Management of a 2-Year-Old with Non-Traumatic Limp
The initial approach must prioritize ruling out septic arthritis—an orthopedic emergency—through urgent hip ultrasound if fever or signs of infection are present, followed by immediate aspiration if effusion is detected. 1
Immediate Clinical Assessment
Your first task is to determine if this is a surgical emergency by assessing for:
- Fever >101.3°F (38.5°C) - highly suggestive of septic arthritis 2
- Refusal to bear weight - concerning for serious pathology 2
- Joint tenderness on examination - strong predictor of septic arthritis (positive likelihood ratio 11.4) 3
- Ill appearance or systemic symptoms 4
If any of these red flags are present, septic arthritis must be assumed until proven otherwise. 1
Initial Diagnostic Pathway
For Children WITH Fever or Signs of Infection:
Obtain blood work immediately: 2
- CBC with differential (WBC >12,000/mm³ suggests septic arthritis)
- ESR (>40 mm/hr suggests septic arthritis)
- CRP (>20 mg/L suggests septic arthritis)
- Blood cultures before antibiotics 5
Perform urgent hip ultrasound - this is the critical first imaging study as it quickly and accurately detects joint effusion and can guide aspiration 1, 6
If effusion is present on ultrasound, perform immediate ultrasound-guided aspiration for synovial fluid analysis (cell count ≥50,000 cells/mm³, Gram stain, culture) 7, 5, 6
Start empiric IV vancomycin immediately after obtaining cultures to cover MRSA, which is increasingly common 7, 5
Consider MRI of the pelvis if septic arthritis is confirmed, as up to 70% have associated osteomyelitis that requires longer treatment 1, 7, 5
For Children WITHOUT Fever or Signs of Infection:
Obtain plain radiographs first - anteroposterior and lateral views of both lower extremities to exclude fractures (especially toddler's fracture of the tibia), tumors, and provide baseline assessment 6, 2
Consider hip ultrasound even without fever, as hip pathology can refer pain to the thigh, knee, or buttock, leading to diagnostic confusion 1, 6
If radiographs are negative but limp persists, obtain MRI - highly sensitive for detecting stress fractures, early osteonecrosis, inflammatory changes, and bone marrow pathology that may be missed on plain films 1
Common Diagnoses by Age and Presentation
At age 2, the most likely diagnoses are: 8, 4
- Transient synovitis (37% of cases) - most common, benign, self-limiting
- Viral myositis (16% of cases) - associated with recent viral illness
- Toddler's fracture - spiral tibial fracture, often missed on initial radiographs (41% only visible on follow-up films) 1, 6
- Septic arthritis - uncommon but critical not to miss
- Osteomyelitis - consider if fever present without effusion 1
Critical Pitfalls to Avoid
- Never delay antibiotics to obtain imaging if septic arthritis is suspected clinically 5
- False-negative ultrasound can occur if performed within 24 hours of symptom onset 1
- Negative initial radiographs do not exclude toddler's fracture - approximately 41% are only visible on follow-up imaging 1, 6
- Hip pain can be referred to the knee or thigh - always examine and image the hip even if child points to knee 1, 6
- Approximately one-third of serious diagnoses are missed at initial ED visit 8
- Concomitant osteomyelitis occurs in up to 30% of children with septic arthritis and requires longer treatment (consider MRI even with confirmed septic arthritis) 7, 5
Disposition Decisions
Admit for IV antibiotics and surgical consultation if: 7, 5
- Septic arthritis confirmed or highly suspected
- Osteomyelitis diagnosed
- Unable to exclude serious infection despite workup
Discharge with close follow-up (24-48 hours) if: 8, 4
- Transient synovitis diagnosed (afebrile, normal or mildly elevated inflammatory markers)
- Viral myositis with reassuring examination
- Toddler's fracture managed conservatively
The key is maintaining a high index of suspicion for septic arthritis in any febrile limping child, as permanent joint damage can occur within hours of bacterial proliferation. 1, 7