Reproducibility of bone mineral density measurements using dual X-ray absorptiometry in daily clinical practice

Bone mineral density (BMD) measurements are frequently performed repeatedly for each patient. Subsequent BMD measurements allow reproducibility to be assessed. Previous studies have suggested that reproducibility may be influenced by age and clinical status. The purpose of the study was to examine the reproducibility of BMD by dual energy X-ray absorptiometry (DXA) and to investigate the practical value of different measures of reproducibility in three distinct groups of subjects: healthy young volunteers, postmenopausal women and patients with chronic rheumatic diseases. Two hundred twenty-two subjects underwent two subsequent BMD measurements of the spine and hip. There were 60 young healthy subjects, 102 postmenopausal women and 60 patients with chronic rheumatic diseases (33 rheumatoid arthritis, 10 ankylosing spondylitis and 10 other systemic diseases). Forty-five patients (75%) among the third group were receiving corticosteroids. Reproducibility was expressed as the smallest detectable difference (SDD), coefficient of variation (CV), least significant change (LSC) and intraclass correlation coefficient (ICC). Sources of variation were investigated by linear regression analysis. The median interval between measurements was 0 days (range 0–7). The mean difference (SD) between the measurements (g/cm²) was –0.0001 (±0.003) and –0.0004 (±0.002) at L1-L4 and the total hip, respectively. At L1-L4 and the total hip, SDD (g/cm²) was ±0.04 and ±0.02, CV (%) was 2.02 and 1.29, and LSC (%) 5.60 and 3.56, respectively. The ICC at the spine and hip was 0.99 and 0.99, respectively. Only a minimal difference existed between the groups. Reproducibility in the three groups studied was good. In a repeated DXA scan, a BMD change, the least significant change (LSC) or the SDD should be regarded as significant. Use of the SDD is preferable to use of the CV and LSC because of its independence from BMD and its expression in absolute units. Expressed as SDD, a BMD change of at least ±0.04 g/cm² at L1-L4 and ±0.02 g/cm² at the total hip should be considered significant. This reproducibility seems independent from age and clinical status and improved in the hips by measuring the dual femur.     

Precision Assessment and Radiation Safety for Dual-Energy X-Ray Absorptiometry: Position Paper of the International Society for Clinical Densitometry

Measurement of bone mineral density (BMD) by dual-energy X-ray absorptiometry (DXA) is used to diagnose osteoporosis, assess the risk of fracture, and monitor changes in BMD over time. Because biological changes in BMD are usually small in proportion to the error inherent in the test itself, interpretation of serial BMD tests depends on knowledge of the smallest change in BMD that is beyond the range of error. This value, called the least significant change (LSC), varies according to the instrument used, the patient population being tested, the measurement site, the skill of the technologist at positioning the patient and analyzing the test, and the confidence interval used in the calculation. The precision and LSC values provided by the manufacturer cannot be applied to clinical bone densitometry centers because of the differences in the patients being tested and the technologist performing the test. Because harmful errors in clinical management may occur from incorrectly interpreting serial BMD tests, it is recommended that every DXA technologist conduct a precision assessment and calculate the LSC for each measurement site and DXA instrument used. Precision assessment provides direct benefit to patients by allowing clinicians to make clinical decisions based on genuine change or stability of BMD. The patient-care benefits of precision assessment outweigh the risk of exposure to trivial doses of ionizing radiation.     

