Bone Densitometry:Applications and

LimitationsReprinted from JOGC

June 2002, Volume 24, Number 6

THE SOCIETY OFOBSTETRICIANS AND

GYNAECOLOGISTS OF CANADA

LA SOCIÉTÉDES OBSTÉTRICIÉNSET GYNÉCOLOGUES

DU CANADA

JOGC JUNE 2002JOGC JUNE 20021

G Y N A E C O L O G Y

Abstract: Osteoporosis is clinically diagnosed in its advancedstages, usually following a fracture.Accurate, precise, and nonin-vasive skeletal assessment is now possible for early detection ofosteoporosis at a preclinical stage. Currently, the gold standardin bone mass measurement and fracture prediction is dualenergy X-ray absorptiometry (DEXA) of the hip and spine.Exponential increases in fracture risk have been observed withsmall decreases in bone mineral density. Bone mineral density(BMD) should be considered in conjunction with independentclinical risk factors for fracture, including: low body weight, his-tory of postmenopausal fracture, family history of fracture, andpoor neuromuscular function. The World Health Organization(WHO) diagnostic criteria for osteoporosis and osteopenia areappropriate for postmenopausal Caucasian women and areapplicable to DEXA assessments at the hip, spine, or forearm.This review explores the relationship between BMD and frac-ture risk, the principles of bone densitometry interpretation,and the applications as well as the limitations of DEXA tech-nology, and presents cases illustrating common errors seen inthe interpretation of DEXA studies.

Résumé : L’ostéoporose est cliniquement diagnostiquée le plussouvent après une fracture, alors qu’elle est déjà à un stadeavancé. Il est maintenant possible d’évaluer le squelette demanière précise, exacte et non effractive, et de faire une détec-tion précoce de l’ostéoporose à un stade préclinique. À l’heureactuelle, l’étalon-or de la mesure de la masse osseuse et de laprédiction des fractures est l'absorptiométrie à rayons X endouble énergie (DEXA) de la hanche et de la colonne. On aconstaté des augmentations exponentielles du risque de frac-ture liées à de légères diminutions de la densité minéraleosseuse. Il faudrait tenir compte de la densité minérale osseuse(DMO) en combinaison avec d'autres facteurs cliniques derisque de fracture indépendants, notamment : un faible poidscorporel, des antécédents de fracture après la ménopause, desantécédents familiaux de fracture et un fonctionnement neuro-musculaire inadéquat. Les critères diagnostiques de l’ostéo-porose et de l’ostéopénie, énoncés par l’Organisation mondialede la santé (OMS), conviennent pour les femmes blanchesménopausées et s'appliquent aux évaluations de la hanche, de la

colonne et de l’avant-bras au moyen de DEXA. Cet articlepasse en revue le rapport entre la DMO et le risque de frac-ture, les principes de l’interprétation de l’absorptiométrieosseuse et ses applications, ainsi que les limites de la techniqueDEXA. Il présente des cas illustrant des erreurs fréquentesfaites dans l'interprétation des examens menés par DEXA.

J Obstet Gynaecol Can 2002;24(6):476-84.

INTRODUCTION

Osteoporosis is associated with an increased risk of fracture (II-1).1 Vertebral fractures result in the development of dorsalkyphosis and height loss and can also result in chronic back pain.2

A significant proportion of vertebral fractures are not identifiedand only one-third of vertebral fractures come to medical atten-tion (II-1).1 Hip fractures are associated with a significantlyincreased morbidity and a mortality of approximately 20% with-in the first year following a hip fracture (II-A).1,3,4

Clinically, the diagnosis of osteoporosis is made in itsadvanced stages and usually following a bone fracture.2 As thepresenting fracture is associated with an increased risk of sub-sequent fractures, it is important to diagnose and treat osteo-porosis prior to the development of the first fracture (II-1).5-6

Osteoporotic fractures are preventable (I).2 Spinal X-rays areof value in identifying the presence of vertebral compressionfractures and also in excluding the presence of other skeletalconditions, which can result in vertebral compression such asmetastatic bone disease or osteomyelitis.7 X-rays, however, arenot as helpful in evaluating bone mineral density (BMD), assignificant bone loss is necessary before bone loss becomes evi-dent on plain films (II-1).7 Currently, the gold standard in bonemass measurement and fracture prediction is dual energy X-ray absorptiometry (DEXA) of the hip and spine.7

This paper reviews the relationship between BMD andfracture risk, the principles of bone densitometry interpreta-tion, and the applications as well as the limitations of DEXAtechnology, and presents cases illustrating common errors seenin the interpretation of DEXA studies. The quality of evidencehas been described using the Evaluation of Evidence criteriaoutlined in the Report of the Canadian Task Force on the Peri-odic Health Exam.8

Zeba Syed, MD,1 Aliya Khan, MD, FRCPC, FACP2

BONE DENSITOMETRY: APPLICATIONS AND LIMITATIONS

Key WordsBone densitometry, osteoporosis, fracture risk, interpretation,limitations

Competing interests: None declared.

