Gerrit Engelbrecht
DefinitionsOsteopenia
Poverty of bone Decreased quality or quantity of bone
Radiologically identified as radiolucencyCauses
Diffuse Regional osteopenia
OsteosclerosisIncreased density of bone
Diffuse osteopeniaOsteoporosis osteomalacia hyperparathyroidismmultiple myelomadiffuse metastasesdrugs,mastocytosis osteogenesis imperfecta
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 = Sudeck dystrophy Regional migratory osteoporosis, transient regional
osteoporosis of hip Rheumatologic disorders Infection: osteomyelitis, tuberculosis Osteolytic tumorLytic phase of Paget diseaseEarly phase of bone infarct and hemorrhageBurns + frostbite
OsteosclerosisDiffuse 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 Osteopathia striata Osteopetrosis Osteopoikilosis Pachydermoperiostosis Pyknodysostosis Van Buchem disease Williams syndrome
OsteoporosisWHO
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 toosteoclastic resorption
(85 trabecular, endosteal, intracortical subperiosteal
osteocytic resorption (15%)
Etiology of osteoporosisA. CONGENITAL DISORDERSB. IDIOPATHIC C. NUTRITIONAL DISTURBANCESD. ENDOCRINOPATHYE. RENAL OSTEODYSTROPHYF. IMMOBILIZATIONG. COLLAGEN DISEASE, RHEUMATOID
ARTHRITISH. BONE MARROW REPLACEMENTI. DRUG THERAPYJ. RADIATION THERAPYK. LOCALIZED OSTEOPOROSIS
Role of diagnostic imagingTwo principal aims:
Identify the presence of osteoporosis
Quantify bone mass with use of:
Semiquantitative (conventional radiography) Quantitative (densitometry) methods.
Conventional radiographyRadiologic appearance stay the same
whatever the cause.
Most common modality to diagnose osteoporosis
Drawback: Start picking up bone loss at 30 % and more
Generalized osteoporosisIncreased
radiolucencyCause: resorption
and thinning of trabeculae
Trabeculae respond faster to metabolic bone changes
Prominent Axial skeleton Ends of long bones
Cortical thinningCause: osseous
resorption Endosteal
Scalloping Intracortical
Longitudinal striations( cortical tunneling )
Periosteal Irregular definition of
the outer bone surface(Most specific for high bone turnover)
Osteoporosis in the axial skeletonPicture framing ( loss of the trabeculae in relation
to cortex )Loss of horizontal trabeculaeCompression fractures
Usually lumbothoracic junctionNumberDegree
Wedge ( anterior height reduce > 4mm : posterior height )
Endplate ( midheight : posterior height ) Crush ( all the heights in relation to neighbouring
vertebrae)
Osteoporosis in a vertebrae
• Radiolucency• Well
demarcated cortical rim
• Verticalization of trabeculae
Saville index
Genant fracture definition
Vertebral deformity between T4 and L4Height loss > 20 %Area reduction 10-20 %
Genant scoring systemSeverity index of vertebral fracturesGrades:
Grade 0: No fractureGrade 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
Point to remember
Isolated fractures above the T7 level are rare in osteoporosis and should alert clinicians to a cause other than osteoporosis
Genant ( semiquantitative)
Appendicular skeletonChanges first apparent : Ends of long and
tubular bonesMain sites:
HandProximal femurCalcaneus
HandMetacarpal bones ( second, third and fourth )Corticomedullar index
Second metacarpal ( accurate)Longest established quantitative methods ( > 70
years)Automated ( digital x-ray radiogrammetry)-2001
Converted to BMDHigh 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
Jhamariacalcaneal index
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.
Principles of DXAMobile x-ray sourceTwo 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
Principles of DXAThe attenuation is compared to known
standard attenuation values from phantoms => relation between atenuation and BMD.
