Fracture risk based on HR-pQCT measures does not vary with age in older adults - the bone microarchitecture international consortium (BoMIC) prospective cohort study

Fracture risk increases with lower areal BMD (aBMD); however, aBMD-related estimate of risk may decrease with age. This may depend on technical limitations of 2-dimensional (2D) DXA which are reduced with 3D high-resolution peripheral quantitative computed tomography (HR-pQCT). Our aim was to examine whether the predictive utility of HR-pQCT measures with fracture varies with age. We analyzed associations of HR-pQCT measures at the distal radius and distal tibia with two outcomes: incident fractures and major osteoporotic fractures. We censored follow-up time at first fracture, death, last contact or 8 years after baseline. We estimated hazard ratios (HR) and 95%CI for the association between bone traits and fracture incidence across age quintiles. Among 6835 men and women (ages 40-96) with at least one valid baseline HR-pQCT scan who were followed prospectively for a median of 48.3 months, 681 sustained fractures. After adjustment for confounders, bone parameters at both the radius and tibia were associated with higher fracture risk. The estimated HRs for fracture did not vary significantly across age quintiles for any HR-pQCT parameter measured at either the radius or tibia. In this large cohort, the homogeneity of the associations between the HR-pQCT measures and fracture risk across age groups persisted for all fractures and for major osteoporotic fractures. The patterns were similar regardless of the HR-pQCT measure, the type of fracture, or the statistical models. The stability of the associations between HR-pQCT measures and fracture over a broad age range shows that bone deficits or low volumetric density remain major determinants of fracture risk regardless of age group. The lower risk for fractures across measures of aBMD in older adults in other studies may be related to factors which interfere with DXA but not with HR-pQCT measures.

Correlates of Circulating Osteoprotegerin in Women with a Pathogenic or Likely Pathogenic Variant in the BRCA1 Gene

BACKGROUND

Lower levels of osteoprotegerin (OPG), the decoy receptor for receptor activator of NFκB (RANK)-ligand, have been reported among women with a BRCA1 mutation, suggesting OPG may be marker of cancer risk. Whether various reproductive, hormonal, or lifestyle factors impact OPG levels in these women is unknown.

METHODS

BRCA1 mutation carriers enrolled in a longitudinal study, no history of cancer, and a serum sample for OPG quantification, were included. Exposure information was collected through self-reported questionnaire at study enrollment and every 2 years thereafter. Serum OPG levels (pg/mL) were measured using an ELISA, and generalized linear models were used to assess the associations between reproductive, hormonal, and lifestyle exposures at the time of blood collection with serum OPG. Adjusted means were estimated using the fully adjusted model.

RESULTS

A total of 701 women with a median age at blood collection of 39.0 years (18.0-82.0) were included. Older age (Spearman r = 0.24; P < 0.001) and current versus never smoking (98.82 vs. 86.24 pg/mL; Pcat < 0.001) were associated with significantly higher OPG, whereas ever versus never coffee consumption was associated with significantly lower OPG (85.92 vs. 94.05 pg/mL; Pcat = 0.03). There were no other significant associations for other exposures (P ≥ 0.06). The evaluated factors accounted for 7.5% of the variability in OPG.

CONCLUSIONS

OPG is minimally influenced by hormonal and lifestyle factors among BRCA1 mutation carriers.

IMPACT

These findings suggest that circulating OPG levels are not impacted by non-genetic factors in high-risk women.

Systematic review of computed tomography parameters used for the assessment of subchondral bone in osteoarthritis

OBJECTIVE

To systematically review the published parameters for the assessment of subchondral bone in human osteoarthritis (OA) using computed tomography (CT) and gain an overview of current practices and standards.

DESIGN

A literature search of Medline, Embase and Cochrane Library databases was performed with search strategies tailored to each database (search from 2010 to January 2023). The search results were screened independently by two reviewers against pre-determined inclusion and exclusion criteria. Studies were deemed eligible if conducted in vivo/ex vivo in human adults (>18 years) using any type of CT to assess subchondral bone in OA. Extracted data from eligible studies were compiled in a qualitative summary and formal narrative synthesis.

RESULTS

This analysis included 202 studies. Four groups of CT modalities were identified to have been used for subchondral bone assessment in OA across nine anatomical locations. Subchondral bone parameters measuring similar features of OA were combined in six categories: (i) microstructure, (ii) bone adaptation, (iii) gross morphology (iv) mineralisation, (v) joint space, and (vi) mechanical properties.

