Once-monthly oral ibandronate improves biomechanical determinants of bone strength in women with postmenopausal osteoporosis

Use of DXA-based finite element analysis of the proximal femur in a longitudinal study of hip fracture

Bone mineral density (BMD) measured by dual-energy X-ray absorptiometry (DXA) is used for clinical assessment of fracture risk; however, measurements that incorporate bone strength could improve predictive ability. The aim of this study was to determine whether bone strength derived from finite element (FE) analysis was associated with hip fracture risk in a longitudinal study. We studied 728 women (mean age 82 years), 182 with subsequent hip fracture. FE models were generated from baseline DXA scans of the hip to determine femoral bone strength and load-to-strength ratio (LSR). The baseline LSR was significantly higher in fracture cases (median 1.1) compared with controls (0.7, p < 0.0001). Femoral strength and BMD were also significantly lower in cases (median 1820 N, 0.557 g/cm(2)) compared with controls (2614 N, 0.618 g/cm(2) ) both p < 0.0001. Fracture risk increased per standard deviation decrease in femoral strength (odds ratio [OR] = 2.2, 95% confidence interval [CI] 1.8-2.8); femoral neck (FN) BMD (OR = 2.1, 95% CI 1.7-2.6); total hip BMD (OR = 1.8, 95% CI 1.5-2.1); and per SD increase in LSR (OR = 1.8, 95% CI 1.5-2.1). After adjusting for FN BMD, the odds ratio for femoral strength (OR = 1.7, 95% CI 1.2-2.4) and LSR (OR = 1.4, 95% CI 1.1-1.7) remained significantly greater than 1. The area under the curve (AUC) for LSR combined with FN BMD (AUC 0.69, 95% CI 0.64-0.73) was significantly greater than FN BMD alone (AUC 0.66, 95% CI 0.62-0.71, p = 0.004). Strength and LSR remained significant when adjusted for prevalent fragility fracture, VFA, and FRAX score. In conclusion, the DXA-based FE model was able to discriminate incident hip fracture cases from controls in this longitudinal study independently from FN BMD, prior fracture, VFA, and FRAX score. Such an approach may provide a useful tool for better assessment of bone strength to identify patients at high risk of hip fracture who may benefit from treatment to reduce fracture risk.

A comparison of DXA and CT based methods for estimating the strength of the femoral neck in post-menopausal women

The study goal was to compare simple two-dimensional (2D) analyses of bone strength using dual energy x-ray absorptiometry (DXA) data to more sophisticated three-dimensional (3D) finite element analyses using quantitative computed tomography (QCT) data. DXA- and QCT-derived femoral neck geometry, simple strength indices, and strength estimates were well correlated.

INTRODUCTION

Simple 2D analyses of bone strength can be done with DXA data and applied to large data sets. We compared 2D analyses to 3D finite element analyses (FEA) based on QCT data.

METHODS

Two hundred thirteen women participating in the Study of Women's Health Across the Nation (SWAN) received hip DXA and QCT scans. DXA BMD and femoral neck diameter and axis length were used to estimate geometry for composite bending (BSI) and compressive strength (CSI) indices. These and comparable indices computed by Hip Structure Analysis (HSA) on the same DXA data were compared to indices using QCT geometry. Simple 2D engineering simulations of a fall impacting on the greater trochanter were generated using HSA and QCT femoral neck geometry; these estimates were benchmarked to a 3D FEA of fall impact.

RESULTS

DXA-derived CSI and BSI computed from BMD and by HSA correlated well with each other (R=0.92 and 0.70) and with QCT-derived indices (R=0.83-0.85 and 0.65-0.72). The 2D strength estimate using HSA geometry correlated well with that from QCT (R=0.76) and with the 3D FEA estimate (R=0.56).

CONCLUSIONS

Femoral neck geometry computed by HSA from DXA data corresponds well enough to that from QCT for an analysis of load stress in the larger SWAN data set. Geometry derived from BMD data performed nearly as well. Proximal femur breaking strength estimated from 2D DXA data is not as well correlated with that derived by a 3D FEA using QCT data.

A nonlinear QCT-based finite element model validation study for the human femur tested in two configurations in vitro

PURPOSE

Femoral fracture is a common medical problem in osteoporotic individuals. Bone mineral density (BMD) is the gold standard measure to evaluate fracture risk in vivo. Quantitative computed tomography (QCT)-based homogenized voxel finite element (hvFE) models have been proved to be more accurate predictors of femoral strength than BMD by adding geometrical and material properties. The aim of this study was to evaluate the ability of hvFE models in predicting femoral stiffness, strength and failure location for a large number of pairs of human femora tested in two different loading scenarios.

METHODS

Thirty-six pairs of femora were scanned with QCT and total proximal BMD and BMC were evaluated. For each pair, one femur was positioned in one-legged stance configuration (STANCE) and the other in a sideways configuration (SIDE). Nonlinear hvFE models were generated from QCT images by reproducing the same loading configurations imposed in the experiments. For experiments and models, the structural properties (stiffness and ultimate load), the failure location and the motion of the femoral head were computed and compared.