Received on October 29, 2001

Revised and accepted on March 26, 2002

1McMaster University, Hamilton ON2Associate Clinical Professor of Medicine, Divisions of Geriatrics and Endocrinology, McMaster University, Hamilton ON

JOGC JUNE 20022

DEXA BONE DENSITOMETRY

Noninvasive bone densitometry utilizing X-ray absorptiometryenables accurate evaluation of bone mass and the diagnosis ofosteoporosis in asymptomatic individuals prior to fracture.2 DEXAuses two X-ray beams of different energy levels to scan the lumbarspine or the hip site. The degree of attenuation is measured asthe beam passes through the bone. Using the dual energy beams,corrections for soft tissue are made, enabling an assessment ofBMD.2 DEXA technology can also be used to measure bone den-sity at peripheral skeletal sites such as the radius or finger.2

There is a strong inverse relationship between bone miner-al density and fracture risk.2,7 A two- to three-fold increase in theincidence of fractures has been seen for each standard deviationreduction in bone mineral density (II-1).9,10 This relationshipbetween BMD and fracture risk has been confirmed prospec-tively in a number of large well-designed studies (II-1).9-15 TheRotterdam study9 prospectively observed 7046 men and womenover the age of 55 for an average of 3.8 years, following base-line DEXA of the femoral neck. For each standard deviationdecline in femoral neck bone density, the relative risk of hip frac-ture increased 2.5-fold (II-1).9 The Study of Osteoporotic Frac-ture11 prospectively followed approximately 10,000 Caucasianwomen 65 years of age or over. During the observation period,192 women experienced their first hip fracture.11 In this study,each standard deviation decrease in baseline femoral neck bonedensity was associated with a 2.6-fold increase in the age-adjust-ed risk of hip fracture.11,16 Similar relationships between declinesin bone density and relative risk for fracture have been prospec-tively observed in other large studies.17

Schott and colleagues followed approximately 8000 post-menopausal women over the age of 75 for a 3-year period.18

The incidence of fracture was found to be greatest in thosewomen who had a low bone mineral density as well as low stiff-ness on heel ultrasound.12 Schott et al.’s study prospectively con-firmed the relationship between bone density and fracture,utilizing either central or peripheral technology. The predictivepower of BMD for hip fracture is similar to the predictive powerof blood pressure for stroke and better than the predictive powerof serum cholesterol for cardiovascular disease (II-1).10

A meta-analysis of 11 prospective cohort studies confirmedthat measurement of BMD predicts fracture risk (II-1).10 Bonemineral density measurements at the hip, spine, calcaneous,or radius have been shown to be similar in their predictive abili-ty for future fragility fractures.10 However, assessment of BMDat the hip has been shown to be the best predictor for future hipfractures.10 Similarly, assessment of BMD at the spine has beenshown to be the best predictor for future spine fracture.10 Diag-nostic thresholds utilizing DEXA have been best validated atthe hip, and the hip remains the best single site for assessment.19

Bone mineral density assessments should include DEXAevaluation of the hip and spine. Both sites are of value in glob-

al fracture prediction. Spine scans are of particular benefit in theyounger postmenopausal female as the spine is a site rich in can-cellous bone and is often the first site to reflect early post-menopausal bone loss (II-1).20 The lumbar spine bone densitymay be falsely elevated due to the presence of degenerativechange, vertebral compression fractures, or aortic calcification,all of which increase with age.20 Thus, in the elderly popula-tion, the diagnosis of osteoporosis may be missed if the spineBMD is falsely elevated, and in this population, it is importantto supplement a central spine assessment with a hip or lateralspine DEXA or peripheral evaluation. In the elderly popula-tion, as the spine assessments are more likely to be falsely ele-vated, it is particularly important to review the hip scan andconsider intervention based on the bone density at the hip site.

