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