RESULTS

In both configurations, hvFE models predicted both stiffness (R(2)=0.82 for STANCE and R(2)=0.74 for SIDE) and femoral ultimate load (R(2)=0.80 for STANCE and R(2)=0.85 for SIDE) better than BMD and BMC. Moreover, the models predicted qualitatively well the failure location (66% of cases) and the motion of the femoral head.

CONCLUSIONS

The subject specific QCT-based nonlinear hvFE model cannot only predict femoral apparent mechanical properties better than densitometric measures, but can additionally provide useful qualitative information about failure location.

Oral ibandronate in postmenopausal osteoporotic women alters micromechanical properties independently of changes in mineralization

Postmenopausal osteoporotic (PMOP) women treated with ibandronate had higher bone mineral density, lower bone turnover, and decreased incidence of new vertebral fractures. The aim of this study was to investigate the effect of daily or intermittent oral ibandronate on the degree of mineralization (DMB) of bone and microhardness (Hv) at the bone tissue and bone structural unit (BSU) levels. A total of 110 iliac biopsies were taken from patients treated for 22 or 34 months with an oral placebo (n = 36), 2.5 mg daily oral ibandronate (n = 40), or 20 mg intermittent oral ibandronate (n = 34). These regimens provide annual cumulative exposures (ACEs) that are about half of the therapeutic doses currently licensed for PMOP women. DMB and Hv were measured at the global level (i.e., cortical or cancellous) and the focal level (i.e., BSU). At the global level, DMB and its distribution were not significantly different from placebo after 22 and 34 months of treatment. Hv was significantly higher in the cortical, cancellous, and total bone after 22 and 34 months of ibandronate versus placebo for both regimens. At the focal level, DMB and Hv, measured simultaneously in 3,760 BSUs, were significantly and positively correlated in all groups (r = 0.59-0.65, p < 0.0001). However, analysis of covariance highlighted the differences in the y intercepts of the linear regressions of the placebo- and ibandronate-treated groups. We infer that a low ACE of oral ibandronate altered the bone micromechanical properties irrespective of changes in secondary mineralization.

QCT bone mineral density responses to 1 year of oral bisphosphonate after total knee replacement for knee osteoarthritis

Bone mineral density (BMD) declined in more than half (53.7%) of post-total knee arthroplasty (TKA) patients (44 of the 82) after 1 year of oral bisphosphonate treatment, and that this decline was significant in bilateral TKA patients.

INTRODUCTION

TKA has proven to be an extremely successful procedure in terms of improving ambulatory function. However, the effects of such improvements in ambulatory function and of bisphosphonate on axial BMD have not been established. The purpose of this study was to determine the effect of 1 year of oral bisphosphonate in postmenopausal patients that have undergone TKA and to identify factors related to BMD changes using lumbar spine quantitative computed tomography (QCT).

METHODS

Eighty-two postmenopausal women that underwent primary TKA for knee osteoarthritis and who received once-weekly oral alendronate 70 mg for 12 months after TKA were enrolled. The effect of 1 year of oral bisphosphonate treatment post-TKA and the factors related to general lumbar spine BMD changes by using QCT were determined.

RESULTS

Some 53.7% of patients (44 of the 82) experienced an average lumbar spine QCT BMD decline of -6 mg/ml (range -15 to -0.5 mg/ml) after 1 year of oral bisphosphonate treatment, whereas the remaining 38 patients (46.3%) experienced an average increase of 6.8 mg/ml (range 0.6 to 15.7 mg/ml). Logistic and linear regression analysis showed that bilateral TKA was significantly related to a BMD decline (p < 0.05). Other factors, such as, age, body mass index, number of comorbidities, and Knee Society scores were not found to be significantly related to BMD response.

CONCLUSIONS

BMD declined in more than half (53.7%) of the patients after bisphosphonate treatment, and that this decline was significant in bilateral TKA patients. We believe that reduced mobility during rehabilitation was probably responsible for these BMD reductions.

Site-specific differential effects of once-yearly zoledronic acid on the hip assessed with quantitative computed tomography: results from the HORIZON Pivotal Fracture Trial

We used new approaches to the analysis of diagnostic scans to detect changes in bone density in different regions of the hip after 3 years of treatment with the zoledronic acid. We showed that the drug significantly increases hip bone density compared to placebo at regions where hip fractures usually occur.

INTRODUCTION

This study aims to identify whether treatment with zoledronic acid exerts site-specific differential effects on volumetric bone mineral density (vBMD) at the hip.

METHODS

We analysed quantitative computed tomography scans of the hip obtained at baseline and 36 months in 179 women participating in the HORIZON Pivotal Fracture Trial. Cortical, trabecular and integral BMDs were determined at three main regions of interest-the femoral neck (FN), trochanter (TR) and total hip (TH)-and several sub-regions of interest, namely the proximal, middle, distal, anterior, posterior, inferomedial and superolateral FN, and the middle and distal TR.