Some Physical and Clinical Factors Influencing the Measurement of Precision Error,Least Significant Change,and Bone Mineral Density in Dual-Energy X-Ray Absorptiometry

Dual-energy X-ray absorptiometry (DXA) is the standard method of measuring bone mineral density (BMD) at highly trabecular bone, which can be statistically linked to the risk of fracture. For DXA, precision error (PE) and phantom-based accuracy studies are among the most important routine quality control procedures. A precision study was performed at our institution using International Society for Clinical Densitometry guidelines. Comparing our results with those reported by other investigators, we draw the following general conclusions: the PE was higher for the spine than the hip, which we attribute to the better geometric reproducibility at the hip. The hypothesis that the DXA calculates BMD relative to water was validated. Whether follow-up measurements are performed by the same technologist on the same day—or different technologists on subsequent days—does not appear to have a clinically significant impact on PE or least significant change (LSC). Mixing beam types (i.e., fan and pencil) may affect lumbar PE and LSC measurements more significantly than those of the hip. The use of a single technologist may reduce the PE for the lumbar spine but appears to increase it for the hip. Restricting the patient population to the female gender has the apparent effect of narrowing the gap between lumbar and hip PEs. Finally, the degree of BMD measurement accuracy can be affected by the type of phantom being used (e.g., European Spine Phantom vs Lunar phantom) and the faults in specific DXA edge detection algorithms.     

Reproducibility of metacarpophalangeal bone mass measurements obtained by dual-energy X-ray absorptiometry in healthy volunteers and patients with early arthritis.

The prognostic value of measuring hand bone mineral density (BMD) in patients with early arthritis (EA) has been recently assessed. In this work, we evaluate the reproducibility of measuring juxta-articular BMD by dual-energy X-ray absorptiometry (DXA) at the second to fifth metacarpophalangeal (MCP) joints. We obtained whole hand (WH) and MCP joint BMD measurements from 16 healthy subjects and from 22 patients with EA. The coefficient of variation, intraclass correlation coefficient (ICC), and smallest detectable difference (SDD) were calculated. The coefficient of variation ranged from 1.3% to 0.7% at MCP joints and from 1.4% to 0.9% in the WH measurements, respectively. The intra- and interobserver ICC for both WH and MCP joints ranged from 0.97 to 0.99. The SDD at the different anatomical locations analyzed ranged from 0.006 to 0.022 g/cm2 in healthy controls and from 0.005 to 0.010 g/cm2 in EA. Interestingly, patients who fulfilled rheumatoid arthritis criteria showed a lower bone mass than those with undifferentiated arthritis. Therefore, BMD measurements obtained by DXA at MCP joints were reproducible and it might be useful in the study of patients with EA.     

Precision and Accuracy of a Transportable Dual-Energy X-ray Absorptiometry Unit for Bone Mineral Measurements in Guinea Pigs

Dual energy X-ray absorptiometry (DXA) is a valuable tool for measuring bone mineral content (BMC) and bone mineral density (BMD) in small-animal research. The present study was devised to establish guidelines and to define sites for bone mineral measurements in guinea pigs and to evaluate the accuracy of a new transportable research DXA unit. Repeated scans were performed on 30 guinea pig hindlimbs (in situ) as well as the isolated bones from these limbs (ex situ). Nine exactly specified regions of interest (ROIs) were analyzed twice for BMC and BMD by three different observers. Additionally, the BMC of whole bones and bone segments as measured by DXA was correlated to ash weights of bone in a subset of five animals to determine the accuracy of the DXA measurements. On ex situ scans, intra-observer variability for BMD ranged from 0.09% to 2.33% and inter-observer variability from 0.23% to 5.86% depending on the site studied, with smaller ROIs exhibiting more variability. Coefficients of variance (CV) for BMC measurements were slightly higher than for BMD. However, BMC offered a better correlation between in situ and ex situ values than BMD. On in situ scans, observer variability for BMD and BMC for comparable sites was higher than the ex situ variability. The results of this study indicate that DXA provides an accurate measurement of BMC even in small specimens. The precision of BMC and BMD measurements in situ can be improved considerably by using specific, well-defined ROIs and by careful placement of the bones to be scanned in close proximity to the scanning surface.     