CONCLUSIONS

Clinically meaningful parameter categories were identified as well as categories with the potential to become relevant in the clinical field. Furthermore, we stress the importance of quantification of parameters to improve their sensitivity and reliability for the evaluation of OA disease progression and the need for standardised measurement methods to improve their clinical value.

A Fracture Risk Assessment Tool for High Resolution Peripheral Quantitative Computed Tomography

Most fracture risk assessment tools use clinical risk factors combined with bone mineral density (BMD) to improve assessment of osteoporosis; however, stratifying fracture risk remains challenging. This study developed a fracture risk assessment tool that uses information about volumetric bone density and three-dimensional structure, obtained using high-resolution peripheral quantitative compute tomography (HR-pQCT), to provide an alternative approach for patient-specific assessment of fracture risk. Using an international prospective cohort of older adults (n = 6802) we developed a tool to predict osteoporotic fracture risk, called μFRAC. The model was constructed using random survival forests, and input predictors included HR-pQCT parameters summarizing BMD and microarchitecture alongside clinical risk factors (sex, age, height, weight, and prior adulthood fracture) and femoral neck areal BMD (FN aBMD). The performance of μFRAC was compared to the Fracture Risk Assessment Tool (FRAX) and a reference model built using FN aBMD and clinical covariates. μFRAC was predictive of osteoporotic fracture (c-index = 0.673, p < 0.001), modestly outperforming FRAX and FN aBMD models (c-index = 0.617 and 0.636, respectively). Removal of FN aBMD and all clinical risk factors, except age, from μFRAC did not significantly impact its performance when estimating 5-year and 10-year fracture risk. The performance of μFRAC improved when only major osteoporotic fractures were considered (c-index = 0.733, p < 0.001). We developed a personalized fracture risk assessment tool based on HR-pQCT that may provide an alternative approach to current clinical methods by leveraging direct measures of bone density and structure. © 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).

The impact of sarcopenia on clinical outcomes in men with metastatic castrate-resistant prostate cancer

INTRODUCTION

Sarcopenia is common in men with metastatic castrate-resistant prostate cancer (mCRPC) and has been largely assessed opportunistically through computed-tomography (CT) scans, excluding measures of muscle function. Therefore, the impact of a comprehensive assessment of sarcopenia on clinical outcomes in men with mCRPC is poorly understood. The objectives of this study were to comprehensively assess sarcopenia through CT scans and measures of muscle function and examine its impact on severe treatment toxicity, time to first emergency room (ER) visit, disease progression, and overall mortality in men initiating chemotherapy or androgen receptor-targeted axis (ARAT) therapy for mCRPC.

METHODS

This was a secondary analysis of a prospective observational study of men with mCRPC at the Princess Margaret Cancer Centre between July 2015-May 2021. Participants were classified as sarcopenic if they had CT-based low muscle mass or low muscle density, a grip strength and gait speed score of <35.5kg and <0.8m/s, respectively, prior to treatment initiation. The impact of sarcopenia on severe treatment toxicity was assessed using multivariable logistic regression. Multivariable Cox regression models were used to determine the impact of sarcopenia on risk of visiting the ER, prostate-specific antigen progression, radiographic progression, and overall mortality.

RESULTS

A total of 110 men (mean age: 74.6) were included in the analysis. At baseline, 30 (27.3%) were classified as sarcopenic. Sarcopenia was a significant predictor of severe toxicity (aOR = 6.26, 95%CI = 1.17-33.58, P = 0.032) and ER visits (aHR = 4.41, 95%CI = 1.26-15.43, p = 0.020) in men initiating ARAT but not in men initiating chemotherapy. Sarcopenia was also a predictor of radiographic progression (aHR = 2.39, 95%CI = 1.06-5.36, p = 0.035) and overall mortality (aHR = 2.44, 95%CI = 1.17-5.08, p = 0.018) regardless of treatment type.

CONCLUSIONS

Baseline sarcopenia predicts radiographic progression and overall mortality in men with mCRPC regardless of the type of treatment and may also predict severe treatment toxicity and ER visits in men initiating ARAT.

