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Difficulty: MediumOrthopedic Surgery

A 6565-year-old woman is evaluated on postoperative day 77 following a right total knee arthroplasty for severe osteoarthritis. She reports sudden, severe pain in the right knee that began yesterday and has progressively worsened. The patient has been compliant with prophylactic apixaban and routine postoperative physical therapy. Her temperature is 38.6∘C38.6^\circ\text{C} (101.5∘F101.5^\circ\text{F}), blood pressure is 130/80130/80 mmHg, pulse is 102102/min, and respirations are 1616/min. Physical examination reveals a right knee that is significantly swollen, erythematous, and warm to the touch. The surgical incision is closed and intact without any frank purulent drainage, but there is marked tenderness over the joint capsule. Passive range of motion is extremely limited due to severe pain. Laboratory studies show a leukocyte count of 14,000/mm314,000/\text{mm}^3 and an erythrocyte sedimentation rate of 85 mm/h85\text{ mm/h}. Which of the following is the most appropriate next step in management?

  1. A
    Initiation of empirical intravenous vancomycin and cefepime
  2. B
    Venous duplex ultrasonography of the right lower extremity
  3. Arthrocentesis of the right kneeAnswer
  4. D
    Magnetic resonance imaging of the right knee
  5. E
    Reassurance and escalation of oral opioid analgesics

Answer

The most appropriate next step is to perform an arthrocentesis of the right knee to obtain synovial fluid for cell count, Gram stain, and culture.
The correct answer is arthrocentesis of the knee. This patient's presentation of acute fever, marked localized swelling, erythema, and severe pain with passive motion one week after joint replacement is highly suspicious for an acute prosthetic joint infection (PJI). The essential first step in management is to establish a definitive microbiological diagnosis via arthrocentesis (synovial fluid analysis for cell count, Gram stain, and culture). This fluid must be obtained prior to the administration of any antibiotics to prevent false-negative cultures, which would severely compromise the ability to provide targeted long-term antimicrobial therapy.

Step-by-Step Solution

1
Analyze the clinical presentation and timeframe.
The patient has acute fever, severe joint pain, swelling, erythema, and restricted range of motion 77 days after a total knee arthroplasty.
Identifying the timeline and focal inflammatory signs raises high clinical suspicion for an acute early prosthetic joint infection (PJI).
2
Determine the diagnostic requirements for the suspected condition.
Definitive diagnosis of a PJI requires identifying the causative organism from the synovial fluid or periprosthetic tissue.
Accurate microbiological data is essential for guiding targeted antimicrobial therapy and determining the surgical approach (e.g., debridement and implant retention).
3
Select the intervention that best achieves the diagnostic goal safely.
Arthrocentesis of the affected joint is selected as the immediate next step.
Joint fluid must be aspirated and sent for analysis before administering any systemic antibiotics to avoid sterilizing the culture.

Key Concept

Diagnosis and initial management of acute prosthetic joint infections.
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Topics

Orthopedic Surgery

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