The World Health Organization (WHO) definition ofosteoporosis is based on the relationship between BMD andfracture risk.7 It is based on data for postmenopausal Caucasianwomen.7 The WHO criteria are only applicable to DEXAassessments at the spine, hip, and forearm in this population.7

WHO defined osteoporosis as a BMD more than 2.5 standarddeviations below the mean for young adult women.7 Osteope-nia is defined as a bone density between 1.0 and 2.5 standarddeviations below the mean for young adult women.7 The T-score is defined as the number of standard deviations thepatient’s BMD is above or below the sex-matched mean refer-ence value of young adults.2 The T-score thus provides a com-parison of the patient’s BMD to the mean peak bone mass.2

The Z-score is defined as the number of standard deviationsthe patient’s BMD is above or below the sex-matched meanreference value for individuals of the same gender and age.2

The Z-score, therefore, enables a comparison of the patient’sBMD to individuals of the same age.2

The precise relationship between bone mineral density andfracture risk in younger, premenopausal women is currentlynot clear as fracture data have been obtained predominantly inthe elderly over the age of 65. There is insufficient data regard-ing the relationship between BMD and fracture risk in non-Caucasian women and men. In the absence of suitablediagnostic criteria, the WHO definition of osteoporosis maybe used for men and non-Caucasians as it represents the onlydiagnostic classification currently available.

There are no established diagnostic criteria for osteoporo-sis for technologies other then central DEXA or for sites otherthen the spine, hip, and forearm.21

FRACTURE RISK ASSESSMENT

Assessment of an individual’s risk of fracture requires consider-ation of the BMD in conjunction with clinical risk factors forfracture. Independent risk factors for fracture include age, pos-itive family history for hip fracture, personal history of a frac-ture, low body weight (< 127 lb or 57 kg) as well as a history of

JOGC JUNE 20023

smoking.22 The risk of falls will also determine how likely anindividual is to sustain a fracture. Individuals with an increasedrate of bone turnover are also at an increased risk of fracture.22

It is necessary to take the BMD in conjunction with other clin-ical risk factors for fracture in order to help define an individ-ual’s absolute risk of fracture. Currently, we do not have a usefultool to calculate an individual’s absolute fracture risk.

The National Osteoporosis Foundation recommends ini-tiating pharmacologic intervention if an individual’s hip BMDreveals a T-score of less than –1.5 in the presence of risk factorsfor fracture.2 In those women with a hip T-score of less than–2, pharmacologic intervention is recommended as there isstrong evidence (I) that intervention effectively prevents frac-tures and is a reasonable use of resources.19

NEW DENSITOMETRY TECHNOLOGY

Although over the past five years new technologies utilizingultrasound as well as other radiographic techniques have becomeavailable, DEXA technology remains the gold standard for mea-suring BMD at the hip and the spine.20 Other technologiesavailable for measuring BMD include quantitative computedtomography (QCT),20 single energy X-ray absorptiometry(SXA),20 ultrasound,20 and radiographic absorptiometry.20

QCT is capable of distinguishing between cortical and can-cellous bone and can exclude artifact, which may be a problemwith DEXA assessments of the spine in the anteroposteriorview.20 QCT, however, does result in a relatively high radiationexposure and this limits its usefulness in clinical practice.20 Sin-gle X-ray absorptiometry (SXA) can only be used to measurebone density at peripheral sites such as the wrist or the heel wherethere is minimal soft tissue present.20 Peripheral DEXA tech-nology has essentially replaced SXA in clinical practice today.

Radiographic absorptiometry (RA) allows assessment ofthe BMD at the metacarpal and the phalangeal sites using plainradiographs of the hand.20 An aluminum wedge allows cor-rection for radiation exposure and voltage settings. Ultrasounddensitometry is available for assessment of the heel and thetibia.20 As the ultrasound wave passes through bone, attenua-tion occurs due to scattering and absorption of the wave. High-er attenuation is seen in normal bone in comparison toosteoporotic bone.20

HEEL ULTRASOUND DENSITOMETRY

Two large studies have prospectively evaluated the use of heelultrasound in elderly women and assessed the risk of hip frac-ture.12,16 These studies showed that a decrease in broadbandultrasound attenuation of one standard deviation was associat-ed with an increase in the relative risk for hip fracture by two-fold.12,16 Further trials are needed, however, to evaluate the riskof fracture prospectively based on heel ultrasound assessments.

