High Yield Overview

Nuclear Medicine in Orthopaedics

Functional Imaging for Bone, Infection & Tumour Assessment

Tc-99mMost common radionuclide (6-hour half-life)

MDPMethylene diphosphonate (bone-seeking tracer)

3-phaseFlow, blood pool, delayed bone phases

95%Sensitivity of bone scan for metastases

F-18 FDGPET tracer for metabolic activity

WBC scanIn-111 or Tc-99m labelled for infection

2-4hDelayed phase imaging time post-injection

LowSpecificity — bone scan is sensitive but not specific

Nuclear Medicine Studies in Orthopaedics

Bone Scintigraphy (Tc-99m MDP): Whole-body skeletal survey — sensitive for metastases, infection, occult fracture

Three-Phase Bone Scan: Adds flow and blood pool phases — helps differentiate infection from other causes

SPECT-CT: Combines SPECT (3D nuclear) with CT — better anatomical localisation

PET-CT (F-18 FDG): Detects metabolic activity — superior for tumour staging and infection localisation

Labelled WBC Scan: Gold standard for prosthetic joint infection — labels patient's own white cells

Key: Nuclear medicine provides FUNCTIONAL information about biological processes, complementing the ANATOMICAL information from radiography, CT, and MRI

Critical Must-Knows

Bone scintigraphy with Tc-99m MDP detects areas of increased osteoblastic activity — it reflects bone TURNOVER, not a specific diagnosis.
The three-phase bone scan adds vascular (flow and blood pool) phases to the standard bone phase, improving differentiation of infection from other causes of increased uptake.
Bone scans are highly SENSITIVE (95%) but poorly SPECIFIC — virtually any process that increases bone turnover will cause uptake.
PET-CT with F-18 FDG detects metabolically active tissue (infection, tumour) with better specificity and resolution than bone scintigraphy.
Labelled white cell scans (In-111 or Tc-99m HMPAO) are the gold standard nuclear medicine test for prosthetic joint infection.

Examiner's Pearls

"
A 'cold' lesion on bone scan (photopenic/absent uptake) suggests: aggressive tumour outpacing bone response, myeloma, avascular necrosis, or early infection before osteoblastic response.
"
The three-phase bone scan: Phase 1 (flow) = arterial vascularity, Phase 2 (blood pool) = soft tissue hyperaemia, Phase 3 (delayed) = bone turnover. All three positive in infection.
"
PET-CT is increasingly replacing bone scan for metastatic workup due to superior sensitivity, specificity, and anatomical localisation.
"
Bone scan remains positive for 1-2 YEARS after joint replacement — normal postoperative uptake. A WBC scan helps differentiate infection from normal healing.
"
The 'superscan' pattern (diffuse intense skeletal uptake with faint/absent kidneys) indicates widespread metastatic disease or metabolic bone disease.

Exam Warning

Nuclear medicine is commonly examined in the context of: (1) investigation of suspected bone metastases, (2) workup of prosthetic joint infection, (3) differentiation of stress fractures from other lesions, and (4) evaluation of avascular necrosis. You must understand the three-phase bone scan phases, the concept of sensitivity vs specificity, the indications for PET-CT vs bone scan, and the role of labelled WBC scans. A classic trap is not knowing that bone scans can be FALSELY NEGATIVE in myeloma (lytic lesions without osteoblastic response).

Mnemonic

FBDThree-Phase Bone Scan Phases

Flow phase (arterial, immediate)

Dynamic images taken during the first 30-60 seconds after injection. Shows arterial blood flow to the region. Increased flow indicates hypervascularity (infection, tumour, fracture)

Blood pool phase (soft tissue, 5-10 minutes)

Static image at 5-10 minutes showing distribution of tracer in the soft tissue and blood pool. Increased blood pool suggests soft tissue hyperaemia (infection, inflammation)

Delayed phase (bone, 2-4 hours)

Static whole-body images at 2-4 hours after injection. Tc-99m MDP is now bound to hydroxyapatite at sites of active bone turnover. Focal increased uptake indicates osteoblastic activity

Memory Hook:FBD: Flow first (seconds), Blood pool next (minutes), Delayed last (hours) — the three-phase bone scan progresses from seconds to hours.