Accuracy and precision of in vivo bone mineral measurements in sheep using dual-energy X-ray absorptiometry

We evaluated the precision and accuracy of in vivo measurements of spine bone mineral density (BMD) and bone mineral content (BMC) in five ewes using dual-energy X-ray absorptiometry (DXA, Lunar DPX-L). The short-term in vivo reproducibility expressed as the coefficient of variation (CV) varied from 0.9 to 1.6% for spine BMD and from 1 to 3.1% for spine BMC. The ex vivo measurements, performed in 20 cm of water to simulate soft tissue thickness, correlated closely with the in vivo measurements, yielding an r value of 0.98 and 0.97 for spine BMD and BMC, respectively. The accuracy was determined by comparing the total BMC of each vertebra measured in vivo with the corresponding ash weight. The correlation coefficient between the two measurements was r = 0.98, with an accuracy error of 5.6%. We concluded that the DXA allows a precise and accurate measurement of spine bone mineral in live ewes using the methodology designed for humans. Received: 19 March 1999 / Accepted: 26 July 1999     

Metacarpal bone mass in normal and osteoporotic Japanese women using computed X-ray densitometry

The metacarpal bone mineral density (BMD) and metacarpal index (MCI) of the second metacarpal bone were measured by computed X-ray densitometry (CXD) (Teijin Ltd., Tokyo), which we have established with the development of microdensitometry of radiographs. In this study, we evaluated the basic attributes of this CXD method and determined the age-related changes in both metacarpal measurements in normal Japanese women. The precision in vivo was measured in eight subjects. The precision errors [coefficient of variation (CV)] were 0.2–1.2% CV for metacarpal BMD and 0.4–2.0% CV for MCI, respectively. We have obtained low precision error and more rapid analysis, within 3 minutes respectively, compared with the previous methods. Age-related changes in the metacarpal measurements were evaluated in 1438 normal women. Both measurements showed the most significant decrease in the sixth decade of life. The rate of decrease in the sixth decade was 1.6%/year for metacarpal BMD and 1.5%/year for MCI. On comparison between metacarpal BMD by CXD and spine BMD using dual energy X-ray absorptiometry (DXA) in 248 normal women with and without menstruation, the two measurements were found to be similarly decreased in the subjects within 5 years after menopause. There was also no significant difference in the Z-score between metacarpal BMD and spine BMD within 5 years after menopause. These results indicate that early postmenopausal bone loss occurs not only in the spine but also in the metacarpal bone. The metacarpal BMD for patients with osteoporosis was significantly lower than that for age-matched normal controls, although the Z-score for spine BMD (-1.46) was significantly better than that for metacarpal BMD (-0.82). In conclusion, because CXD has excellent low precision error and is widely available at relatively low cost, it appears potentially to be applicable to problems in the diagnosis and management of osteoporosis, when used in association with DXA.     

DXA测量骨密度的精密度评估及其应用

目的通过短期精密度实验,统计分析双能X线吸收测定法(dual energy X-ray absorptiometry,DXA)测量骨密度(bone mineral density,BMD)的最小显著性变化值(least significant change,LSC),并探讨其临床应用价值。方法 4名技术员(A、B、C和D)使用GE Lunar Prodigy型双能X线骨密度仪均分别测量31名受检者(共124名)的腰椎和髋部的BMD,每位受检者连续测量2次,计算其精密度误差(precision error,PE)和LSC。结果 (1)不同技术员测量各部位BMD的各指标水平有差异,同一技术员每个测量位点的PE和LSC也不同;腰椎的PE和LSC较双侧股骨的波动幅度小,本实验中4位技术员之间对于L1～4,左、右股骨颈和左、右全髋部测量的PE变异系数(coefficient of variation,CV)差异皆无统计学意义(P0.05);(2)本团队测量L1～4的PE为:RMS-SD=0.011 g/cm~2、RMS-CV=0.011,LSC为:LSC-SD=0.031 g/cm~2、LSC-CV=0.031;左全髋的PE为:RMS-SD=0.013 g/cm~2、RMS-CV=0.014,LSC为:LSC-SD=0.036 g/cm~2、LSC-CV=0.039,右全髋的PE为:RMS-SD=0.010 g/cm~2、RMS-CV=0.011,LSC为:LSC-SD=0.026 g/cm~2、LSC-CV=0.030。结论使用DXA测量骨密度的PE小、精密度高;预计随访间隔时间(monitoring time interval,MTI)应随着感兴趣区PE的增加而延长,随着预计BMD年变化的增加而缩短。     

