Test your medicine knowledge with the MKSAP challenge, in partnership with the American College of Physicians.
A 48-year-old man is evaluated for a 2-day history of right anterior knee pain and swelling. The pain began suddenly and has increased in intensity. He currently rates his pain as an 8 on a 10-point scale. He has no knee instability and reports no fever or chills. He has no history of trauma and has never had this problem before. Other than his right knee pain and swelling, he feels well. He is employed as a carpet layer. His only medication is ibuprofen, which provides minimal relief.
On physical examination, vital signs are normal. BMI is 28. On examination of the right knee, there is a palpable fluid collection that is located anterior to the patella. The right knee has full range of motion. There is no medial or lateral joint line tenderness or laxity with varus or valgus forces. Anterior drawer, posterior drawer, and Lachman tests are all negative.
Which of the following is the most appropriate next step in management?
C. Glucocorticoid injection
D. Right knee radiographs
MKSAP Answer and Critique
The correct answer is A. Aspiration.
The most appropriate next step in management of this patient is to aspirate the bursal fluid collection for diagnostic and therapeutic purposes. Bursal fluid aspiration and analysis should be performed in all patients who present with prepatellar bursitis. Aspiration is necessary to definitively distinguish the cause of prepatellar bursitis (namely, trauma, gout, and infection). Gram stain and culture of the bursal fluid should be obtained and analyzed for leukocyte count and for the presence of crystals. An extremely elevated leukocyte count (>50,000/µL [50 × 109/L]) should raise suspicion for septic bursitis, although a lower count does not entirely eliminate this possibility.
Compression is indicated only after bursal fluid aspiration has been performed. Dressings should be worn for 24 to 48 hours, and patients should be advised to avoid applying direct pressure to the bursa. Once the compression dressing is removed, patients should be advised to wear a neoprene sleeve.
Glucocorticoid injection into the fluid collection is not indicated for patients presenting with acute prepatellar bursitis. Instead, glucocorticoid injection should be reserved for chronic prepatellar bursitis that has a noninfectious cause or that is postinfectious (negative cultures have been obtained after antibiotic administration).
Imaging, either with plain radiography or ultrasonography, is not usually required for the diagnosis of prepatellar bursitis. Plain radiography may show soft-tissue swelling on lateral views but rarely aids in establishing the correct diagnosis. Ultrasonography will show a fluid collection but will not help identify the cause. Therefore, plain radiography or ultrasonography is not indicated in this patient.
- Bursal fluid aspiration should be performed for both therapeutic and diagnostic purposes in all patients who present with prepatellar bursitis.
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