Mnemonic

FITMAPCauses of Increased Uptake (Hot Spots)

Fracture (stress or acute)

Both acute fractures and stress fractures show increased uptake due to osteoblastic healing response

Infection (osteomyelitis)

Infection stimulates osteoblastic activity — all three phases are positive in acute osteomyelitis

Tumour (primary or metastatic)

Both primary bone tumours and metastases cause increased osteoblastic activity — bone scan is highly sensitive for blastic metastases

Metabolic bone disease (Paget's)

Paget disease causes intensely increased uptake at affected sites. Hyperparathyroidism may cause generalised increased uptake

Arthritis (inflammatory or degenerative)

Both inflammatory arthritis (RA, gout) and degenerative OA cause increased periarticular uptake

Post-surgical/prosthetic

Post-operative healing causes increased uptake for 1-2 years. Normal periprosthetic uptake must be distinguished from infection

Memory Hook:FITMAP: virtually any process causing increased bone turnover produces a hot spot. Bone scan is sensitive but NOT specific.

Mnemonic

MARLCauses of Decreased Uptake (Cold Spots)

Myeloma (no osteoblastic response)

Multiple myeloma produces purely lytic lesions without stimulating osteoblasts — bone scan is often FALSELY NEGATIVE

Avascular necrosis (early)

Before revascularisation, there is no active bone turnover — the infarcted area appears photopenic. Later, a ring of increased uptake surrounds the necrotic area

Rapidly destructive tumour

Very aggressive tumours (e.g., MFH, lymphoma) may destroy bone faster than osteoblastic response occurs

Lesion previously irradiated

Previous radiation therapy decreases vascularity and bone turnover in the treated field

Memory Hook:MARL cold spots: Myeloma, AVN, Rapidly destructive tumour, and irradiated Lesions — these are potential false negatives on bone scan.

Overview

Nuclear medicine imaging in orthopaedics provides unique functional information about biological processes within bone and soft tissue that cannot be obtained from anatomical imaging modalities (radiography, CT, MRI). Unlike anatomical imaging which shows structural changes, nuclear medicine detects PHYSIOLOGICAL changes — increased bone turnover, metabolic activity, white cell accumulation, and blood flow — often before structural abnormalities are visible.

The fundamental principle is that a radioactive tracer (radiopharmaceutical) is administered to the patient, typically intravenously. The tracer is designed to accumulate at sites of specific biological activity. A gamma camera detects the emitted radiation and creates images showing the distribution of the tracer throughout the body. Areas of increased accumulation ('hot spots') indicate increased biological activity, while areas of decreased accumulation ('cold spots') may indicate avascularity, bone destruction, or tissue death.

Key Principle: Functional vs Anatomical

Nuclear medicine shows FUNCTION (how active the bone is), while radiography/CT/MRI show STRUCTURE (what the bone looks like). This is critical because: (1) Functional changes often precede structural changes (e.g., stress fracture on bone scan 1-2 weeks before visible on X-ray). (2) Functional imaging can assess the ENTIRE skeleton in one study (whole-body bone scan for metastatic survey). (3) Functional information helps characterise lesions that look similar on anatomical imaging (differentiating infection from tumour). The trade-off: nuclear medicine has lower spatial resolution and lower specificity than anatomical modalities.

Key Radiotracers

Tc-99m MDP (methylene diphosphonate): binds to hydroxyapatite at sites of osteoblastic activity. The workhorse of skeletal nuclear medicine. F-18 FDG (fluorodeoxyglucose): glucose analogue taken up by metabolically active cells. Used in PET-CT for tumour and infection. In-111 oxine-labelled WBC: labels the patient's own white cells, which then migrate to infection sites. Used for prosthetic joint infection. Ga-67 citrate: accumulates in infection and some tumours. Largely replaced by FDG-PET and WBC scans.

Clinical Imaging

Imaging Gallery

Whole-body bone scintigraphy showing normal and abnormal tracer distribution — Whole-body bone scintigraphy (Tc-99m MDP) showing the distribution of tracer throughout the skeleton. Normal physiological uptake is seen at sites of active bone metabolism. Focal areas of increased uptake (hot spots) indicate pathological bone turnover — the clinical challenge is determining whether these represent metastases, fractures, infection, or degenerative change.Credit: Open-i (NIH) (Open Access (CC BY))

Nuclear medicine imaging demonstrating abnormal uptake patterns in orthopaedic pathology — Nuclear medicine imaging demonstrating abnormal uptake patterns. The interpretation of focal uptake requires correlation with the clinical history, anatomical imaging, and the specific pattern of uptake across the three phases (for three-phase bone scan) to narrow the differential diagnosis.Credit: Open-i (NIH) (Open Access (CC BY))