Precision of Bone Mineral Density Measurements Around Total Ankle Replacement Using Dual Energy X-ray Absorptiometry

Introduction: Joint prosthesis survival is associated with the quality of surrounding bone. Dual-energy X-ray absorptiometry (DXA) is capable to evaluate areal bone mineral density (BMD) around different prosthetic implants, but no studies evaluated periprosthetic bone around total ankle replacement (TAR). Our aim is to determine the precision of the DXA periprosthetic BMD around TAR. Methodology: Short-term precision was evaluated on 15 consecutive patients. Each ankle was scanned 3 times both in the posteroanterior (PA) and lateral views with a dedicated patient positioning protocol. Up to four squared regions of interest (ROIs) were placed in the periprosthetic bone around tibial and talar implants, with an additional ROI to include the calcaneal body in the lateral scan. Coefficient of variation (CV%) and least significant change were calculated according to the International Society for Clinical Densitometry. Results: The lateral projection showed lower mean CV values compared to the PA projection, with an average precision error of 2.21% (lateral scan) compared to 3.34% (PA scans). Overall, the lowest precision error was found at both “global” ROIs (CV = 1.25% on PA and CV = 1.3% on lateral). The highest CV value on PA was found at the medial aspect of talar side (ROI 3; CV = 4.89%), while on the lateral scan the highest CV value was found on the posterior aspect of talar side (ROI 2; CV = 2.99%). Conclusions: We found very good reproducibility BMD values of periprosthetic bone around TAR, that were comparable or even better compared to other studies that evaluated periprosthetic BMD around different prosthetic implants. DXA can be used to precisely monitor bone density around ankle prostheses, despite further long-term longitudinal studies are required to assess the clinical utility of such measurements.     

Dual-energy X-ray absorptiometry of human metatarsals: Precision,least significant change and association to ex vivo fracture force

BackgroundFractures are common in foot bones, but clinicians lack adequate indices of bone strength.ObjectivesWe used dual-energy X-ray absorptiometry (DXA) to measure bone mineral density (BMD) and content (BMC) of excised human metatarsals, determined intra- and inter-rater measurement precision, and assessed associations between BMD/BMC and ex vivo bone fracture strength.MethodsTwo raters each made two measurements of whole-bone and sub-regional BMD and BMC in both second and third metatarsals from 10 cadavers. Variance components analysis was used to assess variability attributable to repeat measurements, raters, sub-regions, bones, sides, and cadavers. Root-mean-square standard deviation (RMS-SD) and least-significant change (LSC) were used to assess rater precision and ultimate forces during 3-point bending were tested for correlations with BMD and BMC.ResultsVariation due to repeat measurements and rater was low (<1% combined) for BMD and BMC. RMS-SD for whole metatarsal BMD of both metatarsals ranged from 0.004 to 0.010 g/cm² and 0.062 to 0.086 g for BMC. Whole metatarsal and sub-region BMD and BMC were strongly correlated to ex vivo fracture force (r² = 0.67–0.93).ConclusionsDXA measurements of BMD and BMC have high intra- and inter-rater precision and are strongly correlated to ex vivo bone strength.     

Precision, accuracy, and reproducibility of dual X-ray absorptiometry measurements in mice in vivo.

