Imaging bone density

1. Imaging bone density Gerrit Engelbrecht

2. Definitions • Osteopenia • Poverty of bone • Decreased quality or quantity of bone • Radiologically identified as radiolucency • Causes • Diffuse • Regional osteopenia • Osteosclerosis • Increased density of bone

3. Diffuse osteopenia • Osteoporosis • osteomalacia • hyperparathyroidism • multiple myeloma • diffuse metastases • drugs,mastocytosis • osteogenesis imperfecta

4. Regional osteopenia • Disuse osteoporosis /atrophy • Etiology: local immobilization secondary to • (a) fracture (more pronounced distal to fracture site) • (b) neural paralysis • (c) muscular paralysis • Reflex sympathetic dystrophy = Sudeckdystrophy • Regional migratory osteoporosis, transient regional osteoporosis of hip • Rheumatologic disorders • Infection: osteomyelitis, tuberculosis • Osteolytictumor • Lytic phase of Paget disease • Early phase of bone infarct and hemorrhage • Burns + frostbite

5. Osteosclerosis • Diffuse Osteosclerosis • Metastases • Myelofibrosis • Mastocytosis • Melorheostosis • Metabolic: hypervitaminosis D, fluorosis, hypothyroidism, phosphorus poisoning • Sickle cell disease • Tuberous sclerosis • Pyknodysostosis, Paget disease • Renal osteodystrophy • Osteopetrosis • Fluorosis • Constitutional Sclerosing Bone Disease • Engelmann-Camurati disease • Infantile cortical hyperostosis • Melorheostosis • Osteopathiastriata • Osteopetrosis • Osteopoikilosis • Pachydermoperiostosis • Pyknodysostosis • Van Buchem disease • Williams syndrome

6. Osteoporosis WHO • Osteoporosis, the most common of all metabolic bone disorders, is defined by the World Health Organization (WHO) as “a skeletal disease, characterized by low bone mass and micro-architectural deterioration of bone tissue, with a consequent increase in bone fragility and susceptibility to fracture” • Reduced bone mass of normal composition secondary to • osteoclasticresorption (85 • trabecular, • endosteal, • intracortical • subperiosteal • osteocyticresorption (15%)

7. Etiology of osteoporosis • A. CONGENITAL DISORDERS • B. IDIOPATHIC • C. NUTRITIONAL DISTURBANCES • D. ENDOCRINOPATHY • E. RENAL OSTEODYSTROPHY • F. IMMOBILIZATION • G. COLLAGEN DISEASE, RHEUMATOID ARTHRITIS • H. BONE MARROW REPLACEMENT • I. DRUG THERAPY • J. RADIATION THERAPY • K. LOCALIZED OSTEOPOROSIS

8. Role of diagnostic imaging • Two principal aims: • Identify the presence of osteoporosis • Quantify bone mass with use of: • Semiquantitative(conventional radiography) • Quantitative (densitometry) methods.

9. Conventional radiography • Radiologic appearance stay the same whatever the cause. • Most common modality to diagnose osteoporosis • Drawback: Start picking up bone loss at 30 % and more

10. Generalized osteoporosis • Increased radiolucency • Cause: resorption and thinning of trabeculae • Trabeculae respond faster to metabolic bone changes • Prominent • Axial skeleton • Ends of long bones • Cortical thinning • Cause: osseous resorption • Endosteal • Scalloping • Intracortical • Longitudinal striations( cortical tunneling ) • Periosteal • Irregular definition of the outer bone surface(Most specific for high bone turnover)

11. Osteoporosis in the axial skeleton • Picture framing ( loss of the trabeculae in relation to cortex ) • Loss of horizontal trabeculae • Compression fractures • Usually lumbothoracic junction • Number • Degree • Wedge ( anterior height reduce > 4mm : posterior height ) • Endplate ( midheight : posterior height ) • Crush ( all the heights in relation to neighbouring vertebrae)

12. Osteoporosis in a vertebrae • Radiolucency • Well demarcated cortical rim • Verticalization of trabeculae

13. Saville index

14. Genant fracture definition • Vertebral deformity between T4 and L4 • Height loss > 20 % • Area reduction 10-20 %

15. Genant scoring system • Severity index of vertebral fractures • Grades: • Grade 0: No fracture • Grade 1: Mild fracture ( 20 -25 %reduction in height compared to neighbouring vertebrae ) • Grade 2: Moderate fracture ( 25 -40 % reduction ) • Grade 3: Severe fracture ( > 40 % ) • Index = Sum Grades/ Number of vertebrae

16. Point to remember • Isolated fractures above the T7 level are rare in osteoporosis and should alert clinicians to a cause other than osteoporosis

17. Genant ( semiquantitative)

18. Examples of wedge fractures

19. Appendicular skeleton • Changes first apparent : Ends of long and tubular bones • Main sites: • Hand • Proximal femur • Calcaneus

20. Hand • Metacarpal bones ( second, third and fourth ) • Corticomedullar index • Second metacarpal ( accurate) • Longest established quantitative methods ( > 70 years) • Automated ( digital x-ray radiogrammetry)-2001 • Converted to BMD • High reproducibility • Capacity to help predict future fracture • Potential to provide a simple, widely available, and inexpensive method of assessing patients who are at risk for osteopenia or osteoporosis and might appropriately be referred for central DXA

22. Trabecula of the femur

24. Jhamaria calcaneal index

25. Dual – energy Absorptiometry(DXA) In 1994, the WHO defined the threshold levels for the diagnosis of osteopenia and osteoporosis with DXA. As a consequence, DXA measurements are currently the standard of reference for the clinical diagnosis of osteoporosis with bone densitometry.

