Accuracy and precision study in vitro for peripheral quantitative computed tomography

Effect of Positioning of the ROI on BMD of the Forearm and Its Subregions

Inconsistent positioning of patients and region of interest (ROI) is known to influence the precision of bone mineral density (BMD) measurements in the spine and hip. However, it is unknown whether minor shifts in the positioning of the ROI along the shaft of the radius affect the measurement of forearm BMD and its subregions. The ultradistal (UD-), mid-, one-third, and total radius BMDs of 50 consecutive clinical densitometry patients were acquired. At baseline the distal end of the ROI was placed at the tip of the ulnar styloid as usual, and then the forearm was reanalyzed 10 more times, each time shifting the ROI 1 mm proximally. No corrections for multiple comparisons were necessary since the differences that were significant were significant at p < 0.001. The UD-radius BMD increased as the ROI was shifted proximally; the increase was significant when shifted even 1 mm proximally (p < 0.001). These same findings held true for the mid- and total radius bone density, though the percent increase with moving proximally was significantly greater for the UD radius than for the other subregions. However, there was no significant change in the one-third radius BMD when shifted proximally 1-10 mm. Minor proximal shifts of the forearm ROI substantially affect the BMD of the UD-, mid- and total radius, while having no effect on the one-third radius BMD. Since the one-third radius is the only forearm region usually reported, minor proximal shifts of the ROI should not influence forearm BMD results significantly.

Pediatric reference values for tibial trabecular bone mineral density and bone geometry parameters using peripheral quantitative computed tomography

The purpose of this study was to establish reference data, in relation to age and body height, for tibial trabecular and cortical volumetric bone mineral density, bone mineral content, and cross-sectional bone geometry in healthy children and adolescents using peripheral quantitative computed tomography (pQCT). Over a 2-year period, 432 (207 male and 225 female) healthy children, with an age range of 5 to 19 years, from 6 different geographic areas in Belgium were recruited. Multislice pQCT scanning (XCT2000(®), Stratec Medizintechnik, Pforzheim, Germany) was performed at the distal metaphysis (at the 4% site) and the distal diaphysis (14 and 38% sites) of the tibia of the dominant leg. Gender-specific centile curves in relation to age and body height were generated with the LMS method for total and trabecular volumetric bone mineral density (at 4% site), bone mineral content, total bone cross-sectional area, periosteal circumference (all at 4, 14, and 38% site), cortical volumetric bone mineral density, endosteal circumference, and cortical thickness (at the 14 and the 38% site). These centile curves can be used for the interpretation of pQCT results at the 4, 14, and 38% site of the tibia in European children and adolescents, at least when a similar methodology is used.

Trabecular bone mineral density and bone geometry of the distal radius at completion of pubertal growth in childhood type 1 diabetes

AIM

To identify disease-related risk factors for an altered bone mineral density (BMD) and geometry at young adulthood in patients with diabetes mellitus type 1 (DM1).

METHODS

Fifty-six DM1 patients (23 females, 33 males) with prepubertal onset of diabetes were studied after completion of skeletal growth. Bone parameters at the distal radius were investigated by peripheral quantitative computed tomography. Disease-related parameters, in particular average HbA1c during the 2 years around peak height velocity, were analyzed. Forty-seven healthy controls (32 females, 15 males) were studied.

RESULTS

Trabecular BMD was similar between DM1 patients and controls. The mean (±SD) cross-sectional bone area (CSA) was smaller in DM1 patients compared to controls (282.5 ± 45.4 vs. 326.7 ± 52.2 mm(2), p = 0.002 and males 391.0 ± 61.3 vs. 423.4 ± 81.9 mm(2), p = 0.1). In female DM1 patients, the CSA z-score correlated negatively with the body mass index z-score (r = -0.52, p = 0.01) and positively with the height z-score (r = 0.49, p = 0.02).

CONCLUSIONS

DM1 patients are at risk for smaller bone sizes at the distal radius at the end of pubertal growth, especially females with increased adiposity. Diabetes-specific parameters seem to have a low impact on forearm volumetric apparent mineral density.

Age-related differences of bone mass, geometry, and strength in treatment-naïve postmenopausal women. A tibia pQCT study

Most studies addressing the effects of aging on bone strength have focused mainly on (areal) bone mineral densities and bone mineral content (BMC) and less on bone geometry. We assessed age-related differences of bone mass (grams of bone mineral), geometry, and derived strength in 219 treatment-naïve postmenopausal women using peripheral quantitative computed tomography of the load-bearing tibia. Subjects were separated in 3 age groups: A=48-59yr (N=80), B=60-69yr (N=84), C=70-80yr (N=55). Three slices were obtained for each individual, at the 4% (trabecular), 14% (subcortical and cortical), and 38% (cortical bone) of tibia length sites. Trabecular, subcortical, and cortical BMC (mg per 1-mm slice), volumetric bone mineral densities (mg/cm(3)), bone cross-sectional areas (mm(2)), periosteal (PERI_C, mm) and endosteal circumference (ENDO_C, mm), mean cortical thickness (CRT_THK, mm), and Stress Strain Indexes (SSIs, mm(3)) were studied. Trabecular and cortical BMC and volumetric densities were significantly lower in the elder subjects (group C) compared with younger subjects (groups A and B), p<0.0005. Cortical area and CRT_THK were significantly lower in group C (vs A and B, p<0.0005), whereas total cross-sectional area was higher in group C compared with A and B. ENDO_C was significantly higher in older subjects (group C vs A and B, p<0.0005), whereas PERI_C did not differ significantly between the age groups. SSIs were significantly lower in older subjects at the 14% site (group C vs A, p<0.0005 and C vs B, p<0.005), and at the 38% site (group C vs group A, p<0.01). Our results indicate that age-induced differences on bone strength entail significant alterations not only of bone mass, but also of bone geometry.

Collagen and mineral deposition in rabbit cortical bone during maturation and growth: effects on tissue properties

We characterized the composition and mechanical properties of cortical bone during maturation and growth and in adult life in the rabbit. We hypothesized that the collagen network develops earlier than the mineralized matrix. Growth was monitored, and the rabbits were euthanized at birth (newborn), and at 1, 3, 6, 9, and 18 months of age. The collagen network was assessed biochemically (collagen content, enzymatic and non-enzymatic cross-links) in specimens from the mid-diaphysis of the tibia and femur and biomechanically (tensile testing) from decalcified whole tibia specimens. The mineralized matrix was analyzed using pQCT and 3-point bend tests from intact femur specimens. The collagen content and the Young's modulus of the collagen matrix increased significantly until the rabbits were 3 months old, and thereafter remained stable. The amount of HP and LP collagen cross-links increased continuously from newborn to 18 months of age, whereas PEN cross-links increased after 6 months of age. Bone mineral density and the Young's modulus of the mineralized bone increased until the rabbits were at least 6 months old. We concluded that substantial changes take place during the normal process of development in both the biochemical and biomechanical properties of rabbit cortical bone. In cortical bone, the collagen network reaches its mature composition and mechanical strength prior to the mineralized matrix.