RESULTS

Volumetric BMD increased significantly (p < 0.05) from baseline with zoledronic acid compared to placebo. Trabecular vBMD increased as follows: FN, 5.4 %; FN sub-regions, 6.0 % (proximal), 4.4 % (middle), 5.6 % (distal), 7.5 % (anterior), 7.0 % (superolateral) and 5.4 % (posterior); TR, 6.5 % and TH, 5.7 %. Cortical vBMD increased as follows: FN sub-regions, 5.0 % (proximal FN) and 2.3 % (anterior); TR, 4.6 %; middle TR, 2.7 % and TH, 3.8 %.

CONCLUSIONS

The effects on vBMD of annual infusion of 5 mg of zoledronic acid are site-specific and dominated by trabecular changes.

Assessment of bone quality and strength with new technologies

PURPOSE OF REVIEW

To give an overview of advanced in-vivo imaging techniques for assessing bone quality beyond bone mineral density that have considerably advanced in recent years.

RECENT FINDINGS

Quantitative computed tomography and finite element analysis improve fracture risk prediction at the spine, and help to better understand the pathophysiology of skeletal diseases and response to therapy by quantifying bone mineral density in different bone compartments, determining bone strength, and assessing bone geometry. With new high-resolution techniques, trabecular structure at the spine, forearm, and tibia, and cortical porosity at the forearm and tibia can be measured. Hip structure analysis and trabecular bone score have extended the usefulness of dual X-ray absorptiometry.

SUMMARY

New advanced three-dimensional imaging techniques to quantify bone quality are mature and have proven to be complimentary methods to dual X-ray absorptiometry enhancing our understanding of bone metabolism and treatment.

Distribution of bone density in the proximal femur and its association with hip fracture risk in older men: the osteoporotic fractures in men (MrOS) study

This prospective case-cohort study aimed to map the distribution of bone density in the proximal femur and examine its association with hip fracture. We analyzed baseline quantitative computed tomography (QCT) scans in 250 men aged 65 years or older, which comprised a randomly-selected subcohort of 210 men and 40 cases of first hip fracture during a mean follow-up period of 5.5 years. We quantified cortical, trabecular, and integral volumetric bone mineral density (vBMD), and cortical thickness (CtTh) in four quadrants of cross-sections along the length of the femoral neck (FN), intertrochanter (IT), and trochanter (TR). In most quadrants, vBMDs and CtTh were significantly (p < 0.05) lower in cases compared to the subcohort and these deficits were present across the entire proximal femur. To examine the association of QCT measurements with hip fracture, we merged the two quadrants in the medial and lateral aspects of the FN, IT, and TR. At most sites, QCT measurements were associated significantly (p < 0.001) with hip fracture, the hazard ratio (HR) adjusted for age, body mass index (BMI), and clinical site for a 1-SD decrease ranged between 2.28 (95% confidence interval [CI], 1.44-3.63) to 6.91 (95% CI, 3.11-15.53). After additional adjustment for total hip (TH) areal BMD (aBMD), trabecular vBMDs at the FN, TR, and TH were still associated with hip fracture significantly (p < 0.001), the HRs ranged from 3.21 (95% CI, 1.65-6.24) for the superolateral FN to 6.20 (95% CI, 2.71-14.18) for medial TR. QCT measurements alone or in combination did not predict fracture significantly (p > 0.05) better than TH aBMD. With an area under the receiver operating characteristic curve (AUC) of 0.901 (95% CI, 0.852-0.950), the regression model combining TH aBMD, age, and trabecular vBMD predicted hip fracture significantly (p < 0.05) better than TH aBMD alone or TH aBMD plus age. These findings confirm that both cortical and trabecular bone contribute to hip fracture risk and highlight trabecular vBMD at the FN and TR as an independent risk factor.

Can Hip Fracture Prediction in Women be Estimated beyond Bone Mineral Density Measurement Alone?

The etiology of hip fractures is multifactorial and includes bone and fall-related factors. Low bone mineral density (BMD) and BMD-related and BMD-independent geometric components of bone strength, evaluated by hip strength analysis (HSA) and finite element analysis analyses on dual-energy X-ray absorptiometry (DXA) images, and ultrasound parameters are related to the presence and incidence of hip fracture. In addition, clinical risk factors contribute to the risk of hip fractures, independent of BMD. They are included in the fracture risk assessment tool (FRAX) case finding algorithm to estimate in the individual patient the 10-year risk of hip fracture, with and without BMD. Fall risks are not included in FRAX, but are included in other case finding tools, such as the Garvan algorithm, to predict the 5- and 10-year hip fracture risk. Hormones, cytokines, growth factors, markers of bone resorption and genetic background have been related to hip fracture risk. Vitamin D deficiency is endemic worldwide and low serum levels of 25-hydroxyvitamin D [25(OH)D] predict hip fracture risk. In the context of hip fracture prevention calculation of absolute fracture risk using clinical risks, BMD, bone geometry and fall-related risks is feasible, but needs further refinement by integrating bone and fall-related risk factors into a single case finding algorithm for clinical use.

