December 13, 2024

A 57-year-old man presents with a swollen right knee

By Med-Challenger · 1 minute read

A 57-year-old man presents with a swollen right knee. He has a history of arthritis and has noted pain and swelling of this knee for a few days. The swelling worsened and he noticed that the knee felt hot. He has some mild nausea.

On today's visit, his temperature is 103.3 °F (39.6 °C) and his white blood cell count is normal. The knee is warm, slightly swollen, and erythematous. Aspiration of the knee joint was performed, but only a few drops of fluid were obtained.

What is the most appropriate next step?

Delay antibiotic coverage until more fluid is obtained.
Discard the sample because the scant amount will have a low yield.
Reattempt the joint aspiration.
Test the fluid for bacterial cultures.

The correct answer is:

Test the fluid for bacterial cultures.

Educational Objective:

Characterize appropriate strategies for joint fluid analysis.

Key Point:

Joint fluid analysis is a critical step in analyzing possible septic arthritis, and even a minimal amount of joint fluid can provide suitable culture media.

Explanation:

Culturing of joint fluid is the definitive test to diagnose bacterial arthritis. In situations in which only a few drops of fluid are obtained, it is imperative to establish priorities for diagnostic testing. The most important diagnostic test is a bacterial culture and should be the top priority. If there is an adequate amount of fluid, then a Gram stain and smear, cell count, and crystal analysis would be useful. Even a scant amount should be sent for culture. Reattempting the aspiration after it was properly performed will probably not produce a better yield. Empiric antibiotic coverage should not be delayed while waiting for test results.

References:

Kellerman RD, et al, eds. Conn’s Current Therapy. 2018.

Walls R, et al. Rosen’s Emergency Medicine: Concepts and Clinical Practice. 9th ed., 2018.

This question appears in Med-Challenger Family Medicine Exam Review with CME

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