Bone%20Densitometry

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Bone Densitometry

• Interpretation of DEXA

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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.

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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

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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.

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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

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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

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Osteoporosis

• Bone 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
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Osteoporosis Measurement

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

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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 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

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DEXA
y
x
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DEXA

• 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

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DEXA

• DXA is at present the most precise measurement of
  BMD
• QCT is more sensitive to change

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DEXA

• Interpretation

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Find out as much relevant information as
possible
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Find out as much relevant information as
possible
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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

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Vertebroplasty
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Calcium Tablets
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Wrong levels
Transitional vertebrae
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Bone DensitometryDEXA spine check list

• Look for significant level to level variations
• 15-20 difference between adjacent levels

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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.

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Common problems with spine scans.

• Spine isnt straight.
• Scan starts in sacrum.
• Scan stops too soon.
• Wrong scan mode.
• Scan doesnt include L5.

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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 youll
  require.
• The smaller the patient, the less radiation
  youll require.

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IQ Scan Modes
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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.

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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.

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Typical Spine scan
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Whats wrong with this scan?
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Whats wrong with this scan?
L1 is really T12
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Whats wrong with this scan?
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Whats wrong with this scan?
Divisions dont account for scoliosis
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Whats wrong with this scan?
Everything
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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.

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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.

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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.

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Typical Femur Scan
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Whats wrong with this scan?
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Whats wrong with this scan?
Too much shaft
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Whats wrong with this scan?
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Whats wrong with this scan?
Insufficient tissue below neck
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Whats wrong with this scan?
Set up for wrong leg
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Whats wrong with this scan?
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Bone DensitometryWHO uses T scores

• Normal
• gt -1 SD below young adult
• Osteopenia
• -1 -2.5 SD
• Osteoporosis
• lt-2.5 SD
• Established Osteoporosis
• Fxs, usually spine, hip, proximal humerus,
  wrist, rib

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Template
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Bone Densitometry

• Never round up figures
• -1 is osteopenia, -0.99 is normal
• -2.5 is osteoporosis, -2.49 is osteopenia

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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 1991179735-738
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Bone mass in healthy children

• Make sure we have at least the age and weight of
  the child, if not the Tanner stage.

Radiology 1991179735-738
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BMD in children and adolescents
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BMD in children and adolescents
Girls
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BMD in children and adolescents
Males
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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.

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Two possible reasons for this ladys Z score
being worse than the T score?
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Two possible reasons for this ladys Z score
being worse than the T score? Obesity and race
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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.
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260 lb man, young Z above young T
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Black as Black
Black as White
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Black as Black
Black as White
T same Z up
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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.

2.2lbs1Kg
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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.

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51F 90Kg
53F 51Kg
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1.172
1.176
SD 0.1 both between -2 and -3
1Y, 16lb gain, 5 BMD loss significant increase
in fracture risk
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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

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Bone DensitometryComparison with previous

• David Sartoriss 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.

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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.

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Bone DensitometryComparison with previous

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

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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

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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

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Bone DensitometryComparison with previous

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

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Cases
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63F
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63F
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63F
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63F
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63F
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63?
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63F
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63F
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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.

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35F White 242lbs 62in
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35F White 242lbs 62in
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35F White 242lbs 62in
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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.

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39M
.1551
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39M OGI
.1551
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46 F
Calcified bile
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46 F
Calcified bile
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46 F Calcified bile
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47F
Black
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49F 2Y8M gap Lx spine up, Fem neck down
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49F
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T
49F Sacral agenesis
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50F
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50F dense R femoral neck
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50F dense R femoral neck
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2d earlier
51F
2d later
98
2d earlier
51F
2d later
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51F
Barium in diverticulum from recent enema
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53F 51Kg
47F 59Kg
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53F 51Kg
6 yr later, 8Kg wt loss
47F 59Kg
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53F 51Kg
47F 59Kg
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60F
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60F
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60F OA
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54M ESLD s/p trans
Rec. repeat
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76F response to Rx 15m earlier
15m later
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85M Bil THR
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85M Bil THR