During an Arthrogram, Why Is the Knee Flexed Following Injection

During an arthrogram, why is the knee flexed following injection of contrast media before imaging?

A) To reduce the viscosity of the contrast media
B) To force the contrast media outside of the joint if there is a tear
C) To coat the soft tissue structures with contrast media
D) None of the above; the knee should not be flexed during an arthrogram after injection of contrast media.