Systematic Approach

Systematic Bone Scan Interpretation

Systematic Bone Scan Interpretation Framework

Step	Assessment	Key Considerations
1. Technical adequacy	Assess overall image quality, symmetry, and artefacts	Check for injection site extravasation, urinary contamination, and patient motion artefacts
2. Three-phase correlation	Match findings across flow, blood pool, and delayed phases	All 3 positive = infection/inflammation. Delayed-only positive = stress reaction, metastasis, degeneration
3. Focal hot spots	Identify areas of focally increased uptake	Correlate with clinical history: single vs multiple, location (metaphysis = infection, vertebral body = metastasis), intensity
4. Photopenic areas	Identify areas of decreased or absent uptake (cold spots)	Consider: myeloma, AVN, aggressive tumour, irradiated bone — these are false-negative patterns
5. Pattern recognition	Assess the overall distribution pattern	Superscan = diffuse uptake. Linear = fracture. Juxta-articular = arthritis. Random = metastases. Single = infection/tumour
6. Correlate with anatomy	Relate findings to anatomical imaging (radiographs, CT, MRI)	Always correlate nuclear medicine findings with anatomical imaging for definitive diagnosis

Key Studies

Tc-99m MDP Bone Scintigraphy

Mechanism: Tc-99m MDP (methylene diphosphonate) is administered intravenously and distributes via the bloodstream to the skeleton. MDP binds to calcium hydroxyapatite in bone through chemisorption. Uptake is proportional to: (1) local blood flow (delivery of tracer), and (2) osteoblastic activity (binding of tracer). Therefore, any process that increases blood flow OR osteoblastic activity will produce increased uptake.

Standard three-phase protocol:

Phase 1 (Flow): Dynamic images acquired immediately after injection (30-60 seconds). Assesses arterial blood flow to the region of interest.
Phase 2 (Blood Pool): Static image at 5-10 minutes. Shows soft tissue distribution and venous pooling.
Phase 3 (Delayed Bone): Static images at 2-4 hours. By this time, approximately 50% of the tracer has been taken up by bone, and background soft tissue activity has cleared.

Interpretation of three-phase patterns:

All three phases positive: Osteomyelitis, acute fracture, active tumour, CRPS/RSD
Phase 3 positive only: Stress fracture (subacute), metastasis (established), degenerative change
Phase 1 and 2 positive, Phase 3 negative: Cellulitis (soft tissue infection without bone involvement)

Clinical applications in orthopaedics:

Metastatic skeletal survey (sensitivity approximately 95% for blastic metastases)
Occult fracture detection (visible on bone scan 1-2 weeks before radiographic changes)
Stress fracture diagnosis
Paget disease assessment (extent and activity)
Complex regional pain syndrome (CRPS) — diffuse periarticular uptake

Evidence Base

Bone Scan vs PET-CT for Skeletal Metastases

Meta-Analysis

Qu X, Huang X, Yan W, Wu L, Dai K • European Journal of Radiology (2012)

Key Findings:

PET-CT demonstrated pooled sensitivity of 91% and specificity of 96% for bone metastases across tumour types.
Bone scintigraphy had higher sensitivity (95%) but lower specificity (65%) overall.
PET-CT was superior for detecting lytic metastases (particularly renal cell carcinoma, thyroid carcinoma, and myeloma).

Clinical Implication: PET-CT is increasingly the preferred metastatic survey — superior specificity and detection of lytic/mixed lesions. Bone scan remains valuable for blastic metastases (prostate, breast).

Limitation: PET-CT is more expensive and less widely available. Bone scan remains a valid initial screening test.

Source: Qu X et al. Eur J Radiol 2012;81(12):3866-71

Bone Scan False Negatives in Myeloma

Comparative Study

Woolfenden JM, Pitt MJ, Durie BGM, Moon TE • Radiology (1980)

Key Findings:

Bone scintigraphy detected only 50-75% of myeloma lesions identified on skeletal survey radiographs.
The false-negative rate was due to the purely lytic nature of myeloma lesions — no osteoblastic response means no MDP uptake.
Many patients with extensive myeloma disease had normal bone scans.

