• "Developmental Dysplasia of the Hip"
• "Colles' fracture"
• "Osteomyelitis"
• "Compartment syndrome"
• "Carpal tunnel syndrome"

---

COMPARTMENT SYNDROME

Comprehensive Orthopaedic Exam Notes

Sources: Campbell's Operative Orthopaedics 15th Ed (2026), Bailey & Love's Short Practice of Surgery 28th Ed, Miller's Review of Orthopaedics 9th Ed, Current Surgical Therapy 14th Ed, Recent PubMed Reviews (2021-2026)

---

1. DEFINITION

"Compartment syndrome is raised pressure in a fascial compartment to a level that compromises tissue perfusion." - Bailey & Love, 28th Ed

---

2. CLASSIFICATION

COMPARTMENT SYNDROME
│
├── ACUTE Compartment Syndrome (ACS)
│   ├── Post-traumatic (most common)
│   ├── Post-ischaemia / Reperfusion
│   └── Non-traumatic
│
└── CHRONIC / EXERTIONAL (CECS)
    └── Recurrent exertion-related pressure increase

---

3. ANATOMY - COMPARTMENTS

3a. LEG (4 compartments) - MOST COMMON SITE

The anterior and deep posterior compartments are the most commonly involved.

3b. FOREARM (3 compartments)

3c. THIGH (3 compartments)

3d. OTHER SITES

• Foot (9 compartments - most commonly from calcaneus fractures, incidence ~17%)
• Hand
• Buttock/Gluteal
• Arm
• Shoulder
• Lumbar paraspinous muscles

---

4. AETIOLOGY / CAUSES

Causes by Mechanism

CAUSES OF COMPARTMENT SYNDROME
│
├── DECREASED COMPARTMENT SIZE (external compression)
│   ├── Tight plaster casts or dressings
│   ├── Circumferential burns (especially 3rd degree)
│   ├── Tight closure of fascial defects
│   └── Pneumatic antishock garments
│
└── INCREASED COMPARTMENT CONTENT (volume increase)
    ├── Fractures ← Most common cause (70%)
    ├── Soft-tissue trauma / contusions (23%)
    ├── Arterial injury / ischaemia-reperfusion
    ├── IV fluid extravasation (IV contrast under pressure)
    ├── Spontaneous haematoma (anticoagulants/bleeding disorders)
    ├── Limb compression during altered consciousness
    └── Burns (oedema)

Key fact for exams: Fractures are the most common cause (70%), with tibial shaft fractures being the single highest-risk fracture type. Compartment syndrome CAN occur with open fractures - do not be falsely reassured.

---

5. PATHOPHYSIOLOGY

INITIAL INSULT
(trauma / compression / ischaemia)
        ↓
Increased tissue pressure in closed compartment
        ↓
↓ Capillary perfusion pressure
(perfusion = MAP - compartment pressure)
        ↓
Local tissue hypoxia → Cellular anoxia
        ↓
Histamine release → ↑ Capillary permeability
        ↓
Protein-rich fluid leaks into interstitium → MORE OEDEMA
        ↓
VICIOUS CYCLE: More pressure → More ischaemia
        ↓
Irreversible muscle necrosis (begins at 4-6 hours)
Nerve ischaemia (type C fibres most sensitive first)
        ↓
Rhabdomyolysis → Myoglobinuria → Acute Tubular Necrosis
        ↓
Late: Volkmann's ischaemic contracture (untreated)

• Significant muscle necrosis occurs when intracompartmental pressure (ICP) >30 mmHg sustained for >8 hours
• Higher pressures cause irreversible damage in shorter timeframes
• Exercise alone can increase muscle volume by 20%, raising CECS risk

---

6. CLINICAL FEATURES - THE "6 Ps"

Mnemonic: 6Ps (in order of appearance)

Critical exam point: Pain out of proportion + Pain on passive stretch = hallmark early signs. Paralysis, pallor, and pulselessness are LATE signs - if you wait for these, irreversible damage has occurred.

Pulses are PRESENT in compartment syndrome - their absence is a sign of arterial occlusion, which is a different diagnosis. Do not use presence of pulses to exclude compartment syndrome.

Specific Compartment Signs

---

7. DIAGNOSIS

7a. Clinical Diagnosis

• Pain out of proportion
• Increasing pain despite adequate analgesia
• Pain on passive stretch of muscles in the compartment
• Tense, woody compartment

7b. Compartment Pressure Measurement

• Diagnostic uncertainty
• Altered level of consciousness (head injury, sedation, intubation)
• Polytrauma victims
• Uncooperative or unreliable patients

7c. Pressure Thresholds for Fasciotomy

AAOS Clinical Practice Guidelines: Fasciotomy when ΔP (diastolic BP - compartment pressure) is ≤ 30 mmHg.

Measure multiple sites near (but not in) the fracture, in all compartments of the affected limb.

CPK elevation and myoglobinuria are late markers of tissue destruction - should NOT be used to establish diagnosis.

---

8. ALGORITHM FOR MANAGEMENT

SUSPECTED COMPARTMENT SYNDROME
          │
    ┌─────┴──────────────────────────┐
    ↓                                ↓
Unequivocally                Patient not alert /
positive clinical             Polytrauma /
findings                      Inconclusive findings
    │                                │
    │                    Compartment pressure measurement
    │                         │              │
    │                      > 30 mmHg      < 30 mmHg
    │                         │              │
    │                         │         Continuous monitoring
    │                         │         + serial examination
    │                         │         ↓ (if ΔP ≤ 30 → ↓)
    └─────────────────────────┘
                  │
            FASCIOTOMY
                  │
         ┌────────┴────────┐
    Within 6-8 h         > 12 h
    Best outcomes        ↑ Complications

---

9. TREATMENT

9a. Initial / Emergency Measures

1. Remove all constrictive dressings and split casts to the skin - reduces ICP by 50-85%
2. Position limb at level of heart (NOT elevated) - elevation reduces arterial inflow without improving venous drainage, worsening ischaemia
3. Maintain systemic BP (optimise perfusion)
4. High-flow O2
5. Do NOT delay - if clinical diagnosis is clear → immediate fasciotomy

Do NOT elevate the limb above heart level in compartment syndrome - this is a common mistake.

