The Bernoulli equation comes from Newton's laws of motion. It deals with flowing fluids and says that when a gas such as air flows, its pressure drops. For fluid in the joint the Bernoulli effect means the pressure is lower in a moving fluid than in a fluid that's still.

In the shoulder during arthroscopic surgery, fluid is pushed through the tube of the scope into the joint. This technique helps with several things. First, it clears the joint of any blood obstructing the surgeon's view. Second it pushes the joint open and gives the surgeon more room to work.

Finally lower pressure means less damage in the joint. Each hole that is made in the joint capsule to allow the scope to enter the joint leaves an opening. Fluid can leak out of the joint into the nearby tissues. Keeping fluid flowing through the joint reduces pressure, and keeps the fluid from escaping.