Clinical Implication: Bone scan should NOT be used to screen for or monitor multiple myeloma — it will miss lesions. Skeletal survey, CT, or FDG-PET are preferred.

Limitation: Historical study but the principle remains valid — bone scan detects osteoblastic activity only.

Source: Woolfenden JM et al. Radiology 1980;134(3):723-8

Bone scan sensitivity depends on the osteoblastic response of the underlying lesion.

Australian Context

In Australia, nuclear medicine services are provided by accredited nuclear medicine departments in public hospitals and private imaging practices. ARPANSA regulates the use of radioactive materials, and nuclear medicine physicians must hold appropriate licences for the handling and administration of radiopharmaceuticals.

Bone scintigraphy is widely available across Australia and is funded for clinical indications including: metastatic workup, unexplained bone pain, suspected stress fracture, assessment of Paget disease activity, and suspected prosthetic joint infection. PET-CT is increasingly available, with most major centres having PET-CT capability, and is funded for tumour staging, restaging, and treatment response monitoring.

RANZCR and the relevant nuclear medicine colleges provide clinical practice guidelines for nuclear medicine imaging in orthopaedic settings. The Australian nuclear medicine workforce includes nuclear medicine physicians, nuclear medicine technologists, and radiation safety officers who work collaboratively to deliver safe and effective nuclear imaging services.

Exam Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOStandard

EXAMINER

"A 65-year-old man with prostate cancer presents with back pain. His PSA has risen. You request a bone scan which shows multiple focal areas of increased uptake in the thoracic and lumbar spine, ribs, and pelvis."

EXCEPTIONAL ANSWER

This bone scan shows a pattern highly consistent with widespread skeletal metastatic disease from prostate cancer. The multiple focal areas of increased Tc-99m MDP uptake in a random distribution affecting the axial skeleton (spine, pelvis) and ribs is the classic pattern of metastatic bone disease. Prostate cancer characteristically produces OSTEOBLASTIC (sclerotic) metastases, which stimulate vigorous osteoblastic activity and are therefore highly conspicuous on bone scan. This is why bone scan has a sensitivity of approximately 95% for prostate cancer metastases. Interpretation considerations: (1) The distribution pattern — multiple random foci in the axial skeleton and ribs — is characteristic of metastatic disease. A solitary focus would require more careful differential diagnosis (benign lesion, degenerative change, old fracture). (2) I would correlate with plain radiographs of the affected areas to look for sclerotic lesions corresponding to the hot spots. (3) I would differentiate this from a 'superscan' pattern (diffuse intense skeletal uptake with faint/absent kidney and soft tissue activity), which indicates even more extensive disease or metabolic bone disease. (4) In this patient with known prostate cancer and rising PSA, the clinical context makes metastatic disease overwhelmingly likely. The role of bone scan in metastatic assessment: (1) Highly sensitive for osteoblastic metastases (prostate, breast) — 95% sensitivity. (2) Provides whole-body skeletal survey in a single examination. (3) Can be used for monitoring treatment response (reduction in uptake intensity). (4) LIMITATIONS: poor specificity (hot spots can represent degeneration, fracture, Paget disease), may miss purely lytic metastases (renal cell, myeloma), and lacks anatomical detail. For the latter reasons, PET-CT is increasingly preferred for comprehensive metastatic staging.

KEY POINTS TO SCORE

Multiple random focal hot spots in axial skeleton = classic metastatic pattern

Prostate cancer = osteoblastic metastases = highly conspicuous on bone scan

Bone scan sensitivity approximately 95% for blastic metastases but poor specificity

Superscan = extreme diffuse uptake with absent kidneys/soft tissue

PET-CT is increasingly preferred for comprehensive staging due to better specificity

COMMON TRAPS

✗Not correlating with clinical context (isolated bone scan findings are non-specific)

✗Not knowing that bone scan can miss lytic metastases (myeloma, renal cell)

✗Confusing a metastatic pattern with the superscan pattern

✗Not requesting correlative anatomical imaging (radiographs, CT)

VIVA SCENARIOStandard

EXAMINER

"You are investigating a 60-year-old woman with a painful total knee replacement at 3 years post-operatively. A bone scan shows increased periarticular uptake. The three-phase study is positive in all three phases."

