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

Bone imaging modality precision and agreement between DXA, pQCT, and HR-pQCT

Quantifying precision error for DXA, peripheral QCT (pQCT), and HR-pQCT is crucial for monitoring longitudinal changes in body composition and musculoskeletal outcomes. Agreement and associations between bone variables assessed using pQCT and second-generation HR-pQCT are unclear. This study aimed to determine the precision of, and agreement and associations between, bone variables assessed via DXA, pQCT, and second-generation HR-pQCT. Thirty older adults (mean age: 64.2 ± 8.0 yr; women: 67%) were recruited. DXA scans were performed at the total hip, lumbar spine, and whole body. Distal (4%) and proximal (30%/33%/66%) skeletal sites at the radius and tibia were scanned with pQCT and/or HR-pQCT. Root-mean-squared coefficients of variation (%CVRMS) were calculated to define precision errors, and Bland-Altman plots assessed agreement between densitometric estimates. Pearson correlations and linear regression explored relationships between bone variables at different skeletal sites and proportional bias, respectively. Precision errors ranged between 0.55% and 1.6% for DXA, 0.40% and 4.8% for pQCT, and 0.13% and 30.7% for HR-pQCT. Systematic bias was identified between pQCT- and HR-pQCT-determined radius and tibia volumetric BMD (vBMD) estimates (all p<.001). Proportional bias was not observed between vBMD measures at any skeletal site (all p>.05). pQCT- and HR-pQCT-determined total, trabecular, and cortical vBMD and estimates of bone strength at the radius and tibia were strongly correlated (all p<.05). Precision error was low for most bone variables and within the expected range for all imaging modalities. We observed significant systematic bias, but no proportional bias, between pQCT- and second-generation HR-pQCT-determined vBMD estimates at the radius and tibia. Nevertheless, measures of bone density and strength were strongly correlated at all skeletal sites. These findings suggest that although bone density and strength estimates from both imaging modalities are not interchangeable, they are strongly related and likely have similar fracture prediction capabilities.

Sex-, Ethnic-, and Age-Specific Centile Curves for pQCT- and HR-pQCT-Derived Measures of Bone Structure and Strength in Adolescents and Young Adults

There are presently no adolescent centile curves for bone parameters at the tibial midshaft using peripheral quantitative computed tomography (pQCT) or at the distal radius and tibia using high-resolution pQCT (HR-pQCT). Thus, we aimed to develop sex-, ethnic-, site-, and age-specific centile curves for pQCT and HR-pQCT-derived bone outcomes for youth and young adults aged 10 to 21 years. We acquired pQCT scans (XCT3000 or XCT2000) at the tibial midshaft (50% site) and HR-pQCT scans (XtremeCT) at the distal radius (7% site) and tibia (8% site) in a convenience sample of participants in the mixed-longitudinal University of British Columbia Healthy Bones III Study. We scanned 778 10- to 21-year-olds annually for a maximum of 11 years using pQCT (413 girls, 56% Asian; 365 boys, 54% Asian; n = 3160 observations) and 349 10- to 21-year-olds annually for a maximum of 4 years using HR-pQCT (189 girls, 51% Asian; 165 boys, 50% Asian; n = 1090 observations). For pQCT, we report cortical bone mineral density (BMD), total bone cross-sectional area, and polar strength-strain index. For HR-pQCT, we report standard measures (total BMD, trabecular number, thickness, and bone volume fraction) and automated segmentation measures (total bone cross-sectional area, cortical BMD, porosity, and thickness). We applied finite element analysis to estimate failure load. We applied the lamda, mu, sigma (LMS) method using LMS ChartMaker Light (version 2.5, The Institute of Child Health, London, UK) to construct LMS tables and centile plots. We report sex- and age-specific centiles (3rd, 10th, 25th, 50th, 75th, and 97th) for whites and Asians for pQCT bone parameters at the tibial midshaft and HR-pQCT bone parameters at the distal radius and tibia. These centile curves might be used by clinicians and scientists to interpret values or better understand trajectories of bone parameters in clinical populations, those from different geographic regions or of different ethnic origins. © 2018 American Society for Bone and Mineral Research.

