A trimodality comparison of volumetric bone imaging technologies. Part I: Short-term precision and validity

Effects of twin-block appliance on upper airway parameters in OSA children with class II malocclusion and mandibular retrognathia: a CBCT study

Twin-block appliance had been advocated as a potential treatment option in paediatric obstructive sleep apnoea (OSA) due to their favourable effect in enhancing upper airway parameters and improving OSA symptoms. The aim of this study was to evaluate the effect of twin-block appliance therapy on upper airway parameters/dimensions and the apnoea-hypopnea indexes (AHIs) in OSA children with class II mandibular retrognathic skeletal malocclusion using cone-beam computed tomography. This prospective longitudinal study comprised 34 polysomnography-proven OSA growing children with class II mandibular retrognathic skeletal malocclusion between the ages of 8 and 12 years who had completed myofunctional twin-block therapy and matched corresponding controls. The upper airway was segmented into the nasopharynx, oropharynx, and hypopharynx, and the effect of twin-bock treatment on upper airway parameters/dimensions was assessed pre- and posttreatment using CBCT analysis, while a second standard overnight PSG was performed to determine changes in the AHI. At the nasopharynx level, minimal (nonsignificant) increases in all variables were observed within the twin-block group and between the groups (P > 0.05). At the level of the oropharynx, all variables increased significantly in the treatment group and between groups (P < 0.001), but these increases were nonsignificant in the control group. At the level of the hypopharynx, only the minimum cross-sectional area (MCA) increased significantly in the treatment group (P = 0.003). The change in MCA was also significant between the groups (P = 0.041). In addition, the upper airway length increased significantly in the twin-block group (P = 0.0154), and the AHI decreased by 74.8% (P < 0.001).

CONCLUSION

Correction of class II mandibular retrognathic skeletal malocclusion with twin-block appliance resulted in a significant increase in upper airway volume, MCA, anteroposterior and lateral distances of the MCA at the level of the oropharynx, MCA at the level of the hypopharynx and upper airway length, and a significant decrease in AHI, but it had no effect on nasopharynx parameters.

WHAT IS KNOWN

• CBCT imaging has been shown to be an effective and precise diagnostic tool for analyzing the upper airways and craniofacial structures. • Twin block appliance may be an effective treatment modality in children with OSA.

WHAT IS NEW

• Minimal cross-sectional area of upper ways may be the most relevant potential parameter when explaining how the upper airway anatomy plays role of in the pathogenesis of pediatric OSA. • Twin block appliance induced favorable changes in upper airway morphology (oropharynx area mainly) and respiratory parameters in OSA children with class II malocclusion.

Evaluation of Increasing Dairy Intake on Bone Density in Post-pubertal Youth: A Randomized Controlled Trial Using Motivational Interviewing

BACKGROUND

Adequate nutrition is important for bone health, especially for bone mineral accretion.

OBJECTIVE

The primary objective tested whether increasing dairy intake using the motivational interviewing technique (MInt) improves lumbar spine (LS) bone mineral density (BMD) after 2 years in post-pubertal adolescents with habitual dairy intake of < 2 dairy servings/day.

DESIGN

Participants (14-18.9 y) were randomized to: Group 1 (control), group 2 (target of 3 dairy servings/d), or group 3 (target of ≥ 4 dairy servings/d) for 12 months with groups 2 and 3 using MInt, with an additional 12-month non-intervention follow-up. The primay outcome was LS BMD, and secondary outcomes: whole body (WB), total hip (TH), and 33% distal radius BMD using dual-energy x-ray absorptiometry, bone geometry using peripheral quantitative computed tomography, and bone biomarkers.

RESULTS

Ninety-four adolescents (16.6 ± 1.5 y) were recruited. Seventy-six (80.9%) completed the 12-month assessments. From baseline to 12 months, dairy intake in female groups 2 and 3 increased by 107% and 208%, respectively; and by 48% and 153% in males of group 2 and 3, respectively. In females, group 3 had greater increases in THBMD (4.3 to 7.5%) compared to control (3.7 to 4.9%, P = 0.04) and group 2 (0.0 to 1.7%, P = 0.04) at 12 and 24 months. No effects due to dairy intake were observed for DXA outcomes in males or radial and tibial volumetric BMD in both sexes. None of the bone biomarkers were different among the dairy groups in females or males.

