bone densitometry interpretation of dexa. osteoporosis osteoporosis is the most common metabolic...

Bone Densitometry

Interpretation of DEXA

Osteoporosis

Osteoporosis is the most common metabolic bone disorder. It has been

defined by the National Institutes of Health as an age-related disorder characterized by

decreased bone mass and increased susceptibility to fractures

in the absence of other recognizable causes of bone loss.

Osteoporosis

Type 1. involutional osteoporosis affects mainly trabecular bone, occurs in women during the 15-20 years after the menopause, and is related to a lack of

estrogen. This is thought to account for wrist and vertebral crush fractures, which occur through areas of principally trabecular bone.

Type 2. senile involutional osteoporosis. The fractures of old age seen at the hip, proximal humerus, pelvis and asymptomatic vertebral wedge fractures. This affects both trabecular and cortical bone and represents progressive loss

of bone mass from the peak around the age of 18-35 years.

Secondary osteoporosis is due to an underlying medical condition, such as renal disease, malabsorption, or hormonal imbalance, or to medical treatment

such as steroids or certain anticonvulsants

Osteoporosis

Risk factors

may be superimposed upon either involutional or secondary osteoporosis, including

smoking, alcohol, poor diet, lack of exercise, an early menopause, strong family history and

small frame.

Osteoporosis

The normal rate of bone loss is 2% per year, hence 20-40% of the female bone mass is already lost by the age of 65 years of age,

beginning before the menopause and accelerating afterwards

Osteoporosis

Bone mass is the major determinant of bone strength that can be measured by non-invasive techniques, and accounts for 75-85% of this

parameter

OsteoporosisBone densitometry is clinically indicated for the detection and assessment of osteoporosis and for the evaluation and monitoring of several diseases and therapies. These include:

1. The detection of osteoporosis and assessment of its severity.

2. Evaluation of perimenopausal women for the initiation of estrogen therapy.

3. Evaluation of patients with metabolic diseases that affect the skeleton.

4. Monitoring of treatment and evaluation of disease course.

In addition it may be useful as an epidemiological tool and possibly in the future for screening

American Society of Bone and Mineral Research

Osteoporosis Measurement

• Plain film, Subjective, Radiogrammetry, Osteogram• SPA• DPA• DEXA• QCT• US• MRI

DEXA

Because photons of different energy are differentially attenuated by bone and soft-tissues,by measuring the percentage of each transmitted beam and then applying simplesimultaneous equations, the absorption by bone alone and hence bone density can becalculated. This assumes that soft tissue is uniform, and to hence account for fatinterspersed with water density tissue, the region adjacent to bone is taken as a soft tissuestandard. This measurement is not a true density but rather an areal density, representedin gms/cm2

Because photons of different energy are differentially attenuated by bone and soft-tissues,by measuring the percentage of each transmitted beam and then applying simplesimultaneous equations, the absorption by bone alone and hence bone density can becalculated. This assumes that soft tissue is uniform, and to hence account for fatinterspersed with water density tissue, the region adjacent to bone is taken as a soft tissuestandard. This measurement is not a true density but rather an areal density, representedin gms/cm2

Because photons of different energy are differentially attenuated by bone and soft-tissues, by measuring the percentage of each transmitted

beam and then applying simple simultaneous equations, the absorption by bone alone and hence

bone density can be calculated.

This measurement is not a true density but rather an areal density, represented in gms/cm2

DEXA

Because photons of different energy are differentially attenuated by bone and soft-tissues,by measuring the percentage of each transmitted beam and then applying simplesimultaneous equations, the absorption by bone alone and hence bone density can becalculated. This assumes that soft tissue is uniform, and to hence account for fatinterspersed with water density tissue, the region adjacent to bone is taken as a soft tissuestandard. This measurement is not a true density but rather an areal density, representedin gms/cm2

Because photons of different energy are differentially attenuated by bone and soft-tissues,by measuring the percentage of each transmitted beam and then applying simplesimultaneous equations, the absorption by bone alone and hence bone density can becalculated. This assumes that soft tissue is uniform, and to hence account for fatinterspersed with water density tissue, the region adjacent to bone is taken as a soft tissuestandard. This measurement is not a true density but rather an areal density, representedin gms/cm2

xxyy

DEXA

Because photons of different energy are differentially attenuated by bone and soft-tissues,by measuring the percentage of each transmitted beam and then applying simplesimultaneous equations, the absorption by bone alone and hence bone density can becalculated. This assumes that soft tissue is uniform, and to hence account for fatinterspersed with water density tissue, the region adjacent to bone is taken as a soft tissuestandard. This measurement is not a true density but rather an areal density, representedin gms/cm2