Bone Microarchitecture Phenotypes Identified in Older Adults Are Associated With Different Levels of Osteoporotic Fracture Risk

Prevalence of osteoporosis is more than 50% in older adults, yet current clinical methods for diagnosis that rely on areal bone mineral density (aBMD) fail to detect most individuals who have a fragility fracture. Bone fragility can manifest in different forms, and a "one-size-fits-all" approach to diagnosis and management of osteoporosis may not be suitable. High-resolution peripheral quantitative computed tomography (HR-pQCT) provides additive information by capturing information about volumetric density and microarchitecture, but interpretation is challenging because of the complex interactions between the numerous properties measured. In this study, we propose that there are common combinations of bone properties, referred to as phenotypes, that are predisposed to different levels of fracture risk. Using HR-pQCT data from a multinational cohort (n = 5873, 71% female) between 40 and 96 years of age, we employed fuzzy c-means clustering, an unsupervised machine-learning method, to identify phenotypes of bone microarchitecture. Three clusters were identified, and using partial correlation analysis of HR-pQCT parameters, we characterized the clusters as low density, low volume, and healthy bone phenotypes. Most males were associated with the healthy bone phenotype, whereas females were more often associated with the low volume or low density bone phenotypes. Each phenotype had a significantly different cumulative hazard of major osteoporotic fracture (MOF) and of any incident osteoporotic fracture (p < 0.05). After adjustment for covariates (cohort, sex, and age), the low density followed by the low volume phenotype had the highest association with MOF (hazard ratio = 2.96 and 2.35, respectively), and significant associations were maintained when additionally adjusted for femoral neck aBMD (hazard ratio = 1.69 and 1.90, respectively). Further, within each phenotype, different imaging biomarkers of fracture were identified. These findings suggest that osteoporotic fracture risk is associated with bone phenotypes that capture key features of bone deterioration that are not distinguishable by aBMD. © 2021 American Society for Bone and Mineral Research (ASBMR).

Bisphosphonate Use Is Protective of Radiographic Knee Osteoarthritis Progression Among those With Low Disease Severity and Being Non-Overweight: Data From the Osteoarthritis Initiative

Antiresorptive medications have been explored for treating knee osteoarthritis (OA); however, little data exist on the effects of today's more potent nitrogen-containing oral bisphosphonates on radiographic disease-progression in patients with varying disease-severity, especially those who are not overweight. The primary objective of this cohort study was to determine if the use of bisphosphonates is protective against 2-year radiographic-progression of knee OA in Osteoarthritis Initiative (OAI) participants, stratified by baseline radiographic disease status. Secondary objectives were to examine effects in non-overweight participants (body mass index [BMI] < 25 kg/m² ) and cumulative bisphosphonate exposure effects. We identified female OAI participants aged ≥50 years and excluded those missing baseline radiograph readings, bisphosphonate use information, or all clinical questionnaire information at baseline. Participants reporting bisphosphonate use (69% alendronate) were propensity-matched 1:1 to non-bisphosphonate users and followed until first radiographic knee OA progression (1-unit increase in Kellgren and Lawrence [KL] grade) or data were censored (first missed visit or end of 2-year follow-up). Discrete-time logistic regression models estimated hazard ratios (HRs) between bisphosphonate users versus nonusers, with an interaction term for baseline KL grade (KL <2 or KL ≥2). We identified 1977 eligible women (n = 346 bisphosphonate users). Propensity-matched results indicated that bisphosphonate users with KL grade <2 were protected against progression (HR_KL<2 0.53; 95% CI, 0.35 to 0.79), while bisphosphonate use was not associated with radiographic progression in those with KL grade ≥2 (HR_KL≥2 1.06; 95% CI, 0.83 to 1.35). When restricting analyses to those with BMI <25 kg/m² , effects were strengthened (HR_KL<2 0.49 [95% CI, 0.26 to 0.92]; HR_KL≥2 0.69 [95% CI, 0.33 to 1.26]). Duration of bisphosphonate use had no effect on progression, though sample size was limited. Bisphosphonate therapy may be protective against radiographic knee OA progression in early-stage patients, particularly those who are non-overweight, but less so for those with more advanced disease or more weight-bearing joint stress. © 2020 American Society for Bone and Mineral Research (ASBMR).

Vertebral Fractures: Which Radiological Criteria Are Better Associated With the Clinical Course of Osteoporosis?

STUDY PURPOSE

Morphometric methods categorize potential osteoporotic vertebral fractures (OVF) on the basis of loss of vertebral height. A particular example is the widely used semiquantitative morphometric tool proposed by Genant (GSQ). A newer morphologic algorithm-based qualitative (mABQ) tool focuses on vertebral end-plate damage in recognizing OVF. We used data from both sexes in the Canadian Multicentre Osteoporosis Study (CaMos) to compare the 2 methods in identifying OVF at baseline and during 10 years of follow-up.