9b. Fasciotomy - Definitive Treatment

LOWER LEG FASCIOTOMY

• Releases all 4 compartments
• Anterolateral incision: 20-25 cm, between fibular shaft and tibial crest
  • Anterior compartment released first
  • Then lateral compartment through same incision
• Posteromedial incision: 20-25 cm, 1-2 cm posterior to medial border of tibia
  • Superficial posterior compartment released
  • Detach soleus from tibia to release deep posterior compartment

• Lateral incision in line with fibula, from fibular head to 3-4 cm proximal to lateral malleolus
• Releases all 4 compartments but technically more demanding
• Risk of injury to superficial peroneal nerve

FOREARM FASCIOTOMY

• Volar: Curved incision from antecubital fossa to palm (Henry's approach) - releases superficial + deep volar
• Dorsal: Straight dorsal incision - releases dorsal compartment
• Carpal tunnel release if hand involved
• Consider mobile wad (BR, ECRL, ECRB) release

THIGH FASCIOTOMY (Tarlow et al.)

• Lateral incision from intertrochanteric line to lateral epicondyle
• Incise iliotibial band
• Release lateral intermuscular septum → releases anterior and posterior compartments
• Medial incision only if medial compartment pressure elevated

9c. Post-Fasciotomy Wound Management

Fasciotomy wound LEFT OPEN
        ↓
Vacuum-Assisted Closure (VAC) device applied
(reduces oedema, promotes granulation)
        ↓
Re-inspect at 48-72 hours
        ↓
Delayed Primary Closure (when swelling subsides) OR
Split-Thickness Skin Graft (if cannot close primarily)

Never attempt early primary closure - this may cause recurrence of compartment syndrome.

---

10. CHRONIC EXERTIONAL COMPARTMENT SYNDROME (CECS)

Features

Diagnostic Criteria (Pedowitz Criteria)

Differential Diagnosis of CECS

• Stress fracture
• Nerve entrapment syndrome
• Popliteal artery entrapment syndrome
• Vascular claudication
• Lumbosacral radiculopathy
• Neurogenic claudication
• Myopathy / infection / tumour

Treatment of CECS

CECS TREATMENT
│
├── NONOPERATIVE (1st line)
│   ├── Activity modification / relative rest
│   ├── NSAIDs
│   ├── Physiotherapy (stretching, strengthening)
│   ├── Orthotics
│   ├── Forefoot running technique (↓ ICP, 65-75% success)
│   └── Manual therapy
│
└── OPERATIVE (if non-op fails)
    ├── Fasciotomy of affected compartment(s)
    ├── Anterior fasciotomy: 80-90% success rate
    └── Deep posterior fasciotomy: 50-70% success rate

---

11. COMPLICATIONS

If Compartment Syndrome is Missed / Delayed Treatment

Complications of Fasciotomy Itself

• Wound infection
• Haematoma
• Nerve injury (superficial peroneal nerve at risk in single-incision technique) | Hypertrophic / ugly scarring
• Skin graft morbidity
• Inadequate decompression (missed compartments)

---

12. SPECIAL SITUATIONS

Reperfusion Compartment Syndrome

• After revascularisation of acutely ischaemic limb (prolonged ischaemia >6 hours)
• Prophylactic fasciotomy recommended at time of revascularisation
• More severe the ischaemia, more likely reperfusion CS to develop
• Monitor CPK; if rhabdomyolysis: aggressive IV fluids targeting urine output >100 mL/hr until CPK <5000 U/L; urine alkalisation with bicarbonate

Compartment Syndrome with Open Fractures

• Do not assume fasciotomy is unnecessary with open fractures
• Skin opening does NOT decompress fascial compartments
• High index of suspicion required

Compartment Syndrome in Tibial Plateau Fractures

• High-energy patterns (Schatzker V/VI) carry high risk
• Monitor closely post-op
• Recent review 2022 (PMID: 34799021) highlights tibial plateau fractures as a high-risk group

Compartment Syndrome After Arthroplasty

• Uncommon but well-described after knee and hip arthroplasty
• Review 2022 (PMID: 34799019) in Orthop Clin North Am

---

13. VOLKMANN'S ISCHAEMIC CONTRACTURE

This is the classic end-stage complication of untreated forearm/hand compartment syndrome - very high-yield for exams.

Pathology

Clinical Grading (Seddon's Classification)

---

14. QUICK REVISION TABLE - HIGH-YIELD FACTS

---

15. RECENT EVIDENCE (2021-2026)

---

16. EXAM WRITING TIPS

1. Define → Classify → Anatomy
2. Aetiology → Pathophysiology
3. Clinical features (early vs late) + special clinical tests
4. Diagnosis (clinical + pressure measurement + thresholds)
5. Management (emergency measures → fasciotomy technique → wound care)
6. Complications (of the syndrome and of fasciotomy)
7. Special scenarios (CECS, reperfusion, open fractures)
8. Volkmann's contracture

• "Why do we NOT elevate the limb?" - Elevation decreases arterial inflow without significantly increasing venous outflow
• "Which nerve is most sensitive to compartment ischaemia?" - Type C non-myelinated fibres (sensory)
• "Can compartment syndrome occur with open fractures?" - YES
• "What is the ΔP formula?" - Diastolic BP minus Compartment Pressure ≤ 30 mmHg = fasciotomy
• "What are Pedowitz criteria?" - For CECS diagnosis

---

---

SLIPPED CAPITAL FEMORAL EPIPHYSIS (SCFE / SUFE)

Comprehensive Orthopaedic Exam Notes

---

1. DEFINITION

Correct anatomical terminology: It is technically the metaphysis (femoral neck) that displaces anterolaterally and superiorly relative to the fixed epiphysis - since the epiphysis is held in the acetabulum. The term "slipped epiphysis" is therefore a misnomer, but universally used.

• Commonest hip disorder of adolescence
• Incidence: ~5 per 100,000 population
• Peak age: 10-16 years, puberty
• Boys more than girls (2:1), though peak occurs earlier in girls (due to earlier puberty)

---

2. AETIOLOGY AND RISK FACTORS

Mechanical / Physiological Factors

GROWTH SPURT
     ↓
Physeal changes during puberty:
• ↑ Obliquity of physis (more vertical → ↑ shear forces)
• Thinning of perichondrial ring
• Widening of physis
• ↓ Neck-shaft angle
• ↓ Size of epiphyseal tubercle
• ↑ Growth hormone → weakens hypertrophic zone of physis
     ↓
Weakened physis subjected to torsional/shear forces
     ↓
SCFE

Risk Factors (Campbell's Box 38.8)

Endocrine rule for exams: If SCFE occurs in an atypical patient (age <10 or >16, underweight, bilateral), always investigate for an endocrine cause (especially hypothyroidism).