Effect of rheumatoid arthritis on volumetric bone mineral density and bone geometry, assessed by peripheral quantitative computed tomography in postmenopausal women treated with bisphosphonates

OBJECTIVE

To investigate the effect of rheumatoid arthritis (RA) on volumetric bone mineral density (vBMD) and bone geometry in postmenopausal women treated with bisphosphonates.

METHODS

Fifty-three postmenopausal women with RA and 87 control subjects, comparable in terms of age, body mass index, and years since menopause, underwent peripheral quantitative computed tomography (pQCT) of the nondominant tibia.

RESULTS

At 4% (trabecular site), trabecular bone mineral content (BMC) and vBMD (p < 0.001) were lower in the RA group, while trabecular area was comparable. At 38% (cortical site), cortical BMC (p < 0.01), area (p < 0.05), and thickness (p < 0.001) were lower in the RA group, whereas vBMD was comparable. Endosteal circumference was higher (p < 0.05), whereas periosteal circumference was comparable, indicating cancellization of cortical bone. In the RA group, muscle area was lower (p < 0.001), while at 14% polar stress strength index was significantly lower (p < 0.01) in patients with RA, indicating impairment of bone mechanical properties.

CONCLUSION

RA is associated with negative effects on both cortical and cancellous bone in postmenopausal women treated with bisphosphonates. Cortical geometric properties are also adversely affected mainly by increased endosteal circumference, whereas trabecular geometric properties are generally preserved.

Impact of oral ibandronate 150 mg once monthly on bone structure and density in post-menopausal osteoporosis or osteopenia derived from in vivo μCT

The effect of ibandronate 150 mg/once monthly in the treatment of post-menopausal osteopenia and osteoporosis on bone micro-structure at the distal tibia and radius has not been considered to date. Seventy post-menopausal women with osteoporosis or osteopenia were recruited. All subjects received calcium and vitamin D supplementation and were randomized to either a group which took 150 mg ibandronate oral monthly or a placebo group over a 12-month period. μCT measures of the distal tibia and radius were conducted every three months, with DXA lumbar spine and hip measurements conducted only pre and post and serum markers of bone formation and resorption measured every 6 months. After 12-months no significant impact of ibandronate on the primary outcome measures bone-volume to tissue-volume and trabecular separation at the distal tibia (p≥0.15) was found. Further multiple regression analyses of the primary end-points indicated a significant effect favoring the ibandronate intervention (p=0.045). Analysis of secondary end-points showed greater increases in distal tibia cortical thickness, cortical density and total density (p≤0.043) with ibandronate and no significant effects at the distal radius, but greater increases of hip DXA-BMD and lumbar spine DXA-BMD (p≤0.017). Ibandronate use resulted in a marked reduction in bone turnover (p<0.001). While ibandronate resulted in greater mineralization of bone, this effect differed from one body region to another. There was some impact of ibandronate on bone structure (cortical thickness) at the distal tibia, but not on bone-volume to tissue-volume or trabecular separation.

Effects of strontium ranelate and alendronate on bone microstructure in women with osteoporosis. Results of a 2-year study

Strontium ranelate appears to influence more than alendronate distal tibia bone microstructure as assessed by high-resolution peripheral quantitative computed tomography (HR-pQCT), and biomechanically relevant parameters as assessed by micro-finite element analysis (μFEA), over 2 years, in postmenopausal osteoporotic women.

INTRODUCTION

Bone microstructure changes are a target in osteoporosis treatment to increase bone strength and reduce fracture risk.

METHODS

Using HR-pQCT, we investigated the effects on distal tibia and radius microstructure of strontium ranelate (SrRan; 2 g/day) or alendronate (70 mg/week) for 2 years in postmenopausal osteoporotic women. This exploratory randomized, double-blind trial evaluated HR-pQCT and FEA parameters, areal bone mineral density (BMD), and bone turnover markers.

RESULTS

In the intention-to-treat population (n = 83, age: 64 ± 8 years; lumbar T-score: -2.8 ± 0.8 [DXA]), distal tibia Cortical Thickness (CTh) and Density (DCort), and cancellous BV/TV increased by 6.3%, 1.4%, and 2.5%, respectively (all P < 0.005), with SrRan, but not with alendronate (0.9%, 0.4%, and 0.8%, NS) (P < 0.05 for all above between-group differences). Difference for CTh evaluated with a distance transformation method was close to significance (P = 0.06). The estimated failure load increased with SrRan (+2.1%, P < 0.005), not with alendronate (-0.6%, NS) (between-group difference, P < 0.01). Cortical stress was lower with SrRan (P < 0.05); both treatments decreased trabecular stress. At distal radius, there was no between-group difference other than DCort (P < 0.05). Bone turnover markers decreased with alendronate; bALP increased (+21%) and serum-CTX-I decreased (-1%) after 2 years of SrRan (between-group difference at each time point for both markers, P < 0.0001). Both treatments were well tolerated.

CONCLUSIONS

Within the constraints of HR-pQCT method, and while a possible artefactual contribution of strontium cannot be quantified, SrRan appeared to influence distal tibia bone microstructure and FEA-determined biomechanical parameters more than alendronate. However, the magnitude of the differences is unclear and requires confirmation with another method.