CONCLUSION

MInt effectively increased dairy intake with benefits to bone health only in female adolescents with previously low calcium intake who consumed 4 dairy serving or more/day for 12 months. Larger studies are required to explain the lack of intervention effect in males.This trial was registered at ClinicalTrials.gov as. NCT02236871.

Validation of High-Resolution peripheral Quantitative Computed Tomography-Derived Achilles Tendon Properties Against Diagnostic Ultrasound

OBJECTIVES

1) To assess the precision of high resolution peripheral quantitative computed tomography (HR-pQCT)-derived Achilles tendon (AT) cross-sectional area (HR AT-CSA) and density, and 2) to validate HR AT-CSA against ultrasound-derived AT-CSA (US AT-CSA).

METHODS

Women and men (≥50 years) had HR-pQCT (0.082mm isotropic) and US scans (B-mode) performed on the non-dominant ankle. Linear regression and Bland-Altman analyses assessed systematic differences between HR-pQCT and US-derived AT-CSA. Precision measured by % root mean square coefficients of variation (%RMSCV) and agreement by type 2,1 intraclass correlation coefficients (ICC_2,1), were determined for test-retest US AT-CSA scans, and analysis-reanalysis of 30 HR-pQCT and US images.

RESULTS

Among 44 participants, HR and US AT-CSA were strongly correlated (R²=0.84, p<0.01, B=1.05[0.90-1.19]), with no differences between modalities (p=0.37). Bland-Altman analysis revealed minimal systematic bias (-0.7mm²[-10.7-9.3]; 1.3%) between HR-pQCT and US-derived AT-CSA with smaller AT-CSA values showing larger inter-modality differences (R²=0.098, B=-0.137 [-0.268--0.008], p=0.039). US AT-CSA demonstrated excellent test-retest precision (ICC_2,1=0.998, %RMSCV=1.04%). Analysis-reanalysis of HR-pQCT AT-density and both HR-pQCT and US AT-CSA displayed ICC_2,1 above 0.95 and %RMSCV within 3%.

CONCLUSION

HR-pQCT can examine AT-morphometry with acceptable analytical precision. Future studies should explore these metrics' association with functional outcomes and ankle-bone structural and mechanical properties.

The Assessment of Skeletal Muscle and Cortical Bone by Second-generation HR-pQCT at the Tibial Midshaft

BACKGROUND

Peripheral quantitative computed tomography (pQCT) is the current densitometric gold-standard for assessing skeletal muscle at the 66% proximal tibia site. High resolution peripheral quantitative computed tomography (HR-pQCT) is a leading technology for quantifying bone microarchitecture at the distal extremities, and with the second-generation HR-pQCT it is possible to measure proximal limb sites. Therefore, the objectives of this study were to: (1) assess the feasibility of using HR-pQCT to assess skeletal muscle parameters at the 66% proximal tibia site, and (2) test HR-pQCT skeletal muscle measurement reproducibility at this site.

METHODS

Adult participants (9 males; 7 females; ages 31-75) received 1 pQCT scan and 2 HR-pQCT scans at the 66% proximal site of the nondominant tibia. Participants were repositioned between HR-pQCT scans to test reproducibility. HR-pQCT and pQCT scans were analyzed to quantify muscle cross-sectional area (CSA) and muscle density. Coefficients of determination and Bland-Altman plots compared muscle parameters between pQCT and HR-pQCT. For short-term reproducibility, root-mean-square of coefficient of variance and least significant change were calculated.

RESULTS

HR-pQCT and pQCT measured muscle density and muscle CSA were positively correlated (R² = 0.66, R² = 0.95, p < 0.001, respectively). Muscle density was equivalent between HR-pQCT and pQCT; however, there was systematic and directional bias for muscle CSA, such that muscle CSA was 11% lower with HR-pQCT and bias increased with larger muscle CSA. Root-mean-square of coefficient of variance was 0.67% and 0.92% for HR-pQCT measured muscle density and muscle CSA, respectively, while least significant change was 1.4 mg/cm³ and 174.0 mm² for muscle density and muscle CSA, respectively.