The correlation noted to date between broadband ultrasoundand bone density measurements obtained by DEXA is modest(r = 0.7).20 Currently, there are no agreed-upon diagnostic cri-teria for osteoporosis based on heel ultrasound assessments orwith utilizing other peripheral technologies. The WHO diag-nostic criteria cannot be applied to bone mineral density mea-sured at peripheral skeletal sites. As there are differences in therates of bone loss in the peripheral skeleton in comparison to thecentral skeleton, as well as differences in technology, a T-score of–1 at the heel may not necessarily imply that the patient has nor-mal bone density with a T-score of –1 at the hip or spine. Anindividual with low bone density, as assessed by heel ultrasoundor other peripheral technologies, should be considered for a cen-tral DEXA assessment in order to determine if the WHO diag-nostic criteria are met. Currently, due to the lack of establisheddiagnostic criteria for peripheral skeletal sites, the informationobtained from a peripheral BMD assessment can be consideredas useful data in estimating the risk of fracture and used in con-junction with other risk factors for fracture.20

BMD INDICATIONS AND CONTRAINDICATIONS

National23 and international19 guidelines recognize the need toidentify individuals at risk for osteoporosis. Targeted bone den-sitometry screening is recommended for postmenopausal Cau-casian women who have one or more risk factors for osteoporosisand for all postmenopausal women over the age of 65.19 Theguidelines published by the Osteoporosis Society of Canada23 aswell as the National Osteoporosis Foundation19 advise targetedscreening for postmenopausal women at risk for osteoporosis.

Bone densitometry is indicated in premenopausal womenwith significant risk factors for osteoporosis. These risk factorsinclude prolonged periods of amenorrhea.23 In the presence ofconditions associated with bone loss, bone densitometry is alsorecommended. This would include conditions such as hyper-parathyroidism, hyperthyroidism, hyperprolactinemia, hypercor-tisolism, renal and liver diseases, as well as the use of medicationssuch as anticonvulsants, glucocorticoids, and heparin.22-24

Contraindications for bone densitometry include pregnan-cy,20 although radiation exposure with central DEXA assessmentsis minimal (1–5 microsieverts per scan).20 In individuals who haverecently had gastrointestinal contrast or a nuclear medicine test,BMD should be delayed by at least 72 hours as these tests canaffect the results of the scan.20 As obese individuals weighing morethan 250 pounds or 114 kg cannot be accommodated in the cen-tral DEXA units, peripheral assessments are appropriate.

WHICH SITES TO ASSESS

It is preferred that at least two sites be evaluated,25 particularlyin circumstances where one of the central sites (either the lum-bar spine or the hip) may not be a clinically useful assessment.

JOGC JUNE 20024

The spine assessment may be falsely elevated in the presence ofextensive degenerative change, aortic calcification, or vertebralcompression fractures (Figure 1).25 External artifacts such as navelrings can also result in a falsely elevated spine assessment. The hipbone density can be falsely elevated in the presence of osteoarthri-tis due to the presence of increased bone mineral deposition alongthe medial aspect of the femoral neck. The presence of hardwaresuch as Harrington spinal rods or hip replacements preclude a use-ful BMD assessment at the affected site. In situations where dif-fering T-scores are obtained at the two skeletal sites, the diagnosisof osteoporosis is based on the lower T-score.

It is recommended that bone density at the lumbar spine beevaluated from the first to the fourth lumbar vertebrae.20,25 Atthe hip, the diagnosis of osteoporosis can be based on the T-scoreobtained at the femoral neck, total hip, or trochanteric regions.It is not recommended to base the diagnosis solely on Ward’sregion as this area is too small to be adequately accurate or pre-cise.20,25 The total hip bone density provides greater precisionthan the femoral neck as a larger area of the skeleton is evaluat-ed. The use of additional peripheral sites is of value in conditionssuch as primary hyperparathyroidism, in which preferential boneloss occurs at sites rich in cortical bone.24,26 The one-third radi-al site reflects the effect of primary hyperparathyroidism to agreater degree than BMD measurement at the lumbar spine orthe total hip as this site is essentially purely cortical bone.24,26