Reexamining the Surfaces of Bone in Boys and Girls During Adolescent Growth: A 12-Year Mixed Longitudinal pQCT Study

We revisit Stanley Garn's theory related to sex differences in endocortical and periosteal apposition during adolescence using a 12-year mixed longitudinal study design. We used peripheral quantitative computed tomography to examine bone parameters in 230 participants (110 boys, 120 girls; aged 11.0 years at baseline). We assessed total (Tt.Ar, mm(2)), cortical (Ct.Ar, mm(2)), and medullary canal area (Me.Ar, mm(2)), Ct.Ar/Tt.Ar, cortical bone mineral density (Ct.BMD, mg/cm(3)), and polar strength-strain index (SSIp , mm(3)) at the tibial midshaft (50% site). We used annual measures of height and chronological age to identify age at peak height velocity (APHV) for each participant. We compared annual accrual rates of bone parameters between boys and girls, aligned on APHV using a linear mixed effects model. At APHV, boys demonstrated greater Tt.Ar (ratio = 1.27; 95% confidence interval [CI] 1.21, 1.32), Ct.Ar (1.24 [1.18, 1.30]), Me.Ar (1.31 [1.22, 1.40]), and SSIp (1.36 [1.28, 1.45]) and less Ct.Ar/Tt.Ar (0.98 [0.96, 1.00]) and Ct.BMD (0.97 [0.96, 0.97]) compared with girls. Boys and girls demonstrated periosteal bone formation and net bone loss at the endocortical surface. Compared with girls, boys demonstrated greater annual accrual rates pre-APHV for Tt.Ar (1.18 [1.02, 1.34]) and Me.Ar (1.34 [1.11, 1.57]), lower annual accrual rates pre-APHV for Ct.Ar/Tt.Ar (0.56 [0.29, 0.83]) and Ct.BMD (-0.07 [-0.17, 0.04]), and similar annual accrual rates pre-APHV for Ct.Ar (1.10 [0.94, 1.26]) and SSIp (1.14 [0.98, 1.30]). Post-APHV, boys demonstrated similar annual accrual rates for Ct.Ar/Tt.Ar (1.01 [0.71, 1.31]) and greater annual accrual rates for all other bone parameters compared with girls (ratio = 1.23 to 2.63; 95% CI 1.11 to 3.45). Our findings support those of Garn and others of accelerated periosteal apposition during adolescence, more evident in boys than girls. However, our findings challenge the notion of greater endocortical apposition in girls, suggesting instead that girls experience diminished endocortical resorption compared with boys.

Reproducibility of a peripheral quantitative computed tomography scan protocol to measure the material properties of the second metatarsal

Background

Peripheral quantitative computed tomography (pQCT) is an established technology that allows for the measurement of the material properties of bone. Alterations to bone architecture are associated with an increased risk of fracture. Further pQCT research is necessary to identify regions of interest that are prone to fracture risk in people with chronic diseases. The second metatarsal is a common site for the development of insufficiency fractures, and as such the aim of this study was to assess the reproducibility of a novel scanning protocol of the second metatarsal using pQCT.

Methods

Eleven embalmed cadaveric leg specimens were scanned six times; three times with and without repositioning. Each foot was positioned on a custom-designed acrylic foot plate to permit unimpeded scans of the region of interest. Sixty-six scans were obtained at 15% (distal) and 50% (mid shaft) of the second metatarsal. Voxel size and scan speed were reduced to 0.40 mm and 25 mm.sec^-1. The reference line was positioned at the most distal portion of the 2^nd metatarsal. Repeated measurements of six key variables related to bone properties were subject to reproducibility testing. Data were log transformed and reproducibility of scans were assessed using intraclass correlation coefficients (ICC) and coefficients of variation (CV%).