CONCLUSION

HR-pQCT is capable of assessing skeletal muscle at the 66% site of the tibia with good precision. Measures of muscle density are comparable between HR-pQCT and pQCT.

A Valid and Precise Semiautomated Method for Quantifying Intermuscular Fat Intramuscular Fat in Lower Leg Magnetic Resonance Images

The accumulation of INTERmuscular fat and INTRAmuscular fat (IMF) has been a hallmark of individuals with diabetes, those with mobility impairments such as spinal cord injuries and is known to increase with aging. An elevated amount of IMF has been associated with fractures and frailty, but the imprecision of IMF measurement has so far limited the ability to observe more consistent clinical associations. Magnetic resonance imaging has been recognized as the gold standard for portraying these features, yet reliable methods for quantifying IMF on magnetic resonance imaging is far from standardized. Previous investigators used manual segmentation guided by histogram-based region-growing, but these techniques are subjective and have not demonstrated reliability. Others applied fuzzy classification, machine learning, and atlas-based segmentation methods, but each is limited by the complexity of implementation or by the need for a learning set, which must be established each time a new disease cohort is examined. In this paper, a simple convergent iterative threshold-optimizing algorithm was explored. The goal of the algorithm is to enable IMF quantification from plain fast spin echo (FSE) T1-weighted MR images or from water-saturated images. The algorithm can be programmed into Matlab easily, and is semiautomated, thus minimizing the subjectivity of threshold-selection. In 110 participants from 3 cohort studies, IMF area measurement demonstrated a high degree of reproducibility with errors well within the 5% benchmark for intraobserver, interobserver, and test-retest analyses; in contrast to manual segmentation which already yielded over 20% error for intraobserver analysis. This algorithm showed validity against manual segmentations (r > 0.85). The simplicity of this technique lends itself to be applied to fast spin echo images commonly ordered as part of standard of care and does not require more advanced fat-water separated images.

Bone Marrow and Muscle Fat Infiltration Are Correlated among Postmenopausal Women With Osteoporosis: The AMBERS Cohort Study

Bone and muscle have shown to interact, but little is known about fat within bone and muscle. Clinical studies have isolated fat within bone and muscle using MRI. In this cross-sectional study, we hypothesized that bone marrow adiposity and muscle adiposity are related and that this relationship is associated with osteoporosis. Postmenopausal women aged 60 to 85 years were recruited as part of the Appendicular Muscle and Bone Extension Research Study (AMBERS). Participants completed dual-energy X-ray absorptiometry (DXA) of the hip and spine to diagnose osteoporosis. Muscle adiposity was measured with MRI at the 66% site of the leg. Fat segmentation was achieved using a semi-automated iterative threshold-optimizing algorithm (error < 5%). Peripheral quantitative computed tomography measured marrow density of the 4% distal tibia (surrogate for marrow fat) by threshold-based, edge-detection segmentations and by examining residuals from trabecular bone density regressed on trabecular tissue mineral density. Muscle adiposity from MRI was regressed on marrow density using linear regression. Models were further examined with an interaction with osteoporosis status. Among 312 women (aged 75.4 ± 5.9 years, body mass index [BMI] 29.5 ± 5.7 kg/m² ), a larger amount of muscle fat was associated with lower marrow density at the 66% mid-tibia (B = 84.08 [27.56], p = 0.002) and at the 4% distal tibia (B = 129.17 [55.96], p = 0.022) after accounting for age, height, weight, average daily energy expenditure, hypertension, and diabetes. Interactions of this relationship with osteoporosis status were also significant. Upon probing these interactions, the relationships were significant only in women with osteoporosis but not in those without osteoporosis. Fat from bone marrow and muscle may be related to one another through the same phenomenon, which is likely also responsible for osteoporosis, but independent of hypertension and diabetes. More research should focus on the potential abnormalities in muscle and bone fat metabolism and mesenchymal cell commitment to fat within patients with osteoporosis. © 2019 American Society for Bone and Mineral Research.