INTERPRETATION OF RESULTS

When evaluating a lumbar spine scan, it is important to ensurethat the patient has been positioned properly and that the spineis centred and straight with both iliac crests being visible. Thetops of the iliac crests correspond to the level of the L4/L5 inter-vertebral disc in the vast majority of women (III).27 This land-mark can be used to assist in labelling the lumbar vertebrae. Thebone mineral density of the lumbar vertebrae increases fromT12 to L3 as bone mineral content and area increase.25 T12,therefore, has a lower bone mineral density than L1. It is impor-tant not to mislabel the smaller and less dense T12 as L1 as thiscan result in falsely lower T- and Z-scores. By convention, there-fore, it is recommended that labelling of the lumbar vertebraebe from the bottom up, utilizing the iliac crests as the L4/L5landmark. This will avoid mislabelling the lumbar vertebrae(Figures 2 and 3) and will result in a more appropriate com-parison of the patient’s bone mineral density to the normativereference data.25

Proper positioning of the hip is necessary for appropriateinterpretation of the scan (Figure 4). The hip should be posi-tioned such that the femoral shaft is straight and the lessertrochanter is barely visible.25 The femoral neck region of inter-est box should not overlap portions of the ischium or thegreater trochanter as this can result in a falsely elevated assess-ment of bone mineral density.25,28

ETHNIC DIFFERENCES IN BONE DENSITY

Racial differences in bone mineral density values have been wellrecognized.25 African-Americans have a higher bone density thanCaucasians.25 It is thus important to compare women to theappropriate ethnic normative reference data. The relationshipbetween bone mineral density and fracture risk is not well definedin the non-Caucasian population. Although Asians have a lowerbone density than Caucasians,29 data from the National Healthand Nutrition Examination Survey (NHANES) study in fact havedemonstrated that Asian women actually have a lower risk of hipfractures.30-32 This may be explained on the basis of differences inskeletal size between Asians and Caucasians. Areal BMD measuredby DEXA does not adjust for vertebral depth. Wider and largervertebrae are deeper, thus not adjusting for depth will result inoverestimation of BMD in individuals with larger skeletons.33 Sim-ilarly, BMD is underestimated in individuals with smaller skele-tons. Correcting for the differences in skeletal size significantlyreduces the differences in BMD seen among Asians and Cau-casians.34 Asians have a shorter hip axis length, which may alsoaffect the bone mineral density fracture risk relationship as the riskof hip fracture increases by approximately two-fold for each stan-dard deviation increase in the hip axis length.35 This effect is inde-pendent of bone density and also contributes to the differing ratesof hip fracture observed in different ethnic groups.29,35

Figure 1 is a PA spine scan that illustrates abnormality at L2with sclerosis, resulting in a falsely elevated lumbar spinebone density. Sclerosis or other obvious skeletal abnormali-ties on the spine scan should be further evaluated with spinal X-rays. This patient had radiographic confirmation of Paget’s disease at L2.

JOGC JUNE 2002JOGC JUNE 20025

Figure 3 illustrates the same patient with appropriate labelling from the bottom up. The tops of the iliac crests have been used as a landmark to identify the L4/L5 disc level. By following convention and labelling from the bottom up, we correctly identify thispatient as actually having a normal bone density.

Figure 2 illustrates the common pitfall of incorrect labelling of the lumbar vertebrae. This patient has 6 vertebrae without ribs.The vertebrae should have been labelled by following convention from the bottom up, as it is more common to have 5 lumbar vertebrae with the lowest set of ribs on T11, rather than having 6 lumbar vertebrae. In this scan, the lumbar vertebrae have beenlabelled from the top down, and T12 has been mislabelled as L1, resulting in an unfavourable comparison to the normative data-base. This patient has been inappropriately diagnosed as having osteopenia.

1.44

1.20

0.96

0.72

2.0

0.0

–2.0

–4.0

L2–L4 Comparison to Reference

AGE (years)

BMD

g/c

m2

T Score

20 40 60 80 100

RegionL2–L4

BMD g/cm2

1.041

Young-Adult% T-Score87 –1.3

Age-Matched% Z-Score105 0.4

1.44

1.20

0.96

0.72

2.0

0.0

–2.0

–4.0

L2–L4 Comparison to Reference

AGE (years)

BMD

g/c

m2

T Score

20 40 60 80 100

RegionL2–L4

BMD g/cm2

1.082

Young-Adult% T-Score90 –1.0

Age-Matched% Z-Score109 0.8

JOGC JUNE 20026

It is important for the technologist to ensure that theappropriate race is identified when scanning a non-Caucasianpatient as misidentification will affect the results of the study(Figures 5 and 6). Standards and guidelines for the practice ofdensitometry have been developed by the International Soci-ety for Clinical Densitometry (ISCD), a nonprofit global orga-nization addressing continuing medical education andcertification for physicians and technologists.36