Reproducibility of peripheral quantitative computed tomography measurements at the radius and tibia in healthy pre- and postmenopausal women

PURPOSE

The objectives of this study were to utilise the XCT-2000 pQCT scanner to determine the mean values and the reproducibility of in vivo total, trabecular, and cortical volumetric bone measurements at distal and diaphyseal sites of the radius and the tibia, as well as calf muscle and subcutaneous fat areas, in healthy pre- and postmenopausal women.

METHODS

Twenty-nine women (14 premenopausal and 15 postmenopausal) were recruited to participate in this study. Distal and diaphyseal sites of the radius (at 4% and 20% of the length of the radius) and tibia (at 4%, 38%, and 66% of the length of the tibia) were examined.

RESULTS

The root mean square coefficient of variation for measurements at the distal tibia gave the most favorable reproducibility values for total (1.5%) and trabecular (1.6%) density, whereas the diaphyseal tibia showed the most favorable reproducibility value for cortical density (0.3%). The root mean square coefficients of variation for measurements of muscle and fat cross-sectional areas at the calf were 0.6% and 0.7%, respectively. At the distal tibia, the mean values for total (P < .05) and trabecular (P < .01) density were significantly lower in postmenopausal women than in premenopausal women.

CONCLUSIONS

The data presented here indicate that XCT-2000 pQCT scans at the tibia provide highly reproducible measurements of total, cortical, and trabecular bone as well as muscle and fat cross-sectional areas. Furthermore, significant differences in volumetric bone measurements between healthy pre- and postmenopausal women were evident only at the distal tibia, suggesting that this site warrants further study.

Computed tomography topographic mapping of subchondral density (CT-TOMASD) in osteoarthritic and normal knees: methodological development and preliminary findings

OBJECTIVES

To develop a precise imaging tool which measures three-dimensional (3D) subchondral bone mineral density (BMD), and investigate its ability to distinguish subchondral bone properties in osteoarthritic and normal cadaveric tibiae.

METHODS

We developed a novel imaging tool [Computed tomography topographic mapping of subchondral density (CT-TOMASD)], which employs a surface projection image processing technique to map 3D subchondral BMD measured in relation to depth from the joint surface. Sixteen intact cadaver knees from 10 donors (8M:2F; age: 77.8+/-7.4) were scanned using quantitative computed tomography (QCT). Projections of average BMD to normalized depths of 2.5mm and 5.0mm were acquired, with regional analyses including: (1) medial and lateral BMD, (2) anterior/central/posterior compartmental BMD, (3) max BMD contained within a 10mm diameter 'core', and (4) medial:lateral BMD ratio. Precision was assessed using coefficients of variation (CV%). Osteoarthritis (OA) severity was assessed by examination of computed tomography (CT) and fluoroscopic radiographic images, and categorized using modified Kellgren-Lawrence (mKL) scoring.

RESULTS

Precision errors for CT-TOMASD BMD measures were focused around 1.5%, reaching a maximum CV% of 3.5%. OA was identified in eight compartments of six knees. Substantial qualitative and quantitative differences were observed between the OA and normal knees, with the medial:lateral BMD ratio and peak core regional analyses demonstrating differences greater than 4.7 standard deviations (SDs) when compared with normals. Preliminary results revealed effect sizes ranging from 1.6 to 4.3 between OA and normal knees.

CONCLUSIONS

CT-TOMASD offers precise 3D measures of subchondral BMD. Preliminary results demonstrate large qualitative and quantitative differences and large effect sizes between OA and normal knees. This method has the potential to identify and quantify changes in subchondral BMD associated with OA disease progression.

The impact of accurate positioning on measurements made by peripheral QCT in the distal radius

SUMMARY

Data from pQCT sections at the forearm were examined to assess the impact of positioning on measurements. Two thousand five hundred fifty one scans were analysed. The results showed 25% of scans were not performed in the same anatomical location at follow-up when one section was scanned. These results have implications for accurate follow-up BMD measurements.

INTRODUCTION

pQCT of the distal radius is routinely performed using a single section of 2 mm thickness. Accurate positioning is essential to maximise long-term repeatability. We perform two adjacent sections which, permits us to select sections at baseline and follow-up that are in the most similar anatomical site for calculating longitudinal change. This study aimed to assess baseline and follow-up pQCT forearm data to examine variability and determine whether performing two sections, as opposed to one section, improved accuracy when monitoring long-term change in BMD.

METHODS

Two adjacent 1.2 mm pQCT radial sections were performed at: baseline n = 2,551 (1,896F:655M) and follow-up n = 335F.

RESULTS

Baseline: difference between adjacent 1.2 mm forearm sections: total BMD 19.3 mg/cm(3) (females) and 16.7 mg/cm(3) (males); trabecular BMD 3.1 mg/cm(3) (females) and 2.35 mg/cm(3) (males); CSA 16.2 mm(2) (females) and 17.7 mm(2) (males) (all significant).

FOLLOW-UP

percentage of scans at baseline and follow-up performed in the same anatomical location: one section performed-75%, two sections performed-95%.

CONCLUSION

When performing a single section at the distal radius it is difficult to perform scans in the same anatomical location at visits. Performing two or more sections can overcome this problem in some individuals and provide more accurate BMD measurements.

Bone and muscle parameters of the tibia: agreement between the XCT 2000 and XCT 3000 instruments

Peripheral quantitative computed tomography is a valuable tool to assess bone in children across growth, with long-term studies capturing nuances missed in cross-sectional studies. As children grow, a change from XCT 2000 to a XCT 3000 may be required to accommodate the increasing size of the lower limbs. We examined the precision and agreement between the Stratec XCT 2000 and 3000 on selected bone and muscle parameters. Twenty-eight participants (mean+/-SD; age 27.5+/-6.5 yr) underwent scans at the distal (8%), mid (50%), and proximal (66%) tibia sites, to assess total bone area, total bone density, and trabecular density (8% site); and total bone area, cortical area, cortical density (CoD), polar strength-strain index, and muscle cross-sectional area (50% and 66% sites). Outcomes between instruments were highly correlated; r=0.90-0.99 for CoD across sites, with r=0.97-0.99 for all other measures. Bland and Altman plots showed excellent agreement between instruments for all variables. Regression indicated no significant relationship between instrument and size of measurement (p>0.05). Coefficients of variation were lower than previously reported (0.4-2.4%). For longitudinal studies, the XCT 3000 can replace the XCT 2000 with minimal influence on bone and muscle parameters.

Correlation of quantitative computed tomographic subchondral bone density and ash density in horses

The purpose of this study was to compare subchondral bone density obtained using quantitative computed tomography with ash density values from intact equine joints, and to determine if there are measurable anatomic variations in mean subchondral bone density. Five adult equine metacarpophalangeal joints were scanned with computed tomography (CT), disarticulated, and four 1-cm(3) regions of interest (ROI) cut from the distal third metacarpal bone. Bone cubes were ashed, and percent mineralization and ash density were recorded. Three-dimensional models were created of the distal third metacarpal bone from CT images. Four ROIs were measured on the distal aspect of the third metacarpal bone at axial and abaxial sites of the medial and lateral condyles for correlation with ash samples. Overall correlations of mean quantitative CT (QCT) density with ash density (r=0.82) and percent mineralization (r=0.93) were strong. There were significant differences between abaxial and axial ROIs for mean QCT density, percent bone mineralization and ash density (p<0.05). QCT appears to be a good measure of bone density in equine subchondral bone. Additionally, differences existed between axial and abaxial subchondral bone density in the equine distal third metacarpal bone.

