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