Because photons of different energy are differentially attenuated by bone and soft-tissues,by measuring the percentage of each transmitted beam and then applying simplesimultaneous equations, the absorption by bone alone and hence bone density can becalculated. This assumes that soft tissue is uniform, and to hence account for fatinterspersed with water density tissue, the region adjacent to bone is taken as a soft tissuestandard. This measurement is not a true density but rather an areal density, representedin gms/cm2

DEXA has very high

accuracy (the difference in the measurement from a known standard)

and

precision (observed deviation of serial measurements with time),

both short and long term, to within 1% at the hip and spine

DEXA

Because photons of different energy are differentially attenuated by bone and soft-tissues,by measuring the percentage of each transmitted beam and then applying simplesimultaneous equations, the absorption by bone alone and hence bone density can becalculated. This assumes that soft tissue is uniform, and to hence account for fatinterspersed with water density tissue, the region adjacent to bone is taken as a soft tissuestandard. This measurement is not a true density but rather an areal density, representedin gms/cm2

Because photons of different energy are differentially attenuated by bone and soft-tissues,by measuring the percentage of each transmitted beam and then applying simplesimultaneous equations, the absorption by bone alone and hence bone density can becalculated. This assumes that soft tissue is uniform, and to hence account for fatinterspersed with water density tissue, the region adjacent to bone is taken as a soft tissuestandard. This measurement is not a true density but rather an areal density, representedin gms/cm2

DXA is at present the most precise measurement of BMD

QCT is more sensitive to change

DEXA

Interpretation

Find out as much relevant information

as possible

B o n e D e n s i t y C l i n i c a l I n f o r m a t i o n S h e e t

C i r c l e C o r r e c t R e s p o n s e s

N a m e ( L a b e l ) S e x : M o r F

( P r e m e n o p a u s a l )

F ( P e r i m e n o p a u s a l )

( P o s t m e n o p a u s a l )

O n H o r m o n e R e p l a c e m e n t T h e r a p y ? N YO n o t h e r t r e a t m e n t f o r o s t e o p o r o s i s ? N Y S e e o v e rP r e v i o u s S u r g e r y : S p i n e ? N Y r i g h t

H i p s ? N Y w h i c h ? U t e r u s / O v a r i e s ? N Y l e f t

K n o w n O s t e o a r t h r i t i s ? N Y

P r e v i o u s S c a n s W h e n ? W h e r e ?

R i s k F a c t o r s

P r e v i o u s F r a c t u r e s N Y W h e r e ?F a m i l y H i s t o r y O s t e o p o r o s i s N YM e d i c a t i o n S t e r o i d s N Y

F o r E p i l e p s y N Y W h i c h d r u g ?F o r T h y r o i d N Y W h i c h d r u g ?

D i e t a r y C a l c i u m H i g h L o wC i g a r e t t e S m o k i n g N YK n o w n B o w e l D i s e a s e ( d i a r r h o e a ) N Y D i a g n o s i s ?O t h e r M e d i c a l C o n d i t i o n N Y L i s t

Find out as much relevant information

as possible

Bone densitometry drug sheet

Drugs that may cause osteoporosis

CorticosteroidsDilantin

DiureticsMethotrexate

ThyroxineHeparin

Depomedroxyprogesterone acetateGonadotrophin releasing hormone agonists

Cyclosporin

Drugs to treat osteoporosis

HRT: Estrogen

(SERMS): Raloxifene (Evista)

Calcitonin: (Nasal spray) (Miacalcin)

Bisphosphonates: Alendronate (Fosamax)Etidronate (Didronel)

Risedronate (Actonel)Ibandronate

Pamidronate (Aredia)

Others: Combinations, Thiazides, Fluoride, PTH,Growth Hormone, Bicarbonate, Active Vitamin D

Bone DensitometryDEXA spine check list

• Note the age, sex, ethnicity and weight

• Does this match the reference ranges?

• Is the bottom of L4 roughly at the level of the iliac crests

• Are there any ribs on L1

• Scoliosis

• Are the vertebrae correctly divided

• Anything in the soft tissue

VertebroplastyVertebroplasty

CalciumCalciumTabletsTablets

Transitional vertebraeTransitional vertebrae

Wrong levelsWrong levels

Bone DensitometryDEXA spine check list

• Look for significant level to level variations

• 15-20% difference between adjacent levels

DEXA, what makes a good scan?