Well-nourished cystic fibrosis patients have normal mineral density, but reduced cortical thickness at the forearm

Our goal was to assess mineral density and geometry of the cortex at the level of the forearm in adolescents and young adults with cystic fibrosis, using peripheral quantitative computed tomography. We found that density was normal, but cortical thickness significantly reduced, as well in males as in females.

INTRODUCTION

Our goal was to measure bone mineral density as a volumetric density, as well as total cross-sectional area, cortical area and cortical thickness, using peripheral quantitative computed tomography (pQCT) at the forearm in adolescents and young adults with cystic fibrosis. We evaluated relationships between forearm bone measurements and body composition assessed using dual energy X-ray absorptiometry (DXA).

METHODS

An XCT 2000 pQCT (Stratec, Pforzheim, Germany) and a QDR 4500 A-upgraded to Discovery DXA device (Hologic, Waltham, MA, USA) were used.

RESULTS

Forty-eight patients (31 males,17 females, mean+/-SD 20+/5 years) were studied. Anthropometric features were: height 169+/- 10 cm, SDS 0.05+/-0.12, body mass index 19.8+/- 2.5 kg/m(2), SDS -0.56+/-0.14. Bone mineral density and total cross-sectional area of the forearm and body composition were normal, whereas cortical thickness was significantly reduced in males (mean Z-score - 1.22, p < 0.05), and in females (mean Z-score - 1.61, p < 0.05). Total body lean mass correlated more strongly with cortical thickness (r = 0.72, p < 0.001) than with total bone mineral density at the proximal radius (r = 0.39, p < 0.05).

CONCLUSIONS

Adolescents and young adults with cystic fibrosis, presenting with only a slight degree of underweight, have at the radius a preserved bone mineral density but a reduced cortical thickness.

Methods for measurement of pediatric bone

Many experts believe that optimizing bone mineral accrual early in life may prevent childhood fractures and possibly delay the development of osteoporosis later in life. Adequate nutrition and physical activity are environmental factors important in determining whether or not children acquire an appropriate amount of bone for their body size. Pediatric diseases, or therapeutic interventions used in their treatment, may interfere with normal bone development. Although there are specific methods available for assessing pediatric bone, there is no one method that can adequately assess bone health and identify the specific bone deficits that may be occurring. Understanding the biological basis for bone deficits and the ability of various bone assessment methods to discriminate or measure these deficits is important in understanding normal bone development and how to prevent and treat pediatric bone disease. The purpose of this review is to briefly describe changes in bone with growth, to define "bone density" in biological terms, to discuss some of the issues with pediatric bone measurements, and to review the three main methods for assessing bone parameters in pediatric populations. These methods, including dual energy X-ray absorptiometry (DXA), quantitative ultrasound (QUS) and peripheral quantitative computed tomography (pQCT) will be described, the advantages and disadvantages discussed, and the relationship between bone parameters and fracture risk presented for each of the methods.

Limitations of peripheral quantitative computed tomography metaphyseal bone density measurements

CONTEXT

Peripheral quantitative computed tomography (pQCT) measurements are frequently obtained to assess cancellous bone density in the appendicular skeleton. Large variations in bone morphology associated with skeletal development may limit the interpretation of pediatric pQCT studies based on a single slice.

OBJECTIVE

The objective of the study was to characterize the variability in trabecular bone density values along the length of the metaphysis.

DESIGN

The design was an analysis of pQCT bone density data.

SETTING

The study was conducted at a hospital radiology department.

PATIENTS

The study included 35 children with cerebral palsy aged 6-12 yr.

MAIN OUTCOME MEASURE

Variations in cancellous bone density along the length of the proximal tibial metaphysis were measured.

RESULTS

The patterns of decay in metaphyseal trabecular bone density were different in all subjects, and the density changed from the physis to the shaft at a rate of 16.8 +/- 8.2% per 1 mm (range 8.6-37.9% per 1 mm). The slopes of the density curve drastically changed in some children over a short period of 6 months. Even with a high correlation (r(2) = 0.88) between the density of a slice located a fixed distance from the growth plate and the overall mean metaphysis density, the respective changes in density over 6 months were only moderately correlated (r(2) = 0.58).

CONCLUSIONS

These results underscore the difficulty in interpreting metaphyseal pQCT bone density measurements from a single slice and highlight the need for developing pQCT acquisition techniques that provide more representative bone density determinations in the appendicular skeleton of children.

Changes of microstructure and mineralized tissue in the middle and late phase of osteoporotic fracture healing in rats

BACKGROUND

With osteoporosis emerged as one of the most important health issues, more and more investigations are focusing on osteoporotic fracture healing. However, there are few studies on the changes of microstructure and mineralized tissue of newly formed callus.

OBJECTIVE

We established an osteoporotic fracture rat model to evaluate the changes of microstructure and mineralized tissue during osteoporotic fracture healing.

MATERIALS AND METHODS

A mid-shaft femur fracture model was established 12 weeks after ovariectomy as an osteoporotic fracture group (OPF group). Femurs were then harvested at 4 weeks, 8 weeks and 12 weeks after fracture for peripheral quantitative computed tomography (pQCT), micro-computed tomography (MicroCT), histology and biomechanical test. A sham-operated group was used for comparison, i.e. the normal fracture group (NF group).

RESULTS

The pQCT-derived total external callus area in the OPF group was smaller than that in the NF group at 4 weeks after fracture (P<0.05), whereas it was 21% larger in the OPF group than that in the NF group at 12 weeks after fracture (P<0.01). The pQCT-derived bone mineral density in the OPF group was significantly inferior to the NF group at all the time points (P<0.05 for all the time points, respectively). MicroCT data, at 12 weeks after fracture, showed the total callus, bony callus, and newly formed bone was approximately 20% lower in the OPF group than that in the NP group, and the total connectivity was 56% lower in the OPF group as compared to the NF group. Biomechanical test data, at 12 weeks after fracture, showed that the failure load of the left femur of OPF group was 17% less compared to that of the NF group (P<0.01), and 15% lower bending stiffness (P<0.05), 20% lower bending stress (P<0.01), and 28% lower energy at failure (P<0.01) were observed in the OPF group as compared to the NF group.

CONCLUSION

The decrease in mineralized tissue and the not well connected microstructure in newly formed callus may explain the decline of mechanical impairment of fracture healing in the ovariectomized rats.