Effect of monthly ibandronate on hip structural geometry in men with low bone density

Hip structural analysis (HSA) performed in a subset of participants from the STudy Researching Osteoporosis iN Guys (STRONG) demonstrated that 1 year of ibandronate treatment was associated with a significant improvement in some but not all parameters of hip geometry relative to placebo in men with low bone density.

INTRODUCTION

HSA was performed on dual-energy X-ray absorptiometry (DXA) images in a subset of participants from the STRONG to examine the impact of monthly ibandronate on geometric properties of the hip in men with low bone density.

METHODS

This prespecified subgroup analysis evaluated men in the intent-to-treat population of STRONG with baseline and 12-month DXA data. Cross-sectional geometric parameters of the femoral shaft (FS), intertrochanter region (IT), and narrow neck (NN) were calculated from femoral DXA scans. All analyses were exploratory. Treatment differences were evaluated using analysis of covariance, which adjusted for baseline parameter value, testosterone level, and treatment.

RESULTS

HSA was performed on DXA scans from 89 men (34 placebo; 55 monthly ibandronate). Significant increases in average cortical thickness and cross-sectional area and decreases (i.e., improvements) in the buckling ratio were observed at the FS and IT at 12 months for ibandronate-treated men compared with placebo-treated men. No significant differences were observed between ibandronate and placebo for any NN HSA parameters.

CONCLUSIONS

One year of ibandronate treatment was associated with a significant improvement in some but not all parameters of hip geometry relative to placebo in men with low bone density, suggesting that ibandronate may improve resistance to axial compressive forces and bending forces at the hip.

Femoral strength in osteoporotic women treated with teriparatide or alendronate

To gain insight into the clinical effect of teriparatide and alendronate on the hip, we performed non-linear finite element analysis of quantitative computed tomography (QCT) scans from 48 women who had participated in a randomized, double-blind clinical trial comparing the effects of 18-month treatment of teriparatide 20 μg/d or alendronate 10mg/d. The QCT scans, obtained at baseline, 6, and 18 months, were analyzed for volumetric bone mineral density (BMD) of trabecular bone, the peripheral bone (defined as all the cortical bone plus any endosteal trabecular bone within 3 mm of the periosteal surface), and the integral bone (both trabecular and peripheral), and for overall femoral strength in response to a simulated sideways fall. At 18 months, we found in the women treated with teriparatide that trabecular volumetric BMD increased versus baseline (+4.6%, p<0.001), peripheral volumetric BMD decreased (-1.1%, p<0.05), integral volumetric BMD (+1.0%, p=0.38) and femoral strength (+5.4%, p=0.06) did not change significantly, but the ratio of strength to integral volumetric BMD ratio increased (+4.0%, p=0.04). An increase in the ratio of strength to integral volumetric BMD indicates that overall femoral strength, compared to baseline, increased more than did integral density. For the women treated with alendronate, there were small (<1.0%) but non-significant changes compared to baseline in all these parameters. The only significant between-treatment difference was in the change in trabecular volumetric BMD (p<0.005); related, we also found that, for a given change in peripheral volumetric BMD, femoral strength increased more for teriparatide than for alendronate (p=0.02). We conclude that, despite different compartmental volumetric BMD responses for these two treatments, we could not detect any overall difference in change in femoral strength between the two treatments, although femoral strength increased more than integral volumetric BMD after treatment with teriparatide.

Efficacy and safety of monthly 150 mg oral ibandronate in women with postmenopausal osteoporosis: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND/AIMS

The aim of this study was to assess the efficacy and safety of monthly oral 150 mg ibandronate in women with postmenopausal osteoporosis (PMO).

METHODS

A systematic review and meta-analysis were performed to determine treatment efficacy and safety outcomes between monthly oral 150 mg ibandronate and weekly 70 mg alendronate, daily 2.5 mg ibandronate, and a placebo.

RESULTS

Eight randomized controlled trials were included in this systematic review and meta-analysis. Once-monthly 150 mg ibandronate therapy was clinically comparable to weekly 70 mg alendronate, showing increased bone mineral density (BMD) in both the lumbar spine and total hip. Pooled data from two cross-over trials showed that significantly more women with PMO preferred once-monthly ibandronate therapy to once-weekly alendronate therapy (relative risk [RR], 2.422; 95% confidence interval [CI], 2.111 to 2.825; p < 1 × 10(-8)) and found the monthly ibandronate regimen more convenient than the weekly alendronate regimen (RR, 3.096; 95% CI, 2.622 to 3.622; p < 1 × 10(-8)). Monthly 150 mg ibandronate therapy resulted in a significantly higher change in BMD of the lumbar spine than with the placebo. A once monthly 150 mg regimen produced greater increases in lumbar spine, total hip, femoral neck, and trochanter BMD than daily treatment, with a similar incidence of adverse events between the groups.

CONCLUSIONS

Once monthly 150 mg ibandronate therapy was clinically comparable to weekly 70 mg alendronate, and patients strongly preferred the convenience of monthly ibandronate over weekly alendronate. Monthly 150 mg ibandronate was superior to, and as well tolerated as, the daily treatment.

