DR. CHIRANJIB MURMU

Osteoporosis &Bone Mineral

Density

OUTLINE

IntroductionOsteoporosisModalities for BMD measurementConventional radioghaphyRadiogrammetryPhotodensitometryCompton scatteringNeutron activation analysisSingle and dual photon absorptiometery

OUTLINE

Dual energy X-Ray absorptiometryQuantitative CTQuantitative USGMRIMDCT

Introduction: Osteoporosis

A progressive systematic 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 (WHO).

Can be primary or secondary.

Bone production & Resorption

Target sites of Osteoporosis

Imaging Studies

First, obtain plain radiographs if a decrease in bone mineral density is suspected.

Osteopenia may be apparent as radiographic lucency but is not always noticeable until 30% of bone mineral is lost.

Plain radiography alone is not as accurate as BMD testing.

Indication for BMD

• Woman > 65 years and men > 70 years.

• Radiographic evidence of osteoporotic vertebral fractures or apparent osteopenia.

• History of fragility fractures after age 40.

• Known causes of secondary osteoporosis : Early menopause(< 45 years of age) / hypo gonadism in men/woman. Systemic diseases with adverse effect on bone. Bone toxic drugs.

Indication for BMD• Facilitate desicions regarding initiation/ discontinuation of

drug therapy (biphosphonates /HRT).

• Strong clinical risk factors: Family history of hip fractures or osteoporosis. BMI < 19 kg/m2. Regular C2H5OH intake(>3 drinks/day). Smoking. Poor nutrition /Calcium intake/Vitamin D exposure.

Conventional Radiography

• Increased Radiolucency/Cortical Thinning: 30 – 40 % loss of bone mass need to be present before detection.

• Can detect osteomalacia/hyperparathyroidism.

• Loss of at least 20% or 4 mm vertebral body height required for diagnosis of vertebral fracture.

Osteopenia & collapse

Empty box & cordfish vertebrae

Non osteoporotic Vertebral fractures

• Not pain free within 6-8 weeks

• Non Anterior Wedge

• Posterior Wedge(other than L4+5)

• Above T7

• Concave posterior vertebral border is more likely a sign of benign osteoporotic fracture, whereas a convex posterior border suggests malignant disease.

• Consider :

• Neoplastic disease – multiple myeloma/metastases

• Osteomalacia

• Trauma

• DegenerationMR imaging findings of malignant disease include multiple contrast enhancing

lesions or soft-tissue masses, with or without encasing epidural masses and destructive changes.

Radiogrammetry – Cortical thickness/corticomedullary index

Digital X-Ray grammetry/Vertebral morphometry

Singh Index

Singh index-6 grades

DEXA

DEXA

DEXA

DEXA-Advantage

• Proven ability to predict fracture risk.

• BMD result can be interpreted using WHO T-score.

• Effectiveness of anti-fracture treatments.

• Short scan time.

• Easy patient set-up.

• Low radiation dise.

• Good precision.

• Acceptable accuracy.

• Effective instrument quality control procedure.

DEXA-Limitations

• Meassurement monoplanar – g/cm2 and therefor size dependant (children).

• All calcium in path of electron beam contributes to BMD(Aortic calcifications degenerative/hyperostotic changes/vertebral wedging,metallic pinning) with overestimation of BMD.Exclude these areas from analysis/Lateral scanning.

• Strontium ranelate treatment – artefactual increase in BMD.

• Results of different scanners not interchangeable.

WHO Limitation of DEXA• Low specificity – < 50 % of known osteoporotic fractures

have BMD in osteoporotic range(T < - 2.5).

• Other risk factors like propensity to falls or qualitative risk factors like bone turnover not included.

• Extrapolation to other populations measured at different skeletal sites with other techniques (QUS,QCT) not acceptable.

• Other metabolic bone diseases.

Interpretation

Need appropriate race and sex matched BMD reference ranges – ethnic differences in BMD and fracture prevelance.

Expressed as standard deviation from : Age matched – Z Score Peak bone mass – T Score Normal - > – 1 sd Osteopenia - < -1 > – 2.5 sd Osteoporosis - < -2.5 sd Severe Osteoporosis - < -2.5 sd + 1or > fragility fractures

Screening - DEXA

DEXA of the proximal femur in a young woman DEXA of the proximal femur in a young woman, age 37, with unsuspected femoral-neck osteopenia (T score, -1.6).