Newer developments lateral scanners
BMDMeasurements:
BMD = Bone mineral content ( grams )/Projected area of the measured site ( cm 2 )
Overestimation with increased bone sizeUnderestimation with decreased bone size
Interpretation of DXABMD expressed in terms of standard
deviationT 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)
Normal ≥ -1.0
Osteopenia < - 1.0 , > - 2.5
Osteoporosis ≤ - 2.5
Severe osteoporosis ≤ - 2.5With fragility fracture
Advantages of DXALow radiation doseLow costEase of useRapidity of measurement
Limitations
Two dimensional technique Cannot discriminate between cortical and trabecular
bone Cannot discriminate between geometry and
increased bone density
Axial DXAAreas were it can be used
Lumbar spineProximal 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
Pitfalls of DXAScanner and soft ware
Technologist, patient positioning, analysis of scans
Patient related artefacts
Pitfalls of DXAProper calibration: Phantoms scanned at least once
a weekPositioning
Improper centering of the lumbar spineAbduction or external rotation of the hip
Analytical pitfallsSpine
Numbering of vertebrae Placement of intervertebral markers Detection of bone edges
Hip Placement of ROI Detection of bone edges
Pitfalls of DXAAnatomic artefacts
Degenerative disk diseaseCompression fracturesPost surgical defectsAtherosclerotic artefactsMotion artefacts
Medical devices: Prosthesis, cement etcPersonal belongings and clothes: wallets, coinsResults from different machines not
interchangeable.
Peripheral DXASmall 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
Fracture Risk Assessment ToolBased 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 scanner10 year probability of a major osteoporotic fracture
Quantitative CTSeparate estimates of
Cortical BMDTrabecular BMD
True volumetric density in mg/cm3
Axial Quantitative CT2 to 4 consecutive vertebrae ( T12 – L4 )Commercial CT scannersBone mineral reference standard8-10 mm thick slices, parallel to vertebral endplateMidplane of each vertebraeROI anterior portion of trabecular bone in vertebral
body.Automatic edge detection software then takes over and
calculate the correct ROI with anatomical landmarksCompare attenuation values to a calibration standardConversion to calcium hydroxy apatite/ cm 3
Values•Absolute•T or Z scores•Race dependant•Compared to healthy population
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
New developments of quantitative CT
Volumetric quantitative CT encompass the entire object of interest with stacked sections or spiral CT
BMD of entire structureSeparate analysis of trabecular and cortical
componentsDual energy CT is currently used to study the
bone marrow adipocytes for effects of aging, drugs and disease.
Disadvantages of axial quantitative CT
High radiation dosePoor precision for objects that is complex
instead of longitudinal.High costsOperator dependanceSpaceLimited scanner access.
Peripheral quantitative CTSeparate 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.
MorphometryDigitising
vertebral height
Ratios compared to normal values
> 15 % abnormal
Cannot differentiate from other reason for deformities ( degeneration, congenital)
UltrasoundScreening tool with confirmation by DXANot sensitive enough for long term followup
of osteoporosis.Calcaneus, distal metaphysis of the phalanx,
radius and tibia
Newer advancesAim to better identify the macro and micro
anatomy of bone to improve prediction of fracture risk.( imaging of trabeculae )
MRI3 tesla systemsCalcaneus, knee and wristSeveral studies but no clinical guidelines yet
CT clinical systems not yet able to detect true
trabecular networks but the textureMicro CT with resolutions of 6 micrometer
currently used with in vitro studies.
CT MRI
ReferencesOrtopedic imaging, A practical approach,
Adam GreenspanFundamentals of Diagnostic Radiology, Brant
and HelmsIntegrated imaging approach to osteoporosis:
State of the art review and update. Guiseppe Guglielmi et al, Radiographics 2011; 31:1343
The trabecular pattern of the calcaneus as index of osteoporosis; NL Jhamaria et al., British editorial society of bone and joint surgery, vol 65-B, No2 March 1983