SERIAL ASSESSMENTS

Serial assessments are of value in following an individual’s responseto therapy.25 When performing serial assessments, it is importantto ensure that progressive bone loss has not occurred after intro-duction of antiresorptive therapy, and that BMD has improvedor remained stable. A number of pharmacologic interventions arenow available that have been shown to be effective in reducingthe risk of vertebral and nonvertebral fracture.19The different class-es of antiresorptive agents have differing mechanisms of action, andsignificant reductions in fracture risk have been seen with agentsproviding only a modest gain in BMD.19 If patients demonstrateprogressive bone loss, then a reassessment of the diagnosis is rec-ommended to ensure that a secondary cause of osteoporosis hasnot been overlooked. It is also possible that the patient is a non-responder to that particular form of intervention, and managementmay need to be revised in the presence of progressive bone loss.

In order to determine if a significant change has occurred inthe patient’s BMD, it is necessary to know the precision error ofthe measurement with the technology being utilized at that par-

ticular site. The precision error, expressed as a coefficient of vari-ation at the spine in the PA projection in most centres, is usual-ly 1–1.5%.20 To ensure that a statistically significant change atthe 95% confidence level has occurred, the minimum change inBMD from baseline to follow-up must be 2.8 times the site-specific precision error.37-39 To calculate the change from base-line, the difference between the initial and subsequent BMD val-ues in g/cm2 is divided by the initial BMD:25

BMD 1 – BMD 2 x 100BMD 1

BMD 1 = Baseline BMDBMD 2 = Follow-up BMD

For example: Baseline BMD at lumbar spine = 0.725 g/cm2

Follow-up BMD at lumbar spine = 0.754 g/cm2

Difference = 0.029 g/cm2

Percent change = 0.029/0.725 = 0.04 or 4%increase

If the coefficient of variation at the spine is 1%, then theleast significant change necessary to be statistically significantat the 95% confidence level is 2.8 times 1% (2.8%). Thus, thechange from baseline to follow-up in the above example is astatistically significant change as it is greater than 2.8%.

The total hip precision error is comparable to the precisionerror at the spine. The femoral neck precision error, however,is larger than the total hip precision error, as the femoral neckis a smaller region and greater error can be introduced by dif-ferences in positioning. The femoral neck precision error canvary from up to 2% to 2.5%.20 Thus, when comparing serialassessments completed at the femoral neck, a greater change isnecessary for the difference to be statistically significant. A pre-cision error of 2% would require a change of 5.6% to be sta-tistically significant at the femoral neck. The precision at theproximal radius is usually in the 1–1.5% range, requiring achange of approximately 3% to be significant.20

Serial assessments are appropriate when initiating phar-macologic intervention to assess response to therapy and toensure that progressive bone loss is halted. An assessment maybe completed in 1 to 2 years following initiation of therapy. Incertain circumstances, such as glucocorticoid-induced osteo-porosis or primary hyperparathyroidism, a more frequentevaluation may be appropriate.

BIOCHEMICAL MARKERS OF BONE TURNOVER

The skeleton continually undergoes a process of remodelling,which maintains skeletal strength, repairs microfractures, and isalso essential for calcium homeostasis.40 During the remodelling

Figure 4 illustrates a hip scan with poor positioning. The hiphas not been adequately internally rotated and the lessertrochanter is visible. Inadequate internal rotation results in a higher bone density than achieved with proper positioningof the hip. In this scan, the femoral neck region of interestbox has also been incorrectly placed, overlapping a portionof the ischium.

JOGC JUNE 20027

process, osteoblasts synthesize a number of cytokines, peptides,and growth factors. These peptides are released into the circu-lation and can be measured, thus reflecting bone formationrates.40 The osteoclasts also produce bone degradation productswhich are released into the circulation and eventually clearedrenally. These collagen cross-links can also be measured in theurine and provide an estimation of bone resorption.40 Bone for-mation markers include serum osteocalcin, alkaline phosphatase,and procollagen I carboxy terminal propeptide (PICP).40 Boneresorption markers include urinary hydroxyproline, urinary

pyridinoline, urinary deoxypyridinoline as well as urinary colla-gen type I cross-linked N-telopeptide (NTX) and urinary colla-gen type I cross-linked C-telopeptide (CTX).40 These markersof bone turnover are useful in complementing the BMD assess-ment and evaluating response to therapy. Biomarkers also serveas an independent risk factor for fracture.41 The clinical useful-ness of biomarkers is currently debatable as there is considerablevariability in the biomarkers42 and lack of adequate standard-ization of the assays.

