Paediatric Osteomyelitis
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
Investigations Provided
Laboratory Results
| Test | Result | Normal Range | Interpretation |
|---|---|---|---|
| Haemoglobin | 115 g/L | 110-140 g/L | Normal |
| WCC | 18.5 ×10⁹/L | 5-15 ×10⁹/L | ELEVATED |
| Neutrophils | 14.2 ×10⁹/L | 2-8 ×10⁹/L | ELEVATED |
| Platelets | 450 ×10⁹/L | 150-400 ×10⁹/L | Mildly elevated (reactive) |
| CRP | 185 mg/L | <5 mg/L | MARKEDLY ELEVATED |
| ESR | 65 mm/hr | <10 mm/hr | ELEVATED |
| Blood cultures | Pending | - | Await result |
| Procalcitonin | 2.8 ng/mL | <0.5 ng/mL | ELEVATED (bacterial infection) |
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
Questions & Model Answers
Describe the imaging findings and explain what investigations you would order and why.
What is the microbiology of paediatric osteomyelitis and what empirical antibiotics would you start?
The MRI shows a subperiosteal abscess. What are the indications for surgical drainage and how would you perform it?
Three days post-operatively, the patient has ongoing fevers and CRP rises to 280. What do you do now?
The organism is confirmed as MRSA. You start vancomycin. The child develops facial flushing and a red rash on the upper body during the infusion. What is happening and how do you manage it?
What are the potential complications of paediatric osteomyelitis and how do you monitor for them?
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
- S. aureus is the commonest organism - start flucloxacillin empirically
- MRSA is increasingly common - know local prevalence, add vancomycin if risk factors
- MRI is the gold standard - don't wait for X-ray changes
- Surgical drainage if abscess present - antibiotics alone won't work
- CRP is the best marker - should fall within 48-72 hours of adequate treatment
- Red man syndrome is NOT an allergy - slow the infusion, pre-medicate, continue vancomycin
- Growth disturbance risk - follow until skeletal maturity if physis involved
Common Examiner Follow-ups
Q: "What is the role of bone scan versus MRI?"
| Feature | Bone Scan | MRI |
|---|---|---|
| Sensitivity | 85-90% | >95% |
| Specificity | Lower (many false positives) | Higher |
| Timing | Positive at 24-48 hours | Positive at 24 hours |
| Radiation | Yes | No |
| Anatomic detail | Poor | Excellent |
| Abscess detection | Poor | Excellent |
| Best use | Multifocal disease, skeletal survey | Single site, surgical planning |
MRI is preferred in most centres. Bone scan is useful for screening multiple sites.
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.
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)
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
Related Topics
- Septic Arthritis in Children
- MRSA Infections
- Chronic Osteomyelitis
- Antibiotic Therapy in Orthopaedics
- Physeal Injuries
- Limb Length Discrepancy
- Vancomycin Pharmacology