---

3. PATHOLOGY

• The slip occurs through the hypertrophic zone of the physis (zone of provisional calcification) - same as Salter-Harris Type I fracture
• The epiphysis displaces posteromedially and inferiorly
• Metaphysis (neck) moves anterolaterally and superiorly
• Results in:
  • Increased anteversion lost → retroversion
  • "Cam" type femoroacetabular impingement (FAI) in chronic slips
  • Disruption of blood supply in severe/unstable slips → AVN

---

4. CLINICAL FEATURES

Symptoms

Signs

Key exam point: Drehmann's sign - obligatory external rotation of hip on flexion - is pathognomonic of SCFE.

---

5. INVESTIGATIONS

X-Rays (Mandatory)

Critical point: Frog-leg lateral is more sensitive than AP. Do NOT accept only an AP view in a child with hip/knee pain.

Key Radiological Signs on AP Pelvis

• A line drawn along the superior border of the femoral neck (Klein's line) normally intersects the lateral part of the femoral epiphysis
• In SCFE, the epiphysis is displaced medially/inferiorly → Klein's line fails to intersect the epiphysis (or intersects less than normal)

• Double density (sclerosis) at the metaphysis on AP view
• Due to overlap of the posteriorly displaced epiphysis with the neck

Southwick Slip Angle (Lateral view)

• Measured on frog-leg lateral view
• Normal neck-shaft angle ~12°
• Mild: <30°, Moderate: 30-60°, Severe: >60°

AP Pelvis showing Klein's line bilaterally

MRI

• Useful for preslip (physeal oedema before visible displacement)
• Also for diagnosis in inconclusive X-rays
• Can diagnose contralateral preslip

CT

• Useful to assess degree of slip and plan osteotomy

---

6. CLASSIFICATION

6a. By Duration of Symptoms (Traditional)

Traditional classification is descriptive but has limited prognostic value (Campbell's).

6b. By Stability - Loder Classification (Most Important)

Most widely used and prognostically important classification. An unstable SCFE is a surgical emergency.

Satisfactory results: 96% stable vs 47% unstable (Loder et al.).

6c. By Severity of Slip

6d. Preslip

• Symptomatic physeal weakening without visible displacement
• Widening/irregularity of physis on X-ray
• Physeal oedema on MRI

---

7. MANAGEMENT

Algorithm

SCFE CONFIRMED
       │
  ┌────┴────┐
STABLE    UNSTABLE (emergency - cannot walk)
  │              │
  ↓              ↓
In Situ     Urgent surgery within 24 h
Fixation    Gentle repositioning under GA
(1 cannulated  + Capsulotomy to reduce tamponade
screw)         + Fixation with 1-2 cannulated screws
  │
  ↓
MILD SLIP (Stable)      MODERATE/SEVERE SLIP (Stable)
   │                            │
In situ fixation         In situ fixation OR
(90%+ success)           Modified Dunn procedure
                         (controversial - risk of AVN)
                                │
                     If deformity causes FAI after healing:
                         Osteochondroplasty / Osteotomy

7a. In Situ Pinning (Standard Treatment)

1. Patient supine on fracture table
2. Fluoroscopic guidance (C-arm)
3. Percutaneous single cannulated screw (4.5 or 7.3 mm)
4. Entry point on anterior thigh, adjusted for degree of slip
5. Screw placed perpendicular to physis, in center-center position of femoral head
6. Screw tip should be ≥4 mm from subchondral bone (prevents penetration)
7. Capsulotomy for acute/unstable slips (reduces intracapsular tamponade on blood supply)
8. Confirm non-penetration with multiple fluoroscopic views

• Single screw fixation is standard (Aronson & Carlson)
• 2 screws for acute unstable slips
• Screw perpendicular to physis (not to femoral neck axis) - this is important
• Do NOT attempt forceful reduction in stable/chronic slips

7b. Modified Dunn Procedure (Leunig, Slongo & Ganz - Technique 38.22)

• Lateral decubitus position; Gibson approach
• Trochanteric flip osteotomy
• Surgical dislocation of the femoral head (safe dislocation preserving blood supply via MFCA - deep branch)
• Neck osteotomy and realignment of epiphysis
• Fixation with K-wires/screws
• Trochanteric reattachment

7c. Other Surgical Options

The closer the osteotomy is to the deformity (CORA = at the physis), the better the correction but higher the AVN risk. Intertrochanteric osteotomy trades some correction for lower risk.

---

8. BILATERAL SCFE

Prophylactic Pinning of Contralateral Hip

• Age: females <10 years; males <12 years
• Endocrine abnormalities
• Unreliable follow-up
• Posterior sloping angle >12 degrees (Fig 38.119)
• Open triradiate cartilage
• Low vitamin D
• Hypothyroidism / Severe obesity / Diabetes mellitus
• History of human growth hormone use

Kocher decision analysis: observation is optimal in most, but prophylactic fixation in high-risk patients or poor follow-up.

---

9. COMPLICATIONS

Complications of SCFE Itself

Complications of Surgery

---

10. BLOOD SUPPLY OF FEMORAL HEAD (Key for understanding AVN)

Main blood supply to femoral head in adolescent:
→ LATERAL EPIPHYSEAL VESSELS
  (terminal branches of MEDIAL FEMORAL CIRCUMFLEX ARTERY - deep branch)
  
These vessels run:
- Posterior and superior to femoral neck
- Enter epiphysis at the epiphyseal tubercle
- Supply the lateral 2/3 of femoral head

In SCFE:
- Stable slips: vessels stretch but remain intact → low AVN risk
- Unstable slips: vessels avulsed/compressed → high AVN risk (~47%)
- Forced reduction: can further compromise these vessels → DO NOT REDUCE

---

11. SCFE AND FAI

• Residual deformity after SCFE → prominent anterior femoral neck (metaphysis) = cam-type FAI
• During flexion and internal rotation: cam lesion impinges on acetabular rim → cartilage damage → early OA
• Management: Osteochondroplasty (after physeal closure) - arthroscopic or open
• Modified Dunn procedure aims to prevent this by anatomical realignment

---

12. QUICK REVISION TABLE

---

13. EXAM WRITING TIPS

1. Definition + anatomy (what actually slips and why the name is a misnomer)
2. Incidence + epidemiology
3. Aetiology (mechanical + endocrine/predisposing factors)
4. Pathology (which zone of physis, direction of slip)
5. Classification (Duration: acute/chronic/acute-on-chronic; Loder: stable/unstable; Grade: mild/mod/severe)
6. Clinical features (pain at knee - Hilton's law, Drehmann sign, ER deformity)
7. Investigations (AP + frog lateral; Klein's line; Blanch sign; Southwick angle)
8. Treatment (based on Loder classification + severity)
9. Complications (AVN, chondrolysis, FAI, OA)
10. Bilateral SCFE and prophylactic pinning

