Knee effusion

 Q: It requires at least 50 mL of fluid to be present to appreciate knee effusion on an exam?

A) True

B) False

Answer: B

The objective of this question is to highlight the fact that in comparison to other body cavities knee requires very little fluid to have symptoms. Only 5 mL of fluid can be appreciated with proper examination. The level of quantity requires is pretty low:

• small effusions: 5-10 mL
• moderate effusion: 10-15 mL
• large effusion: 20-30 mL

Bulge, bubble, or wave sign: Performing "milking the fluid", also known as brush or stroke test, can make a clinician appreciate a small effusion. Watch here the maneuver: 

https://youtu.be/LHOmmWB_PFo

#physical-exam

#rheumatology

References:

1. Mathison DJ, Teach SJ. Approach to knee effusions. Pediatr Emerg Care. 2009 Nov;25(11):773-86; quiz 787-8. doi: 10.1097/PEC.0b013e3181bec987. PMID: 19915432.

2. Johnson MW. Acute knee effusions: a systematic approach to diagnosis. Am Fam Physician. 2000 Apr 15;61(8):2391-400. PMID: 10794580.