Bone scan in Orthopaedics
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A bone scan uses radioactive tracers to detect areas of increased or decreased bone activity. It can evaluate bone abnormalities throughout the entire skeleton. Some key points: - Bone scans are useful for detecting cancer metastases, fractures, stress fractures, bone infections, and other bone diseases. - They have advantages of being able to image the whole body and having relatively low radiation exposure. - The most common tracer used is technetium-99m MDP, which concentrates in areas of increased bone formation. - Abnormal findings on bone scans include multiple areas of abnormal uptake indicating cancer metastases, linear areas of uptake indicating fractures, and photopenic defects indicating bone infarcts.
Bone scan in Orthopaedics
- 1. BONE SCAN IN ORTOHPAEDICS UMESH YADAV
- 2. DEFINITION • A bone scan is a test that detects areas of increased or decreased bone activity by injecting a certain radiopharmaceutical ie. Tc-99m MDP. • A/K/A Radionuclide bone scan or Bone scintigraphy
- 3. BONE SCAN ADVANTAGES • Whole-body evaluation in one test/ same rad exposure. • Low radiation exposure • Sensitive evaluation DISADVANTAGES • Needs radiopharms & gamma camera not widely available • Radiation exists • Low specificity • COST…….
- 4. Radiopharmaceutical (“Tracer”) • The most widely used is Tc-99m labeled diphosphonates; • Tc-99m Methylene diphosphonate (Tc-99m MDP) • Tc-99m Medronate Tc-99m MDP Phosphonates concentrate in the mineral phase of bone: nearly two- thirds in hydroxyapatite crystals and one third in calcium phosphate
- 5. PATHOPHYSIOLOGY • Two major factors control accumulation of phosphonates in bone, 1) blood flow , 2)extraction efficiency, which in turn depend on capillary permeability, acid-base balance, parathyroid hormone levels, etc. • Maximum bone accumulation is reached 1 h after injection and the level remains practically constant up to 72 h. • The peak of activity through the kidneys is reached after approximately 20 min. Within 1 h, with normal renal function, more than 30% of the unbound complex has undergone glomerular filtration andwithin 6 h, 60%.
- 6. • Tc-99m MDP uptake depends on osteoblast and osteoclast activity. • Increased uptake - osteoblastic activity present • Decreased uptake - pure lytic lesion , osteoclast activity
- 7. Technique of Bone Scan Preparation: None • Injection of Tc-99m 20-25 mCi IV, good hydration afterwards & frequent voiding • Wait for about 3 hrs to start imaging, avoid contamination • Empty bladder prior to scanning • Change the cloth and remove things likely cause artifact.
- 8. • Can be performed as: – a) Limited bone scintigraphy or spot views (planar images of a selected portion of the skeleton) – b) Whole-body bone scintigraphy (planar images of the entire skeleton in anterior and posterior views) – c) SPECT (single photon emission computed tomography- image of a portion of the skeleton) – d) Multiphase bone scintigraphy (immediate and delayed images to study blood flow) IMAGING ACQUISITION
- 9. Clinical indications Oncological indications • Primary tumours (e.g. Ewing’s sarcoma, osteosarcoma) • Staging, evaluation of response to therapy and follow up of primary bone tumors • Secondary tumours (metastases) – Staging and follow-up of neoplastic diseases – Distribution of osteoblastic activity prior to radiometabolic therapy
- 10. Non-neoplastic diseases Whenever there is an increase in blood flow to a lesion or there is an alteration in osteoblastic activity. – Stress and/or occult fractures. – Trauma – Musculoskeletal inflammation and infection – Bone viability (grafts, infarcts, osteonecrosis). – Metabolic bone disease. – Arthritis – Complications of hardware/prosthetic joint replacement, loose or infected joint prosthesis. – Heterotopic ossification. – Complex regional pain syndrome (CRPS) – Other bone disease, such as Paget disease, Langerhans cell histiocytosis, or fibrous dysplasia. – Congenital or developmental anomalies.
- 11. Normal Bone Scan • Tracer uptake greatest in axial skeleton • Background activity of soft tissue • Kidneys routinely visualized • Skull can appear uneven (variations in calvarial thickness) • Sites of persistently increased symmetric uptake are- Acromial and Coracoid processes of the scapulae, Medial ends of the clavicles, Junction of the body and manubrium of the sternum and the sacral alae
- 12. Normal Bone Scan-Pediatrics Growth Center most intense: distal femur-proximal tibia- proximal humerus (which is also the order of relative occurence of osteosarcoma in children) Costochondral junctions
- 14. METASTATIC BONE DISEASE • The presence of multiple, randomly distributed areas of increased uptake of varying size, shape, and intensity is highly suggestive of bone metastases.