MATERIALS AND METHODS

We obtained lateral thoracic and lumbar spinal radiographs (T4-L4) 3 times, at 5-year intervals, in 828 participants of the population-based CaMos. Logistic regressions were used to study the association of 10-year changes in bone mineral density (BMD) with incident fractures.

RESULTS

At baseline, 161 participants had grade 1 and 32 had grade 2 GSQ OVF; over the next 10 years, only 9 of these participants had sustained incident GSQ OVF. Contrastingly, 21 participants at baseline had grade 1 and 48 grade 2 mABQ events; over the next 10 years, 79 subjects experienced incident grade 1 or grade 2 mABQ events. Thus, incident grades 1 and 2 morphologic fractures were 8 times more common than morphometric deformities alone. Each 10-year decrease of 0.01 g/cm² in total hip BMD was associated with a 4.1% (95% CI: 0.7-7.3) higher odds of having an incident vertebral fracture.

CONCLUSIONS

This analysis further suggests that morphometric deformities and morphologic fractures constitute distinct entities; morphologic fractures conform more closely to the expected epidemiology of OVF.

A Comparison of Peripheral Imaging Technologies for Bone and Muscle Quantification: A Review of Segmentation Techniques

Musculoskeletal science has developed many overlapping branches, necessitating specialists from 1 area of focus to often require the expertise in others. In terms of imaging, this means obtaining a comprehensive illustration of bone, muscle, and fat tissues. There is currently a lack of a reliable resource for end users to learn about these tissues' imaging and quantification techniques together. An improved understanding of these tissues has been an important progression toward better prediction of disease outcomes and better elucidation of their interaction with frailty, aging, and metabolic disorders. Over the last decade, there have been major advances into the image acquisition and segmentation of bone, muscle, and fat features using computed tomography (CT), magnetic resonance imaging (MRI), and peripheral modules of these systems. Dedicated peripheral quantitative musculoskeletal imaging systems have paved the way for mobile research units, lower cost clinical research facilities, and improved resolution per unit cost paid. The purpose of this review was to detail the segmentation techniques available for each of these peripheral CT and MRI modalities and to describe advances in segmentation methods as applied to study longitudinal changes and treatment-related dynamics. Although the peripheral CT units described herein have established feasible standardized protocols that users have adopted globally, there remain challenges in standardizing MRI protocols for bone and muscle imaging.

Cortical and trabecular bone microarchitecture as an independent predictor of incident fracture risk in older women and men in the Bone Microarchitecture International Consortium (BoMIC): a prospective study

BACKGROUND

Although areal bone mineral density (aBMD) assessed by dual-energy x-ray absorptiometry (DXA) is the clinical standard for determining fracture risk, most older adults who sustain a fracture have T scores greater than -2·5 and thus do not meet the clinical criteria for osteoporosis. Importantly, bone fragility is due to low BMD and deterioration in bone structure. We assessed whether indices of high-resolution peripheral quantitative CT (HR-pQCT) were associated with fracture risk independently of femoral neck aBMD and the Fracture Risk Assessment Tool (FRAX) score.

METHODS

We assessed participants in eight cohorts from the USA (Framingham, Mayo Clinic), France (QUALYOR, STRAMBO, OFELY), Switzerland (GERICO), Canada (CaMos), and Sweden (MrOS). We used Cox proportional hazard ratios (HRs) to estimate the association between HR-pQCT bone indices (per 1 SD of deficit) and incident fracture, adjusting for age, sex, height, weight, and cohort, and then additionally for femoral neck DXA aBMD or FRAX.

FINDINGS

7254 individuals (66% women and 34% men) were assessed. Mean baseline age was 69 years (SD 9, range 40-96). Over a mean follow-up of 4·63 years (SD 2·41) years, 765 (11%) participants had incident fractures, of whom 633 (86%) had femoral neck T scores greater than -2·5. After adjustment for age, sex, cohort, height, and weight, peripheral skeleton failure load had the greatest association with risk of fracture: tibia HR 2·40 (95% CI 1·98-2·91) and radius 2·13 (1·77-2·56) per 1 SD decrease. HRs for other bone indices ranged from 1·12 (95% CI 1·03-1·23) per 1 SD increase in tibia cortical porosity to 1·58 (1·45-1·72) per 1 SD decrease in radius trabecular volumetric bone density. After further adjustment for femoral neck aBMD or FRAX score, the associations were reduced but remained significant for most bone parameters. A model including cortical volumetric bone density, trabecular number, and trabecular thickness at the distal radius and a model including these indices plus cortical area at the tibia were the best predictors of fracture.

