Stem cells are progenitor cells in the body that have the ability to differentiate into different cell lines, thus, the ability to generate bone, soft tissue, cartilage, and organ tissue.  In the lab, cells can be made to differentiate and regenerate heart tissue, ear cartilage, etc.  To date, modifying stem cells is not approved by the Food and Drug Administration (FDA).  Fat tissue and bone marrow are sites on the body that can be a source of stem cells.  Bone marrow aspirate concentrate is the only approved source of potential stem cells, as the use of fat, or adipose tissue, requires manipulation to harvest the stem cells and is not approved in the USA.  There are companies that offer fetal umbilical blood and amniotic tissue for injection.  Currently, there are no live FDA approved or allowed umbilical cord, amniotic, or placental products.  If a provider claims to use FDA approved blood or tissue from birth byproducts, they are misleading you.  The cells are either not live or not FDA approved.  Bone marrow aspirate concentrate, where blood and marrow is harvested from the pelvis and then centrifuged to produce a concentrated solution, is a source of potential stem cells and growth factors that may be beneficial for certain conditions.  There are a few published studies that show efficacy in improving pain in patients with knee arthritis and as an adjunct to help healing in rotator cuff repairs.  Injecting bone marrow aspirate concentrate or  commercially available “ fetal stem cells” will not cure arthritis, grow a new meniscus, or stabilize an ACL deficient knee.