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Bone Densitometry

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

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Bone Densitometry

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  1. Bone Densitometry Interpretation of DEXA

  2. 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.

  3. 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

  4. 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.

  5. 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

  6. 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

  7. 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

  8. Osteoporosis Measurement • Plain film, Subjective, Radiogrammetry, Osteogram • SPA • DPA • DEXA • QCT • US • MRI

  9. 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

  10. DEXA y x

  11. 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

  12. DEXA DXA is at present the most precise measurement of BMD QCT is more sensitive to change

  13. DEXA Interpretation

  14. Find out as much relevant information as possible

  15. Find out as much relevant information as possible

  16. 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

  17. Vertebroplasty

  18. Calcium Tablets

  19. Wrong levels Transitional vertebrae

  20. Bone DensitometryDEXA spine check list • Look for significant level to level variations • 15-20% difference between adjacent levels

  21. 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.

  22. Common problems with spine scans. • Spine isn’t straight. • Scan starts in sacrum. • Scan stops too soon. • Wrong scan mode. • Scan doesn’t include L5.

  23. 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.

  24. IQ Scan Modes

  25. 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.

  26. 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.

  27. Typical Spine scan

  28. What’s wrong with this scan?

  29. What’s wrong with this scan? L1 is really T12

  30. What’s wrong with this scan?

  31. What’s wrong with this scan? Divisions don’t account for scoliosis

  32. What’s wrong with this scan? Everything

  33. 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.

  34. 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.

  35. 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.

  36. Typical Femur Scan

  37. What’s wrong with this scan?

  38. What’s wrong with this scan? Too much shaft

  39. What’s wrong with this scan?

  40. What’s wrong with this scan? Insufficient tissue below neck

  41. What’s wrong with this scan? Set up for wrong leg

  42. What’s wrong with this scan?

  43. 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

  44. Template

  45. Bone Densitometry • Never round up figures • -1 is osteopenia, -0.99 is normal • -2.5 is osteoporosis, -2.49 is osteopenia

  46. 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;179:735-738

  47. 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;179:735-738

  48. BMD in children and adolescents

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