Stem cells have been an ongoing study as well as treatment for all sorts of things for the last decade. Even actors like Michael J. Fox (who has Parkinson's disease) have been staunch supporters of using stem cells to treat all kinds of ailments. Fetal/embryonic stem cells are still highly controversial, so a lot of the stem cells used are actually taken from compatible healthy donors or from the bone marrow of the patients themselves. One more recent use of stem cells is to treat knee pain in place of a partial or total knee replacement. Here is how this particular knee pain stem cell treatment works:

Bio-Identical Cells Are Preferred

More and more doctors are recognizing that the best cells to use for these treatments are the bio-identical cells taken from the patient's own body. It is easier to grow and manipulate these cells to make bio-identical cells to those already in the patient's own knee. If, for whatever reason, that is not possible (e.g., cancer can change the stem cells and/or damage them so that they do not work for stem cell treatments), then the doctors look to donor stem cells that are as close a match as possible. Fun fact: Identical twins can use each other's stem cells from bone marrow for all kinds of stem cell treatments for the other twin. 

Bone Marrow Cells are Placed in a Growth Dish and Manipulated 

The next step is to extract the stem cells from the bone marrow and place them in a growth dish. Here, the lab technicians will manipulate the cells to mimic whatever tissue, bone, or synovial fluid that the patient needs to lessen his/her knee pain. It takes a few weeks to grow in the lab, but then the sample is ready for a doctor to inject into the patient's knee. 

A Simple Needle Prick Is All It Takes

Rather than cutting into the knee, opening the knee all the way, or removing bone, muscles, and tendons, the doctor only needs to inject the cells into the knee. It does not matter what kind of cells the doctor requested from the lab. The cells are already "designed" to become exactly what the patient needs. If anything, the patient will only need a small band-aid to prevent the needle stick from bleeding and/or oozing after the stem cells have been injected into the patient's sore knee.