Dual X-ray absorptiometry (DXA) has currently become a clinical standard for the assessment of bone mass and bone mineral density (BMD) at multiple sites for the diagnosis and follow-up assessment of osteoporosis in humans. The precision of DXA measurement in human studies has been well documented during the last two decades. However, there have been no systematic reports on the precision and accuracy of BMD measurements in mice using DXA, although mice have proven to be useful models for the study of osteoporosis. Accordingly, BMD of total body as well as regions of interest (ROIs) was measured twice in mice in vivo after a short (10-min) and long (16-hr) interval between scans by DXA, and scanning variations were calculated. Inter- and intra-analyzer variations from the same scans were also determined. The percent coefficients (%CVs) of short-interval scanning variation and inter- and intra-analyzer variations for total body and regional BMDs were less than 2% at sites, demonstrating high precision of in vivo BMD measurements in mice. Moreover, the BMD values comparing in vivo and ex vivo samples from the same animals were of %CV less than 10% at all sites. The correlation of bone mineral content (BMC) to bone ash was further examined, and the correlation between ROI BMC and bone ash was relatively high at all sites both in vivo and ex vivo, with the latter higher. We conclude that in vivo DXA BMD measurements in mice are very reliable with high precision and acceptable accuracy, and therefore useful for longitudinal studies of the mouse skeleton.     

In vivo intrarater and interrater precision of measuring apparent bone mineral density in vertebral subregions using supine lateral dual-energy x-ray absorptiometry.

Analysis of apparent bone mineral density (BMD) in the lumbar spine is commonly based on anteroposterior (AP) scanning using dual-energy X-ray absorptiometry (DXA). Although not widely used, clinically important information can also be derived from lateral scanning. Vertebral bone density, and therefore strength, can may vary in different subregions of the vertebral body. Therefore, subregional BMD measurements might be informative about fracture risk. However, the intrarater and interrater precision of in vivo subregional BMD assessments from lateral DXA remains unknown. Ten normal, young (mean: 24 yr) and 10 older (mean: 63 yr) individuals with low BMD were scanned on one occasion using an AP/lateral sequence. Each lateral scan was reanalyzed six times at L2 by three raters to determine the intrarater and interrater precision in selecting seven regions of interest (subregions). Precision was expressed using percentage coefficients of variation (% CV) and intraclass correlation coefficients (ICC). Intrarater precision ranged from ICC(1,1) 0.971 to 0.996 (% CV: 0.50-3.68) for the young cohort and ICC(1,1) 0.934 to 0.993 (% CV: 1.46-5.30) for the older cohort. Interrater precision ranged from ICC(2,1) 0.804 to 0.915 (% CV: 1.11-2.35) for the young cohort and ICC(2,1) 0.912 to 0.984 (% CV: 1.85-4.32) for the older cohort. Scanning a subgroup of participants twice with repositioning was used to assess short-term in vivo precision. At L2, short-term in vivo precision ranged from ICC(1,1) 0.867 to 0.962 (% CV: 3.38-9.61), at L3 from ICC(1,1) 0.961 to 0.988 (% CV: 2.02-5.57) and using an L2/L3 combination from ICC(1,1) 0.942 to 0.980 (% CV: 2.04-4.61). This study demonstrated moderate to high precision for subregional analysis of apparent BMD in the lumbar spine using lateral DXA in vivo.     

DXA Scanning of Acetabulum in Patients With Cementless Total Hip Arthroplasty

The aim of this study was to evaluate the reproducibility of bone mineral density (BMD) measurements of the periprosthetic bone in patients with hemispherical acetabular cups in cementless total hip arthroplasty (THA). Thirty patients were treated for primary osteoarthrosis with cementless THA. Dual-energy X-ray absorptiometry (DXA) scanning was performed with a pencil-beam bone densitometer (Norland XR-36). Accuracy and reproducibility was determined by double measurements of BMD in four regions of interest (ROI). The influence of patient postures including various pelvic inclination angles was evaluated as well. Pitman test for a combined netROI revealed a standard deviation ratio of 3.2 for the anterio-posterior scans related to the lateral position. The Wilkinson ROIs showed a high intraobserver agreement. With pelvic tilt increasing until 20 degrees , the precision of DXA scanning decreased. In conclusion, reproducibility of DXA scanning was high. This study demonstrated that the patients can be scanned in the supine position, and BMD measurement of the periacetabular bone can be performed using the Wilkinson model with four rectangular ROIs.     