• "A 12-year-old boy presents with knee pain - what do you do?" → Examine the hip; take AP + frog lateral pelvis
• "What is Drehmann's sign?" → Obligatory ER on hip flexion
• "What is Klein's line?" → Line along superior femoral neck; fails to transect head in SCFE
• "What is the single most important classification?" → Loder (stable vs unstable)
• "What is the AVN risk in unstable SCFE?" → ~47%
• "Why not reduce a chronic stable slip?" → High AVN risk with manipulation; outcomes of in situ fixation are good
• "What is the modified Dunn procedure?" → Surgical dislocation + neck osteotomy + realignment; preserves MFCA blood supply

---

Note: Turek's Orthopaedics and Tuli's Textbook of Orthopaedics were not available in the digital library. Classic concepts from these texts are well incorporated in Campbell's and are covered throughout these notes. If you have specific Tuli or Turek content in mind, please let me know and I can address those points from my knowledge base.

---

DIAGNOSTIC IMAGING IN ORTHOPAEDICS

Comprehensive University Exam Notes

Sources: Campbell's Operative Orthopaedics 15th Ed (2026) | Grainger & Allison's Diagnostic Radiology | Miller's Review of Orthopaedics 9th Ed | Standard Physics of Medical Imaging

---

1. PLAIN RADIOGRAPHY (X-RAYS)

Principles

• Uses ionising radiation (electromagnetic waves, wavelength 0.01-10 nm)
• Differential absorption of X-rays by tissues creates contrast
• Denser tissues (bone) absorb more → appear white (radio-opaque)
• Less dense tissues (air, fat, soft tissue) absorb less → appear dark (radiolucent)

Five Radiographic Densities (Memorise in order)

Air (black) → Fat (dark grey) → Water/Soft tissue (grey) 
         → Bone/Calcium (white) → Metal (bright white)

Standard Views in Orthopaedics

What to Assess on X-Ray (Systematic Approach)

ABCDES Mnemonic:
A - Alignment (fracture, dislocation, deformity)
B - Bone density/texture (osteoporosis, sclerosis, lysis)
C - Cortex (breach, periosteal reaction)
D - Density/soft tissue (calcification, swelling)
E - Erosions/joint space
S - Soft tissues (gas, foreign bodies, swelling)

Periosteal Reactions

Radiation Doses (Important for Radiation Safety)

ALARA Principle: As Low As Reasonably Achievable - fundamental principle of radiation safety. Always justify (benefit > risk), optimise dose, and limit exposure.

---

2. COMPUTED TOMOGRAPHY (CT)

Principles

• Uses X-rays rotating around patient (ionising radiation)
• Hounsfield units (HU) - universal scale of tissue density
• Images reconstructed by computer as cross-sectional slices
• Multiplanar reconstruction (MPR): coronal, sagittal, 3D from axial data

Hounsfield Unit Scale

Air: -1000 HU          ←  (black)
Fat: -100 to -50 HU
Water: 0 HU
Soft tissue: +20 to +80 HU
Bone: +700 to +3000 HU  ←  (white)
Metal: >+3000 HU (causes artefact/streak)

CT Windows

Indications in Orthopaedics

CT Arthrography

• CT + intra-articular contrast
• Useful when MRI contraindicated (metalwork)
• Assesses cartilage, labrum, ligaments

Advantages vs Disadvantages

---

3. MAGNETIC RESONANCE IMAGING (MRI)

Physical Principles

• Uses strong magnetic field (1.5 T or 3 T) + radiofrequency (RF) pulses - NO ionising radiation
• Protons (hydrogen nuclei) in body water/fat align with magnetic field
• RF pulse disturbs alignment; when RF turned off, protons "relax" back → emit signal
• Two relaxation times:
  • T1 relaxation (longitudinal/spin-lattice) - how fast protons recover along B0 field
  • T2 relaxation (transverse/spin-spin) - how fast protons lose coherence with each other

MRI Sequences - THE MOST HIGH-YIELD TOPIC

Core Sequences

Signal Intensities - "Bright on T1" Mnemonic: "FAT CASH"

F - Fat
A - Avasuclar necrosis (early subacute, proteinaceous fluid)
T - Thrombosis (subacute haematoma, methaemoglobin)
C - Calcium (chronic calcific deposits)
A - Adrenal adenoma
S - Slow-flowing blood
H - High protein fluid (mucinous)

STIR Sequence - Dedicated Section (High-Yield for Exams)

Inversion pulse (180° RF) applied
          ↓
Protons inverted; then recovery starts
          ↓
At time = TI (inversion time = ~150 ms for fat, = "tau")
Fat signal passes through ZERO → apply 90° readout pulse HERE
          ↓
Fat signal = 0 (nulled/suppressed)
Water/oedema signal = HIGH (bright)

• Fat appears DARK (suppressed)
• Fluid/oedema appears VERY BRIGHT
• Most sensitive sequence for detecting bone marrow oedema
• NOT affected by field inhomogeneity (unlike frequency-selective fat sat)
• Can be used at any field strength
• Disadvantage: lower SNR than T2 fat-sat; longer acquisition time

Gradient Echo Sequences (GRE)

• Fast acquisition
• Sensitive to magnetic susceptibility → detects blood products, calcification (blooming artefact)
• Used for: cartilage assessment (3D GRE), haemorrhage detection

Contrast-Enhanced MRI (Gadolinium)

• Gadolinium (paramagnetic) shortens T1 → enhances on T1-weighted images
• Indications:
  • Tumour characterisation (vascular, necrotic areas)
  • Infection (abscess rim enhancement)
  • Post-op: recurrent tumour vs scar
  • Arthrography (direct MR arthrogram)
  • AVN - perfusion assessment
• Caution: Nephrogenic systemic fibrosis (NSF) in renal failure; eGFR <30 → avoid

MRI Appearances of Common Orthopaedic Conditions

MRI - Contraindications

• Cardiac pacemaker (older models) - most modern pacemakers are now MRI conditional
• Cochlear implants (most)
• Intraocular metallic foreign body
• Intraorbital metal fragments (history of metalworking)
• Certain intracranial aneurysm clips

• Total hip/knee replacement (significant artefact - use MARS protocol)
• Pregnancy (1st trimester - avoid if possible; safe overall)
• Claustrophobia (use open MRI or sedation)
• Haemodialysis shunts, stents (check MRI safety)

