CIM Case: Paediatric Acute Haematogenous Osteomyelitis

Clinical Scenario

Patient: 5-year-old boy Presentation: 4-day history of right leg pain and limp, fever for 3 days, refusing to weight-bear for 24 hours Relevant history: Previously well, no recent trauma, no overseas travel, vaccinations up to date, no prior infections or hospitalisations, no sick contacts, no known immunodeficiency Examination findings:

• Temperature 38.9°C
• Heart rate 120 bpm, respiratory rate 22
• Unwell appearing, holding leg still
• Right leg held in slight flexion
• Warmth and swelling over proximal tibia
• Exquisite point tenderness at tibial metaphysis (2cm below knee)
• No joint effusion palpable
• Refusing to weight-bear
• No skin changes initially (becoming erythematous during admission)
• Lymphadenopathy: small inguinal nodes palpable
• Rest of examination normal

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Investigations Provided

Laboratory Results

Imaging

Image 1: Plain Radiograph Right Tibia (AP and Lateral)

Radiological features:

• Deep soft tissue swelling at proximal tibial metaphysis
• Periosteal elevation along proximal tibial diaphysis (early)
• Subtle metaphyseal lucency
• No cortical destruction yet (early disease)
• Joint space preserved
• No fracture

Image 2: MRI Right Tibia with Contrast (if performed)

MRI findings:

• T1: Low signal in proximal tibial metaphysis
• T2/STIR: High signal marrow oedema extending into diaphysis
• Post-contrast: Rim-enhancing fluid collection (abscess) 3cm × 2cm
• Subperiosteal abscess with periosteal elevation
• Pyomyositis of posterior tibial musculature
• No transphyseal extension
• No knee joint effusion or septic arthritis

Image 3: Microbiology

Blood culture (48 hours):

• Gram-positive cocci in clusters
• Staphylococcus aureus identified
• Susceptibilities pending

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Questions & Model Answers

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Key Teaching Points

Pattern Recognition

This pattern suggests Acute Haematogenous Osteomyelitis:

• Fever + limp + refusing to weight-bear
• Point tenderness at metaphysis
• Elevated WCC, CRP, ESR
• MRI: marrow oedema ± abscess

Classic Metaphyseal Location:

• Sluggish blood flow in metaphyseal sinusoids
• Bacteria seed and multiply
• Physeal vessels (neonates) allow joint involvement
• In children >18 months, physis acts as barrier

Critical Management Points

1. S. aureus is the commonest organism - start flucloxacillin empirically
2. MRSA is increasingly common - know local prevalence, add vancomycin if risk factors
3. MRI is the gold standard - don't wait for X-ray changes
4. Surgical drainage if abscess present - antibiotics alone won't work
5. CRP is the best marker - should fall within 48-72 hours of adequate treatment
6. Red man syndrome is NOT an allergy - slow the infusion, pre-medicate, continue vancomycin
7. Growth disturbance risk - follow until skeletal maturity if physis involved

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Common Examiner Follow-ups

Q: "What is the role of bone scan versus MRI?"

MRI is preferred in most centres. Bone scan is useful for screening multiple sites.

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Q: "When would you use oral antibiotics from the start?"

Oral-first therapy (emerging evidence):

• Uncomplicated osteomyelitis
• No sepsis or systemic toxicity
• Reliable family/patient
• Good oral intake
• Organism known and susceptible
• Close follow-up available

Traditional approach remains IV-first in most centres for initial disease control.

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Q: "What if cultures are negative?"

Negative cultures occur in 30-50% of cases:

• May be due to prior antibiotics
• Consider Kingella kingae (fastidious, needs specific culture)
• Consider PCR/molecular testing
• Continue empirical therapy if clinical picture fits
• Consider atypical organisms if not responding (TB, fungal, Bartonella)

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Q: "What about neonatal osteomyelitis?"

Key differences in neonates (<3 months):

• Different organisms (Group B Strep, E. coli, Candida in addition to S. aureus)
• Transphyseal vessels allow spread to epiphysis and joint
• Often multifocal
• May present non-specifically (irritability, pseudoparalysis)
• Higher rate of septic arthritis
• More aggressive treatment required
• Higher risk of growth disturbance

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Related Topics

• Septic Arthritis in Children
• MRSA Infections
• Chronic Osteomyelitis
• Antibiotic Therapy in Orthopaedics
• Physeal Injuries
• Limb Length Discrepancy
• Vancomycin Pharmacology