Analyzing cortical bone cross-sectional geometry by peripheral QCT: comparison with bone histomorphometry

A distinct advantage of peripheral quantitative computed tomography (pQCT) is its ability to assess bone strength by measuring cross-sectional geometry and density of cortical bone. For accurate determination of cortical bone cross-sectional area (CoA), it is important to select the appropriate analysis mode and thresholds. No study has assessed which analysis protocol best represents tibial bone geometry--as determined by histomorphometry. We measured bone geometry from 16 human cadaver tibiae (mean age 74 [SD 6] yr) with pQCT (XCT 2000) at the 25% site, measured proximally from the distal tibia plafond. We conducted histomorphometry at the same site as the criterion standard. Scans were analyzed using modes and thresholds recommended by the manufacturer (Norland Stratec Medizintechnic GmbH, Pforzheim, Germany). We also investigated agreement of two additional thresholds (calculated by half-maximum height and inflection point methods) to define the endosteal border of cortical bone. Compared to the criterion, the smallest error (-1.0%, p=0.002) in total cross-sectional area (ToA) was obtained using Contour mode 3 with an outer threshold of 169 mg/cm(3). The smallest error (0.1%, NS) in CoA was obtained with Separation mode 4 (outer threshold 200mg/cm(3), inner threshold 670 mg/cm(3)). CoA was overestimated by 5-7% (p<0.001) from the criterion when an inner threshold of 480 mg/cm(3) was used in combination with any of the recommended outer thresholds. pQCT measurements of bone geometry in vitro vary to some extent between modes and thresholds selected. The effect of variation in bone geometry measurements on the predictive ability of bone strength indices derived from CoA needs to be assessed.

Effect of primary hyperparathyroidism on volumetric bone mineral density and bone geometry assessed by peripheral quantitative computed tomography in postmenopausal women

CONTEXT

Primary hyperparathyroidism (PH) is characterized by inappropriate PTH elevation with or without hypercalcemia. Bone disease involves catabolic action at cortical sites, whereas cancellous sites and geometry might be relatively preserved.

OBJECTIVE

Our objective was to examine the effect of PH on quantitative and qualitative bone characteristics using peripheral quantitative computed tomography at the tibia in postmenopausal women with PH and healthy controls.

DESIGN AND SETTING

We conducted a cross-sectional study at a tertiary referral center.

PATIENTS

Fifty-two postmenopausal women with PH and 56 healthy controls, comparable for age and anthropometric measures, participated.

INTERVENTION

There was no intervention.

MAIN OUTCOME MEASURE

We assessed volumetric bone mineral density (vBMD), bone mineral content (BMC), cortical thickness, cortical and trabecular area, peri- and endosteal circumference, and polar stress strength index assessed by peripheral quantitative computed tomography of the left tibia at 4% (cancellous), 14% (transition zone), and 38% (cortical) from the distal end.

RESULTS

At 4%, there was a significant decrease of trabecular BMC and vBMD (P < 0.001), effect particularly evident in hypercalcemic patients, whereas trabecular area was comparable. At 38%, cortical BMC (P < 0.01), vBMD (P < 0.01), area (P < 0.05), and thickness (P < 0.001) were reduced in the PH group, particularly in hypercalcemic patients. Endosteal circumference increased (P < 0.001), whereas periosteal circumference was comparable, indicating cancellization of cortical bone. At 14%, polar stress strength index was significantly decreased (P < 0.01) in hypercalcemic patients, indicating impairment of bone mechanical properties.

CONCLUSIONS

Normocalcemic PH is characterized by catabolic actions at both cortical and cancellous sites (38 and 4%, respectively), an effect accentuated in hypercalcemic patients. Cortical geometric properties are adversely affected even in normocalcemic patients, whereas trabecular properties are generally preserved.

The use of micro-CT to evaluate cortical bone geometry and strength in nude rats: correlation with mechanical testing, pQCT and DXA

In both clinical and experimental settings, access to quantitative methods enabling the objective evaluation of cortical bone mass, structure, geometry and strength are essential for the assessment of efficacy and safety of different treatments aimed to improve bone strength. The ability of non-invasive methodologies (DXA, pQCT and micro-CT) to assess and quantify cortical bone mass and geometry was tested in a nude rat model in which bone loss was induced by surgical castration. Treatment with a bone antiresorptive (alendronate) or a bone forming (PTH) drug was used to: (A) validate the nude rat model in terms of bone metabolism, (B) test the ability of each technology to detect change in cortical bone geometry and (C) correlate cortical bone geometry with bone strength data obtained by 3-point bending method. Our observations regarding effect of castration and treatment with PTH and alendronate on cortical bone parameters in nude rats is in general agreement with previously published data obtained in immunocompetent male rats under similar experimental conditions. Data presented here support the hypothesis that nude rats have similar bone physiology and response to known bone therapies to that observed in normal rats and therefore could be effectively used to predict skeletal response in humans. All three technologies deployed in this study (DXA, pQCT and micro-CT) proved useful in describing cancellous and/or cortical bone parameters and positive correlations were demonstrated between data obtained by different methods. The cross-sectional area of a bone structure is crucial for resisting loads in bending or torsion and is described as "areal moment of inertia" for bending, and as "polar moment of inertia" in torsion. Novel, three-dimensional micro-CT methodology used in this study to assess geometry of cortical bone provides data that accurately describes cortical bone geometry and parallels cortical bone strength results obtained by the 3-point bending method. Our micro-CT data meet the criteria of providing quick, reproducible and accurate answers regarding cortical bone geometry as a predictor of cortical bone strength.

Accuracy of pQCT for evaluating the aged human radius: an ashing, histomorphometry and failure load investigation

INTRODUCTION

Quantifying the determinants of bone strength is essential to understanding if or how the structure will fail under load. Determining failure requires knowledge of material and geometric properties. However, characterizing the relative contributions of geometric parameters of bone to overall bone strength has been difficult to date because of limitations in imaging technology. Peripheral quantitative computed tomography (pQCT) uses digital images to derive estimates of bone strength in the peripheral skeleton and is a relatively safe technique to differentiate cortical from trabecular bone and assess bone geometry and density. However, in a compromised osteoporotic bone, thin cortices and low scan resolution can limit accurate analysis.

METHODS

Therefore, in this two-part investigation we scanned ten pairs (n=20) of fresh-frozen radial specimens [female, mean (SD) age 79(6) years] using pQCT (XCT 2000) at the 4 and 30% sites of the distal radius. We investigated the accuracy of four different acquisition resolutions (200, 300, 400, 500 microm) and several analysis modes and thresholds. We evaluated (1) the accuracy of the Norland/Stratec XCT 2000 pQCT in assessing low-density bones by comparing pQCT outcomes to ashing and histomorphometry and (2) the association of geometric parameters by pQCT and areal bone mineral density (aBMD) by dual-energy X-ray absorptiometry (DXA) to failure load at the distal radius.

RESULTS

Using histomorphometry and ashing as reference standards, we found that pQCT scans varied systematically and underestimated or overestimated total area and mineral content at the radial midshaft depending on the analysis algorithm and selected threshold. Overall, most pQCT analysis modes were accurate. In the mechanical testing studies, bone mineral content and cortical bone content at the midshaft were strongly associated with failure load. The pQCT parameters that best accounted for failure load were total content at the 4% site and cortical thickness at the 30% site and they accounted for up to 81% of the variance. The best DXA predictor of failure load was total density at the distal third site and it explained 75% of the variance.