Figure 5 illustrates an African-Canadian female who was mistakenly identified as Caucasian at the time of the scan. Upon compari-son to the Caucasian young adult normative data, she was identified as having osteopenia with a T-score of –1.6.

1.5

1.3

1.1

0.9

0.7

0.5

0.3

–2.0

–2.5

Age

BMD

T Score

20 25 30 35 40 45 50 55 60 65 70 75 80 85

Fracture Risk

Not increased

Increased

High

* WHO 1994

WHO Classification*

Normal

Osteropenia

Osteoporosis

Sex: F Menopause Age:

Ethnicity: W Age: 56

Results Summary:

Total BMD: 0.868 g/cm2

Peak reference: 83% T score: –1.6Age matched: 95% Z score: –0.4

Region Area BMC BMD Tscore % PR Z score % AM[cm2] [g] [g/cm2]

L1 10.32 7.54 0.731 –1.8 79% –0.7 90%L2 11.92 10.11 0.848 –1.6 83% –0.5 94%L3 13.85 12.60 0.910 –1.6 84% –0.4 96%L4 14.69 13.85 0.942 –1.6 84% –0.3 96%

Total 50.79 44.10 0.868 –1.6 83% –0.4 95%

Reference Curve: TK 4 November 91Age and Sex Matched

JOGC JUNE 2002JOGC JUNE 20028

SUMMARY

Over the past decade, major advances in bone densitometry haveoccurred and now allow accurate and precise assessment of cen-tral, peripheral, and total skeletal bone mineral density, as wellas estimation of bone strength and prediction of the likelihoodof fracture.31 It is also possible to monitor drug therapy. Largeprospective studies utilizing both central9-11 and peripheral12,16

technologies have confirmed that the likelihood of fracture cannow be predicted. In evaluating fracture risk, bone density should

be considered in conjunction with other clinical risk factors forfracture.32 Important independent risk factors for fractureinclude low body weight, history of postmenopausal fracture,family history of fracture, and poor neuromuscular function.22

Intervention should be based on the assessment of bone miner-al density and other clinical risk factors for fracture (I). Althoughbone density is currently the best method for assessing and quan-tifying fracture risk, it is important to interpret bone densityassessments with caution, being aware of the limitations of cur-rent densitometry technology.

Figure 6 illustrates the same African-Canadian female of Figure 5, now correctly identified as African, enabling the use of raceappropriate normative data. She is actually osteoporotic in comparison to the African young adult normative data.

1.6

1.4

1.2

1.0

0.8

0.6

0.4

–2.0

–2.5

Age

BMD

T Score

20 25 30 35 40 45 50 55 60 65 70 75 80 85

Fracture Risk

Not increased

Increased

High

* WHO 1994

WHO Classification*

Normal

Osteropenia

Osteoporosis

Sex: F Menopause Age:

Ethnicity: B Age: 56

Results Summary:

Total BMD: 0.868 g/cm2

Peak reference: 76% T score: –2.6Age matched: 86% Z score: –1.2

Region Area BMC BMD Tscore % PR Z score % AM[cm2] [g] [g/cm2]

L1 10.32 7.54 0.731 –2.6 72% –1.4 82%L2 11.92 10.11 0.848 –2.6 75% –1.3 86%L3 13.85 12.60 0.910 –2.5 76% –1.2 87%L4 14.69 13.85 0.942 –2.6 77% –1.2 88%

Total 50.79 44.10 0.868 –2.6 76% –1.2 86%

Reference Curve: TK 25 November 96Age, Sex and Ethnicity Matched

JOGC JUNE 20029

REFERENCES

1. Cooper, C, Barker DJ, Morris J, Briggs RS. Osteoporosis, falls and age in fracture of the proximal femur. Br Med J 1987; 295:13-5.

2. Osteoporosis: review of the evidence for prevention, diagnosis, andtreatment and cost effective analysis status report. Osteoporos Int1998;4(Suppl):S1-S88.

3. Cummings SR,Kelsey JL,Nevitt MC,O’Dowd KJ. Epidemiology of osteoporosis and osteoporotic fractures. Epidemiol Rev 1985;7:178-208.

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