A worried father brings his 4-year-old son to the pediatric clinic due to acute-onset refu… — USMLE Step 2 CK

A worried father brings his $4$ -year-old son to the pediatric clinic due to acute-onset refusal to walk over the past $24$ hours. The child was previously healthy except for a mild rhinovirus infection that resolved $10$ days ago. Current vital signs reveal a temperature of $38.9^{\circ}\text{C}$ ( $102.0^{\circ}\text{F}$ ), pulse of $118/\text{min}$ , and respirations of $22/\text{min}$ . On physical examination, the child is irritable and resists any passive range of motion of the right hip, which is held in a flexed, abducted, and externally rotated position. Laboratory analysis demonstrates a leukocyte count of $14,500/\mu\text{L}$ , an erythrocyte sedimentation rate (ESR) of $55 \text{ mm/h}$ , and a C-reactive protein (CRP) level of $32 \text{ mg/L}$ . Which of the following is the most appropriate next step in the management of this patient?

A
Intravenous ceftriaxone and vancomycin
B
Oral ibuprofen and outpatient follow-up
Ultrasound-guided arthrocentesisCevap
D
Magnetic resonance imaging of the right hip
E
Surgical pinning of the right femoral head

Cevap

The most appropriate next step in management is ultrasound-guided arthrocentesis to evaluate for septic arthritis.

The correct next step in management is ultrasound-guided arthrocentesis. This

4

-year-old boy presents with an acute inability to bear weight, fever, and marked elevation of inflammatory markers. The diagnosis of a pediatric limp requires differentiating benign etiologies, such as transient synovitis, from orthopedic emergencies like septic arthritis. The Kocher criteria are classically used to assess the probability of septic arthritis based on four clinical predictors: non-weight-bearing status on the affected side, temperature >

38.5^{\circ}\text{C}

(

101.3^{\circ}\text{F}

), erythrocyte sedimentation rate (ESR)

\geq 40 \text{ mm/h}

, and a serum white blood cell (WBC) count

> 12,000/\mu\text{L}

. This patient meets all four criteria, which correlates with a

>99\%

probability of septic arthritis. Consequently, the immediate next step is an urgent ultrasound-guided arthrocentesis to obtain synovial fluid for cell count, Gram stain, and aerobic/anaerobic cultures. Decompression of the joint space is also critical to prevent irreversible ischemic damage and cartilage destruction.

Adım Adım Çözüm

Evaluate the patient's clinical presentation and laboratory values using the Kocher criteria for the limping child.

The patient exhibits a fever >

38.5^{\circ}\text{C}

, inability to bear weight, an ESR >

40 \text{ mm/h}

, and a serum WBC count >

12,000/\mu\text{L}

Applying these criteria helps differentiate a benign condition (transient synovitis) from a medical emergency (septic arthritis).

Calculate the probability of septic arthritis and determine the corresponding intervention.

Having 4 out of 4 Kocher predictors yields a probability of septic arthritis exceeding 99%.

High-probability cases require immediate diagnostic confirmation and joint decompression to prevent cartilage destruction.

Select the most appropriate initial procedural step before beginning medical therapy.

Diagnostic arthrocentesis (typically ultrasound-guided) must be performed.

Aspiration obtains synovial fluid for cell count, Gram stain, and culture, which is essential to guide targeted antimicrobial therapy before empiric antibiotics are administered.

Anahtar Kavram

Kocher Criteria and Management of Pediatric Septic Arthritis

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Cevap

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