CONCLUSIONS

In summary, analysis mode, resolution and thresholding affected pQCT outputs at the radial midshaft. This study extends our understanding of pQCT analysis and provides important data regarding determinants of bone strength at the distal radius.

Peripheral quantitative computed tomography in evaluation of bioactive glass incorporation with bone

This laboratory study examined the feasibility of non-invasive, in vivo peripheral quantitative computed tomography (pQCT) method in evaluation of bioactive glass incorporation with bone. An intramedullary defect model of the rat tibia was applied. The defect was filled with bioactive glass microspheres (diameter of 250-315 microm) or was left to heal without filling (empty controls). The results of the pQCT analysis were compared with those of histomorphometry. In the control defects, there was a good correlation (r2 = 0.776, p < 0.001) between the pQCT density of the intramedullary space and the amount of new bone measured by histomorphometry. In the defects filled with bioactive glass, the use of thresholding techniques of the applied pQCT system (Stratec XCT Research M) failed in separation of new bone formation and bioactive glass particles. However, detailed analysis of the pQCT attenuation profiles showed time-related changes which well matched with the histomorphometric results of new bone formation both in control and bioactive glass filled defects. The biphasic pQCT attenuation profiles of bioactive glass filled defects could be separated into two distinct peaks. In statistical analysis of various variables, the center (i.e. the value of attenuation) of the major attenuation peak was found to be the most significant indicator of the incorporation process. The center of the peak initially decreased (during the first 4 weeks of healing) and thereafter increased. These two phases probably reflect the primary resorption and reactivity of the bioactive glass microspheres in vivo followed by secondary new bone formation on their surfaces. Based on these results, pQCT-method seems to be suitable for in vivo follow-up of the bioactive glass incorporation processes. Although the imaging technique is not able to discriminate the individual microspheres from invading new bone unambiguously, the attenuation profiling seems to give adequate information about the state of the incorporation process. This information may help to establish non-invasive imaging techniques of synthetic bone substitutes for preclinical and clinical testing of their efficacy.

Optimizing results from pQCT: reliability of operator-dependent pQCT variables in cadavers and humans with low bone mass

Peripheral quantitative computed tomography (pQCT) can assess bone geometric properties and separate cortical from trabecular bone. Despite pQCT's potential benefits for research, most reliability and accuracy studies have used a constant acquisition and analysis protocol. There are, however, numerous steps in the pQCT scan acquisition and analysis that are operator dependent. Whether or not these influence the quality of the pQCT scans and, potentially, the precision and validity of the data collected has been little explored. We investigated how pQCT outputs changed when operator-dependent parameters were varied, particularly when the bone of interest was of low mineral density. We found that bone parameters and scan failure rate varied significantly depending on the acquisition resolution; only one scan slice at the 10 and 30% radius is required to maintain adequate precision, and reference lines for sites should use a reproducible landmark. These results provide a foundation for recommending scan acquisition and analysis options for patients with low bone mass.

Problems in quantifying bone response to exercise in horses: a review

Detecting changes in bone during growth, training, rest from competition (spelling), and disease in horses requires imaging techniques that have a high level of accuracy and precision. Currently, most imaging techniques used in horses do not possess such characteristics and are more suitable for detecting end-stage disease than subtle changes. Some are incapable of detecting changes in bone size. Non-planar techniques should be used for estimating or determining bone strength. This review outlines available imaging techniques and shows why cross-sectional procedures are required to accurately estimate bone strength. If these can be validated and improved for use in the standing horse, serial examination can be used to show the magnitude of changes in bone strength that occur during training or varying management regimens. Such knowledge can then be used to improve training and spelling regimens for equine athletes, hopefully resulting in a reduction in racing or athletic injury.

Comparative assessment of bone mineral measurements obtained by use of dual-energy x-ray absorptiometry, peripheral quantitative computed tomography, and chemical-physical analyses in femurs of juvenile and adult dogs

OBJECTIVE

To compare bone mineral measurements obtained by use of dual-energy x-ray absorptiometry (DEXA), peripheral quantitative computed tomography (pQCT), and chemical-physical analyses and determine effects of age and femur size on values obtained for the various techniques.

SAMPLE POPULATION

Femurs obtained from 15 juvenile and 15 adult large-breed dogs.

PROCEDURE

n each femur, 7 regions of interest were examined by use of DEXA to measure the bone mineral content (BMC) and bone mineral density (BMD), and 5 were examined by use of pQCT to measure BMD. Among these, 1 region was examined by both noninvasive methods and an invasive method. Volume of the femur was determined by water displacement. Volumetric bone density (VBD) was calculated. Calcium (Ca), phosphorus (P), total Ca, and total P contents were determined.

RESULTS

DEXA- and pQCT-derived results revealed that all values increased with age in juvenile dogs. In adults, VBD and pQCT-derived BMD decreased significantly and DEXA-derived BMD increased with increasing femur length. The pQCT-derived BMD correlated well with VBD and Ca content, whereas DEXA-derived BMC was strongly correlated with Ca content. In juveniles, values correlated regardless of the technique used, whereas in adult dogs, DEXA-derived BMD did not correlate with pQCT-derived BMD, Ca concentration, or VBD unless data were adjusted on the basis of femur length.

CONCLUSIONS AND CLINICAL RELEVANCE

DEXA-derived BMD adjusted for femur length yields approximately the same percentage variability in VBD as for pQCT-derived BMD. However, pQCT-derived BMD is still more sensitive for determining variability BMD in Ca concentration, compared with DEXA-derived BMD adjusted for femur length.

Accuracy and precision of peripheral quantitative computed tomography measurements at the tibial metaphysis

The ability of 29 peripheral quantitative computed tomography (pQCT) software analysis modes at defining cortical from trabecular bone at three tibial metaphyseal regions was evaluated using five cadaveric tibiae. The accuracy of pQCT was determined by comparing the bone mineral content (BMC) with the ash weight. The precision of the pQCT scanner was calculated using repeated measurements. All the analysis modes had a good accuracy when measuring total bone area and a poor accuracy when measuring cortical bone area at the proximal 5% and distal 4% regions. For trabecular bone measured at all three regions and cortical bone area measured at the proximal 10% region, the Stratec peel mode 5 was the most accurate analysis mode. Highly significant correlations (r = 0.71-0.98) and a moderate accuracy error (coefficient of variation [CV] = 5-22%) was found between ash weight and BMC when using this mode. The precision of bone mineral density (BMD) measurements was good (total, CV = 2-5%; trabecular, CV = 2-5%; cortical, CV = 4-6%). pQCT is a moderately accurate, precise method of measuring trabecular and total BMD at the tibial metaphysis. The authors recommend caution when interpreting results for cortical BMD, as cortical area measurements at the metaphyseal region are less accurate and less precise.