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.

Peripheral Quantitative Computed Tomography: Review of Evidence and Recommendations for Image Acquisition, Analysis, and Reporting, Among Individuals With Neurological Impairment

In 2015, the International Society for Clinical Densitometry (ISCD) position statement regarding peripheral quantitative computed tomography (pQCT) did not recommend routine use of pQCT, in clinical settings until consistency in image acquisition and analysis protocols are reached, normative studies conducted, and treatment thresholds identified. To date, the lack of consensus-derived recommendations regarding pQCT implementation remains a barrier to implementation of pQCT technology. Thus, based on description of available evidence and literature synthesis, this review recommends the most appropriate pQCT acquisition and analysis protocols for clinical care and research purposes, and recommends specific measures for diagnosis of osteoporosis, assigning fracture risk, and monitoring osteoporosis treatment effectiveness, among patients with neurological impairment. A systematic literature search of MEDLINE, EMBASE^©, CINAHL, and PubMed for available pQCT studies assessing bone health was carried out from inception to August 8th, 2017. The search was limited to individuals with neurological impairment (spinal cord injury, stroke, and multiple sclerosis) as these groups have rapid and severe regional declines in bone mass. Of 923 references, we identified 69 that met review inclusion criteria. The majority of studies (n = 60) used the Stratec XCT 2000/3000 pQCT scanners as reflected in our evaluation of acquisition and analysis protocols. Overall congruence with the ISCD Official Positions was poor. Only 11% (n = 6) studies met quality reporting criteria for image acquisition and 32% (n = 19) reported their data analysis in a format suitable for reproduction. Therefore, based on current literature synthesis, ISCD position statement standards and the authors' expertise, we propose acquisition and analysis protocols at the radius, tibia, and femur sites using Stratec XCT 2000/3000 pQCT scanners among patients with neurological impairment for clinical and research purposes in order to drive practice change, develop normative datasets and complete future meta-analysis to inform fracture risk and treatment efficacy evaluation.

Peripheral Quantitative Computed Tomography (pQCT) Measures Contribute to the Understanding of Bone Fragility in Older Patients With Low-trauma Fracture

Dual-energy X-ray absorptiometry (DXA) as currently used has limitations in identifying patients with osteoporosis and predicting occurrence of fracture. We aimed to express peripheral quantitative computed tomography (pQCT) variables of patients with low-trauma fracture as T-scores by using T-score scales obtained from healthy young women, and to evaluate the potential clinical utility of pQCT for the assessment of bone fragility. Fracture patients were recruited from a fracture liaison service at the Royal Melbourne Hospital. Reference pQCT data were obtained from studies on women's health conducted by our group. A study visit was arranged with fracture patients, during which DXA and pQCT were applied to measure their bone strength. A total of 59 fracture patients were recruited, and reference data were obtained from 78 healthy young females. All DXA variables and most pQCT variables were significantly different between healthy young females and fracture patients (p < 0.05), except polar stress-strain index (p = 0.34) and cortical bone density (p = 0.19). Fracture patients were divided into osteoporosis and non-osteoporosis groups according to their DXA T-scores. Significant differences were observed in most pQCT variables (p < 0.05), except trabecular area and cortical density (p > 0.9 and p = 0.5, respectively). By applying pQCT T-scores, 11 (27%) of patients who were classified as having low or medium risk of osteoporosis on DXA T-scores alone were reclassified as high risk. Results of logistic regression suggested trabecular bone density as an independent predictor of osteoporosis status. More patients can be identified with osteoporosis by applying pQCT T-score variables in older people with low-trauma fracture. Peripheral QCT T-scores contribute to the understanding of bone fragility in this population.