• 5-15 Lines of Iliac Crest. I recommend 1/2 of L5.

• 5-10 Lines of T12.

• 2 cm of tissue on both sides of the spine.

• Spine should be straight.

• No metal in spine.

• Spine isn’t straight.

• Scan starts in sacrum.

• Scan stops too soon.

• Wrong scan mode.

• Scan doesn’t include L5.

Common problems with spine scans.

What is a scan mode?

• This determines the speed the arm travels, and how much radiation the patient receives.

• The bigger the patient, the more radiation you’ll require.

• The smaller the patient, the less radiation you’ll require.

IQ Scan Modes

IQ Patient Thickness

• 12-15 cm is Medium 750

• 15-22 cm is Fast 3000

• 22-30 cm is Medium 3000

• Most patients fall in the Fast 3000 range.

Bone Densitometry

• In preventing Fxs it is the worst scenario that matters.

• Generally a slight increase in density as descend the L spine. Approx 6% increase between L1 and L4.

Typical Spine scan

What’s wrong with this scan?

What’s wrong with this scan?

L1 is really T12

What’s wrong with this scan?

What’s wrong with this scan?

Divisions don’t account for scoliosis

What’s wrong with this scan?

Everything

DEXA Femur check listHints for a good scan.

• Patient should be straight on table.

• Pack patient with rice bags.

• Shaft of femur should be straight.

• Rotate leg inward, this will hide the lesser Trochanter.

DEXA Femur check listHints for a good scan.

• The Wards area is roughly half the neck area

• Trochanteric area 8-14cm2 in women, 10-16cm2 in men

• Check left and right and state side being used in report.

nonIQ DPX scanning

• Show 15-30 scan lines prior to seeing ischium.

• There should be little or no lesser Trochanter.

• Straight shaft.

• 25 lines or more above the Greater Trochanter.

Typical Femur Scan

What’s wrong with this scan?

What’s wrong with this scan?

Too much shaft

What’s wrong with this scan?

What’s wrong with this scan?

Insufficient tissue below neck

What’s wrong with this scan?

Set up for wrong leg

What’s wrong with this scan?

Bone DensitometryWHO uses T scores

• Normal• > -1 SD below young adult

• Osteopenia• -1 -2.5 SD

• Osteoporosis• <-2.5 SD

• Established Osteoporosis• + Fxs, usually spine, hip, proximal humerus, wrist, rib

TemplateTemplate

CLINICAL HISTORY:

REFERENCE FILMS:

FINDINGS:FEMUR:The bone mineral density is _________ gm/cm aq.Percentage of young normal mean is ________%.T-Score is __________.Percentage age-matched mean is _________%Z-Score is __________.

World Health Organization and National Osteoperosis Foundation Classification is

COMMENTS:

LUMBAR SPINE:The bone mineral density is _________gm/cm aq.Percentage of young normal mean is ___________%.T-Score is __________%.Percentage of age-matched mean is _________%.Z-Score is ________.

World Health Organization and National Osteoperosis Foundation Classification is

COMMENTS:

IMPRESSION:

Bone Densitometry

• Never round up figures

– -1 is osteopenia, -0.99 is normal

– -2.5 is osteoporosis, -2.49 is osteopenia

Bone mass in healthy children

Increases with age, weight and pubertal Tanner stage.

Tanner stage and weight are best predictors of bone mass.

Age, sex, race, activity and diet are not good predictors, when weight and

Tanner stage are controlled.Radiology 1991;179:735-738Radiology 1991;179:735-738

Bone mass in healthy children

Make sure we have at least the age and weight of the child, if not the

Tanner stage.

Radiology 1991;179:735-738Radiology 1991;179:735-738

BMD in childrenBMD in children and adolescentsand adolescents

BMD in children and adolescentsBMD in children and adolescents

Girls

BMD in children and adolescentsBMD in children and adolescents

Males

Bone Densitometry

• T score is compared to reference population, 20-45 years, same sex, any race, any weight.

• Z score is matched for age, sex, weight and ethnicity.

Two possible reasons for this lady’s Z score being

worse than the T score?

Two possible reasons for this lady’s Z score being

worse than the T score? Obesity and race

The T score is based on a white, same sex, age 20-40population. The patient's BMD is compared to this population's BMD.A lower T score means that the patient BMD is low compared to this

young, healthy normal weight population.