EXCEPTIONAL ANSWER

This is a classical and tricky clinical scenario. A bone scan at 3 years after total knee replacement showing periarticular uptake positive in all three phases raises the concern for prosthetic joint infection. However, interpretation requires caution: (1) Normal post-operative bone scan findings: Bone scan around a total knee replacement can remain positive for up to 1-2 years after surgery due to normal healing and remodelling. At 3 years, persistent or new uptake is more concerning. (2) Three-phase positivity: All three phases positive (increased flow, increased blood pool, increased delayed uptake) suggests an active inflammatory or infectious process — NOT just simple mechanical loosening or normal healing. This pattern is highly sensitive for infection but poorly specific. Differential diagnosis in this context: infection (PJI), loosening with active bone remodelling, CRPS, heterotopic ossification, or stress fracture/periprosthetic fracture. Additional investigation: I would request a combined labelled white cell (WBC) scan with bone marrow scan. This is the nuclear medicine gold standard for PJI. The patient's white cells are harvested, labelled with In-111 oxine or Tc-99m HMPAO, and reinjected. If the WBC scan shows focal uptake around the prosthesis that is DISCORDANT with the bone marrow scan (i.e., WBC accumulation at sites where there is no corresponding marrow activity on the sulphur colloid scan), this is highly specific for infection (specificity 90-95%). Concordant uptake (WBC and marrow in the same distribution) indicates normal marrow displacement by the prosthesis and is NOT infection. Other complementary investigations: serum CRP and ESR, synovial fluid aspiration with cell count, differential, and culture — these are essential components of the PJI workup alongside nuclear imaging.

KEY POINTS TO SCORE

Bone scan at 3 years post-TKR with three-phase positivity is concerning for PJI

Normal post-operative bone scan uptake should resolve by 1-2 years

Bone scan alone is sensitive but NOT specific for PJI (specificity only 33%)

Combined WBC/marrow scan is the nuclear medicine gold standard for PJI (specificity 90-95%)

Discordant WBC uptake (WBC positive, marrow negative) indicates infection

COMMON TRAPS

✗Diagnosing infection based on bone scan alone (poor specificity for PJI)

✗Not knowing the WBC/marrow scan combination technique

✗Not knowing that normal bone scan uptake persists for 1-2 years post-arthroplasty

✗Not including serum inflammatory markers and aspiration in the workup

VIVA SCENARIOChallenging

EXAMINER

"An examiner asks: 'A 45-year-old patient presents with widespread bone pain. You notice a bone scan showing diffusely increased skeletal uptake with virtually no renal or soft tissue activity. What is the diagnosis?'"

EXCEPTIONAL ANSWER

This is the 'superscan' pattern (also called the 'beautiful bone scan' ironically because the image quality appears excellent with very bright bones and no background). It is characterised by: (1) Diffusely increased skeletal uptake — intense, homogeneous tracer accumulation throughout the entire skeleton. (2) Absent or markedly reduced renal activity — the kidneys, which normally show prominent uptake (because Tc-99m MDP is renally excreted), are faint or invisible. (3) Markedly reduced soft tissue background — the bones appear very bright relative to the dark background. The mechanism: When the entire skeleton has massively increased osteoblastic activity, the bones extract such a high proportion of the injected Tc-99m MDP that there is very little remaining in the blood and soft tissue for renal excretion. Essentially, the skeleton is acting as a 'sink' for the tracer. Differential diagnosis of the superscan: (1) Widespread skeletal metastatic disease — the most important cause. Prostate and breast cancer are the most common malignancies producing this pattern due to their osteoblastic metastatic behaviour. (2) Metabolic bone disease — particularly renal osteodystrophy (secondary hyperparathyroidism in renal failure) and primary hyperparathyroidism. The generalized increase in bone turnover produces diffuse uptake. (3) Paget disease (polyostotic) — if affecting a large proportion of the skeleton. (4) Myelofibrosis — diffuse marrow replacement with fibrosis stimulates osteoblastic reaction. Clinical approach: I would correlate with the clinical history (known malignancy? renal function? calcium/phosphate?), check serum calcium, phosphate, ALP, and PTH, and request plain radiographs/CT of selected regions to distinguish metastatic disease from metabolic bone disease. Metastases will show focal lesions on CT, while metabolic bone disease will show diffuse osteopaenia with cortical resorption.

