Diagnostic Approach to Bilateral Knee Pain in Children

Immediate Priority: Rule Out Emergent Conditions

The American College of Radiology recommends checking for fever, inability to bear weight, refusal to move the joint, and systemic toxicity to assess for septic arthritis 1
Septic arthritis is an orthopedic emergency because bacterial proliferation can rapidly destroy cartilage 1
The knee is the most common site for septic arthritis in children 1
In children under 2 years old, septic arthritis is more common than osteomyelitis 1
Laboratory markers such as ESR ≥40 mm/hour, WBC ≥12,000 cells/mm³, and CRP >2.0 mg/dL are predictive of septic arthritis 1

The American College of Radiology suggests obtaining plain radiographs of both knees (AP and lateral views) as the initial imaging step 2
Radiographs are safe, inexpensive, and can identify fractures, osteomyelitis changes, or alternative diagnoses 7
If hip pathology is suspected clinically, obtain hip radiographs simultaneously 2
Ultrasound of the affected joint(s) is the next step if infection is suspected, to quickly identify joint effusions and guide arthrocentesis 2

Hip pathology, such as transient synovitis, septic arthritis, or Legg-Calvé-Perthes disease, can present as knee pain 2
Abdominal pathology, such as appendicitis with retrocecal abscess, can masquerade as knee pain with fever and inability to bear weight 2
Lumbar spine pathology must be considered if knee imaging is normal 3

If septic arthritis is confirmed, immediate orthopedic consultation for arthrotomy, irrigation, and debridement is necessary 1
IV antibiotics targeting Staphylococcus aureus (most common pathogen) should be administered if septic arthritis is confirmed 1
If osteomyelitis is confirmed, IV antibiotics followed by prolonged oral course should be administered 1
If transient synovitis or benign cause is diagnosed, expectant management with NSAIDs and activity modification is recommended 1