26. Principles of DXA • Mobile x-ray source • Two different photon energies ( constant and pulsed ) • Attenuation difference between the soft tissue and mineralized bone is used to identify the soft tissue attentuation which is then substracted leaving only the attentuation values of the bone

27. Principles of DXA • The attenuation is compared to known standard attenuation values from phantoms => relation between atenuation and BMD. • Newer developments lateral scanners

28. BMD • Measurements: • BMD = Bone mineral content ( grams )/Projected area of the measured site ( cm 2 ) • Overestimation with increased bone size • Underestimation with decreased bone size

30. Interpretation of DXA • BMD expressed in terms of standard deviation • T score: dev from mean BMD standard young adult population ( 20- 30 years ) • Z score: Dev. from mean BMD of age and gender match controls ( NB in 75 years or older ) • WHO( T score in Lumbar spine, proximal femur and forearm)

31. Advantages of DXA • Low radiation dose • Low cost • Ease of use • Rapidity of measurement • Limitations • Two dimensional technique • Cannot discriminate between cortical and trabecular bone • Cannot discriminate between geometry and increased bone density

32. Axial DXA • Areas were it can be used • Lumbar spine • Proximal femur • Total hip • Femoral neck • Trochanter • Ward area • Cannot completely discriminate between patients that have fractures or not • The lower the BMD the higher is the risk of a fracture

33. Pitfalls of DXA • Scanner and soft ware • Technologist, patient positioning, analysis of scans • Patient related artefacts

34. Pitfalls of DXA • Proper calibration: Phantoms scanned at least once a week • Positioning • Improper centering of the lumbar spine • Abduction or external rotation of the hip • Analytical pitfalls • Spine • Numbering of vertebrae • Placement of intervertebral markers • Detection of bone edges • Hip • Placement of ROI • Detection of bone edges

35. Pitfalls of DXA • Anatomic artefacts • Degenerative disk disease • Compression fractures • Post surgical defects • Atherosclerotic artefacts • Motion artefacts • Medical devices: Prosthesis, cement etc • Personal belongings and clothes: wallets, coins • Results from different machines not interchangeable.

38. Positional problems with DEXA Normal External rotation Degenerative changes

39. DXA of the lumbar spine Good scan Problem scan

40. Peripheral DXA • Small portable scanner • Distal radius : predicative of wrist fractures ( T ≤ -2.5) • Calcaneus: predicative of spine fractures ( T -1.0 to – 1.5 ) • Especially in elderly with degenerative disease

41. Fracture Risk Assessment Tool • Based on • BMD of the femur neck • Age • Sex, height and weight • Seven clinical risk factors • Previous fracture • Hip fracture • Current smoking • Glucocorticoid use • RA • Secondary osteoporosis • 3 or more unit of alcohol daily • Enter the name of the scanner • 10 year probability of a major osteoporotic fracture

42. Quantitative CT • Separate estimates of • Cortical BMD • Trabecular BMD • True volumetric density in mg/cm3

43. Axial Quantitative CT • 2 to 4 consecutive vertebrae ( T12 – L4 ) • Commercial CT scanners • Bone mineral reference standard • 8-10 mm thick slices, parallel to vertebral endplate • Midplane of each vertebrae • ROI anterior portion of trabecular bone in vertebral body. • Automatic edge detection software then takes over and calculate the correct ROI with anatomical landmarks • Compare attenuation values to a calibration standard • Conversion to calcium hydroxy apatite/ cm 3

44. Values • Absolute • T or Z scores • Race dependant • Compared to healthy population

45. Advantages of Axial Quantitative CT • Better than DXA at predicting vertebral fractures • Good sensitivity measurement of age related bone loss after menopause • Exclude measurement of structures that does not contribute to spine mechanical resistance but to BMD values • Selective measurement of trabeculae which is the most metabolic active part of bone and main determinant of the compressive strength of bone • Allow evaluation of the macro architecture of the vertebrae

46. New developments of quantitative CT • Volumetric quantitative CT encompass the entire object of interest with stacked sections or spiral CT • BMD of entire structure • Separate analysis of trabecular and cortical components • Dual energy CT is currently used to study the bone marrow adipocytes for effects of aging, drugs and disease.

47. Disadvantages of axial quantitative CT • High radiation dose • Poor precision for objects that is complex instead of longitudinal. • High costs • Operator dependance • Space • Limited scanner access.

48. Peripheral quantitative CT • Separate accessments of cortical and trabecular bone • Bone geometry at appendicular sites. • Indexes of bone stability in response to bending and torsion which are the most important biomechanical measures of susceptibility fracture and may improve accuracy in the prediction of fractures.

49. Peripheral quantitative CT

50. Peripheral quantitative CT