Association of hip strength estimates by finite-element analysis with fractures in women and men

Finite-element analysis (FEA) of quantitative computed tomography (QCT) scans can estimate site-specific whole-bone strength. However, it is uncertain whether the site-specific detail included in FEA-estimated proximal femur (hip) strength can determine fracture risk at sites with different biomechanical characteristics. To address this question, we used FEA of proximal femur QCT scans to estimate hip strength and load-to-strength ratio during a simulated sideways fall and measured total hip areal and volumetric bone mineral density (aBMD and vBMD) from QCT images in an age-stratified random sample of community-dwelling adults age 35 years or older. Among 314 women (mean age ± SD: 61 ± 15 years; 235 postmenopausal) and 266 men (62 ± 16 years), 139 women and 104 men had any prevalent fracture, whereas 55 Women and 28 men had a prevalent osteoporotic fracture that had occurred at age 35 years or older. Odds ratios by age-adjusted logistic regression analysis for prevalent overall and osteoporotic fractures each were similar for FEA hip strength and load-to-strength ratio, as well as for total hip aBMD and vBMD. C-statistics (estimated areas under ROC curves) also were similar [eg, 0.84 to 0.85 (women) and 0.75 to 0.78 (men) for osteoporotic fractures]. In women and men, the association with prevalent osteoporotic fractures increased below an estimated hip strength of approximately 3000 N. Despite its site-specific nature, FEA-estimated hip strength worked equally well at predicting prevalent overall and osteoporotic fractures. Furthermore, an estimated hip strength below 3000 N may represent a critical level of systemic skeletal fragility in both sexes that warrants further investigation.

Bisphosphonate effects on bone turnover, microdamage, and mechanical properties: what we think we know and what we know that we don't know

The bisphosphonates (BPs) have been useful tools in our understanding of the role that bone remodeling plays in skeletal health. The purpose of this paper is to outline what we know, and what is still unknown, about the role that BPs play in modulating bone turnover, how this affects microdamage accumulation, and ultimately what the effects of these changes elicited by BPs are to the structural and the material biomechanical properties of the skeleton. We know that BPs suppress remodeling site-specifically, probably do not have a direct effect on formation, and that the individual BPs vary with respect to speed of onset, duration of effect and magnitude of suppression. However, we do not know if these differences are meaningful in a clinical sense, how much remodeling is sufficient, the optimal duration of treatment, or how long it takes to restore remodeling to pre-treatment levels following withdrawal. We also know that suppression is intimately tied to microdamage accumulation, which is also site-specific, that BPs impair targeted repair of damage, and that they can reduce the energy absorption capacity of bone at the tissue level. However, the BPs are clearly effective at preventing fracture, and generally increase bone mineral density and whole bone strength, so we do not know whether these changes in damage accumulation and repair, or the mechanical effects at the tissue level, are clinically meaningful. The mechanical effects of BPs on the fatigue life of bone, or BP effects on bone subject to an impact, are entirely unknown. This paper reviews the literature on these topics, and identifies gaps in knowledge that can be addressed with further research.

Hounsfield units for assessing bone mineral density and strength: a tool for osteoporosis management

BACKGROUND

Measurements obtained from clinical computed tomography examinations may yield information leading to the diagnosis of decreased bone mineral density, without added expense to the patient. The purpose of the present study was to determine if Hounsfield units, a standardized computed tomography attenuation coefficient, correlate with bone mineral density and compressive strength.

METHODS

Twenty-five patients (including eighteen female and seven male patients with a mean age of 71.3 years) undergoing both lumbar spine dual x-ray absorptiometry scans and computed tomography imaging were evaluated to determine if Hounsfield units correlated with bone mineral density and T-scores. Normative data were generated from lumbar spine computed tomography examinations for eighty consecutive trauma patients and were stratified by age and sex. Separately, polyurethane foam blocks of varying densities were imaged with computed tomography and were subjected to mechanical testing to determine compressive strength. Compressive strength values and Hounsfield units were analyzed for correlation.

RESULTS

Significant correlations were found between Hounsfield units and bone mineral density, age, and T-scores and between Hounsfield units and compressive strength (p < 0.001).

CONCLUSIONS

Hounsfield units obtained from clinical computed tomography scans that are made for other purposes correlate with dual x-ray absorptiometry scores as well as compressive strengths based on osseous models and potentially provide an alternative method for determining regional bone mineral density at no additional cost to the patient. The information could conceivably be applied toward fracture risk assessment, diagnosis of osteoporosis, and early initiation of needed treatment.