INTERPRETATION

HR-pQCT indices and failure load improved prediction of fracture beyond femoral neck aBMD or FRAX scores alone. Our findings from a large international cohort of men and women support previous reports that deficits in trabecular and cortical bone density and structure independently contribute to fracture risk. These measurements and morphological assessment of the peripheral skeleton might improve identification of people at the highest risk of fracture.

FUNDING

National Institutes of Health National Institute of Arthritis Musculoskeletal and Skin Diseases.

Osteoporotic fractures and obesity affect frailty progression: a longitudinal analysis of the Canadian multicentre osteoporosis study

BACKGROUND

Despite knowing better how to screen older adults, understanding how frailty progression might be modified is unclear. We explored effects of modifiable and non-modifiable factors on changes in frailty in community-dwelling adults aged 50+ years who participated in the Canadian Multicentre Osteoporosis Study (CaMos).

METHODS

Rates of change in frailty over 10 years were examined using the 30-item CaMos Frailty Index (CFI). Incident and prevalent low-trauma fractures were categorized by fracture site into hip, clinical vertebral and non-hip-non-vertebral fractures. Multivariable generalized estimating equation models accounted for the time of frailty assessment (baseline, 5 and 10 years), sex, age, body mass index (BMI, kg/m²), physical activity, bone mineral density, antiresorptive therapy, health-related quality of life (HRQL), cognitive status, and other factors for frailty or fractures. Multiple imputation and scenario analyses addressed bias due to attrition or missing data.

RESULTS

The cohort included 5566 women (mean ± standard deviation: 66.8 ± 9.3 years) and 2187 men (66.3 ± 9.5 years) with the mean baseline CFI scores of 0.15 ± 0.11 and 0.12 ± 0.10, respectively. Incident fractures and obesity most strongly predicted frailty progression in multivariable analyses. The impact of fractures differed between the sexes. With each incident hip fracture, the adjusted mean CFI accelerated per 5 years by 0.07 in women (95% confidence interval [CI]: 0.03 to 0.11) and by 0.12 in men (95% CI: 0.08 to 0.16). An incident vertebral fracture increased frailty in women (0.05, 95% CI: 0.02 to 0.08) but not in men (0.01, 95% CI: -0.07 to 0.09). Irrespective of sex and prevalent fractures, baseline obesity was associated with faster frailty progression: a 5-year increase in the adjusted mean CFI ranged from 0.01 in overweight (BMI: 25.0 to 29.9 kg/m²) to 0.10 in obese individuals (BMI: ≥ 40 kg/m²). Greater physical activity and better HRQL decreased frailty over time. The results remained robust in scenario analyses.

CONCLUSIONS

Older women and men with new vertebral fractures, hip fractures or obesity represent high-risk groups that should be considered for frailty interventions.

Investigating the Effects of Motion Streaks on pQCT-Derived Leg Muscle Density and Its Association With Fractures

Lower peripheral quantitative computed tomography (pQCT)-derived leg muscle density has been associated with fragility fractures in postmenopausal women. Limb movement during image acquisition may result in motion streaks in muscle that could dilute this relationship. This cross-sectional study examined a subset of women from the Canadian Multicentre Osteoporosis Study. pQCT leg scans were qualitatively graded (1-5) for motion severity. Muscle and motion streak were segmented using semi-automated (watershed) and fully automated (threshold-based) methods, computing area, and density. Binary logistic regression evaluated odds ratios (ORs) for fragility or all-cause fractures related to each of these measures with covariate adjustment. Among the 223 women examined (mean age: 72.7 ± 7.1 years, body mass index: 26.30 ± 4.97 kg/m²), muscle density was significantly lower after removing motion (p < 0.001) for both methods. Motion streak areas segmented using the semi-automated method correlated better with visual motion grades (rho = 0.90, p < 0.01) compared to the fully automated method (rho = 0.65, p < 0.01). Although the analysis-reanalysis precision of motion streak area segmentation using the semi-automated method is above 5% error (6.44%), motion-corrected muscle density measures remained well within 2% analytical error. The effect of motion-correction on strengthening the association between muscle density and fragility fractures was significant when motion grade was ≥3 (p interaction <0.05). This observation was most dramatic for the semi-automated algorithm (OR: 1.62 [0.82,3.17] before to 2.19 [1.05,4.59] after correction). Although muscle density showed an overall association with all-cause fractures (OR: 1.49 [1.05,2.12]), the effect of motion-correction was again, most impactful within individuals with scans showing grade 3 or above motion. Correcting for motion in pQCT leg scans strengthened the relationship between muscle density and fragility fractures, particularly in scans with motion grades of 3 or above. Motion streaks are not confounders to the relationship between pQCT-derived leg muscle density and fractures, but may introduce heterogeneity in muscle density measurements, rendering associations with fractures to be weaker.

