Red flags — MCQs

Question 1: A 3-year-old boy is brought to the emergency department with fever, irritability, and refusal to walk for 12 hours. His parents report he had a fall 3 days ago but seemed fine afterward. Temperature is 39.2°C (102.5°F), pulse 140/min. He cries when his right hip is moved and holds it in flexion and external rotation. WBC is 18,000/μL, ESR 65 mm/hr, CRP 8.5 mg/dL. He appears ill and has not responded to acetaminophen. Apply clinical reasoning to determine the most appropriate next step.

• A. Blood cultures and empiric IV antibiotics while awaiting outpatient orthopedic evaluation
• B. Obtain hip radiographs and discharge with NSAIDs if normal
• C. MRI of the hip to evaluate for occult fracture from recent trauma
• D. Immediate hip ultrasound followed by emergent arthrocentesis if effusion present (Correct Answer)
• E. Presumptive diagnosis of transient synovitis; prescribe rest and follow-up in 48 hours

Explanation: ***Immediate hip ultrasound followed by emergent arthrocentesis if effusion present*** - The patient meets all four **Kocher criteria** (fever, non-weight bearing, ESR >40 mm/hr, WBC >12,000/μL), which indicates a high probability (>93%) of **septic arthritis**. - Emergent **ultrasound** is used to identify a joint effusion, followed by **arthrocentesis** for synovial fluid analysis to definitively diagnose and decompress the joint. *Obtain hip radiographs and discharge with NSAIDs if normal* - Radiographs are often normal in early **septic arthritis** and should not be used to rule out an infection in a systemically ill child. - Discharging the patient with **NSAIDs** is dangerous as it delays the surgical management required to prevent **permanent joint destruction**. *Presumptive diagnosis of transient synovitis; prescribe rest and follow-up in 48 hours* - **Transient synovitis** usually follows a viral illness, presents with lower inflammatory markers, and doesn't typically cause a **high-grade fever** or toxic appearance. - Waiting 48 hours is inappropriate when **septic arthritis** is suspected, as irreversible **cartilage damage** can occur within 6-12 hours. *MRI of the hip to evaluate for occult fracture from recent trauma* - While **MRI** is sensitive, it is time-consuming and often requires sedation in a 3-year-old, leading to a delay in life-saving **surgical drainage**. - The clinical context of **high fever** and elevated **CRP/ESR** strongly points toward infection rather than a traumatic **occult fracture**. *Blood cultures and empiric IV antibiotics while awaiting outpatient orthopedic evaluation* - While blood cultures are necessary, antibiotics should ideally be administered **after joint aspiration** to maximize the yield of synovial fluid cultures. - Outpatient evaluation is never appropriate for suspected **septic arthritis**, as it is an **orthopedic emergency** requiring immediate inpatient treatment and likely surgical washout.