Stem cells used in injections come from a handful of sources in the human body, most commonly bone marrow, fat tissue, and blood. Some clinics also use cells derived from birth tissues like umbilical cords and amniotic fluid. The source depends on the type of procedure, whether the cells come from your own body or a donor, and what the injection is meant to treat.
Bone Marrow: The Most Common Source
Bone marrow is the gold standard source for stem cell injections, particularly in orthopedic and sports medicine. The marrow inside certain bones contains mesenchymal stem cells, which can develop into cartilage, bone, and other connective tissues. To collect them, a doctor inserts a needle into a bone, draws out a small volume of liquid marrow, then spins it in a centrifuge to concentrate the stem cells into a preparation called bone marrow aspirate concentrate, or BMAC.
The harvest site depends on what joint is being treated. For knee procedures, marrow is typically drawn from the upper shinbone (proximal tibia). For shoulder procedures, it comes from the upper arm bone near the shoulder. For hip procedures, it’s pulled from the front of the pelvis at the iliac crest. The back of the pelvis actually yields the highest concentration of cells, but it requires the patient to be positioned face-down, which is less practical for most surgeries. After centrifugation, the final concentrate is usually just 2 to 5 milliliters of fluid, enough for a targeted injection.
The entire process, from harvest to injection, is typically completed in two to three hours during a single clinic visit. Because these are your own cells (autologous), there’s no risk of immune rejection.
Fat Tissue: A Cell-Rich Alternative
Adipose tissue, the fat beneath your skin, is another rich source of stem cells. Fat-derived stem cells are collected through a mini-liposuction procedure, usually from the abdomen or thigh. The extracted fat is then processed to isolate what’s called the stromal vascular fraction (SVF), a mix of cell types that includes stem cells, progenitor cells, immune cells, and cells that support blood vessel formation.
Fat tissue is appealing because it’s abundant and relatively easy to access. A small liposuction can yield a large number of cells compared to bone marrow. Like bone marrow procedures, fat-derived injections use your own tissue, so they’re autologous. Some clinics prefer this approach for patients who need a higher cell count or who want to avoid a bone marrow aspiration.
Umbilical Cord and Birth Tissues
A growing number of clinics offer injections sourced from birth-associated tissues, specifically the umbilical cord and its internal connective tissue known as Wharton’s jelly. These cells are collected after a healthy delivery, with the mother’s consent, from tissue that would otherwise be discarded. No embryos are involved, which avoids the ethical concerns associated with embryonic stem cell research.
Stem cells from Wharton’s jelly have some distinct biological advantages. Because they come from newborn tissue, they haven’t been exposed to the aging processes that affect adult cells. They multiply faster than bone marrow stem cells, can be expanded more extensively in the lab, and produce higher levels of anti-inflammatory signaling molecules. They also share some characteristics with embryonic stem cells without the risk of forming tumors.
These are donor cells (allogeneic), meaning they come from someone else’s body. However, umbilical cord stem cells have natural immune-suppressing properties that make rejection less likely than you might expect.
Blood-Derived Stem Cells
Stem cells can also be collected from the bloodstream, though this method is used more often in cancer treatment than in orthopedic injections. Normally, very few stem cells circulate in your blood. To increase that number, patients receive daily injections of a growth factor for four to five days. This medication coaxes stem cells out of the bone marrow and into the bloodstream, a process called mobilization. Once enough cells are circulating, blood is drawn and run through a machine that separates out the stem cells while returning the rest of the blood to the patient.
This approach is the backbone of peripheral blood stem cell transplants used for leukemia and lymphoma. It’s less common for joint or soft tissue injections.
Amniotic Fluid Products: A Key Distinction
Many clinics market “amniotic stem cell injections,” but the name can be misleading. While amniotic fluid does contain stem cells that can be isolated and expanded in a laboratory setting, commercially available amniotic products sold for injection have typically been processed, sterilized, and frozen in ways that may not preserve living cells. The regenerative potential of these off-the-shelf products is a subject of ongoing debate, and they should not be assumed equivalent to freshly harvested stem cells from bone marrow or fat.
If a clinic offers an amniotic or placental injection, it’s worth asking whether the product contains live, viable stem cells or whether it primarily consists of growth factors and extracellular matrix proteins. The distinction matters for what you can realistically expect.
Your Own Cells vs. Donor Cells
Stem cell injections fall into two broad categories. Autologous injections use your own cells, harvested from your bone marrow or fat during the same procedure. The main advantage is zero risk of immune rejection, since your body recognizes its own tissue. The drawback is that cell quality declines with age, so a 65-year-old’s marrow yields fewer and less vigorous stem cells than a 30-year-old’s.
Allogeneic injections use donor cells, typically from umbilical cord tissue or amniotic sources. These cells are younger and more potent, but they introduce the variable of immune compatibility. In practice, mesenchymal stem cells from birth tissues are considered “immune-privileged,” meaning they’re less likely to trigger a rejection response than other transplanted cells.
How Regulation Shapes What’s Available
In the United States, the FDA regulates stem cell products based on how much they’ve been processed. If cells are only minimally manipulated and used for the same basic function they perform naturally (called homologous use), they fall under a lighter regulatory framework. Bone marrow concentrate and simple fat-tissue processing generally qualify under these rules.
If cells are cultured, expanded in a lab, or used for a function different from their original role, the product is regulated as a drug or biologic and requires premarket approval, including clinical trials. This is why most U.S. clinics offering same-day stem cell procedures stick to minimally processed bone marrow or fat. Products that go beyond minimal manipulation without FDA approval are technically being marketed illegally, though enforcement has been inconsistent.
What the Evidence Shows for Joint Injections
Most people searching for stem cell injection sources are considering treatment for a joint problem, especially knee osteoarthritis. A Cochrane review of the available evidence found that stem cell injections improved pain by about 1.2 points on a 10-point scale compared to placebo injections at six months. Function scores improved by about 14 points on a 100-point scale. Those are modest but real differences: patients who received stem cells rated their pain at 3.3 out of 10 versus 4.5 for placebo, and their function at 32 out of 100 versus 46.
These results suggest stem cell injections can help, but they’re not a cure. The improvements are meaningful for some patients and underwhelming for others, and the evidence base still has significant variability between studies. The source of stem cells, the concentration injected, and the severity of joint damage all influence outcomes.