Age-related changes in bone mineral content and density in intact male F344 rats

This study was undertaken to determine whether age-related bone loss occurs in intact male F344 rats. Bone loss was assessed in male F344 rats aged 3 to 27 months by scanning different bones using peripheral quantitative computed tomography (pQCT) densitometry. Cancellous and cortical bones were analyzed at the vertebra, proximal tibial metaphysis (PTM), and the neck of the femur. Cortical bone was also analyzed at the tibial and femoral diaphysis and at the tibio-fibula junction. In the vertebra, cancellous bone mineral content (Cn. BMC) did not change significantly with age. Cancellous bone mineral density (Cn. BMD) gradually decreased from 9 months onwards; and at 27 months of age, there was a 29% (p < 0.0001) decrease, when compared with 9-month-old animals. No significant change was observed in cortical bone mineral content (Ct. BMC) and cortical bone mineral density (Ct. BMD) with age. In the PTM, bone loss started to occur after 18 months of age. At 27 months of age, Cn. BMC decreased by 58% (p < 0.0001) and Cn. BMD also decreased by 58% (p < 0.0001). Ct. BMC decreased by 28% (p < 0.0001) in 27-month-old animals, whereas Ct. BMD was not affected by aging. At the tibio-fibula junction, Ct. BMC and Ct. BMD decreased after 18 months of age. At 27 months, Ct. BMC and Ct. BMD had decreased by 8% (p < 0.001) and 3% (p < 0.0001), respectively. Ct. BMC in the tibial diaphysis did not change significantly with age, whereas Ct. BMD decreased by 1% (p < 0.05) at 27 months. In the neck of the femur, Cn. BMC increased up to 24 months of age. Cn. BMD increased up to 18 months of age and decreased by 9% (p < 0.05) at 24 months and 11% (p < 0.001) at 27 months of age when compared with 18-month-old animals. Ct. BMC and Ct. BMD increased with age. In conclusion, although some components of the PTM decreased appreciably with age, in this study, most of the bone parameters analyzed either increased or did not change significantly with age. We conclude that unlike male Sprague Dawley rats, male F344 rats appear not to be a good model for studying age-related bone loss as occurs in aging men.

Effect of nickel-titanium shape memory metal alloy on bone formation

The aim of this study was to determine the biocompatibility of NiTi alloy on bone formation in vivo. For this purpose we used ectopic bone formation assay which goes through all the events of bone formation and calcification. Comparisons were made between Nitinol (NiTi), stainless steel (Stst) and titanium-aluminium (6%)-vanadium (4%) alloy (Ti-6Al-4V), which were implanted for 8 weeks under the fascia of the latissimus dorsi muscle in 3-month-old rats. A light-microscopic examination showed no chronic inflammatory or other pathological findings in the induced ossicle or its capsule. New bone replaced part of the decalcified matrix with mineralized new cartilage and bone. The mineral density was measured with peripheral quantitative computed tomography (pQCT). The total bone mineral density (BMD) values were nearly equal between the control and the NiTi samples, the Stst samples and the Ti-6Al-4V samples had lower BMDs. Digital image analysis was used to measure the combined area of new fibrotic tissue and original implanted bone matrix powder around the implants. There were no significant differences between the implanted materials, although Ti-6Al-4V showed the largest matrix powder areas. The same method was used for measurements of proportional cartilage and new bone areas in the ossicles. NiTi showed the largest cartilage area (p < or = 0.05). Between implant groups the new bone area was largest in NiTi. We conclude that NiTi has good biocompatibility, as its effects on ectopic bone formation are similar to those of Stst, and that the ectopic bone formation assay developed here can be used for biocompatibility studies.

Analysis of cancellous bone turnover by multiple slice analysis at distal radius: a study using peripheral quantitative computed tomography

We compared the results of peripheral quantitative computed tomography (pQCT) measurements (XCT-900; Stratec) at the 4% site of the distal radius (section 1; slice thickness of 2 mm) and in two proximally adjacent sections (sections 2 and 3). The study population consisted of 138 ambulatory patients (age 16.4 +/- 5.6 yr; mean +/- SD; 71 female) who were referred to a pediatric densitometry unit. Total volumetric bone mineral density (BMD) increased, whereas the area of the radial cross-section decreased in a proximal direction. There was a decrease in bone mineral content between sections 1 and 3, which was more pronounced in subjects under age 16. Cancellous BMD significantly decreased from section 1 to 3 only under the age of 16. In 12 patients under age 17 who suffered from increased bone fragility, cancellous BMD decreased about 2.5 times more between sections 1 and 3 than in age-matched patients who received anticonvulsant therapy but had a normal neurologic and musculoskeletal status (-21.4% +/- 16.9 vs -8.1% +/- 6.3; p = 0.02). This suggests that in the bone fragility group, trabeculae were removed faster during longitudinal growth of the radius. In conclusion, multiple slice analysis may provide information on the dynamic turnover of metaphyseal trabeculae during growth.

Bone loss. Quantitative imaging techniques for assessing bone mass in rheumatoid arthritis

Osteoporosis is associated with low bone mass and microarchitectural deterioration of bone tissue with clinical manifestation of low trauma fractures. Rheumatoid arthritis (RA) is a risk factor due to generalized and articular bone loss. This minireview presents past and current bone mass measurement techniques in RA. These techniques include: plain radiographs, absorptiometry, quantitative computed tomography (QCT) and ultrasound. The most widely used technique is dual x-ray absorptiometry (DXA). RA patients have lower bone mass as compared with normals and substantial bone loss may occur early after the onset of disease. Measurement of bone mineral density (BMD) at the hand using either DXA or ultrasound maybe a useful tool in the management of RA patients.

Differential effects of menopause and metabolic disease on trabecular and cortical bone assessed by peripheral quantitative computed tomography (pQCT)

The usefulness of peripheral quantitative computed tomography (pQCT) was investigated in the diagnosis of metabolic bone diseases, including osteoporosis, and especially in the different diagnostic values in trabecular and cortical components. The subjects were 460 Japanese women aged 20-86 years, including 318 healthy volunteers, 58 osteoporotics with fracture and 84 patients with diseases including amenorrhoea, steroid-induced osteoporosis, renal osteodystrophy (ROD) and primary hyperparathyroidism. Bone mineral density (BMD) was measured for more than 4 years in 74 of the healthy volunteers. BMD was measured by spinal QCT, dual X-ray absorptiometry (DXA) of the spine, radius, and heel, and pQCT of the radius and tibia. High resolution images were obtained for geometry of the radius. Radial pQCT showed a higher correlation with radial DXA than with spinal QCT, and spinal QCT showed a higher correlation with spinal DXA than with radial pQCT. The annual bone loss rates at predominantly trabecular bone sites were accelerated in both the axial and appendicular skeleton. In the fracture study, radial pQCT showed a higher odds ratio (OR = 4.4) than radial DXA, and cortical area ratio seemed to be a good predictor of fracture risk (OR = 5.2). Amenorrhoea and steroid-induced osteoporosis predominantly affected trabecular bone, ROD predominantly affected cortical bone and hyperparathyroidism affected both components, especially the cortical component. pQCT is useful for assessing both trabecular and cortical bone, to provide information on individual bone changes in metabolic bone disease and to estimate the risk of fracture.