Results

Reproducibility of the measurements without repositioning were estimated as: trabecular area (ICC 0.95; CV% 2.4), trabecular density (ICC 0.98; CV% 3.0), Strength Strain Index (SSI) - distal (ICC 0.99; CV% 5.6), cortical area (ICC 1.0; CV% 1.5), cortical density (ICC 0.99; CV% 0.1), SSI – mid shaft (ICC 1.0; CV% 2.4). Reproducibility of the measurements after repositioning were estimated as: trabecular area (ICC 0.96; CV% 2.4), trabecular density (ICC 0.98; CV% 2.8), SSI - distal (ICC 1.0; CV% 3.5), cortical area (ICC 0.99; CV%2.4), cortical density (ICC 0.98; CV% 0.8), SSI – mid shaft (ICC 0.99; CV% 3.2).

Conclusions

The scanning protocol generated excellent reproducibility for key bone properties measured at the distal and mid-shaft regions of the 2^nd metatarsal. This protocol extends the capabilities of pQCT to evaluate bone quality in people who may be at an increased risk of metatarsal insufficiency fractures.

Factors affecting short-term precision of musculoskeletal measures using peripheral quantitative computed tomography (pQCT)

Few studies have investigated factors influencing the precision of peripheral quantitative computed tomography (pQCT) measures. This study found time between repeat scans and subject anthropometric characteristics to influence short-term precision of pQCT-derived measures in the lower leg. These findings have implications for both investigators and clinicians utilizing pQCT outcomes.

INTRODUCTION

Peripheral quantitative computed tomography (pQCT) is increasingly being used to investigate musculoskeletal changes associated with age, disease and/or intervention. Precision of pQCT measures is of paramount importance in this endeavor. This study aimed to establish the short-term precision of pQCT-derived musculoskeletal measures of the lower leg and investigate factors influencing this precision.

METHODS

Thirty healthy subjects had a series of six pQCT scans of the lower leg (66% of tibial length proximal from its distal end) performed on two separate days by two different testers. The influences of different testers, time between repeat scans, and subject anthropometric characteristics on precision were explored.

RESULTS

Overall precision error (root mean square) increased from bone (<1%) to muscle (<1.5%) to fat (3%). The two testers were equally precise in performing pQCT measures; however, precision error increased when repeat scans were repeated 1 week apart as opposed to on the same day. Subject anthropometric characteristics influenced precision errors with the general finding being that an increase in subject size was associated with less precise pQCT measures.

CONCLUSIONS

pQCT is a relatively precise technique for the assessment of bone and muscle, but precision is influenced by time between repeat scans and subject anthropometric characteristics. Investigators and clinicians need to be aware of these factors influencing pQCT outcomes as they may influence statistical power in clinical studies and the characterization of change in individual patients.

Compromised bone strength index in the hemiparetic distal tibia epiphysis among chronic stroke patients: the association with cardiovascular function, muscle atrophy, mobility, and spasticity

SUMMARY

The purpose of this study was to identify the determinants of the bone strength index of the distal tibia epiphysis in chronic stroke patients. The results showed that lower cardiovascular fitness, more muscle atrophy, poorer mobility, and more severe spasticity were independently associated with lower tibial bone strength index.

INTRODUCTION

To identify the determinants of the bone strength index (BSI) at the distal tibia in chronic stroke patients

METHODS

Sixty-three chronic stroke survivors underwent scanning of the distal tibia at the 4% site on both sides using peripheral quantitative computed tomography. The primary outcomes were trabecular bone mineral density (BMD; milligram per cubic centimeter), total BMD (milligram per cubic centimeter), total bone area (square millimeter), and BSI (square gram per centimeter to the power of four). Cardiovascular fitness, leg lean mass, gait velocity, and spasticity were also measured.

RESULTS

Scans from 45 subjects were deemed to have acceptable quality and were included for subsequent analysis. The paretic side had significantly lower trabecular BMD, total BMD, and BSI than the nonparetic side (p < 0.05). However, the total bone area demonstrated no significant side-to-side difference (p > 0.05). After adjusting for relevant biological factors, peak oxygen consumption, leg muscle mass, and gait velocity remained positively associated with tibial BSI on both sides (R (2) change = 6.9-14.2%), whereas spasticity of the paretic leg was negatively associated with tibial BSI on the same side (R (2) change = 4.8%).

