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Difficulty: EasyPediatric Musculoskeletal Disorders

A 5-year-old boy is brought to the emergency department with a 1-day history of severe right hip pain and fever. He refuses to walk or bear any weight on his right leg. His temperature is 38.9°C (102.0°F). On physical examination, he appears irritable. His right hip is held rigidly in flexion, abduction, and external rotation; any attempt at passive range of motion elicits severe pain and crying. You suspect a severe acute joint infection. Arrange the following steps in the most appropriate sequential order for the standard diagnostic evaluation and management of this patient's condition.

  1. 1Obtain a complete blood count, erythrocyte sedimentation rate, and C-reactive protein level.
  2. 2Perform bilateral hip ultrasonography to evaluate for the presence of a joint effusion.
  3. 3Perform ultrasound-guided arthrocentesis of the right hip for synovial fluid analysis.
  4. 4Administer empiric intravenous antibiotics and perform surgical irrigation and drainage.

Answer

The correct sequence is: 1) Obtain inflammatory markers and complete blood count, 2) Perform hip ultrasonography, 3) Perform ultrasound-guided arthrocentesis, and 4) Administer intravenous antibiotics and perform surgical drainage.
The correct sequence prioritizes non-invasive risk stratification using the Kocher criteria (blood labs), followed by rapid, non-radiating imaging to confirm a joint effusion (ultrasound). Once an effusion is confirmed in a high-risk patient, obtaining a microbiological sample via arthrocentesis is mandatory before initiating therapies that could obscure the diagnosis (antibiotics). The pathway concludes with definitive source control via surgical drainage.

Step-by-Step Solution

1
Recognize the clinical presentation of suspected septic arthritis.
The patient has acute onset of hip pain, fever, inability to bear weight, and classic positioning (flexed, abducted, externally rotated), requiring urgent evaluation.
Septic arthritis is an orthopedic emergency that can rapidly cause irreversible joint destruction and avascular necrosis.
2
Determine the first step in the diagnostic pathway.
Laboratory studies (complete blood count, erythrocyte sedimentation rate, C-reactive protein) are ordered first.
These blood tests evaluate the Kocher criteria, which help risk-stratify the patient and differentiate septic arthritis from transient synovitis.
3
Identify the appropriate initial imaging modality.
Hip ultrasound is the next procedural step.
Ultrasonography is highly sensitive for detecting a joint effusion, which confirms intra-articular pathology and guides the need for aspiration.
4
Determine the necessary procedure before administering pharmacotherapy.
Ultrasound-guided arthrocentesis is performed.
Synovial fluid must be obtained for culture and analysis prior to antibiotic administration to prevent sterilizing the sample and obscuring the microbiological diagnosis.
5
Identify the definitive management.
Intravenous antibiotics and surgical drainage are initiated.
Empiric antibiotics treat the underlying infection, while surgical drainage decompresses the joint, removing destructive inflammatory mediators and preventing vascular compromise.

Key Concept

The diagnostic and management sequence for pediatric septic arthritis involves risk stratification with laboratory markers (Kocher criteria), confirmation of effusion with ultrasound, diagnostic arthrocentesis, and subsequent empiric antibiotic therapy with surgical drainage.
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Pediatric Musculoskeletal Disorders

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