- 15. Metastatic Bone Disease ? • Multiple Fractures • Radiotracer accumulation in both the vertebral body + pedicles =metastatic disease, whereas vertebral body and facets but spare the pedicles = benign lesions • Activity confined to the vertebral body can be due to tumor, trauma, or infection
- 16. Flare phenomenon • Seen in patients who are responding to treatment, reflects healing of the bone lesions and has been described as the “flare” phenomenon. • Usually observed within 3 months after initiation of treatment and is often associated radiographically with the sclerotic changes that indicate healing. • Continued increase in the number and intensity of lesions beyond 6 months is usually indicative of disease progression
- 17. Flare Phenomenon Usually occurs 3-6 months post chemotherapy
- 18. SUPERSCAN • When the metastatic process is diffuse, virtually all of the radiotracer is concentrated in the skeleton, with little or no activity in the soft tissues or urinary tract. The resulting pattern, with excellent bone detail, known as SUPERSCAN. • A superscan may also be associated with metabolic bone disease. Unlike in metastatic disease, however, the uptake in metabolic bone disease is more uniform in appearance and extends into the distal appendicular skeleton.
- 19. Multiple Myeloma • Unless associated fracture present bone scan often normal
- 20. Osteoid Osteoma “DOUBLE DENSITY” SIGN OR “ HEADLIGHT IN FOG SIGN”
- 21. TRAUMA • Bone scintigraphy is a very sensitive exam for the detection of acute fractures . • About 80% of bone scans will show increased activity at a site of fracture by 24 hours, and 95% by 72 hours. •Whole body bone scan showing multiple occult bilateral rib fractures (arrowed). •The linear alignment is typical of fractures.
- 22. Stress Fractures • Plain radiograph can be negative • Occurs in normal bone that undergoes abnormal stress (insufficiency fractures occur with normal stress in bones that are weakened) • Common sites are the femoral neck and tibia. • Typical pattern is oval area of increased uptake with long axis parallel to axis of bone
- 23. Shin Splints (Periostitis) • exercise induced pain along medial or posteromedial aspect of tibia • associated with increased tracer uptake • >1/3 of bone length,middle to distal tibia • usually bilateral (not necessarily symmetrical)
- 24. Bone Infarction/AVN • Appearance depends on time course – In acute phase of vascular compromise, no radiotracer is delivered to the bone tissue. So the affected part of the bone appears as a photopenic defect. – After revascularization, exuberant osteoblastic repair manifests as intense radiotracer uptake. – Subsequently, when repair is complete, radiotracer uptake may return to baseline levels • Less sensitive than MRI
- 25. Plantar fascitis
- 26. 3 PHASE BONE SCAN • 3 stages which follow IV injection of the tracer. • 1) Flow phase • 2 to 5-sec images are obtained for 60 seconds after injection • Demonstrates perfusion and characterises the blood flow to a particular area • 2) Blood pool phase • the blood-pool image is obtained 5 min after injection • demonstrated the blood pool, not the blood flow • inflammation causes capillary dilatation and increased blood flow • If the study is going to be a triphasic bone scan, a third phase is added. • 3) Delayed phase • the bone image is obtained 2 - 4 hours later • urinary excretion has decreased the amount of the radionuclide in soft tissue • DIFFERNTIATE OSTEOMYELITIS FROM CELLULITIS
- 27. OSTEOMYELITIS • The classic appearance of osteomyelitis on three-phase bone scans consists of focal hyperperfusion, focal hyperemia, and focally increased bone uptake • Phase I + Phase II with negative Phase III- Cellulitis • All positive- OM
- 28. SOME OTHER TRACERS • GALLIUM-67 -Sensitive for detection of inflammatory process. - HOT in ABSCESS ( Vertebral OM) - LYMPHOMA - SARCOIDOSIS
- 29. • INDIUM 111- • Tagged with leucocytes. • More sensitive than Ga67 scans. • Used with Sulfur Colloid Scan – Delineate areas of normal bone activity IN 111 labelled Leucocyte- Highlight involved region. - SO INCONGURENCE OF BOTH IS HIGHLY SUGGESTIVE OF INFECTION
- 30. PAINFUL PROSTHESIS- LOSSENING OR INFECTION • 3 PHASE BONE SCAN- • Focally increased uptake- Loosening • Diffuse , Uniformly distribution – Infection • Not very specific • Ga-67 SCAN- • Differntiate between pure mechanical loosening and infection