Paediatric Acute Osteomyelitis
CIM Case: Paediatric Acute Osteomyelitis
Clinical Scenario
Patient: 7-year-old boy Presentation: 5-day history of right leg pain, fever (38.8°C), and refusal to weight-bear Relevant history: Previously well child, no recent trauma, no immunocompromise. Attends school swimming. Examination findings:
- Tender, swollen distal tibia with overlying erythema and warmth
- Unable to actively dorsiflex ankle due to pain
- Knee and hip movements painless (important to exclude septic arthritis)
- No draining sinus
Investigations Provided
Laboratory Results
| Test | Result | Normal Range | Interpretation |
|---|---|---|---|
| Hb | 118 g/L | 115-135 g/L | Normal |
| WCC | 18.5 ×10⁹/L | 5-13 ×10⁹/L | ↑ Leucocytosis |
| Neutrophils | 14.2 ×10⁹/L | 1.5-8.0 ×10⁹/L | ↑ Left shift |
| Platelets | 420 ×10⁹/L | 150-400 ×10⁹/L | ↑ Reactive thrombocytosis |
| CRP | 186 mg/L | <5 mg/L | ↑↑ Significantly elevated |
| ESR | 68 mm/hr | <10 mm/hr | ↑↑ Elevated |
| Blood cultures | Pending | Negative | Awaiting result |
| Procalcitonin | 2.4 ng/mL | <0.5 ng/mL | ↑ Suggests bacterial infection |
Imaging
Image 1: AP and Lateral Radiograph of Right Tibia
Radiological features:
- Soft tissue swelling overlying distal tibial metaphysis
- Loss of normal fat planes
- Subtle periosteal thickening along distal tibial shaft
- No obvious lytic lesion (early presentation - bone changes take 10-14 days)
- Growth plates appear normal
Image 2: MRI Right Tibia (T1, T2/STIR, Post-contrast)
MRI findings:
- Extensive bone marrow oedema in distal tibial metaphysis (low T1, high STIR signal)
- 12mm subperiosteal abscess collection along anterolateral tibia
- Periosteal elevation with rim enhancement
- Inflammatory changes in adjacent soft tissues
- Intact physis with no transphyseal spread
- No associated joint effusion (excludes concurrent septic arthritis)
Questions & Model Answers
Describe the investigation findings
What is the differential diagnosis?
What further investigations and initial management would you request?
Given the subperiosteal abscess, how would you manage this patient surgically?
Blood cultures grow MRSA. After starting vancomycin, the child develops facial flushing and an erythematous rash. What is the diagnosis and management?
At 72 hours, the child has persistent fevers and CRP has risen to 280 mg/L. What are your concerns and actions?
Key Teaching Points
Pattern Recognition
This pattern suggests Acute Haematogenous Osteomyelitis:
- Child with fever, localised bone pain, and refusal to weight bear
- Metaphyseal location (vascular anatomy predisposes this area)
- Elevated inflammatory markers (CRP >100, leucocytosis)
- MRI: marrow oedema with periosteal reaction ± abscess
Distinguish from Septic Arthritis:
- Septic arthritis: joint effusion, severely restricted ROM in all planes
- Osteomyelitis: metaphyseal tenderness, may have preserved joint movement
- Can coexist (especially hip) - always image the adjacent joint
Distinguish from Ewing Sarcoma:
- Ewing: more chronic presentation, "onion-skin" periosteal reaction, permeative destruction
- Osteomyelitis: acute illness, soft tissue abscess, responds to antibiotics
Critical Management Points
- Blood cultures before antibiotics - positive in 30-50%
- MRI is gold standard - but don't delay antibiotics
- Abscess = surgery - drainage is essential
- CRP for monitoring - most useful marker for response
- Duration: 3-6 weeks total - IV to oral switch when improving
Common Examiner Follow-ups
Q: "What organism is most likely in a 2-year-old with osteomyelitis?"
Kingella kingae is increasingly recognised in children aged 6 months to 4 years. Standard cultures may miss it - requires prolonged incubation and specific culture techniques. Consider if blood cultures negative but clinical picture fits.
Q: "What are the complications of paediatric osteomyelitis?"
| Complication | Features |
|---|---|
| Chronic osteomyelitis | Sequestrum, involucrum, sinus formation |
| Growth disturbance | If physis involved - angular deformity, limb length discrepancy |
| Pathological fracture | Through weakened bone |
| Septic arthritis | Spread to adjacent joint (especially hip) |
| Sepsis/metastatic infection | Endocarditis, septic emboli |
Q: "When would you consider this child has chronic osteomyelitis?"
Chronic osteomyelitis is defined as symptoms persisting beyond 6 weeks or recurrence after treatment. Radiographic features include:
- Sequestrum (dead bone)
- Involucrum (new bone formation around sequestrum)
- Cloaca (drainage tract through involucrum)
- Sinus tract formation
Q: "What are the Kocher criteria and when do you use them?"
Kocher criteria are used to distinguish septic arthritis from transient synovitis of the hip in children:
- Fever >38.5°C
- Non-weight bearing
- WCC >12,000
- ESR >40 mm/hr
Probability of septic arthritis: 0 criteria = 0.2%, 4 criteria = 99.6%
Related Topics
- Septic Arthritis (Paediatric)
- Chronic Osteomyelitis
- MRSA Infections in Orthopaedics
- Transient Synovitis vs Septic Hip
- Kocher Criteria