Muscle and Myotendinous Tissue Properties at the Distal Tibia as Assessed by High-Resolution Peripheral Quantitative Computed Tomography

High-resolution peripheral quantitative computed tomography (HR-pQCT) quantifies bone microstructure and density at the distal tibia where there is also a sizable amount of myotendinous (muscle and tendon) tissue (M_T); however, there is no method for the quantification of M_T. This study aimed (1) to assess the feasibility of using HR-pQCT distal tibia scans to estimate M_T properties using a custom algorithm, and (2) to determine the relationship between M_T properties at the distal tibia and mid-leg muscle density (MD) obtained from pQCT. Postmenopausal women from the Hamilton cohort of the Canadian Multicenter Osteoporosis Study had a single-slice (2.3 ± 0.5 mm) 66% site pQCT scan measuring muscle cross-sectional area (MCSA) and MD. A standard HR-pQCT scan was acquired at the distal tibia. HR-pQCT-derived M_T cross-sectional area (M_TCSA) and M_T density (M_TD) were calculated using a custom algorithm in which thresholds (34.22-194.32 mg HA/cm³) identified muscle seed volumes and were iteratively expanded. Pearson and Bland-Altman plots were used to assess correlations and systematic differences between pQCT- and HR-pQCT-derived muscle properties. Among 45 women (mean age: 74.6 ± 8.5 years, body mass index: 25.9 ± 4.3 kg/m²), M_TD was moderately correlated with mid-leg MD across the 2 modalities (r = 0.69-0.70, p < 0.01). Bland-Altman analyses revealed no evidence of directional bias for M_TD-MD. HR-pQCT and pQCT measures of M_TCSA and MCSA were moderately correlated (r = 0.44, p < 0.01). Bland-Altman plots for M_TCSA revealed that larger MCSAs related to larger discrepancy between the distal and the mid-leg locations. This is the first study to assess the ability of HR-pQCT to measure M_T size, density, and morphometry. HR-pQCT-derived M_TD was moderately correlated with mid-leg MD from pQCT. This relationship suggests that distal M_T may share common properties with muscle throughout the length of the leg. Future studies will assess the value of HR-pQCT-derived M_T properties in the context of falls, mobility, and balance.

A Comparison of Peripheral Imaging Technologies for Bone and Muscle Quantification: a Mixed Methods Clinical Review

PURPOSE OF REVIEW

Bone and muscle peripheral imaging technologies are reviewed for their association with fractures and frailty. A narrative systematized review was conducted for bone and muscle parameters from each imaging technique. In addition, meta-analyses were performed across all bone quality parameters.

RECENT FINDINGS

The current body of evidence for bone quality's association with fractures is strong for (high-resolution) peripheral quantitative computed tomography (pQCT), with trabecular separation (Tb.Sp) and integral volumetric bone mineral density (vBMD) reporting consistently large associations with various fracture types across studies. Muscle has recently been linked to fractures and frailty, but the quality of evidence remains weaker from studies of small sample sizes. It is increasingly apparent that musculoskeletal tissues have a complex relationship with interrelated clinical endpoints such as fractures and frailty. Future studies must concurrently address these relationships in order to decipher the relative importance of one causal pathway from another.

Development of a Skeletal Muscle Mimic Phantom Compatible with QCT and MR Imaging

OBJECTIVE

The purpose of this study was to develop a skeletal muscle mimic phantom compatible with quantitative computed tomography (QCT) and magnetic resonance imaging, yielding physiologically appropriate values.

