Fluctuation Test: How to Check for Knee Swelling

The Fluctuation Test is a clinical assessment used to detect significant swelling or effusion within the knee joint. It works on the hydraulic principle that pressure applied to fluid in one area will be transmitted to another.

1. Purpose

The primary purpose of the Fluctuation Test is to **detect** the presence of a significant joint effusion (fluid) within the knee capsule. It relies on the principle that fluid is incompressible and will transmit pressure from one area to another.

2. How to Perform

1. The patient is positioned in supine (lying on their back) with the knee extended and relaxed.
2. The examiner places one hand superior to the patella (over the suprapatellar pouch).
3. The examiner places the other hand inferior to the patella (over the joint line/anterior knee).
4. The examiner presses down firmly with one hand while keeping the other hand resting lightly against the skin.
5. The examiner then alternates pressure between the two hands.

3. Positive & Negative Sign

Positive Sign (Test is POSITIVE):
A positive test (indicating effusion) is:

• A palpable "fluid wave" or expansion is felt in the resting hand when pressure is applied by the other hand.
• This indicates that fluid is being pushed from one part of the capsule to the other.

Negative Sign (Test is NEGATIVE):
A negative test is when no transmission of pressure or fluid wave is felt between the hands.