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BONE DENSITOMETRY. Bone Densitometry. NOMENCLATURE: DXA NOT DEXA Dual-energy X-ray Absorptiometry BMD bone mineral density VFA vertebral fracture analysis (not DVA, LVA, IVA, RVA, etc.). Bone Densitometry.

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BONE DENSITOMETRY


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    1. BONE DENSITOMETRY

    2. Bone Densitometry NOMENCLATURE: • DXA NOT DEXA Dual-energy X-ray Absorptiometry • BMD bone mineral density • VFA vertebral fracture analysis (not DVA, LVA, IVA, RVA, etc.)

    3. Bone Densitometry • T-score number of standard deviations the patient’s BMD is above or below average peak BMD of young adult reference population. • Z-score number of standard deviation the patient’s BMD is above or below age- and sex-matched mean reference value. Z-score should be population specific where adequate reference data exist, including ethnicity.

    4. T-score WHO CLASSIFICATION • Normal T-score ≥ -1.0 • Low bone mass (osteopenia) T-score between -1.0 and -2.5 • Osteoporosis T-score ≤ -2.5 • Severe osteoporosis T-score ≤ -2.5 with history of fragility fracture

    5. Z-score Z-scores are used instead of T-scores for children, pre-menopausal women and men younger than age 50! A Z-score ≤ -2.0 is defined as "below the expected range for age." A Z-score > -2.0 is "within the expected range for age."

    6. Z-score Pediatric patients (ages 5-19) Require dedicated software package and need to scan lumbar spine and total body minus head. NOT hip. Do not use T-scores. A Z-score ≤ -2.0 is defined as "below the expected range for age." A Z-score > -2.0 is "within the expected range for age."

    7. BoneCortical or compact = dense cortexTrabecular or cancellous = marrow area

    8. Bone • Spine: about 2/3 trabecular/cancellous bone on PA view, remainder cortical/compact bone. • Hip: 25% trabecular bone at neck and 50% trabecular bone at trochanter • Forearm: almost entirely cortical bone and only 1% trabecular bone

    9. Osteoporosis • Skeletal disorder characterized by compromised bone strength predisposing to an increased risk of fracture. • Bone strength reflects the integration of two main features: bone density and bone quality. • There are no symptoms from low bone mass unless fracture occurs.

    10. Why do we care? • Fractures painful • Debilitating • Decrease mobility • Decrease independence • Expensive

    11. Why do we care? 2/3 of vertebral fractures are clinically silent –i.e. morphometric, discovered by X-ray or imaging! Only 25-30% of fractures seen on X-ray are diagnosed clinically.

    12. Why do we care? Complications of hip fractures --especially nursing home patients: 24-30% excess mortality within 1 year 50% of survivors are permanently incapacitated 20% of survivors require long-term nursing home care

    13. Bone density on average: • Males > Females • Blacks > Whites • Peak bone mass achieved in teens or early 20's. • Then relative plateau until 35 years old.

    14. Bone density on average: • Then age-related bone loss occurs at a rate of 0.5%-1.0%/year. • Bone loss accelerates with menopause (1.0-2.0%/year) and accelerated phase lasts 5-10 years. • Age-related bone loss continues, with bone loss eventually going back down to pre-adolescent levels.

    15. www.arthritisresearchuk.org

    16. Central DXA Current gold standard for DIAGNOSTIC classification of BMD and osteoporosis. However, multiple other techniques are well-validated for fracture risk assessment but not diagnosis of osteoporosis.

    17. Central DXA Excellent reproducibility (but it’s up to us!) Low radiation dose (1-10 µSv) or 1/10 the dose of a CXR, about one day’s worth of natural daily background exposure. Most epidemiologic studies and clinical pharmaceutical trials backing it up.

    18. Indications for BMD Testing • Women ≥ 65 y/o. • Postmenopausal women (natural or surgical) < 65 y/o with risk factors for fx • Women during the menopausal transition (perimenopausal) with clinical risk factors for fx, e.g. low body weight, prior fx, or high-risk medication use. • Men ≥ 70 y/o. • Men < 70 y/o with clinical risk factors for fracture. • Adults with a fragility fracture*.

    19. Indications for BMD Testing • 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.

    20. FRAGILITY FRACTURE Fracture from falling from standing height or lower, at walking speed or slower, often vertebral, hip or wrist. Fracture occurring in the absence of obvious trauma or minimal trauma not usually expected to cause a fracture. Excludes pathologic fractures (underlying abnormal bone, e.g. bone metastasis), and fractures of digits, hands, ankles & feet & skull fractures.

    21. FRAGILITY FRACTURE Although not part of the WHO classification, the presence of a fragility fracture -regardless of T-score– should be considered diagnostic of osteoporosis ! (provided other causes for the fracture have been excluded)

    22. Spine • Use positioning block to straighten lordosis. • Centered • Straight and not tilted or leaning • If scoliotic, try to center curvature in the middle, off set pelvis if necessary

    23. Spine • Both iliac crests visible • Mid T12 to mid L5 included • 12th rib (optional) • L3 usually has the longest transverse processes

    24. Spine Example GE

    25. Spine Example Hologic

    26. Spine Look at raw data and histograms to confirm disk levels. Angle as appropriate. Check ROI and bone margins -excluding large osteophytes? -too narrow and excluding bone?