METHODS

Agar-based phantoms contained varying concentrations of CuCl₂ and EDTA to adjust T2 relaxation time and phantom density concurrently. T2 relaxation times were quantified using a 4-mm single-slice fast spin echo sequence repeated for six serial echo times at 937-μm resolution. T2 relaxation maps were generated using the Levenberg-Marquardt equation. A peripheral QCT scanner measured linear attenuation coefficients of phantoms, which were converted to density (mg/cm3) values. Five 2.3 ± 0.5 mm thick slices were acquired at 15 mm/s scan speed and 500-μm resolution. Logarithmic or linear regression models were fitted to EDTA or CuCl₂ versus density and T2 relaxation data.

RESULTS

Density (D) was linearly dependent on CuCl₂ (D = 0.27 [CuCl₂] + 63.92, R² = 0.84, P = 0.01) and invariant to EDTA. T2 relaxation time was related negatively to CuCl₂ (T2 = -10.13 ln [CuCl₂] + 66.70, R² = 0.91, P < .01) and positively to EDTA (T2 = 5.72 ln [EDTA] + 54.47, R² = 0.86, P < .01). Reproducibility within and between phantoms of the same compositions was acceptable (<5% error). Long-term stability was achieved for density but poorer for T2 relaxation time.

CONCLUSIONS

This phantom optimization method provides a means for altering a soft tissue phantom suited for calibrating magnetic resonance imaging and QCT signals within values representative of muscle. Phantoms can be used during scans for calibrating magnetic resonance signals between and within individuals over time and can cross-calibrate different scanners.

Improving reliability of pQCT-derived muscle area and density measures using a watershed algorithm for muscle and fat segmentation

In peripheral quantitative computed tomography scans of the calf muscles, segmentation of muscles from subcutaneous fat is challenged by muscle fat infiltration. Threshold-based edge detection segmentation by manufacturer software fails when muscle boundaries are not smooth. This study compared the test-retest precision error for muscle-fat segmentation using the threshold-based edge detection method vs manual segmentation guided by the watershed algorithm. Three clinical populations were investigated: younger adults, older adults, and adults with spinal cord injury (SCI). The watershed segmentation method yielded lower precision error (1.18%-2.01%) and higher (p<0.001) muscle density values (70.2±9.2 mg/cm3) compared with threshold-based edge detection segmentation (1.77%-4.06% error, 67.4±10.3 mg/cm3). This was particularly true for adults with SCI (precision error improved by 1.56% and 2.64% for muscle area and density, respectively). However, both methods still provided acceptable precision with error well under 5%. Bland-Altman analyses showed that the major discrepancies between the segmentation methods were found mostly among participants with SCI where more muscle fat infiltration was present. When examining a population where fatty infiltration into muscle is expected, the watershed algorithm is recommended for muscle density and area measurement to enable the detection of smaller change effect sizes.

Peripheral quantitative computed tomography-derived muscle density and peripheral magnetic resonance imaging-derived muscle adiposity: precision and associations with fragility fractures in women

PURPOSE

To determine the degree to which muscle density and fractures are explained by inter and intramuscular fat (IMF).

METHODS

Women ⋝50 years of age (Hamilton, ON, Canada) had peripheral magnetic resonance imaging and peripheral quantitative computed tomography scans at 66% of the tibial length. Muscle on computed tomography images was segmented from subcutaneous fat and bone using fixed thresholds, computing muscle density. IMF was segmented from muscle within magnetic resonance images using a region-growing algorithm, computing IMF volume. Fracture history over the last 14 years was obtained. Odds ratios for fractures were determined for muscle density, adjusting for IMF volume, total hip BMD, age and body mass index.

RESULTS

Women with a history of fractures were older (N=32, age:75.6±8.3 years) than those without (N=39, age: 67.0±5.2 years) (<0.01). IMF volume explained 49.3% of variance in muscle density (p<0.001). Odds for fractures were associated with lower muscle density even after adjusting for IMF volume but were attenuated after adjusting for age.

CONCLUSIONS

Muscle adiposity represents only 50% of the muscle density measurement. Properties of muscle beyond its adiposity may be related to fractures, but larger and prospective studies are needed to confirm these associations.

Bone-muscle indices as risk factors for fractures in men: the Osteoporotic Fractures in Men (MrOS) Study

OBJECTIVE

To assess bone-muscle (B-M) indices as risk factors for incident fractures in men.