Measurement error of DXA: interpretation of fat and lean mass changes in obese and non-obese children.

Information on reproducibility of dual-energy X-ray absorptiometry (DXA) measurements is essential because DXA is frequently used by clinicians and researchers to assess body composition changes. We estimated measurement error and absolute and relative smallest detectable differences (SDDs) for fat, lean, and bone mass in children. The SDD is the change necessary to be confident that the change is not a consequence of measurement error. Duplicate whole body DXA (Hologic QDR 4500A, Hologic Inc., Waltham, MA) scans were obtained on 32 obese and 34 non-obese children ages 6-19 yr. Absolute (kg) and relative (coefficient of variation) measurement error and SDD were calculated. Absolute SDDs for fat and lean were higher for obese (1.39 and 1.30 kg, respectively) than for non-obese children (0.42 and 0.47 kg, respectively). The %SDD for fat was lower for obese (3.58%) than non-obese children (5.24%), but for lean the %SDD was higher for obese (2.60%) than non-obese children (1.32%). The SDDs for bone mass were similar for obese and non-obese children. An obese child must lose or gain more absolute fat and lean mass than a non-obese child to be confident that the change is not a reflection of measurement error. Overall, SDD values for fat, lean, and bone mass are low.     

Short-term Reproducibility of Proximal Femur Bone Mineral Density in the Elderly

Densitometric measurements are prone to imprecision in elderly subjects and the present study was primarily designed to dissect out the effects of age and bone mineral density on proximal femur dual energy x-ray absorptiometry (DXA) reproducibility. The study comprised 17 elderly women (mean age 74.6 years, range 65–84 years), 13 early postmenopausal women with osteopenia (mean age 56.2 years, range 50-63 years), and 17 elderly men (mean age 73.8 years, range 65-86 years). Each subject was given triplicate proximal femur scans by a QDR 2000 Densitometer (Hologic Inc., Waltham, MA) with repositioning between scans. Because of subject selection in the early postmenopausal women there were no significant differences in bone mineral density (BMD) at any site among the three groups. Despite this, reproducibility errors expressed as either coefficient of variation (CV) % or mean standard deviation (SD) were greater in the elderly subjects, regardless of gender, when compared with the younger female subjects. The variability in measurement errors with age were least marked for the total hip and trochanteric sites. Within the elderly subjects, BMD appeared to exert little influence on measurement errors. We conclude that short-term proximal femur reproducibility is dependent on age-related factors other than BMD. There is no influence of gender on the measurement errors. It is likely that local factors (e.g., hip osteoarthritis) or general frailty may influence repositioning but this needs further exploration. In the meantime, the total hip and trochanteric sites should be used as they provide the most reproducible measurements in the elderly. Received: 19 November 1997 / Accepted: 8 April 1998     

Bone densitometry of the forearm: Comparison of single-photon and dual-energy X-ray absorptiometry

