Initial Approach for Knee Pain in Children

Immediate Clinical Assessment

The American College of Radiology recommends obtaining plain radiographs (anteroposterior and lateral views) as the initial imaging study to assess for septic arthritis versus traumatic injury based on clinical presentation, with urgent aspiration if infection is suspected 1, 2, 3
A trauma history should be determined, including if there was a fall, twisting injury, or significant mechanism, to assess the likelihood of traumatic injury 1, 3
The presence of fever and systemic symptoms suggests septic arthritis, which is an orthopedic emergency requiring immediate intervention 4
The ability to bear weight is a critical Ottawa rule criterion, and inability to take four weight-bearing steps may indicate a fracture or other serious condition 1, 3
Focal bony tenderness, including palpation of the patella, fibular head, and tibial plateau, should be assessed to identify potential fracture sites 1, 3
The ability to flex the knee to 90 degrees is an Ottawa rule criterion, and inability may indicate a fracture or other serious condition 1, 3
Gross deformity or palpable mass mandates immediate radiographs regardless of other criteria 1, 2

The American College of Radiology recommends obtaining a minimum of two views (anteroposterior and lateral at 25-30 degrees flexion) if any Ottawa rule criteria are present 1, 2, 3
Additional views, such as cross-table lateral with horizontal beam, patellofemoral view, and internal and external oblique views, may be considered to comprehensively assess for fractures and other injuries 1, 2

The American College of Radiology suggests that age <5 years and C-reactive protein >2.0 mg/dL together predict >90% probability of septic arthritis in a child with painful swollen knee 4
Fever, refusal to bear weight or move the joint, and bacteremia or recent infection elsewhere are red flags for infection 4
Urgent ultrasound-guided joint aspiration is recommended if clinical suspicion for septic arthritis is high, or if atraumatic effusion of unknown etiology is present 4

If radiographs show fracture, orthopedic consultation is recommended for fracture management 1, 2
If radiographs are normal but trauma history is present, conservative management with close follow-up is appropriate if the child can bear weight 5
MRI may be considered at 5-7 days if significant persistent effusion, inability to fully bear weight, mechanical symptoms, or joint instability are present 5

MRI is not routinely used as initial imaging for acute knee trauma but becomes appropriate when radiographs are normal and pain persists, or when soft tissue injury evaluation is needed 3, 5
CT may be considered if radiographically occult fractures are suspected, as it shows high sensitivity for tibial plateau fractures 3