A 4-year-old presents with a 2-day history of increasingly severe right leg pain and limp. He has the hip flexed and externally rotated, passive ROM limited by pain. X-ray is normal and there is no history of falls or trauma. What is the most likely diagnosis and the next step?

A 4-year-old presents with a 2-day history of increasingly severe right leg pain and limp. He has the hip flexed and externally rotated, passive ROM limited by pain. X-ray is normal and there is no history of falls or trauma. What is the most likely diagnosis and the next step?

• A. Transient synovitis; measurement of serum inflammatory markers
• B. Septic arthritis; joint aspiration
• C. Osteomyelitis; MRI
• D. Fracture; CT scan of right hip

Answer: (A)

In a young child with acute hip pain, the priority is to distinguish a benign inflammatory process from a joint infection because septic arthritis needs urgent treatment to prevent damage. This child is four years old with a two-day history of severe leg pain and a limp; the hip is held in flexion with external rotation and active/passive motion is limited by pain. The normal X-ray and lack of trauma point toward an irritable hip pattern, most commonly transient synovitis, which often follows a viral illness and is self-limited. The best next step is to check inflammatory markers, such as the ESR and CRP. These tests help separate transient synovitis from septic arthritis: septic arthritis usually causes elevated inflammatory markers and systemic signs, pushing you toward urgent joint aspiration and antibiotics. If the inflammatory markers are normal or only mildly elevated, transient synovitis remains the more likely diagnosis and treatment is supportive (rest, fluids, NSAIDs). If they’re elevated or clinical concern remains high, joint aspiration would be pursued to analyze synovial fluid and guide therapy.

In a young child with acute hip pain, the priority is to distinguish a benign inflammatory process from a joint infection because septic arthritis needs urgent treatment to prevent damage. This child is four years old with a two-day history of severe leg pain and a limp; the hip is held in flexion with external rotation and active/passive motion is limited by pain. The normal X-ray and lack of trauma point toward an irritable hip pattern, most commonly transient synovitis, which often follows a viral illness and is self-limited.

The best next step is to check inflammatory markers, such as the ESR and CRP. These tests help separate transient synovitis from septic arthritis: septic arthritis usually causes elevated inflammatory markers and systemic signs, pushing you toward urgent joint aspiration and antibiotics. If the inflammatory markers are normal or only mildly elevated, transient synovitis remains the more likely diagnosis and treatment is supportive (rest, fluids, NSAIDs). If they’re elevated or clinical concern remains high, joint aspiration would be pursued to analyze synovial fluid and guide therapy.