CONCLUSIONS

Cardiovascular function, muscle atrophy, mobility, and spasticity are independently associated with BSI of the distal tibia epiphysis among chronic stroke patients.

Bone mineral density alterations in upper and lower extremities 12 months after stroke measured by peripheral quantitative computed tomography and DXA

To evaluate the loss of trabecular and cortical bone mineral density (BMD) and geometric parameters of bone strength expressed by stress-strain index (SSI) in the proximal and distal forearm and the alterations of BMD in the hip of hemiplegic patient and 12 mo after stroke. Sixty-seven hemiplegic patients (43 men and 24 women) with a history of single completed strokes associated with unilateral weakness were enrolled in this prospective study. All patients underwent bone densitometry measurements at 3, 6, and 12 mo after the initial episode of stroke. Both paretic and normal forearms were examined by peripheral quantitative computed tomography (pQCT) at the 4% and 20% sites of the forearm length and both hips were examined by dual-energy X-ray absorptiometry (DXA) including the area of femoral neck and greater trochanter. The diagnosis of stroke was confirmed by cranial computed tomography. Motor function was assessed by the functional ambulation category (FAC) and spasticity by the modified Ashworth scale (MAS). We found statistically significant trabecular and cortical bone density reductions during the course of our study in the forearm, which was more profound on the paretic side. Trabecular bone loss and SSI measured at 4% of the paretic forearm in the male group represented a 12-mo decrease of 14.01% and 28.61%, respectively, and in the female group 9.29% and 19.17%, respectively. Cortical bone and SSI measured at the 20% site of paretic forearm in the male group corresponded to a 12-mo decrease of 4.02% and 7.43%, respectively, and in the female group 2.59% and 6.97%, respectively. Paretic femoral neck and trochanter measurements in males showed a reduction of 11.76% and 10.38%, respectively, and in females 13.04% and 12.6%, respectively. A significant loss of BMD and bone strength was found during the first year after stroke in both trabecular and cortical bone at the forearm and at the neck and great trochanter on the paretic hip. Most prominent BMD reduction was evident in men compared with perimenopausal women in the same age.

Tibial bone geometry in chronic stroke patients: influence of sex, cardiovascular health, and muscle mass

This study aimed to examine the geometry of the tibia in chronic stroke survivors. Fifty-five ambulatory individuals with chronic stroke were included in the study. pQCT was used to obtain a cross-sectional scan of the tibia at the 30% site on both the paretic and nonparetic sides. Leg lean mass was derived from a total body scan using DXA. Each subject was also evaluated for peak oxygen consumption rate, spasticity, and functional mobility. Paired t-tests were used to compare the pQCT parameters between the two sides. Multiple linear regression analysis was used to identify the significant determinants of tibial bone strength index (BSI). In men, marrow cavity area on the paretic side was significantly greater than the nonparetic side (p = 0.011), whereas the total bone area showed no significant side-to-side difference (p = 0.252). In women, total bone area on the paretic side was significantly smaller than the nonparetic side (p = 0.003), whereas the marrow cavity area had no side-to-side difference (p = 0.367). Peak oxygen consumption (r(2) = 0.739, F(5,49) = 22.693, p < 0.001) and paretic leg lean mass (r(2) = 0.802, F(6,48) = 32.475, p < 0.001) remained independently associated with tibial BSI, after controlling for age, sex, body mass index, years since stroke onset, and physical activity level. The geometry of the tibia in stroke patients showed sex-specific side-to-side differences. The results suggested that, whereas endosteal resorption was apparent in men, periosteal resorption was more predominant in women. The results also highlight the potential importance of promoting cardiovascular health and leg muscle mass in enhancing bone geometry in chronic stroke survivors.

A 19-week exercise program for people with chronic stroke enhances bone geometry at the tibia: a peripheral quantitative computed tomography study

BACKGROUND

We assessed the impact of a 19-week exercise program on bone health in chronic stroke.

RESULTS

Those who underwent the program reported significantly more gain in tibial trabecular bone content and cortical bone thickness on the affected side.

CONCLUSION

Regular exercise is thus beneficial for enhancing bone health in this population.