Microvilli (singular: microvillus) are microscopic cellular membrane protrusions that increase the surface area of cells and minimize any increase in volume, and are involved in a wide variety of functions, including absorption, secretion, cellular adhesion, and mechanotransduction. 1 Locations.
When youâre experiencing back knee pain, the cause of the problem may be due to a condition known as a Bakerâs cyst. When the back knee pain is associated with a Bakerâs cyst, it isnât a cyst in the usual sense. Itâs a popliteal cyst. What this means is that fluid is present in the joint at the back of the knee.
1 It often develops at the site of a previous injury. Other types of arthritis, such as rheumatoid arthritis, gout, and lupus, also can cause knee pain, swelling, and stiffness.  Osgood-Schlatter disease causes pain, swelling, and tenderness in the front of the knee below the kneecap.