Imaging methods for bone mass evaluation during childhood and adolescence: an update

The objective of the work was to prepare an update on imaging methods for bone evaluation during childhood and adolescence. The text was based on original and review articles on imaging methods for clinical evaluation of bone mass in children and adolescents up to 20 years old. They were selected from BIREME and PUBMED by means of the following keywords: bone density; osteoporosis/diagnosis; densitometry; tomography; ultrasonography; magnetic resonance imaging; and radiogrammetry and published in Portuguese or English, in the last 10 years (2006-2016). The article was organized into topics with the description of peculiarities, advantages and disadvantages of each imaging method and their possible clinical applicability. Despite the emergence of new technologies, dual energy X-ray absorptiometry (DXA) remains the gold standard method for low bone mass diagnosis in all age groups. However, interpretation is complex in children and adolescents and demands skilled people. Quantitative computed tomography (QCT) [central QCT, peripheral QCT (pQCT) and high resolution-pQCT (HR-pQCT)] and magnetic resonance imaging (MRI) evaluate real bone density, but are not yet available for routine use. Quantitative bone ultrasound (QUS) shows good perspectives for its use in primary prevention actions. Automated radiogrammetry shows promise as a method able to flag individuals who might benefit from a complete bone assessment, but the clinical value of the measures still needs to be established.

Three doses of vitamin D, bone mineral density, and geometry in older women during modest weight control in a 1-year randomized controlled trial

The effects of higher than recommended vitamin D doses on bone mineral density (BMD) and quality are not known. In this study, higher intakes, in postmenopausal women undergoing weight control over 1 year, had no effect on areal or volumetric BMD but prevented the deterioration in cortical bone geometry.

INTRODUCTION

Studies examining how bone responds to a standard dose of vitamin D supplementation have been inconsistent. In addition, the effects of higher doses on BMD and quality are not known. Postmenopausal women undergoing weight control to improve health outcomes are particularly at risk for bone loss and might benefit from supplemental vitamin D intake above the recommended allowance.

METHODS

This 1-year-long, randomized, double-blind controlled study addresses whether vitamin D supplementation, in healthy overweight/obese older women, affects BMD and bone structural parameters. In addition, bone turnover and serum total, free, and bioavailable 25-hydroxyvitamin D (25OHD) responses to one of three daily levels of vitamin D₃ (600, 2000, 4000 IU) with 1.2 Ca g/day during weight control were examined.

RESULTS

Fifty-eight women (age, 58 ± 6 years; body mass index, 30.2 ± 3.8 kg/m², serum 25OHD, 27.3 ± 4.4 ng/mL) were randomized to treatment. After 1 year, serum 25OHD concentrations increased to 26.5 ± 4.4, 35.9 ± 4.5, and 41.5 ± 6.9 ng/mL, in groups 600, 2000, and 4000 IU, respectively, and differed between groups (p < 0.01). Weight change was similar between groups (-3.0 ± 4.1 %). Cortical (Ct) thickness of the tibia changed by -1.5 ± 5.1 %, +0.6 ± 3.2 %, and +2.0 ± 4.5 % in groups 600, 2000, and 4000 IU, respectively, and each group was significantly different from each other (p < 0.05).

CONCLUSION

The decline in Ct thickness was prevented with higher vitamin D₃ supplementation, but there were no other significant changes due to treatment over 1 year. Whether these findings translate to changes in biomechanical properties leading to reduced fracture risk should be addressed in future studies.

A comparison of peripheral imaging technologies for bone and muscle quantification: a technical review of image acquisition

The choice of an appropriate imaging technique to quantify bone, muscle, or muscle adiposity needs to be guided by a thorough understanding of its competitive advantages over other modalities balanced by its limitations. This review details the technical machinery and methods behind peripheral quantitative computed tomography (pQCT), high-resolution (HR)-pQCT, and magnetic resonance imaging (MRI) that drive successful depiction of bone and muscle morphometry, densitometry, and structure. It discusses a number of image acquisition settings, the challenges associated with using one versus another, and compares the risk-benefits across the different modalities. Issues related to all modalities including partial volume artifact, beam hardening, calibration, and motion assessment are also detailed. The review further provides data and images to illustrate differences between methods to better guide the reader in selecting an imaging method strategically. Overall, investigators should be cautious of the impact of imaging parameters on image signal or contrast-to-noise-ratios, and the need to report these settings in future publications. The effect of motion should be assessed on images and a decision made to exclude prior to segmentation. A more standardized approach to imaging bone and muscle on pQCT and MRI could enhance comparability across studies and could improve the quality of meta-analyses.

