Collagen is a natural protein component of the skin that acts like a scaffold and the main building block for cells, tissues and organs. About a third of the protein content in your body is made up of collagen, which is found in the bones, muscles, and tissues of the organs.
1 There can be the accumulation of fluid on the knee after an accident. 2  In most cases, the fluid is blood which can be through a fracture caused to the knee. 3  The swelling of the knee often takes place within some minutes of the injury occurring. 4  Gout and pseudo-gout can also cause fluid on the knee.
The buildup can be seen and felt at the top of the kneecap. It is not something you would see under the knee. An injury such as a contusion (soft tissue bruise) to the kneecap may also cause localized swelling. In some cases, the buildup of blood and fluid may mimic an acute injury of the knee joint. Source: Gupte, C. and St. Mart, J. The acute swollen knee: diagnosis and management..