METHODS

Participants of the Osteoporotic Fractures in Men (MrOS) Study completed a peripheral quantitative computed tomography scan at 66% of their tibial length. Bone macrostructure, estimates of bone strength, and muscle area were computed. Areal bone mineral density (aBMD) and body composition were assessed with dual-energy X-ray absorptiometry. Four year incident non-spine and clinical vertebral fractures were ascertained. B-M indices were expressed as bone-to-muscle ratios for: strength, mass and area. Discriminative power and hazards ratios (HR) for fractures were reported.

RESULTS

In 1163 men (age: 77.2±5.2 years, body mass index (BMI): 28.0±4.0 kg/m(2), 4.1±0.9 follow-up years, 7.7% of men ⋝1 fracture), B-M indices were smaller in fractured men except for bending and areal indices. Smaller B-M indices were associated with increased fracture risk (HR: 1.30 to 1.74) independent of age and BMI. Strength and mass indices remained significant after accounting for lumbar spine but not total hip aBMD. However, aBMD correlated significantly with B-M indices.

CONCLUSION

Mass and bending B-M indices are risk factors for fractures in men, but may not improve fracture risk prediction beyond that provided by total hip aBMD.

Multiplanar reconstruction recovers morphological cartilage assessment reproducibility from maloriented coronal MRI scans

The study's purpose was to assess the effect of multiplanar reconstruction on precision of weight-bearing medial and lateral femoral cartilage (cMF, cLF) morphometry in maloriented coronal MR images. Twenty knees were scanned four times with a 1.0 Tesla extremity imager using a fat-suppressed T1-weighted three-dimensional spoiled gradient recalled echo sequence; twice with "best as" double bull's-eye orientation of the femoral condyles, and once each with 5° internal and external rotation. Multiplanar reconstruction was applied to maloriented scans to recover double bull's-eye orientation. Medial and lateral femoral cartilages were segmented and precision of bone area, cartilage volume and thickness (ThCtAB) evaluated for all scans. Test-retest precision (RMSCV%) of the double bull's-eye scans was 1.1% for total bone area and 4.1% for cartilage volume. Differences in precision between double bull's-eye and maloriented images were assessed. Higher precision errors were observed in malorientated images for all outcomes (1.7-4.8% for internally rotation scans; 1.7-4.8% for external rotation scans). Precision generally improved with multiplanar reconstruction correction (1.7-5.6% for internally rotated scans; 1.2-3.5% for external rotation scans). Precision of femoral cartilage morphometry is generally reduced when maloriented images are acquired. Multiplanar reconstruction can correct malorientated scans and recover precision losses. Measurements are affected in a rotationally and compartmentally dependent manner.

Reproducibility of computer-assisted joint alignment measurement in OA knee radiographs

OBJECTIVES

(1) To investigate the reproducibility of computer-assisted measurements of knee alignment angle (KA) from digitized radiographs of osteoarthritis (OA) participants requiring total knee arthroplasty (TKA) and (2) to determine whether landmark choice affects the precision of KA measurements on radiographs.

METHODS

Using a custom algorithm, femoral, central, and tibial measurement-guiding rules were interactively placed on digitized posteroanterior fixed-flexion knee radiographs by mouse control and positioned according to different anatomic landmarks. The angle subtended by lines connecting these guiding rules was measured by three readers to assess interobserver, intraobserver and experience-inexperience reproducibility. Test-retest reproducibility was evaluated with duplicate radiographs from a healthy cohort. Reproducibility was assessed using root-mean square coefficients of variation (RMSCV%). The Bland-Altman method was performed on data obtained from varying anatomic landmarks (confidence interval, CI= 95%).

RESULTS

From 16 healthy and 30 TKA participants, reproducibility analyses revealed a high degree of intraobserver (n=38, RMSCV=0.56%), interobserver (n=38, RMSCV=0.72%), test-retest (n=16, RMSCV=0.87%) and experience-inexperience (n=38, RMSCV=0.73%) reproducibility with variances below 1%. Varying the orientation of tibial and femoral rules according to anatomic landmarks produced a difference that exceeded an a priori limit of agreement of -1.11 degrees to +1.67 degrees.

CONCLUSION

Our custom-designed software provides a robust method for measuring KAs within digitized knee radiographs. Although test-retest analyses were only performed in a healthy cohort, we anticipate a similar degree of reproducibility in an OA sample. A standardized set of anatomic landmarks employed for KA measurement is recommended since arbitrary selection of landmarks resulted in imprecise KA measurement even with a computer-assisted technique.