Bone healing and mineralization, implant corrosion, and trace metals after nickel-titanium shape memory metal intramedullary fixation

Its shape memory effect, superelasticity, and good wear and damping properties make the NiTi shape memory alloy a material with fascinating potential for orthopedic surgery. It provides a possibility for making self-locking, self-expanding, and self-compressing implants. Problems, however, may arise because of its high nickel content. The purpose of this work was to determine the corrosion of NiTi in vivo and to evaluate the possible deleterious effects of NiTi on osteotomy healing, bone mineralization, and the remodeling response. Femoral osteotomies of 40 rats were fixed with either NiTi or stainless steel (StSt) intramedullary nails. The rats were killed at 2, 4, 8, 12, 26, and 60 weeks. Bone healing was examined with radiographs, peripheral quantitative computed tomography, (pQCT) and histologically. The corrosion of the retrieved implants was analyzed by electron microscopy (FESEM). Trace metals from several organs were determined by graphite furnace atomic absorption spectrometry (GF-AAS) or by inductively coupled plasma-atomic emission spectrometry (ICP-AES). There were more healed bone unions in the NiTi than in the StSt group at early (4 and 8 weeks) time points. Callus size was equal between the groups. The total and cortical bone mineral densities did not differ between the NiTi and StSt groups. Mineral density in both groups was lower in the osteotomy area than in the other areas along the nail. Density in the nail area was lower than in the proximal part of the operated femur or the contralateral femur. Bone contact to NiTi was close. A peri-implant lamellar bone sheet formed in the metaphyseal area after 8 weeks, indicating good tissue tolerance. The FESEM assessment showed surface corrosion changes to be more evident in the StSt implants. There were no statistically significant differences in nickel concentration between the NiTi and StSt groups in any of the organs. NiTi appears to be an appropriate material for further intramedullary use because it has good biocompatibility in bone tissue.

Accuracy of cortical and trabecular bone measurements with peripheral quantitative computed tomography (pQCT)

In order to assess the accuracy of peripheral QCT (Stratec XCT 960) we analysed scans of the European Forearm Phantom and another phantom consisting of K2HPO4 encased in aluminium tubes to simulate cortical walls. Additionally 14 cadaveric forearm specimen scans were compared to CT scans acquired on a GE9800Q. The accuracy for density assessment of the European Forearm Phantom was better than 3%. A small increase in density was observed with increasing thickness of the aluminium wall (10% for each mm). Density measurements within the wall were confounded by limited spatial resolution. For a thickness of less than 4 mm, the density within the wall was underestimated by up to 40%. The measurement of mineral content was not influenced by this effect and showed an accuracy error of less than 6%. The agreement of density measurements on the different CT systems was very strong (R2 > 0.96; RMSE < 6.2%). Our findings suggest that the Stratec pQCT scanner very accurately measures volumetric trabecular and total bone mineral densities at the distal radius while the assessment of cortical density is associated with considerable inaccuracies due to limited spatial resolution.

Distal radius fractures: mechanisms of injury and strength prediction by bone mineral assessment

The strength of the radius depends on the mechanical properties of cancellous and cortical bone. By assessing both compartments quantitatively with bone densitometry, we tried to identify the specificity of each in predicting the load at which the distal radius will fracture. Twenty human cadaver forearms were scanned for bone mineral and geometric properties with quantitative computed tomography and dual x-ray absorptiometry. In both a neutral loading situation and one in which the wrist was extended 45 degrees, the load distribution was determined with pressure-sensitive films, and a fracture simulating a fall on the hand was produced with a material testing machine. Fractures that occur with the wrist in extension were produced by a central impact of the scaphoid onto the radiocarpal joint, and those that occur under neutral loading conditions were produced by a more commonly distributed loading pattern. The load at fracture was most specifically predicted (r2=0.74) by bone mineral and geometric measures of the cortex at the shaft of the radius. Bone mineral density measures of trabecular (r2=0.64) and total (r2=0.66) bone were less successful in predicting the fracture load. After adjustment for bone size, the geometric and density measures revealed similar specificity. Cortical bone, therefore, contributes significantly to the strength of the distal radius and may play an important role in the prediction of osteoporotic wrist fractures.

Femoral neck strength of mouse in two loading configurations: method evaluation and fracture characteristics

We evaluated the mechanical strength of murine femoral neck in two loading configurations. The mechanical strength of the left femora of 25 male mice (weight 39 +/- 4 g) were measured in an axial configuration simulating one-legged stance in a human, and the right femora were tested in a configuration simulating a fall to the lateral side, on the trochanter. The reproducibility of the mechanical testing was 1.6% in the axial configuration and 3.7% in the fall configuration. The femoral neck was slightly stronger in the fall configuration. Typically, a load in the fall direction associated with a basicervical fracture, while axial loading resulted in both mid- and basicervical fractures. The linear bivariate correlation coefficient between the mechanical strengths in the two loading configurations was 0.83. Total bone mineral content (BMC), cortical bone mineral content (CtBMC), volumetric cortical bone mineral density (vCtBMD), and cross-sectional cortical area (CSA), measured at the femoral neck by peripheral quantitative computed tomography (pQCT), had a significant relationship with the femoral neck strength in the axial configuration. The coefficient of variation of the pQCT measurements was 9.1, 5.5, 2.3 and 5.5% for BMC, CtBMC, vCtBMD and CSA, respectively. We conclude that the precision of pQCT is moderate in evaluating the femoral neck of the mouse, and vCtBMD is the most reproducible parameter. The mechanical strength of the murine femoral neck can be measured with high precision by the two mechanical testing configurations presented here.

Clinical evaluation of a high-resolution new peripheral quantitative computerized tomography (pQCT) scanner for the bone densitometry at the lower limbs

Precision, long-term stability, linearity and accuracy of the x-ray peripheral quantitative computerized tomographic (pQCT) bone scanner XCT 3000 (Norland-Stratec Medical Sys.) were evaluated using the European Forearm Phantom (EFP). In vivo measurements were assessed using a standardized procedure at the distal femur and the distal tibia. In the patient-scan mode, the spatial resolution of the system was 1.04 +/- 0.05 lp/mm as measured at the 10% level of the modulation transfer function (MTF). The contrast-detail diagram (CDD) yielded a minimal difference in attenuation coefficient (AC) of 0.07 cm(-1) at an object size of 0.5 mm. The effective dose for humans was calculated to be less than 1.5 microSv per scan. Short-term precision in vivo was expressed as root mean square standard deviation of paired measurements of 20 healthy volunteers (RMSSD = 0.5%). At the distal femur total volumetric density (ToD) and total cross-sectional area (ToA) were found to be less sensitive to positioning errors than at the distal tibia. Structural parameters like the polar cross-sectional moment of inertia (CSMIp) or the polar cross-sectional moment of resistance (CSMRp) showed a good short-term precision at the distal femur (RMSSD = 1.2 and 1.4%). The relation between the two skeletal sites with respect to CSMIp or CSMRp showed a high coefficient of determination (r2 = 0.77 and 0.74).