In vivo discrimination of hip fracture with quantitative computed tomography: results from the prospective European Femur Fracture Study (EFFECT)

In assessing osteoporotic fractures of the proximal femur, the main objective of this in vivo case-control study was to evaluate the performance of quantitative computed tomography (QCT) and a dedicated 3D image analysis tool [Medical Image Analysis Framework--Femur option (MIAF-Femur)] in differentiating hip fracture and non-hip fracture subjects. One-hundred and seven women were recruited in the study, 47 women (mean age 81.6 years) with low-energy hip fractures and 60 female non-hip fracture control subjects (mean age 73.4 years). Bone mineral density (BMD) and geometric variables of cortical and trabecular bone in the femoral head and neck, trochanteric, and intertrochanteric regions and proximal shaft were assessed using QCT and MIAF-Femur. Areal BMD (aBMD) was assessed using dual-energy X-ray absorptiometry (DXA) in 96 (37 hip fracture and 59 non-hip fracture subjects) of the 107 patients. Logistic regressions were computed to extract the best discriminates of hip fracture, and area under the receiver characteristic operating curve (AUC) was calculated. Three logistic models that discriminated the occurrence of hip fracture with QCT variables were obtained (AUC = 0.84). All three models combined one densitometric variable--a trabecular BMD (measured in the femoral head or in the trochanteric region)--and one geometric variable--a cortical thickness value (measured in the femoral neck or proximal shaft). The best discriminant using DXA variables was obtained with total femur aBMD (AUC = 0.80, p = .003). Results highlight a synergistic contribution of trabecular and cortical components in hip fracture risk and the utility of assessing QCT BMD of the femoral head for improved understanding and possible insights into prevention of hip fractures.

Calcium plus vitamin D supplementation has limited effects on femoral geometric strength in older postmenopausal women: the Women's Health Initiative

Calcium plus vitamin D (CaD) supplementation has a modest but significant effect on slowing loss of femoral bone mass and reducing risk of hip fractures in adherent postmenopausal women. The goal of this study was to determine if CaD supplementation influences hip structural parameters that are associated with fracture risk. We studied 1,970 postmenopausal women enrolled in the Women's Health Initiative randomized controlled trial of CaD at one of three bone mineral density (BMD) clinical centers. Hip structural analysis software measured BMD and strength parameters on DXA scans at three regions: femoral narrow neck, intertrochanter, and shaft. Random effects models were used to test the average differences in hip BMD and geometry between intervention and placebo. There was greater preservation of hip BMD at the narrow neck with CaD relative to placebo across 6 years of intervention. CaD also altered the underlying cross-sectional geometry at the narrow neck in the direction of greater strength, with small increases in cross-sectional area and section modulus and a decrease in buckling ratio with CaD relative to placebo. While trends at both the intertrochanter and shaft regions were similar to those noted at the narrow neck, no significant intervention effects were evident. There was no significant interaction of CaD and age or baseline calcium levels for hip structural properties. CaD supplementation is associated with modest beneficial effects on hip structural features at the narrow neck, which may explain some of the benefit of CaD in reducing hip fracture risk.

Regional distribution of spine and hip QCT BMD responses after one year of once-monthly ibandronate in postmenopausal osteoporosis

In the published placebo-controlled Ibandronate Quality (IQ) study, 12 months of once-monthly oral ibandronate increased femoral and vertebral integral and trabecular bone mineral density (BMD) measured by quantitative computed tomography (QCT). Ibandronate showed significant improvements versus placebo in finite element analysis of femoral and vertebral strength. This post hoc analysis examined QCT BMD changes in novel superior and inferior vertebral volumes of interest (VOIs) and femoral and vertebral subcortical, extended cortical, and extended trabecular VOIs. Ninety-three postmenopausal women (BMD(a)T-scores< or =-2.0 at lumbar spine, total hip, or femoral neck) received ibandronate 150 mg/month (n=47) or placebo (n=46) for 12 months. QCT with Medical Imaging Analysis Framework (MIAF)-Spine and MIAF-Femur used automated segmentation and coordinate system-based identification of integral, cortical, subcortical, and trabecular VOIs and combinations (extended cortical=cortical+subcortical; extended trabecular=trabecular+subcortical). Between-group differences in mean percentage changes from baseline were determined by treatment- and center-adjusted analysis of variance. P values were post hoc, exploratory, descriptive, and unadjusted for multiple comparisons. Ibandronate increased vertebral superior and inferior trabecular and extended cortical midsection BMD (4.9%, p=0.032; 4.6%, p=0.055; 3.9%, p=0.014, respectively) versus placebo. Femoral BMD treatment differences (ibandronate versus placebo) were significant in total hip (extended trabecular 4.0%, p=0.005; extended cortical 1.5%, p=0.047; subcortical 3.7%, p=0.009), trochanter (extended trabecular 5.2%, p=0.007; extended cortical 2.4%, p=0.01), and extended trabecular femoral neck (4.0%, p=0.02). Monthly oral ibandronate for 12 months improved QCT BMD versus placebo in the vertebral periphery, subcortical total hip, and all femoral extended trabecular regions.