Forearm bone mineral densitometry was performed initially by single-photon absorptiometry (SPA), but is now achievable by dual-energy X-ray absorptiometry (DXA) as well, with a good correlation between both measurements. However, it is still unknown whether: (1) short-term precision of DXA is superior to SPA and (2) identical regions of interest (ROT) are mandatory to correlate SPA with DXA. The aim of this study was to answer these questions using a commercial system for DXA (DXA-FAS) and to test an in-house system using spine DXA and a soft-tissue compensator (DXA-STC). In ten subjects, four measurements on the same day showed significantly lower (p < 0.05) coefficients of variation (CV) for bone mineral density (BMD) by DXA-FAS (proximal site: 0.74%; ultradistal site: 1.20%) than by SPA (1.26% and 2.25%). However, the CV for bone mineral content (BMC) were similar for DXA-FAS (0.73% and 1.58%) and SPA (0.79% and 1.34%). The significant difference (p < 0.05) for surface calculation by DXA-FAS (1.24% and 0.93%) compared with SPA (2.36% and 1.28%) explains all the advantages of DXA-FAS for short-term precision. The measurements taken on the same day on the ulna and the radius or on the radius alone by SPA, DXA-FAS, and DXA-STC on 108 subjects aged 18–80 years were highly correlated [r ranging from 0.925 to 0.995 (p < 0.0001) and standard error of the estimate from 3.15% to 8.89%]. The need for a manual adjustment of the ROT was found to be mandatory for BMC but not BMD assessment. The use of DXA-STC is a fast method for forearm bone densitometry and its correlation with SPA is very high. However, its short-term precision for BMC (3.00% and 1.54%), BMD (2.15% and 1.12%), and surfaces (1.99% and 1.12%) is significantly higher (p < 0.05) than that of DXA-FAS. We conclude that short-term precision of DXA is better than that of SPA only for BMD and surface measurement but not for BMC. ROT should be adjusted manually for the assessment of BMC but not for that of BMD.     

Factors Affecting Short‐Term Bone Density Precision Assessment and the Effect on Patient Monitoring

The most widely used procedure for performing a BMD reproducibility assessment (same‐technologist with simple repositioning on the same day) systematically underestimates precision error and will lead to over categorization of change in a large fraction of monitored patients. Introduction: The most common procedure for establishing the least significant change (LSC) to monitor bone mineral density (BMD) with DXA is for the same technologist to perform repeat subject scans on the same day with simple repositioning. The objective of the current report is to determine how the reproducibility scanning procedure impacts on the precision assessment and categorization of change in routine clinical practice. Materials and Methods: The study population was drawn from the database of the Manitoba Bone Density Program which includes all clinical DXA test results for the Province of Manitoba, Canada. All patients who had baseline and follow up total spine (L1–4) and the total hip BMD measurements on the same instrument up to March 31, 2007 were included as the ‘clinical monitoring population’ (N = 5048 scan‐pairs). BMD precision was assessed in a convenience sample of patients who were agreeable to undergoing a repeat assessment (50% performed on the same day with repositioning, 68% by different technologists) (N = 331 spine and 328 hip scan‐pairs). Results: Precision error was greater when the scan‐pairs were acquired on different days than on the same day for both the total spine (p < .001) and total hip (p < .01). No other factor was consistently associated with precision error. The reference LSC (different days and different technologists) categorized the smallest fraction of the monitored population with change, whereas other combinations gave a significant rate of over categorization (up to 19.3% for the lumbar spine and up to 18.3% for the total hip). Conclusions: The most widely procedure for performing a BMD reproducibility assessment (same‐technologist with simple repositioning on the same day) systematically underestimates precision error and will lead to over categorization of change in a large fraction of monitored patients.     

Influence of the quality of tibial plateau alignment on the reproducibility of computer joint space measurement from Lyon schuss radiographic views of the knee in patients with knee osteoarthritis

RATIONALE: The quality of medial tibial plateau (MT-Plateau) alignment is one of the key elements for accuracy and sensitivity to change of knee radiography in knee osteoarthritis (OA). AIM: To evaluate the influence of the quality of the MT-Plateau alignment on the reproducibility of joint space width (JSW) measurement in knee radiographs. METHODS: One hundred and twenty-seven knee radiographs (99 OA), performed using a standardized radiographic procedure (Lyon schuss (LS) view). Evaluation of the quality of MT-Plateau alignment. Computerized measurement of the JSW, twice, 1-month apart, using a semi-automated and an automated method of measurement. Assessment of the reproducibility of repeated measurements: calculation of intra-observer coefficient of correlation, smallest detectable difference (SDD) and coefficient of variation (CV). RESULTS: MT-Plateau alignment was satisfactory in 99 radiographs (77.9%). Reproducibility was excellent in both satisfactory and non-satisfactory radiographs, irrespective of the method of measurement used. The automated measurement was more reproducible than the semi-automated one (CV 1.15% and 3.23%). SDD and CV were better in satisfactory than in non-satisfactory MT-Plateau aligned radiographs. CONCLUSION: These results confirm that computer measurement of the medial tibio-femoral JSW, from LS digitized radiographs, is highly reproducible, irrespective of the quality of the radiograph. However, the quality of the MT-Plateau alignment influences the reproducibility of JSW measurement. The automated measurement was more reproducible than the semi-automated one.     