MARS MRI (Metal Artefact Reduction Sequences) - used for imaging around metallic implants (e.g., failed arthroplasty, ALVAL, ARMD detection around hip resurfacing)

MRI Indications in Orthopaedics

---

4. ULTRASOUND (USG)

Principles

• Uses high-frequency sound waves (2-18 MHz) - NO ionising radiation
• Sound reflects differently at tissue interfaces → creates image
• Real-time, dynamic imaging
• Doppler mode: blood flow assessment

Properties

Orthopaedic Indications

Advantages vs Disadvantages

---

5. RADIONUCLIDE BONE SCAN (Scintigraphy)

Principles

• Radiopharmaceutical: Technetium-99m (Tc-99m) labelled methylene diphosphonate (MDP)
• Tc-99m MDP concentrates where there is active bone turnover (osteoblastic activity)
• Gamma camera detects gamma rays emitted as Tc-99m decays
• Half-life of Tc-99m: 6 hours
• Whole-body imaging possible

Three-Phase Bone Scan

Interpretation

Important: Multiple myeloma produces COLD spots (lytic, minimal osteoblast response) - use PET-CT or whole-body MRI instead.

Indications in Orthopaedics

SPECT (Single Photon Emission CT)

• 3D version of bone scan
• Better localisation of lesion (e.g., pars interarticularis in spondylolysis)
• SPECT-CT combines anatomical (CT) + functional (SPECT) data

---

6. PET SCAN AND PET-CT

Principles

• Positron Emission Tomography
• Radiotracer: FDG (Fluorine-18-labelled fluorodeoxyglucose) - most common
• FDG is a glucose analogue → taken up by metabolically active (high glucose uptake) cells
• Cancer cells (high metabolism) concentrate FDG
• Positrons from F-18 decay annihilate with electrons → two 511 keV gamma rays at 180° → detected by PET camera
• PET-CT combines metabolic (PET) + anatomical (CT) information
• Half-life of F-18: ~110 minutes

Indications in Orthopaedics

PET vs Bone Scan

Other PET Tracers in Orthopaedics

---

7. DUAL-ENERGY X-RAY ABSORPTIOMETRY (DEXA)

Principles

• Uses two X-ray beams of different energies
• Differential absorption by bone vs soft tissue calculated
• Provides Bone Mineral Density (BMD) in g/cm²
• Very low radiation dose (~0.001-0.01 mSv)

Sites Measured

1. Lumbar spine (L1-L4) - PA projection preferred
2. Proximal femur (Femoral neck + Total hip)
3. Forearm (1/3 radius) - when spine/hip not assessable
4. Whole body composition

Scores

WHO Classification (T-score, Postmenopausal Women + Men >50)

Each SD decrease in BMD = ~2-2.5x increase in fracture risk.

DEXA Indications

DEXA Limitations

Trabecular Bone Score (TBS) - software adjunct to DEXA; assesses bone microarchitecture; improved fracture risk prediction beyond BMD alone.

---

8. ARTHROGRAPHY

Principles

• Injection of contrast agent (iodinated or gadolinium) into a joint under image guidance
• Distends joint capsule → improves visualisation of intra-articular structures

Types

MR Arthrography - Specific Indications

Direct vs Indirect Arthrography

---

9. IMAGE-GUIDED BIOPSY

Indications

• Bone or soft tissue tumour biopsy
• Suspected osteomyelitis / deep infection
• Intervertebral disc biopsy (discitis)

Guidance Modalities

Principles of Biopsy in Tumours (Critical for Exams)

The biopsy tract must pass through the planned surgical field so it can be excised en bloc with the tumour.

• Plan with surgeon before biopsy
• Avoid contaminating compartments
• Avoid neurovascular structures
• Core needle biopsy preferred over FNAC (provides tissue architecture)
• Send for histology + microbiology + special stains
• Poorly planned biopsy can change operability and worsen prognosis (Mankin's study - classic reference)

---

10. RADIATION SAFETY (Must Know)

Principles

Dose Limits (ICRP)

Radiation Units

Tissue Radiosensitivity (Most to Least Sensitive)

Bone marrow / Lymphoid > Gonads > Lens > Thyroid > Breast 
         > Lung > Bone > Muscle > Connective tissue > Nerve

Protection Measures

In Orthopaedic Theatre

• Lead aprons worn by all staff during fluoroscopy
• Surgeon stands at least 90 cm from X-ray source when possible
• C-arm positioned with X-ray tube below the table (not above) to reduce scatter to surgeon
• Hands out of beam whenever possible
• Dosimetry badges worn at collar level (above apron)

---

11. COMPARISON TABLE: MODALITY SELECTION IN ORTHOPAEDICS

"Which Imaging to Choose?"

---

12. MRI vs CT - CLASSIC EXAM QUESTION

---

13. QUICK REVISION TABLE - HIGH-YIELD EXAM FACTS

---

14. PREVIOUS UNIVERSITY QUESTION ANSWERS

Q1: MRI vs CT - Compare and Contrast

Q2: STIR Sequence - Explain in Detail

Q3: Bone Scan - Indications

Q4: DEXA - What is it, How is it interpreted?

Q5: PET Scan in Orthopaedics

---

---

What's in These Notes

1. Plain X-Ray - Principles, 5 radiographic densities, periosteal reactions (Codman's triangle, sunburst, onion skin), ABCDES systematic approach
2. CT - Hounsfield units with full scale, windowing (bone/soft tissue/lung windows), all orthopaedic indications, CT arthrography
3. MRI - Full physics (T1/T2 relaxation), all sequences with signal intensity tables, dedicated STIR section with mechanism explained step by step, gadolinium indications/contraindications, MARS protocol, appearances of all major orthopaedic conditions
4. STIR vs T2 Fat-Sat - Side-by-side comparison table (high-yield)
5. Ultrasound - Graf's DDH screening, dynamic imaging, guided procedures
6. Bone Scan - 3-phase technique, hot vs cold spots, ALL orthopaedic indications, SPECT-CT
7. PET-CT - F-18 FDG mechanism, Ewing sarcoma (directly cited from Campbell's 15e), response monitoring, PET vs bone scan comparison table
8. DEXA - T-score/Z-score, WHO classification, all indications, limitations (osteophyte artefact)
9. Arthrography - Direct vs indirect MRA, joint-specific indications
10. Image-Guided Biopsy - Critical biopsy tract principle (Mankin's study)
11. Radiation Safety - ALARA, ICRP dose limits, theatre C-arm positioning
12. MRI vs CT Comparison - Dedicated table for the classic exam question
13. Modality Selection Table - All clinical scenarios with first/second choice
14. Previous University Questions - Direct answers to all 5 listed past questions

