How to diagnose osteomyelitis in children?

Diagnosing Osteomyelitis in Children

MRI is the imaging modality of choice for diagnosing osteomyelitis in children due to its high sensitivity (82-100%) and specificity (75-96%), with fluid-sensitive sequences often sufficient for diagnosis. 1

Clinical Presentation

• Osteomyelitis commonly occurs in young children, with half of cases reported in children under 5 years of age 1
• Although hematogenous bacterial seeding is the most common cause, a history of trauma (often minor) is frequently elicited 1
• Infants and toddlers often present with a limp, though localizing the site of involvement on physical examination can be difficult 1
• Staphylococcus aureus is the most common causative organism, though Kingella kingae is increasingly common in children under 4 years 2, 3
• Children under 2 years are more likely to have septic arthritis than osteomyelitis, while those between 2-10 years have slightly more osteomyelitis than septic arthritis 3

Diagnostic Algorithm

Step 1: Initial Imaging

• Plain radiographs should be the initial imaging test, though they are often not diagnostic in acute osteomyelitis 1
• Radiographs provide anatomic evaluation and can suggest alternative diagnoses such as fracture or tumor 1
• Normal conventional imaging does not exclude osteomyelitis 4

Step 2: Advanced Imaging

• MRI is the modality of choice for suspected bone infections due to:

  • High sensitivity (82-100%) and specificity (75-96%) 1
  • Excellent soft tissue contrast and delineation of anatomic detail 1
  • 100% negative predictive value for excluding osteomyelitis (normal marrow signal reliably excludes infection) 1

• MRI findings suggestive of osteomyelitis include:

  • Decreased T1-weighted bone marrow signal 1
  • Increased signal on fluid-sensitive sequences (T2-weighted fat-saturated and short tau inversion recovery) 1
  • Subperiosteal fluid, which is a distinguishing feature of osteomyelitis 1

• For children under 5 years, extended field-of-view MRI (from neck to feet) should be considered as:

  • It can provide important additional information in 21.6% of cases 5
  • It only adds a median of 6:51 minutes to the examination time 5
  • It can identify multifocal osteomyelitis, which is common in young children 1

Step 3: Joint Evaluation (When Joint Involvement Suspected)

• Ultrasound is highly sensitive for diagnosing joint effusion, particularly in the hip 1
• Absence of hip joint effusion virtually excludes septic arthritis (false negative rate of only 5%) 1
• Ultrasound can detect hip effusions as small as 1 mL 1

Step 4: Definitive Diagnosis

• Image-guided aspiration of affected joint or bone is crucial for definitive diagnosis 1, 6
• Aspirated fluid should be sent for Gram stain, culture, cell count, and crystal analysis 7
• Blood cultures should be obtained before initiating antibiotic therapy 7

Special Considerations

• Children with sickle cell disease pose a diagnostic dilemma because marrow infarction and osteomyelitis may present similarly 1, 3
• Concomitant osteomyelitis and septic arthritis are common in children and may occur in >50% of cases 3, 6
• In children with septic arthritis, concomitant osteomyelitis occurs in up to 30% of cases and requires longer treatment 7, 6
• Contrast-enhanced MRI improves detection of abscesses and infection of unossified growth cartilage (chondritis) in children under 6 years 1
• Distinguishing osteomyelitis from conditions like Ewing sarcoma and Langerhans cell histiocytosis can be challenging on imaging 1

Treatment Principles

• Most cases of early osteomyelitis without a drainable abscess can be treated with a short course of intravenous antibiotics followed by at least 3 weeks of oral antibiotics 2
• Surgical management is usually indicated in the presence of an abscess and/or failed antibiotic therapy 2
• Clinical examination, fever, and C-reactive protein testing should guide conversion to oral antibiotics, total antibiotic regimen duration, and need for additional surgical debridement 2