KEY POINTS TO SCORE

Superscan: diffuse intense skeletal uptake + absent kidney/soft tissue activity

Mechanism: skeleton extracts nearly all tracer, leaving little for renal excretion

Differential: widespread metastases (prostate, breast), metabolic bone disease (renal osteodystrophy), Paget disease

NOT a normal scan — despite appearing 'beautiful', it is always pathological

Correlate with biochemistry (Ca, PO4, ALP, PTH) and anatomical imaging

COMMON TRAPS

✗Misinterpreting the superscan as a 'normal' high-quality scan

✗Not recognising the absent kidney activity as the key diagnostic clue

✗Only considering metastases (metabolic bone disease is an important differential)

✗Not requesting biochemistry to differentiate metastatic from metabolic causes

Nuclear Medicine in Orthopaedics — Exam Day Reference

High-Yield Exam Summary

Three-Phase Bone Scan (FBD)

•Phase 1 (Flow): arterial vascularity — first 30-60 seconds
•Phase 2 (Blood pool): soft tissue — 5-10 minutes
•Phase 3 (Delayed bone): osteoblastic activity — 2-4 hours
•All three positive: infection, acute fracture, active tumour
•Phase 3 only positive: stress fracture, degenerative, metastasis

Hot Spots (FITMAP)

•Fracture, Infection, Tumour, Metabolic, Arthritis, Post-surgical
•Sensitive (95%) but NOT specific — virtually any bone turnover shows up

Cold Spots (MARL — False Negatives)

•Myeloma (no osteoblastic response — bone scan NEGATIVE)
•AVN (early avascular phase before revascularisation)
•Rapidly destructive tumour (outpaces osteoblastic response)
•Lesion previously irradiated

Prosthetic Joint Infection

•Bone scan: sensitive but NOT specific for PJI (specificity 33%)
•Combined WBC/marrow scan: gold standard for PJI (sensitivity 83%, specificity 94%)
•Discordant WBC uptake (WBC+/marrow-) = infection
•Normal bone scan uptake after arthroplasty persists 1-2 years

PET-CT vs Bone Scan

•PET-CT: better specificity, detects lytic lesions, soft tissue disease
•Bone scan: better sensitivity for blastic metastases, cheaper, more available
•PET-CT increasingly preferred for comprehensive tumour staging
•Bone scan remains valid for prostate and breast cancer screening

Systematic Bone Scan Interpretation

Systematic Bone Scan Interpretation Framework

Step	Assessment	Key Considerations
1. Technical adequacy	Assess overall image quality, symmetry, and artefacts	Check for injection site extravasation, urinary contamination, and patient motion artefacts
2. Three-phase correlation	Match findings across flow, blood pool, and delayed phases	All 3 positive = infection/inflammation. Delayed-only positive = stress reaction, metastasis, degeneration
3. Focal hot spots	Identify areas of focally increased uptake	Correlate with clinical history: single vs multiple, location (metaphysis = infection, vertebral body = metastasis), intensity
4. Photopenic areas	Identify areas of decreased or absent uptake (cold spots)	Consider: myeloma, AVN, aggressive tumour, irradiated bone — these are false-negative patterns
5. Pattern recognition	Assess the overall distribution pattern	Superscan = diffuse uptake. Linear = fracture. Juxta-articular = arthritis. Random = metastases. Single = infection/tumour
6. Correlate with anatomy	Relate findings to anatomical imaging (radiographs, CT, MRI)	Always correlate nuclear medicine findings with anatomical imaging for definitive diagnosis

Tc-99m MDP Bone Scintigraphy

Standard three-phase protocol:

Phase 1 (Flow): Dynamic images acquired immediately after injection (30-60 seconds). Assesses arterial blood flow to the region of interest.

Phase 2 (Blood Pool): Static image at 5-10 minutes. Shows soft tissue distribution and venous pooling.

Phase 3 (Delayed Bone): Static images at 2-4 hours. By this time, approximately 50% of the tracer has been taken up by bone, and background soft tissue activity has cleared.

