of bone strength at the distal tibia by HR-pQCT and DXA

BACKGROUND

Areal bone mineral density (aBMD) at the distal tibia, measured at the epiphysis (T-EPI) and diaphysis (T-DIA), is predictive for fracture risk. Structural bone parameters evaluated at the distal tibia by high resolution peripheral quantitative computed tomography (HR-pQCT) displayed differences between healthy and fracture patients. With its simple geometry, T-DIA may allow investigating the correlation between bone structural parameter and bone strength.

METHODS

Anatomical tibiae were examined ex vivo by DXA (aBMD) and HR-pQCT (volumetric BMD (vBMD) and bone microstructural parameters). Cortical thickness (CTh) and polar moment of inertia (pMOI) were derived from DXA measurements. Finally, an index combining material (BMD) and mechanical property (polar moment of inertia, pMOI) was defined and analyzed for correlation with torque at failure and stiffness values obtained by biomechanical testing.

RESULTS

Areal BMD predicted the vBMD at T-EPI and T-DIA. A high correlation was found between aBMD and microstructural parameters at T-EPIas well as between aBMD and CTh at T-DIA. Finally, at T-DIA both indexes combining BMD and pMOI were strongly and comparably correlated with torque at failure and bone stiffness.

CONCLUSION

Ex vivo, at the distal tibial diaphysis, a novel index combining BMD and pMOI, which can be calculated directly from a single DXA measurement, predicted bone strength and stiffness better than either parameter alone and with an order of magnitude comparable to that of HR-pQCT. Whether this index is suitable for better prediction of fracture risk in vivo deserves further investigation.

Comparative examination of human proximal tibiae in vitro by ultrasonic guided waves and pQCT

The velocity of ultrasonic guided waves in long bones is dependent upon two determinants of bone strength: the cortical thickness and the material properties. In this study, six human proximal tibiae in vitro were examined to test the efficacy of an ultrasonic method based on guided waves. Peripheral quantitative computed tomography (pQCT) was used as the comparative reference modality. The guided wave velocity (c(F)) was derived from two-dimensional (2-D) spatial-temporal waveform profiles formed by multiple ultrasonic signals acquired along the bones at 100 kHz frequency and passed wavelet processing. The ultrasonic profiles from the examined bones were ranged according to pQCT measurements of cortical thickness (CTh), and cortical bone mineral density (CBMD). Strong correlations between c(F) and CTh (r(S) = 0.83, p < 0.0001) and CBMD (r(S) = 0.88, p < 0.0001) resulted. The study confirmed a potential for guided waves to assess atrophic changes of the proximal tibia.