    27. Spine If have difficulty numbering due to rib variability and transitional vertebrae, count from below, with L4-L5 considered at the iliac crests if possible. Usually L4-5 is at the iliac crests or slightly lower. 1 in 6 patients have variants! 4,5 or 6 lumbar vertebrae and lowest ribs T11, T12, or L1.

    28. Spine • Exclude vertebrae with fracture --check VFA, X-rays too! • Exclude if hardware, vertebroplasty or kyphoplasty (=vertebral augmentation) or laminectomy. • Check for artifact, stent grafts, surgical clips, barium, calcification, foreign bodies, bra hooks and underwires, external to patient? If external to patient, remove and repeat!

    29. Spine Careful because DXA does subtract soft tissue! So even if outside the spine ROI it can affect the measurement, especially if within global ROI. Remove, remove, remove if possible and repeat scan. If not then neutralize it.

    30. Spine QA QA IMPORTANT!!! Look at BMDs and T-scores! L1 usually lowest BMD. BMC and area progressively increase from L1 to L4. BMD tends to increase from L1 to L3. BMD of L4 similar or less than L3.

    31. Spine QA Exclude vertebrae if clearly abnormal and non-assessable within resolution of the system. Exclude vertebra if there is > 1.0 T-score difference between the vertebra in question and adjacent vertebrae. Assess for cause, often increased T-score due to subtle fracture or increased degenerative change & sclerosis (so usually drop high T-score vertebra)

    32. Spine QA Occasionally see spurious decrease in T-score due to interval surgery or laminectomy –drop low T-score. Sometimes T-scores change > 1.0 between every vertebrae. "Art of medicine" may be invoked on challenging cases. e.g. if dropping a vertebra doesn't change diagnosis may not want to drop it.

    33. Spine QA Use all evaluable vertebrae and only exclude vertebrae that are affected by structural change or artifact.

    34. Spine QA Use all evaluable vertebrae and only exclude vertebrae that are affected by structural change or artifact. However, if only one evaluable vertebra remains, then must use other skeletal sites and exclude spine. Must have ≥ 2 vertebrae to use spine BMD.

    35. Spine QA Use all evaluable vertebrae and only exclude vertebrae that are affected by structural change or artifact. However, if only one evaluable vertebra remains, then must use other skeletal sites and exclude spine. Must have ≥ 2 vertebrae to use spine BMD. If lots of variation between vertebral bodies, likely will need additional imaging of hips/dominant forearm in the future or now!

    36. Spine QA COMPARISON QA Check and see if positioning and numbering is the same.

    37. Spine QA COMPARISON QA Check and see if positioning and numbering is the same. If numbering is questionable, keep consistent with prior study unless prior study clearly mislabeled.

    38. Spine QA COMPARISON QA Check and see if positioning and numbering is the same. If numbering is questionable, keep consistent with prior study unless prior study clearly mislabeled. Some DXA units will let you correct and reanalyze prior data.

    39. Spine QA COMPARISON QA Are ROIs similar? Check edges.

    40. Spine QA COMPARISON QA Are ROIs similar? Check edges. Compare prior BMDs and T-scores at EVERY level.

    41. Spine QA COMPARISON QA Are ROIs similar? Check edges. Compare prior BMDs and T-scores at EVERY level. Is one level or two significantly different?

    42. Spine QA COMPARISON QA Are ROIs similar? Check edges. Compare prior BMDs and T-scores at EVERY level. Is one level or two significantly different? Review images for cause. e.g. interval fracture, procedure, overlying artifact, etc..

    43. Spine QA COMPARISON QA --we depend on YOU!! Consistency and precision are critical! --Spine BMD has the best precision and is the most responsive to therapy. Patient care is impacted. --Significant BMD changes affect therapy decisions. “Significant” is often just a few or several percent difference.

    44. Spine QA COMPARISON QA --we depend on YOU!! Consistency and precision are critical! Precision errors affect health care costs, may result in unnecessary change in treatment (more expensive or more side effects) or lack of treatment or unnecessary specialist referral or additional diagnostic work-up to assess for secondary osteoporosis, patient anxiety, etc..

    45. Spine QA COMPARISON QA A national bone metabolism and bone health expert reported : #1 reason for referral for significant bone loss, despite appropriate medical therapy… ???

    46. Spine QA COMPARISON QA A national bone metabolism and bone health expert reported : #1 reason for referral for significant bone loss, despite appropriate medical therapy… POOR COMPARISON TECHNIQUE!!

    47. HIP • Positioning -remove shoes and foot in positioning device Shoes can vary year to year, depending on the season, etc.

    48. HIP • Positioning -remove shoes and foot in positioning device -femoral neck centered in the image

    49. HIP • Positioning -remove shoes and foot in positioning device -femoral neck centered in the image -minimal lesser trochanter apparent (internally rotated)