Age-dependence of femoral strength in white women and men

Although age-related variations in areal bone mineral density (aBMD) and the prevalence of osteoporosis have been well characterized, there is a paucity of data on femoral strength in the population. Addressing this issue, we used finite-element analysis of quantitative computed tomographic scans to assess femoral strength in an age-stratified cohort of 362 women and 317 men, aged 21 to 89 years, randomly sampled from the population of Rochester, MN, and compared femoral strength with femoral neck aBMD. Percent reductions over adulthood were much greater for femoral strength (55% in women, 39% in men) than for femoral neck aBMD (26% in women, 21% in men), an effect that was accentuated in women. Notable declines in strength started in the mid-40s for women and one decade later for men. At advanced age, most of the strength deficit for women compared with men was a result of this decade-earlier onset of strength loss for women, this factor being more important than sex-related differences in peak bone strength and annual rates of bone loss. For both sexes, the prevalence of "low femoral strength" (<3000 N) was much higher than the prevalence of osteoporosis (femoral neck aBMD T-score of -2.5 or less). We conclude that age-related declines in femoral strength are much greater than suggested by age-related declines in femoral neck aBMD. Further, far more of the elderly may be at high risk of hip fracture because of low femoral strength than previously assumed based on the traditional classification of osteoporosis.

Higher doses of bisphosphonates further improve bone mass, architecture, and strength but not the tissue material properties in aged rats

We report the results of a series of experiments designed to determine the effects of ibandronate (Ibn) and risedronate (Ris) on a number of bone quality parameters in aged osteopenic rats to explain how bone material and bone mass may be affected by the dose of bisphosphonates (BP) and contribute to their anti-fracture efficacy. Eighteen-month old female rats underwent either ovariectomy or sham surgery. The ovariectomized (OVX) groups were left untreated for 2 months to develop osteopenia. Treatments started at 20 months of age as follows: sham and OVX control (treated with saline), OVX + risedronate 30 and 90 (30 or 90 microg/kg/dose), and OVX + ibandronate 30 and 90 (30 or 90 microg/kg/dose). The treatments were given monthly for 4 months by subcutaneous injection. At sacrifice at 24 months of age the 4th lumbar vertebra was used for microCT scans (bone mass, architecture, and degree of mineralization of bone, DMB) and histomorphometry, and the 6th lumbar vertebra, tibia, and femur were collected for biomechanical testing to determine bone structural and material strength, cortical fracture toughness, and tissue elastic modulus. The compression testing of the vertebral bodies (LVB6) was simulated using finite-element analysis (FEA) to also estimate the bone structural stiffness. Both Ibn and Ris dose-dependently increased bone mass and improved vertebral bone microarchitecture and mechanical properties compared to OVX control. Estimates of vertebral maximum stress from FEA were correlated with vertebral maximum load (r=0.5, p<0.001) and maximum stress (r=0.4, p<0.005) measured experimentally. Tibial bone bending modulus and cortical strength increased compared to OVX with both BP but no dose-dependent effect was observed. DMB and elastic modulus of trabecular bone were improved with Ibn 30 compared to OVX but were not affected in other BP-treated groups. DMB of tibial cortical bone showed no change with BP treatments. The fracture toughness examined in midshaft femurs did not change with BP even with the higher doses. In summary, the anti-fracture efficacy of BP is largely due to their preservation of bone mass and while the higher doses further improve the bone structural properties do not improve the localized bone material characteristics such as tissue strength, elastic modulus, and cortical toughness.

Quantifying the material and structural determinants of bone strength

The ability of a bone to resist fracture depends on the amount of bone present, the spatial distribution of the bone mass as cortical and trabecular bone and the intrinsic properties of the bone material. Whereas low areal bone mineral density (aBMD) predicts fractures, its sensitivity and specificity is low, as over 50% of fractures occur in persons without osteoporosis by BMD testing and most women with osteoporosis do not sustain a fracture. New non-invasive imaging techniques, including three-dimensional (3D) assessments of bone density and geometry, microarchitecture and integrated measurements of bone strength such as finite element analysis (FEA), provide estimates of bone strength that can be used to increase the sensitivity and specificity of fracture risk assessment. Initial observations have shown that these techniques provide information that will improve our understanding of the pathophysiology of skeletal fragility and suggest that these techniques are likely to have a role in the clinical management of individuals at risk for fracture.

Ibandronate: a review of its use in the management of postmenopausal osteoporosis

Ibandronate (ibandronic acid; Bonviva, Boniva), a nitrogen-containing bisphosphonate available in once-monthly oral and quarterly intravenous formulations for intermittent administration, has been approved for the treatment of osteoporosis in postmenopausal women in the EU, the US and many other countries worldwide. The once-monthly oral formulation has also been approved for the prevention of postmenopausal osteoporosis in the US. Ibandronate is an effective and generally well tolerated bisphosphonate that offers an alternative to other bisphosphonates as a first-line treatment for postmenopausal osteoporosis. It occupies a similar position with respect to the prevention of osteoporosis in postmenopausal women at risk for the disease. The once-monthly oral and quarterly intravenous dosage regimens have the potential to improve treatment adherence and persistence, and hence clinical outcomes, compared with more frequently administered oral bisphosphonates. Intravenous ibandronate may be particularly useful for postmenopausal osteoporotic women who are noncompliant with, or are unable to tolerate or receive, oral bisphosphonates. Thus, intermittent ibandronate extends the range of pharmacological therapies for the treatment and prevention of postmenopausal osteoporosis.