DEXA of the lumbar spine in a young woman, age 37, with unsuspected lumbar spine osteopenia (T = -1.8)

NOFSA guidelines: Osteoporosis

• Confirm diagnosis with BMD or presence of fragility fracture before initiation of treatment with bone active drugs.

• Axial BMD to be used to diagnose and access rate of bone loss/gain. QCT/QUS not recommended and results cannot be applied to T score based WHO diagnostic classification

• Lowest BMD value measured at spine,total femur and femur neck(or distal radius if invalid)

• Express results for post menopausal Caucasian woman as T scores and Z scores for pre menopausal woman and men < 50 year

• Men over 50 years : Employ female reference data to determine T score

• Local black population : use reference data for Caucasian females for all subjects of all races until local reference values become available.

NOFSA guidelines: Osteoporosis

• Children:Low BMD + significant fracture history

• Follow up scans every 18-24 months or earlier in GIOP

• Search for evidence of vertebral compression fractures in all who qualify for BMD measurement – Standard x-ray and use modified Genant semiquintative system to grade (Gr.1-3) Higher grade = higher risk for subsequent fractures of hip and vertebrae or DXA VFA .

DEXA-VFA• Reduce the high subjectivity and poor reproducibility of

qualitative readings.

• Vertebral fractures are one of the most important RF – 60% asymptomatic and go undetected if not routinely searched for.

• Visualize lateral spine on DXA with VFA software.

• Lower radiation dose and cost compared to conventional radiography.

• Conventional radiography remain gold standard – often only requested if fracture is suspected.

Morphometric X-Ray absorptiometryVertebral Deformity

Quantitative Computed Tomography

Quantitative computed tomography measures BMD as a true volume density in g/cm3, which is not influenced by bone size.

This technique can be used for both adults and children. Disadvantages in that (1) it only determines bone density at the

spine, (2) osteophytes can interfere with measurement, and (3) it is associated with significant radiation exposure and high cost

Quantitative Computed Tomography

• Separate estimation of cortical and trabecular bone.

• True volumetric density – g/cm3 making it non size dependant (children/small stature).

• Performed with calibration reference phantom to transform HU into BMD equivalents.

• Radiation dose compares favourably with conventional radiography.

• Excellent for predicting vertebral fractures and serially measuring bone loss - selectively assesses the metabolically active and structurally trabecular bone.

• Increase in marrow fat is age related, single-energy CT data can be corrected with use of age-related reference databases.

Quantitative Computed Tomography

High resolution bone MR Imaging(3T)

• Can be used to detect differences in trabecular structure depending on patient age, BMD, and osteoporotic status.

• Most often performed at peripheral sites such as the calcaneum, knee and wrist.

• Substantial improvement in fracture discrimination made possible by considering structural information as well as BMD.

• May replace biopsy when this would be advocated.

High resolution bone MR Imaging(3T)

Quantitative Ultrasonography

• Quantitative ultrasonography of the calcaneum(trabecular bone) can be used for general screening at >65 yr age groups.

• Transducer: 200kHz to 1.5 MHz.

• Screening purpose.

• Its advantages include low cost, portability, and lack of ionizing radiation

Screening- Ultrasound DensitometryUltrasound densitometry can assess the density and structure of the skeleton and appears to predict fracture risk in the elderly. The apparatus is relatively inexpensive, portable, and uses no radiation but can be used only in peripheral sites (eg, the heel), where bone is relatively superficial. Ultrasound devices measure the speed of sound (SOS), as well as specific changes in sound waves (broadband attenuation or BUA) as they pass through bone. QUS measurements provide information on fracture risk by providing an indication of bone density and possibly also information on the quality of the bone. Ultrasound devices do not expose the patient to ionizing radiation.

Compton Scattering• Based on scattered radiation from a source of 100 to 700 KV

gamma rays.

• Used for Calcaneum, spine and radius.

• Radiation dose 200 to 2000 mrem.

• Research tool.

Neutron Activation Analysis• Neutrons from an accelerator or rector bombard a small

fraction of total Ca(48) in the body changing it to Ca(49) which is radioactive isotope. By counting its activity, total calcium content of body is estimated.

• Usually used for population study.

• Limitation: study of peripheral long bone and measures primarily cortex.

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