1. WHO Osteoporosis Definition (1996)
“A systemic skeletal disease characterized by low bone mass and microarchitectural deterioration, with a consequent increase in bone fragility with susceptibility to fracture.”*
Bone density T-score  2.5 SD below young normal mean†
*Consensus Development Conference: Diagnosis, prophylaxis, and treatment of osteoporosis, Am J Med 1993;94:646.
† Kanis JA et al, J Bone Miner Res 1994;9:1137.

2. Who Is At Risk? Early menopause, surgical menopause
Low body weight compared to height
Diet - low intake of milk products and lack of vitamin D
Life-style factors: cigarette smoking, caffeine, alcohol abuse, lack of exercise
Drugs and diseases, corticoseroid treatment, hyperthyroidism, anorexia nervosa, amenorrhoea, arthritis
Genetic factors (family history, race)

3. Bone turnover Trabecular bone Cortical bone 20% of the skeletal mass
80% of bone turnover
Cortical bone
80% of the skeletal mass
20% of bone turnover

4. Bone Loss or Low Peak Bone Mass
100 80 60
Normal
(% ideal peak bone mass)
Relative Bone Mass
Low Peak 40
Fast Loss 20 20 30 40 50 60 70 80
Age (years)

5. Osteoporosis
Age (years)

6. INDICATIONS FOR BONE MINERAL DENSITY (BMD) TESTING
Women aged 65 and older
Postmenopausal women under age 65 with risk factors
Men aged 70 and older
Adults with a fragility fracture
Adults with a disease or condition associated with low bone mass or bone loss
Adults taking medications associated with low bone mass or bone loss
Anyone being considered for pharmacologic therapy
Anyone being treated, to monitor treatment effect
Anyone not receiving therapy in whom evidence of bone loss would lead to treatment
Women discontinuing estrogen
INTERNATIONAL SOCIETY FOR CLINICAL DENSITOMETRY, Official position 2005

7. Bone Densitometry

8. Bone Densitometry Non-invasive test for measurement of BMD
Major technologies
Dual-energy X-ray Absorptiometry (DXA)
Quantitative Ultrasound (QUS)
Quantitative Computerized Tomography (QCT)
Many manufacturers
Numerous devices
Different skeletal sites

9. Dual energy X Ray absorptiometry

10. DXA Technology
Detector (detects 2 tissue types - bone and soft tissue)
Very low radiation to patient.
Very little scatter radiation to technologist
Patient
Collimator (pinhole for pencil beam, slit for fan beam)
Photons
X-ray Source (produces 2 photon energies with different attenuation profiles)

11. DXA “Gold-standard” for BMD measurement
Measures “central” or “axial” skeletal sites: spine and hip
May measure other sites: total body and forearm
Extensive epidemiologic data
Correlation with bone strength in-vitro
Validated in many clinical trials
Available

12. Dual-energy X-ray absorptiometry (DXA)
What is measured?
BMC: Bone Mineral Content (g)
BMD: Bone Mineral Density (g/cm²)
T-score: BMD compared to young normal
Z-score: BMD compared to same age

13. What DXA Really Measures
“Areal” BMD is calculated in g/cm2
“T-score” compares the patient’s BMD with the young-normal mean BMD and expresses the difference as a standard deviation (SD) score

14. DXA T=-3,1 Z=-0,4 T-score and Z-score Peak Bone Mass = 1.047
BMD = 0.700
AGE = 80
T-score and Z-score

15. Patient’s BMD – Young-Adult Mean BMD 1 SD of Young-Adult Mean BMD
T-score
Patient’s BMD – Young-Adult Mean BMD
1 SD of Young-Adult Mean BMD
Example:
T-score =
0.7 g/cm g/cm2
0.1 g/cm2 =

16. Z-score Patient’s BMD – Age-Matched Mean BMD
1 SD of Age-Matched Mean BMD in g/cm2
Low Z-score (less than -2.0) may suggest increased likelihood of secondary osteoporosis, however . . .
This is not validated in clinical trials
High index of suspicion for secondary causes of osteoporosis is suggested in all patients

17. DXA WHO definition of diagnostic categories Normal: T > -1
Osteopenia: > T > -2,5
Osteoporosis: ,5 > T
Severe osteoporosis: plus fracture
Which Skeletal Sites Should Be Measured?
Spine L1-L4
Hip (Total Proximal Femur, Femoral Neck)
Use lowest T-score of these sites

18. AP Spine

19. AP Femur

22. Diagnosis Caveats
T-score -2.5 or less does not always mean osteoporosis (osteomalacia)
Clinical diagnosis of osteoporosis may be made with T-score greater than -2.5
Example: atraumatic vertebral fracture with T-score equals -1.9
Low T-score does not identify the cause
Medical evaluation should be considered
Example: celiac disease with malabsorption

23. Diagnosis Caveats BMD measurements are not accurate in patients with
degenerative disease
compression fractures
Soft tissue calcifications
Metallic hardware

24. Why T-score And Not Z-score?
T-score is related to bone strength
T-score is related to fracture risk
Using Z-scores would result in many “normal” patients having fragility fractures, and suggest that osteoporosis does not increase with age

25. T-score Discordance
Different skeletal sites have different peak bone mass at different times and lose bone at different rates
Different machines
Different ROIs
Different reference databases have different means and SD (the hip is the only skeletal site with a standardized reference database used by all manufacturers – National Health and Nutrition Examination Survey III)

26. Kanis JA et al. J Bone Miner Res. 1994;9:1137.
Why -2.5?
“Such a cutoff value identifies approximately 30% of postmenopausal women as having osteoporosis using measurements made at the spine, hip or forearm. This is approximately equivalent to the lifetime risk of fracture at these sites.”
Kanis JA et al. J Bone Miner Res. 1994;9:1137.