---

DIAGNOSTIC IMAGING IN ORTHOPAEDICS

Comprehensive University Exam Notes

Sources: Campbell's Operative Orthopaedics 15e (2026) | Rockwood & Green's Fractures in Adults 10e (2025) | Grainger & Allison's Diagnostic Radiology | Miller's Review of Orthopaedics 9e

---

1. PLAIN RADIOGRAPHY (X-RAYS)

Basic Principles

• Uses ionising electromagnetic radiation (wavelength 0.01–10 nm)
• Differential absorption of X-rays by different tissues creates image contrast
• Denser tissue → more absorption → appears white (radio-opaque)
• Less dense tissue → less absorption → appears dark (radiolucent)

Five Radiographic Densities (Dense to Least Dense)

METAL      →  Bright white (implants, foreign bodies)
BONE/CA²⁺  →  White (cortical > cancellous)
SOFT TISSUE →  Grey
FAT        →  Dark grey
AIR        →  Black

Minimum X-Ray Requirements (Rockwood & Green 10e)

"A true AP and lateral radiograph of the injured bone with inclusion of the proximal and distal joints is the minimum required medical imaging."

Systematic Reading: ABCDES

A  - Alignment       → Fracture line, dislocation, angulation, shortening
B  - Bone density    → Osteoporosis, sclerosis, lytic lesion, periosteal reaction
C  - Cartilage/joint space → Narrowing, erosions, loose bodies
D  - Density changes → Calcification, gas, soft tissue swelling, fat pads
E  - Edges (cortex)  → Breach, cortical destruction, periosteal new bone
S  - Soft tissues    → Swelling, foreign bodies, gas (infection/open injury)

Periosteal Reactions - Exam Favourite

Special Radiographic Signs to Know

Radiation Doses (Must Know for Exam)

---

2. COMPUTED TOMOGRAPHY (CT)

Principles

• Rotating X-ray tube + detector array around patient (ionising radiation)
• Computer reconstructs cross-sectional images from multiple projections
• Uses Hounsfield Unit (HU) scale - universal tissue density measurement
• Multiplanar Reconstruction (MPR): coronal/sagittal/3D from axial data
• 3D CT: invaluable for pre-operative planning of complex fractures

Hounsfield Unit Scale

Air            : -1000 HU ← (black)
Fat            : -100 to -50 HU
Water          :    0 HU
Soft tissue    :  +20 to +80 HU
Acute blood    :  +50 to +80 HU
Cortical bone  : +700 to +3000 HU ← (white)
Metal implant  : >+3000 HU (streak artefact)

CT Windows - Essential Knowledge

Indications in Orthopaedics

(Rockwood & Green 10e): "In modern trauma practice, total-body contrast CT will often include CT angiography of badly injured limbs providing rapid detailed cross-sectional imaging."

CT-Guided Procedures

• Biopsy: Deep lesions (spine, pelvis, chest wall) - safe, accurate, relatively inexpensive
• Aspiration: Deep joints, paravertebral abscess
• Limitation: reduced diagnostic readability in patients already on antibiotics

CT Arthrography

• CT after intra-articular iodinated contrast injection
• Indications: MRI contraindicated (metalwork), cartilage assessment, labral tears
• Can image after metal implants (less artefact than MRI)

---

3. MAGNETIC RESONANCE IMAGING (MRI)

Physical Principles

• Uses strong magnetic field (1.5 T or 3.0 T) + radiofrequency (RF) pulses
• NO ionising radiation
• Hydrogen protons (abundant in body water and fat) align with magnetic field
• RF pulse perturbs alignment; signal emitted as protons return to equilibrium
• Two independent relaxation times measured:
  • T1 (longitudinal/spin-lattice): time for protons to realign with main field
  • T2 (transverse/spin-spin): time for proton coherence to decay

The MRI Sequences - HIGHEST YIELD TOPIC

Signal Behaviour at a Glance

T1-Weighted

• Short TR, Short TE
• Fluid = dark; Fat = bright
• Best for: anatomy, fat, fatty marrow, AVN (marrow changes), subacute haemorrhage, gadolinium enhancement (fat-suppressed post-contrast)
• Mnemonic - "T1 = Tissue (anatomy is clearest)"

T2-Weighted

• Long TR, Long TE
• Fluid = bright; Fat = intermediate-bright
• Best for: pathology, fluid, oedema, disc degeneration (discs normally T2-bright when hydrated)
• Mnemonic - "T2 = fluiD Two (fluid is bright)"

STIR Sequence - DEDICATED HIGH-YIELD SECTION

Mechanism (Must be able to explain in exam)

Step 1: 180° inversion RF pulse applied
        → All protons inverted (pointing opposite to B₀ field)
        ↓
Step 2: Protons begin T1 recovery (returning to alignment with B₀)
        ↓
Step 3: At time = TI (Inversion Time ~150 ms for fat):
        Fat protons are passing through ZERO magnetisation
        ↓
Step 4: 90° readout pulse applied at exactly this moment
        → Fat signal = ZERO (nulled / suppressed)
        → Water/oedema: still recovering → gives HIGH SIGNAL
        ↓
RESULT:  Fat = DARK (black)
         Oedema / fluid = VERY BRIGHT (white)

Gradient Echo (GRE) Sequences

• Fast acquisition (short TR/TE, flip angle <90°)
• Magnetic susceptibility sensitive → blood products and calcification appear very dark ("blooming")
• 3D GRE (e.g., DESS, VIBE) for cartilage assessment
• T2* GRE: detects haemosiderin (pigmented villonodular synovitis - PVNS)

MRI Contrast - Gadolinium

• Bone tumour: vascular vs necrotic zone differentiation
• Infection: rim enhancement of abscess wall
• Post-operative: recurrent tumour vs scar tissue (tumour enhances, scar does not)
• Direct MR arthrography (intra-articular gadolinium)
• AVN: perfusion assessment of femoral head
• Synovitis: pannus enhancement in RA

MRI Contraindications

• Cochlear implants (most older models)
• Intraocular metallic foreign body
• Intraorbital metal fragments (esp. occupational history - metalworking)
• Certain intracranial aneurysm clips (ferromagnetic)
• Cardiac pacemakers (older models; most modern devices are now "MRI Conditional")

• Metallic orthopaedic implants (artefact; use MARS protocol)
• 1st trimester pregnancy (avoid gadolinium; MRI itself considered safe when necessary)
• Claustrophobia (open MRI / sedation)

MARS MRI (Metal Artefact Reduction Sequences) = Modified imaging protocols to reduce artefact around metallic implants. Used for periprosthetic pathology: ALVAL (aseptic lymphocyte-dominated vasculitis), ARMD (adverse reaction to metal debris) around metal-on-metal hips, periprosthetic infection assessment.