Diagnostic sensitivity of peripheral quantitative computed tomography measurements at ultradistal and proximal radius in postmenopausal women

Peripheral quantitative computed tomography (pQCT) is a bone densitometry technique that is able to provide real volumetric bone density values not only of the total but also of trabecular and cortical bone separately. Normal reference curves were constructed with cross-sectional data obtained in 275 postmenopausal women (50-85 years), measured at 4% of the ulnar length (ultradistal region), and data for total, trabecular, and cortical bone density were obtained. In these postmenopausal subjects, continuously significant (p < 0.0001) age-dependent declines in bone density of 1.14%, 1.1%, and 0.57% for total, trabecular, and cortical bone, respectively, were observed while similar declines of 0.9%, 0.9%, and 0.4% per year since menopause, respectively, were found. The estimated mechanical stability index also showed linear dependencies with decreases of 0.84%/year and 0.6%/year since menopause (p < 0.0001). A more proximal acquisition at 15% of the ulnar length, an almost pure cortical region, resulted in linear declines of 0.41%/year and 0.27%/year (p < 0.0001) for the cortical bone and the mechanical stability index with significant changes of -0.27% and -0.23% per year, respectively, since menopause. Covariance analysis showed similar age dependencies of the different bone indices obtained in both regions of interest except for the stability index. A significant size adaptation of the bone with age was also observed, which was seen in the relationships of the trabecular and cortical bone areas to age and to bone density. Diagnostic sensitivity of all parameters for established osteoporosis was assessed by receiver operating characteristic (ROC) curves, comparing 99 patients with at least one fracture to the reference population. The area under these curves was highest in the ultradistal pure trabecular density of the radius (75%), followed by stability index (72%) and the area of cortical bone (65%) of the proximal site. No distinguishing power was seen for the cortical bone density values obtained in either the ultradistal (51%) or proximal radius (52%).

Peripheral quantitative computed tomography in human long bones: evaluation of in vitro and in vivo precision

Despite the excellent performance in clinical practice and research, the dual-energy X-ray absorptiometry is restricted by the inherent planar nature of the measurement and the inability to discriminate between trabecular and cortical components of bone. Recently, a new peripheral tomographic scanner (Norland/Stratec XCT 3000) was introduced for versatile measurements of human long bone characteristics in vivo, including trabecular and cortical density (TrD and CoD, respectively), respective cross-sectional areas (TrA and CoA), bone strength index (BSI), and bone mineral content (BMC). We evaluated the technical performance of the scanner using different phantoms and determined the in vivo precision of the above-noted applications by measuring twice several sites of upper and lower limbs of 19 and 36 volunteers aged 23-60 years. The bone scans were performed, with intermediate positioning of the subject, at two different anatomic sites of the forearm, three sites of the upper arm, three sites of the shank, and two sites of the thigh, with the respective skeletal sites representing different bone compositions and sizes. According to phantom measurements, the XCT 3000 appeared to be a highly linear, stable, and precise (coefficient of variation [CV] about 0.2%) system in vitro. The soft tissue thickness, however, had a linear effect on density values and a nonlinear effect on BMC, whereas the effect on cross-sectional area was marginal. The in vivo root mean square CV (CVrms) values for the long bone ends ranged from 0.9% (distal tibia) to 2.7% (distal femur) for TrD, from 1.8% (distal femur) to 7.6% (distal radius) for TrA, from 2.0% (distal tibia) to 6.8% (proximal tibia) for CoD, from 1.8% (distal femur) to 4.9% (proximal tibia) for CoA, and from 4.2% (distal tibia) to 7.7% (distal radius) for BSI. The corresponding CVrms values for the long bone shafts ranged from 0.5% (midshaft of humerus) to 1.4% (midshaft of fibula) for CoD, from 1.7% (midshaft of tibia) to 4.6% (proximal shaft of humerus) for CoA, and from 2.5% (midshaft of tibia) to 7.5% (proximal shaft of humerus) for BSI. There was no interoperator effect on precision. This study provided, for the first time, independent precision data for the new XCT 3000 peripheral quantitative computed tomography (pQCT) scanner in various applications of human long bones (radius, ulna, humerus, tibia, fibula, and femur) and gave practical guidelines and procedures on how to employ this versatile method in clinical and research applications. The technical performance of the tested system was excellent and it allowed, with a low radiation dose, precise in vivo evaluation of trabecular and cortical density, cross-sectional area, and BMC of selected skeletal sites. The potential effect of the soft tissue thickness on density and mineral content values need to be recognized. The pQCT measurement seems to be useful in supplementing the integral, planar DXA data and obviously opens new possibilities for clinical practice and research.

Nondestructive determination of iliac crest cancellous bone strength by pQCT

The close relationship between apparent bone density and compressive strength is well established. In clinical situations, histomorphometry and determination of the compressive strength on bone biopsies are destructive methods and require two separate biopsies from each patient. The aim of this study was to evaluate whether volumetric bone density measured by peripheral quantitative computed tomography (pQCT) could be used as a nondestructive method for estimating trabecular bone strength of iliac crest bone biopsies, thereby allowing the same biopsy to be used for subsequent histomorphometry. Materials consisted of trabecular bone samples prepared from unilateral transiliac crest bone samples obtained at autopsy [total 95 specimens; 41 females (21-90 years) and 54 males (23-87 years)]. From these, the apparent density of the cancellous bone was evaluated by pQCT in a 1-mm-thick slice in the middle of the biopsy and also by ash density measurement. Bone strength was measured by compression test. A strong power relationship was found between density measured by pQCT and compressive strength (r = 0.93, p < 0.00001). Likewise, there was a strong power relationship between ash density and compressive strength (r = 0.97, p < 0.00001). A linear correlation was found between pQCT measurement and ash density (r = 0.98, p < 0.00001), indicating a very high accuracy for the pQCT measurement. In conclusion, pQCT provides a very good estimate of cancellous bone strength. This nondestructive assessment of strength of iliac crest bone biopsies thereby enables biomechanical information as well as histomorphometric measurements to be obtained from the same biopsy.

Peripheral measurement techniques for the assessment of osteoporosis

Peripheral measurement techniques have been the first to be developed for the assessment of osteoporosis, and they remain useful. Besides traditional approaches such as radiographic absorptiometry (RA), radiogrammetry, and single-photon absorptiometry (SPA), new peripheral approaches have been developed that offer powerful ways to assess skeletal status in osteoporosis. These include single x-ray absorptiometry (SXA), peripheral dual x-ray absorptiometry (pDXA), peripheral quantitative computed tomography (pQCT), quantitative ultrasound (QUS) techniques, and magnetic resonance imaging (MRI) approaches. This review describes the current role of peripheral imaging techniques vis-à-vis their central imaging counterparts. Peripheral measurement techniques are attractive because equipment cost is substantially lower, radiation exposure is small, and the devices require less space and sometimes are even portable. Additionally, QUS and MRI offer the potential to measure aspects of bone status beyond the limits of bone densitometry. Peripheral techniques represent important diagnostic methods for the assessment of osteoporosis.