The Z score compares the patient to an adjusted population, it adjustsfor age, weight, and ethnic background. The Z score can be lower for the patient, if the average patient in this population has a higher BMD

than the average in the T score population. This can be seen in patients with higher weights, (which increases bone density), and in

African American groups, (which show increased bone density).

If the patients comparison group has a generally higher bone density, then it is possible to have a poorer comparison to others of same age,

than to younger comparisons in generally lower density group.

260 lb man, young Z above young T260 lb man, young Z above young T

BlackBlackasasBlackBlack

BlackBlackasasWhiteWhite

BlackBlackasas

BlackBlack

BlackBlackasas

WhiteWhite

T sameT sameZ upZ up

Bone DensitometryWeight gain/loss and Z

• Weight gain (or loss) will not affect Z score comparison, since Z scores are weight matched.but should cause an increase (or decrease) in absolute BMD.

• An increase in weight, pushes up the reference range, and therefore the Z score may seem reduced, and vice versa.

2.2lbs=1Kg2.2lbs=1Kg

Bone DensitometryWeight gain/loss and T

• Weight gain (or loss) should cause an increase (or decrease) in absolute BMD.

• Weight gain (or loss) will affect T score comparison, since reference range will not have changed.

• Hence an increase in weight with a corresponding increase in bone density, will look like a good improvement in T score, but fracture risk is unchanged.

51F51F90Kg90Kg

53F53F51Kg51Kg

1Y, 16lb gain, 5% BMD loss= significant increase in fracture risk

1.1761.176 1.1721.172

SD = 0.1 both between -2 and -3

Bone DensitometryComparison with previous

• Are the studies comparable

• Always compare like with like– Thornton L1-4 – 4th and Lewis L2-4

• Any intervening events

• Cannot compare Hologic and Lunar

Bone DensitometryComparison with previous

• David Sartoris’s previous studies that do not mention the region or levels measured, were standardized for L1-4 and the femoral neck.

• He usually did not quote BMD.

• Many previous studies were prior to the current database.

• Use the percent young adult as a guide to percentage change.

Bone DensitometryComparison with previous

• If over a period of time there is an increase in BMD in the lower lumbar spine and decrease in the upper lumbar spine, it is likely there is OA of the lower facet joints, and the upper lumbar spine is a truer reflection of useful BMD.

Bone DensitometryComparison with previous

• Increase in BMD of the femoral neck can be due to calcar buttressing with OA of the hip.

Bone DensitometryComparison with previous

• If you want to eyeball the % for a comparison, use the young adult since the reference range will not change with age.

• A static bone density is actually a good result over a significant period of time

• If a test is 1% precise, then a change has to be greater than 2% to be significant

Bone DensitometryComparison with previous

• If you would have expected the bone density to have fallen 4% in 2 years, and it is static, then this is a positive response to RX

Bone DensitometryComparison with previous

• Generally Rx affects all levels equally. OA does not.

Cases

63F

63F

63F

63F

63F

6363

63F

63F

Report

Because of the previous laminectomy at L4, which may also be affecting the reading on the inferior aspect of L3, the BMD is averaged at L1-2.

Note is also made of mild decrease in the L4 vertebral height.

35F White 242lbs 62in35F White 242lbs 62in

35F White 242lbs 62in35F White 242lbs 62in

35F White 242lbs 62in35F White 242lbs 62in

Report

Because of the patients weight, the T score may not fully represent the fracture risk, and note should be

made that the Z score is xSD below age and weight matched.

39M39M

.1551.1551

39M OGI39M OGI

.1551.1551

46 F46 F

Calcified bileCalcified bile

46 F46 F Calcified bileCalcified bile

46 F Calcified bile46 F Calcified bile

47F47F

BlackBlack

49F 2Y8M gap Lx spine up, Fem neck down49F 2Y8M gap Lx spine up, Fem neck down

49F49F

49F Sacral agenesis49F Sacral agenesis

T

50F50F

50F dense R femoral neck50F dense R femoral neck

50F dense R femoral neck50F dense R femoral neck

2d earlier2d earlier

2d later2d later

51F51F

2d earlier2d earlier

2d later2d later

51F51F

Barium in diverticulum from recent enema

51F51F

53F53F51Kg51Kg

47F47F59Kg59Kg

53F51Kg

47F59Kg

6 yr later, 8Kg wt loss

53F51Kg

47F59Kg

60F

60F60F

60F OA

54MESLDs/p trans

Rec. repeat

76Fresponse to Rx

15m earlier

15m later

85MBil THR

85MBil THR