MRI Indications in Orthopaedics

---

4. ULTRASOUND (USG)

Principles

• High-frequency sound waves (2–18 MHz) - NO ionising radiation
• Sound reflects at tissue interfaces → images created from returning echoes
• Real-time, dynamic imaging - unique advantage over other modalities
• Doppler mode: colour and power Doppler for blood flow
• Portable: point-of-care use in OPD, bedside, and theatre

Frequency Selection

Key Artefact - Anisotropy

• Tendons appear dark (hypoechoic) when NOT perpendicular to probe
• Mimic pathology if not recognised
• Solution: angle probe perpendicular to tendon

Orthopaedic Indications

Graf Classification for DDH (Ultrasound)

---

5. RADIONUCLIDE BONE SCAN (SCINTIGRAPHY)

Principles

• Radiopharmaceutical: Tc-99m MDP (methylene diphosphonate)
• Tc-99m selectively accumulates on bone mineral matrix surface → depicts osteoblastic activity
• Gamma camera detects gamma rays from Tc-99m decay
• Half-life of Tc-99m: 6 hours (convenient - image same day)
• Whole-body imaging in a single acquisition

Three-Phase Bone Scan

(Rockwood & Green 10e): "In low-grade infection, the third phase may be the only indication of an infection as the first two phases are commonly negative." "If all three phases of the bone scan are negative, it essentially excludes infection."

Interpretation

Multiple Myeloma = COLD on bone scan → use PET-CT or whole-body MRI instead.

Orthopaedic Indications

Leucocyte (WBC) Scintigraphy (Rockwood & Green 10e)

• Autologous WBCs labelled with Indium-111 (¹¹¹In-oxyquinoline) or Tc-99m-HMPAO
• Two imaging time points: 3–4 hrs and 20–24 hrs
• Increase in size/intensity over time = infection; decrease = inflammation / marrow uptake
• Used for: periprosthetic joint infection, chronic osteomyelitis, diabetic foot

SPECT / SPECT-CT (Rockwood & Green 10e)

• 3D version of planar bone scan
• (Rockwood & Green 10e): "Newer systems like SPECT collect images from different angles around the patient creating a 3D image, which leads to higher contrast and improved sensitivity."
• SPECT-CT (hybrid): combines functional SPECT + anatomical CT → near-perfect correlation of pathophysiology with anatomy
• Indications: osteoid osteoma (target sign), spondylolysis (pars stress reaction), periprosthetic loosening

---

6. PET SCAN AND PET-CT

Principles (Rockwood & Green 10e)

• Positron Emission Tomography
• Tracer: F-18 FDG (Fluorine-18-labelled fluorodeoxyglucose)
• FDG = glucose analogue → taken up proportional to metabolic activity
• Cancer cells (high glycolysis = Warburg effect) → high FDG uptake
• Positron (β⁺) emitted → annihilates with electron → two 511 keV gamma rays at exactly 180° → detected by coincidence detection
• Half-life of F-18: ~110 minutes
• PET-CT = fusion of metabolic (PET) + anatomical (CT) data
• (Rockwood & Green 10e): "Software developments support the use of hybrid camera systems...allowing for an almost perfect correlation of pathophysiologic with anatomical features."

Indications in Orthopaedics

PET vs Bone Scan - Classic Exam Comparison

Other PET Tracers

---

7. DUAL-ENERGY X-RAY ABSORPTIOMETRY (DEXA)

Principles (Grainger & Allison - full section read)

• Two X-ray beams at different energies → differential absorption by bone vs soft tissue
• Calculates BMD (Bone Mineral Density) = areal measurement in g/cm²
• Radiation dose: 1–6 µSv (extremely low; 1000x less than chest X-ray)
• Accuracy: 3–8%; Precision (CV%): <1% for spine and total femur

DEXA Images of Spine, Hip, and Wrist

Sites Measured

T-score and Z-score

Z-score < -2.0 = "below the expected range for age" (does NOT mean osteoporosis diagnosis)

WHO Diagnostic Classification (T-score)

Each 1 SD decrease in BMD = 2–2.5x increase in fracture risk

Indications for DEXA

DEXA Pitfalls / Limitations (Very High-Yield)

(Grainger & Allison): "Osteoporosis cannot be defined using DXA BMD alone in premenopausal women, men younger than 50 and children."

Vertebral Fracture Assessment (VFA)

• Additional lateral DXA scan of spine
• Identifies prevalent vertebral fractures (T4-L4)
• Radiation dose: up to 50 µSv (still very low)
• Indicates high fracture risk even if T-score borderline

FRAX (Fracture Risk Assessment Tool)

• WHO tool combining BMD + clinical risk factors
• Calculates 10-year probability of major osteoporotic fracture and hip fracture
• Used to guide treatment decisions

---

8. ARTHROGRAPHY

Principles

• Injection of contrast (iodinated contrast or gadolinium) into a joint under imaging guidance
• Distends joint capsule → improves visualisation of intra-articular structures

Types of Arthrography

MR Arthrography - Gold Standard

• Dilute gadolinium injected directly into joint under fluoroscopic guidance
• Joint distended → improved delineation of intra-articular structures
• Contrast = bright on T1 fat-suppressed images

Joint-Specific Indications

---

9. IMAGE-GUIDED BIOPSY

Indications

• Bone or soft tissue tumour
• Suspected osteomyelitis / deep infection (culture + histology)
• Vertebral/disc biopsy (discitis)
• Lymph node biopsy

Guidance Modalities

CRITICAL RULE FOR TUMOUR BIOPSY (Exam Essential)

BIOPSY TRACT RULE:
The biopsy tract MUST pass THROUGH the planned surgical
excision field so it can be EXCISED EN BLOC with the tumour.

A poorly planned biopsy that contaminates a different
compartment or neurovascular bundle can:
  → Make a resectable tumour UNRESECTABLE
  → Change limb-salvage to AMPUTATION
  → Worsen prognosis significantly

(Mankin et al., JBJS 1982 - classic study showing that
biopsy errors change management in 10-19% of cases)

Always plan biopsy with the treating orthopaedic oncologist before the procedure.