Interpretation of three-phase patterns:

All three phases positive: Osteomyelitis, acute fracture, active tumour, CRPS/RSD

Phase 3 positive only: Stress fracture (subacute), metastasis (established), degenerative change

Phase 1 and 2 positive, Phase 3 negative: Cellulitis (soft tissue infection without bone involvement)

Clinical applications in orthopaedics:

Metastatic skeletal survey (sensitivity approximately 95% for blastic metastases)

Occult fracture detection (visible on bone scan 1-2 weeks before radiographic changes)

Stress fracture diagnosis

Paget disease assessment (extent and activity)

Complex regional pain syndrome (CRPS) — diffuse periarticular uptake

Bone Scan vs PET-CT for Skeletal Metastases

Meta-Analysis

Qu X, Huang X, Yan W, Wu L, Dai K • European Journal of Radiology (2012)

Key Findings:

PET-CT demonstrated pooled sensitivity of 91% and specificity of 96% for bone metastases across tumour types.
Bone scintigraphy had higher sensitivity (95%) but lower specificity (65%) overall.
PET-CT was superior for detecting lytic metastases (particularly renal cell carcinoma, thyroid carcinoma, and myeloma).

Limitation: PET-CT is more expensive and less widely available. Bone scan remains a valid initial screening test.

Source: Qu X et al. Eur J Radiol 2012;81(12):3866-71

Bone Scan False Negatives in Myeloma

Comparative Study

Woolfenden JM, Pitt MJ, Durie BGM, Moon TE • Radiology (1980)

Key Findings:

Bone scintigraphy detected only 50-75% of myeloma lesions identified on skeletal survey radiographs.
The false-negative rate was due to the purely lytic nature of myeloma lesions — no osteoblastic response means no MDP uptake.
Many patients with extensive myeloma disease had normal bone scans.

Clinical Implication: Bone scan should NOT be used to screen for or monitor multiple myeloma — it will miss lesions. Skeletal survey, CT, or FDG-PET are preferred.

Limitation: Historical study but the principle remains valid — bone scan detects osteoblastic activity only.

Source: Woolfenden JM et al. Radiology 1980;134(3):723-8

Bone scan sensitivity depends on the osteoblastic response of the underlying lesion.

Nuclear Medicine in Orthopaedics

Nuclear Medicine in Orthopaedics

Nuclear Medicine in Orthopaedics

Nuclear Medicine Studies in Orthopaedics

Critical Must-Knows

Examiner's Pearls

Exam Warning

FBDThree-Phase Bone Scan Phases

FITMAPCauses of Increased Uptake (Hot Spots)

MARLCauses of Decreased Uptake (Cold Spots)

Overview

Key Principle: Functional vs Anatomical

Key Radiotracers

Clinical Imaging

Imaging Gallery

Systematic Approach

Systematic Bone Scan Interpretation

Systematic Bone Scan Interpretation Framework

Key Studies

Tc-99m MDP Bone Scintigraphy

F-18 FDG PET-CT

Labelled White Cell Scans

Evidence Base

Bone Scan vs PET-CT for Skeletal Metastases

Bone Scan False Negatives in Myeloma

WBC Scan for Prosthetic Joint Infection

Three-Phase Bone Scan for Osteomyelitis

FDG-PET for Spinal Infection

Australian Context

Exam Viva Scenarios

Nuclear Medicine in Orthopaedics — Exam Day Reference

Three-Phase Bone Scan (FBD)

Hot Spots (FITMAP)

Cold Spots (MARL — False Negatives)

Prosthetic Joint Infection

PET-CT vs Bone Scan

Nuclear Medicine in Orthopaedics

Nuclear Medicine in Orthopaedics

Nuclear Medicine in Orthopaedics

Nuclear Medicine Studies in Orthopaedics

Critical Must-Knows

Examiner's Pearls

Exam Warning

FBDThree-Phase Bone Scan Phases

FITMAPCauses of Increased Uptake (Hot Spots)

MARLCauses of Decreased Uptake (Cold Spots)

Overview

Key Principle: Functional vs Anatomical

Key Radiotracers

Clinical Imaging

Imaging Gallery

Systematic Approach

Systematic Bone Scan Interpretation

Systematic Bone Scan Interpretation Framework

Key Studies

Tc-99m MDP Bone Scintigraphy

F-18 FDG PET-CT

Labelled White Cell Scans

Evidence Base

Bone Scan vs PET-CT for Skeletal Metastases

Bone Scan False Negatives in Myeloma

WBC Scan for Prosthetic Joint Infection

Three-Phase Bone Scan for Osteomyelitis

FDG-PET for Spinal Infection

Australian Context

Exam Viva Scenarios

Nuclear Medicine in Orthopaedics — Exam Day Reference

Three-Phase Bone Scan (FBD)

Hot Spots (FITMAP)

Cold Spots (MARL — False Negatives)

Prosthetic Joint Infection

PET-CT vs Bone Scan