Bone lead (Pb) content at the tibia is associated with thinner distal tibia cortices and lower volumetric bone density in postmenopausal women

Conflicting evidence suggests that bone lead or blood lead may reduce areal bone mineral density (BMD). Little is known about how lead at either compartment affects bone structure. This study examined postmenopausal women (N=38, mean age 76 ± 8, body mass index (BMI): 26.74 ± 4.26 kg/m(2)) within the Hamilton cohort of the Canadian Multicentre Osteoporosis Study (CaMos), measuring bone lead at 66% of the non-dominant leg and at the calcaneus using (109)Cadmium X-ray fluorescence. Volumetric BMD and structural parameters were obtained from peripheral quantitative computed tomography images (200 μm in-plane resolution, 2.3 ± 0.5mm slice thickness) of the same 66% site and of the distal 4% site of the tibia length. Blood lead was measured using atomic absorption spectrometry and blood-to-bone lead partition coefficients (PBB, log ratio) were computed. Multivariable linear regression examined each of bone lead at the 66% tibia, calcaneus, blood lead and PBB as related to each of volumetric BMD and structural parameters, adjusting for age and BMI, diabetes or antiresorptive therapy. Regression coefficients were reported along with 95% confidence intervals. Higher amounts of bone lead at the tibia were associated with thinner distal tibia cortices (-0.972 (-1.882, -0.061) per 100 μg Pb/g of bone mineral) and integral volumetric BMD (-3.05 (-6.05, -0.05) per μg Pb/g of bone mineral). A higher PBB was associated with larger trabecular separation (0.115 (0.053, 0.178)), lower trabecular volumetric BMD (-26.83 (-50.37, -3.29)) and trabecular number (-0.08 (-0.14, -0.02)), per 100 μg Pb/g of bone mineral after adjusting for age and BMI, and remained significant while accounting for diabetes or use of antiresorptives. Total lead exposure activities related to bone lead at the calcaneus (8.29 (0.11, 16.48)) and remained significant after age and antiresorptives-adjustment. Lead accumulated in bone can have a mild insult on bone structure; but greater partitioning of lead in blood versus bone revealed more dramatic effects on both microstructure and volumetric BMD.

Least significant changes and monitoring time intervals for high-resolution pQCT-derived bone outcomes in postmenopausal women

BACKGROUND

Least Significant Change (LSC) assists in determining whether observed bone change is beyond measurement precision. Monitoring Time Interval (MTI) estimates time required to reliably detect skeletal changes. MTIs have not been defined for bone outcomes provided by high resolution peripheral quantitative computed tomography (HR-pQCT). The purpose of this study was to determine the LSCs and MTIs for HR-pQCT derived bone area, density and micro-architecture with postmenopausal women.

METHODS

Distal radius and tibia of 33 postmenopausal women (mean age: 77, SD: ±7 years), from the Saskatoon cohort of the Canadian Multicentre Osteoporosis Study (CaMos), were measured using HR-pQCT at baseline and 1-year later. We determined LSC from precision errors and divided them by the median annual percent changes to define MTIs for bone area, density, and micro-architecture.

RESULTS

Distal radius: HR-pQCT LSCs indicated a 1-8% observed change was needed for reliable monitoring of bone area and density while a 3-18% change was needed for micro-architectural measures. The longest MTIs (>3 years) pertained to cortical and trabecular area and density measures, cortical thickness and bone volume fraction; the shortest MTIs (~2 years) pertained to bone micro-architectural measures (trabecular number, thickness, separation and heterogeneity). Distal tibia: LSCs indicated a <1-5% observed change was needed for reliable monitoring of bone area and density, while a 3-19% change was needed for micro-architectural measures. The longest MTIs (>3 years) pertained to trabecular density, bone volume fraction, number, separation and heterogeneity; the shortest MTIs (~1 year) pertained to cortical and trabecular area, cortical density and thickness.

CONCLUSION

MTIs suggest that performing HR-pQCT follow-up measures in postmenopausal women every 2 years at the distal radius and every 1 year at the distal tibia to monitor true skeletal changes as indicated by the LSCs.