Biopsy Technique Principles

• Core needle biopsy preferred over FNAC (provides tissue architecture for histology)
• Send specimens for: histology + microbiology (aerobic, anaerobic, TB, fungal) + special stains
• Haemostasis important (avoid tumour cell spill)
• CT-guided biopsy is safe, accurate, relatively inexpensive (Rockwood & Green 10e)
• Limitation: reduced accuracy in patients already on antibiotics (for infection)

---

10. RADIATION SAFETY

ALARA Principle

1. Justification - benefit must outweigh risk before any exposure
2. Optimisation - minimise dose (ALARA)
3. Dose limitation - regulatory annual limits

ICRP Annual Dose Limits

Radiation Units

Tissue Radiosensitivity (Most → Least Sensitive)

Bone marrow & lymphoid tissue > Gonads > Lens of eye 
> Thyroid > Breast > Lung > Bone > Muscle > Nerve

Protection Principles: Time, Distance, Shielding

Radiation Safety in Orthopaedic Theatre

C-ARM POSITIONING RULE:
  X-ray tube BELOW the table (not above)
  → Reduces scatter radiation dose to surgeon's hands and face

SURGEON POSITION:
  Stand at least 90 cm from X-ray source when possible
  Hands OUT of primary beam
  Lead apron + thyroid shield mandatory
  
PULSED FLUOROSCOPY:
  Use instead of continuous fluoroscopy
  Significantly reduces dose (can reduce by >50%)

---

11. COMPARISON TABLES (Exam Essentials)

Modality Selection Guide

MRI vs CT - The Classic Exam Question

---

12. QUICK REVISION TABLE - ALL HIGH-YIELD FACTS

---

13. ANSWER TEMPLATES FOR PREVIOUS UNIVERSITY QUESTIONS

Q1: Compare MRI and CT in Orthopaedics

Q2: STIR Sequence - Write a note

Q3: Bone Scan - Indications

Q4: DEXA

Q5: PET Scan in Orthopaedics

---

---

What's New in This Version (vs Previous Session)

---

📋 NOTES ALREADY COMPILED — COMPLETE CHAPTER GUIDE

---

Section 1 — PLAIN RADIOGRAPHY

• X-ray principles (ionising radiation, differential absorption)
• Five radiographic densities (Air → Fat → Soft tissue → Bone → Metal)
• Standard views for every body part (table)
• ABCDES systematic reading approach
• Periosteal reactions (Codman's triangle, sunburst, onion skin, solid) — with associations
• Special radiographic signs (Looser's zones, rugger jersey, bone-in-bone, pencilling)
• Radiation dose table for all modalities

---

Section 2 — CT

• Hounsfield Unit scale (Air -1000 → Bone +3000)
• CT windows (bone/soft tissue/lung — settings given)
• All orthopaedic indications with rationale
• CT arthrography, CT-guided biopsy
• "Span, scan, plan" protocol (Rockwood & Green 10e)

---

Section 3 — MRI ⭐ Most Detailed Section

• Physical principles (T1, T2 relaxation)
• Signal intensity table for all sequences + all tissues
• T1, T2, STIR explained individually
• STIR - full mechanism step-by-step, TI = 150 ms, fat suppression by inversion recovery
• STIR vs T2 Fat-Sat comparison table
• STIR orthopaedic indications (stress fractures, AVN, marrow oedema, near metal)
• Gradient Echo, Gadolinium (NSF risk, eGFR <30), MARS protocol
• MRI appearances of common conditions (AVN double-line sign, chordoma T2 bright, etc.)
• MRI contraindications (absolute and relative)
• Full indications table

---

Section 4 — ULTRASOUND

• Principles, frequency, anisotropy artefact
• Graf's method for DDH — alpha angle classification table (Type I–IV)
• Full indications table (rotator cuff, Achilles, DDH, guided injections, nerve entrapment)

---

Section 5 — BONE SCAN ⭐ High-Yield

• Tc-99m MDP, half-life 6 hours, osteoblastic mechanism
• Three-phase scan — timing, what each phase shows (table + image from Rockwood & Green)
• Hot vs cold spots with causes
• Multiple myeloma = COLD (use PET-CT instead)
• Full orthopaedic indications
• Leucocyte (WBC) scintigraphy — Indium-111
• SPECT and SPECT-CT

---

Section 6 — PET-CT ⭐ High-Yield

• F-18 FDG mechanism, half-life 110 min, Warburg effect
• Direct textbook quote on Ewing sarcoma from Campbell's 15e
• Indications (Ewing, myeloma, response, infection, recurrence)
• PET vs Bone Scan comparison table (8 parameters)
• Other tracers (NaF-18, Ga-68 PSMA)

---

Section 7 — DEXA ⭐ High-Yield

• Introduced 1987; two X-ray beams; areal BMD in g/cm²
• Radiation dose = 1–6 µSv (negligible)
• Sites: L1–L4 spine, proximal femur, distal 1/3 radius
• T-score vs Z-score — what each compares to, when to use
• WHO classification (Normal >-1.0 / Osteopenia -1 to -2.5 / Osteoporosis ≤-2.5)
• Full indications table (steroids, fragility fracture, postmenopausal, men >70)
• Pitfalls — osteophytes/artefacts = falsely elevated BMD
• Textbook DEXA image (spine, hip, wrist with BMD-age graphs)
• VFA and FRAX

---

Section 8 — ARTHROGRAPHY

• Fluoroscopic, CT, direct MRA, indirect MRA — compared
• Joint-specific indications (shoulder SLAP/Bankart, hip labrum, wrist TFCC, ankle OCD, knee post-meniscectomy)

---

Section 9 — IMAGE-GUIDED BIOPSY

• CT-guided vs ultrasound-guided vs fluoroscopy
• Critical biopsy tract rule (Mankin's study) — must be in surgical excision field

---

Section 10 — RADIATION SAFETY

• ALARA principle
• ICRP annual dose limits (worker 20 mSv, public 1 mSv, foetus 1 mSv)
• Gray vs Sievert vs Becquerel
• Tissue radiosensitivity order
• C-arm tube BELOW the table, inverse square law (double distance = ¼ dose)

---

Sections 11–13 — COMPARISON TABLES + EXAM TEMPLATES

• Modality selection for 25 clinical scenarios
• MRI vs CT full comparison table (12 parameters)
• Quick revision table — 50 high-yield facts
• Answer templates for all 5 past university questions (MRI vs CT / STIR / Bone scan / DEXA / PET)

---