Which bone densitometry and which skeletal site are clinically useful for monitoring bone mass?

Long-term precision, as well as reproducibility, is important for monitoring bone mineral density (BMD) alteration in response to aging or therapy. In order to investigate which bone densitometry and which skeletal site are clinically useful for monitoring bone mass, we examined the standardized long-term precision of several bone density measurements in 83 healthy Japanese women. Annual BMD measurements were performed for 5 or 6 years using dual X-ray absorptiometry (DXA) on the lumbar spine, radius (EXP5000) and calcaneus (HeelScan); peripheral quantitative computed tomography (pQCT) on the radius (Densiscan1000); and quantitative ultrasound (QUS) on the calcaneus (Achilles+). The long-term precision error for the individual subject was given by the standard error of estimate (SEE), and the standardized long-term precision was defined as the percentage coefficient of variation (CV%) divided by the percentage ratio of the annual bone-loss rate. Based on the CV% of spinal DXA, speed of sound (SOS) and diaphyseal pQCT showed significantly higher precision than others, while radial ultradistal (UD) DXA and heel DXA showed significantly lower precision. The long-term precision errors of other measurements were statistically the same as that of the spinal DXA. The spinal DXA, the radial DXA, and pQCT at both the distal metaphysis and diaphysis showed high rates of annual bone loss. The radial trabecular BMD (pQCT) was significantly higher than that of spinal DXA. The annual rates of bone loss of QUS and of heel DXA were significantly lower than that of spinal DXA. Taken together, standardized long-term precision was obtained in the spinal DXA and radial pQCT. In conclusion, spinal DXA and radial pQCT were considered the most useful monitoring method for osteoporosis, while QUS was considered less useful.     

Individual smallest detectable difference in bone mineral density measurements.

Bone mineral density (BMD) measurement is a major outcome measure in osteoporosis. The BMD changes observed must exceed the variability inherent in the measurement process to be considered related to disease progression. The objective of the study was to estimate short-term variability of BMD measurement and to propose a cut-off value for the smallest detectable BMD changes for an individual. To estimate the short-term variability, 70 healthy postmenopausal women aged 53 +/- 4 years (group 1) and 57 elderly osteoporotic postmenopausal women aged 80 +/- 6 years (group 2) had two repeated BMD measurements of the lumbar spine (L2-L4) and the proximal femur with dual-energy X-ray absorptiometry, with complete repositioning within 1 h. Cut-offs derived from short-term variability were either estimated from the coefficient of variation (CV) (which is a function of the measured value) or from the standard deviation (SD), and applied to 330 postmenopausal women (group 3) who had BMD measurements at baseline and 2 years later. The short-term intrasubject variability was greater at the lumbar spine in group 2 versus group 1 (0.0123 vs. 0.0059 g/cm2, p < 10-4), whereas it was not at the femoral neck (0.0098 vs. 0.0076 g/cm2, p = 0.28). There was no statistically significant correlation between short-term intrasubject variability (SD) and BMD as demonstrated with an analysis of covariance (p values ranging from 0.17 to 0.90). Cut-offs estimated with SD and CV were individually applied to group 3 patients. Using these two cut-offs, discrepancies in assessment of progression were observed in 1.7-8.6% of cases. Short-term BMD variability is constant in a wide range of BMD values. Consequently, to determine cut-off values for the smallest detectable differences in BMD at the individual level, precision errors should be based on SD (expressed in absolute units) rather than on CV (expressed in percentage).