Stem Cell Injections

It is important to distinguish between two fundamentally different approaches:

1. Same-Day Concentrated Aspiration (e.g., Bone Marrow Aspirate Concentrate [BMAC])

In this approach, cells are harvested, concentrated through centrifugation, and re-injected into the patient within the same clinical visit. The process is similar to PRP preparation. Bone marrow aspirate concentrate (BMAC) is the most established version of this treatment and is FDA-approved because it involves only minimal manipulation of the harvested material—no chemical modification or laboratory expansion.

One practical limitation is that bone marrow aspirates contain a relatively small proportion of true stem cells (approximately 0.001% of the total cell population), and not all of those cells possess equal regenerative potential. The aspirate is a mixed population of cells with varying functional capabilities.

BMAC may offer anti-inflammatory effects beyond what PRP alone provides, in part because bone marrow contains interleukin-1 receptor antagonist, a potent natural inhibitor of joint inflammation. This may account for the relatively prompt symptom relief some patients experience after the procedure.

2. Culture-Expanded Stem Cell Therapy (True Stem Cell Therapy)

This method involves laboratory isolation of the most regeneratively capable stem cells, followed by weeks of controlled culturing to produce a substantially larger, purer population. The resulting cells may have greater therapeutic potential, but this approach requires FDA approval for use in the United States outside of a formal clinical trial—approval it does not currently hold. Accordingly, it cannot be offered as a standard clinical treatment in this country at present.

Two main strategies exist for delivering stem cells to the target site. The first is direct injection of a cell-containing fluid into the joint, which is best suited to diffuse conditions like osteoarthritis. The second involves embedding cells within a scaffold—a membrane or matrix that is surgically implanted in the area of injury—which offers more precise localization but may impair the cells’ ability to detect environmental signals and behave as intended. Importantly, emerging evidence suggests the healing response may actually be driven not by the injected cells themselves, but by the signals those cells send to recruit the body’s own repair mechanisms from elsewhere.

Despite considerable public interest and marketing surrounding stem cell therapies, the clinical evidence base remains limited. Available data suggest modest improvements in symptoms, and no major adverse events have been widely reported. However, the possibility of a placebo effect has not been ruled out in several studies.

In one well-designed randomized trial from the Mayo Clinic, BMAC was injected in one knee and a saline solution in the other in patients with bilateral knee osteoarthritis. Researchers found no significant difference in outcomes between the two knees at six months or one year following injection. Reports on outcomes for culture-expanded stem cell therapies are similarly limited.

Reported adverse event rates for BMAC procedures range from approximately 6 to 10 percent of patients, with temporary pain and swelling being the most common complaints. Culture-expanded stem cells carry additional theoretical risks, including potential tumor formation from expanded cells and contamination introduced during laboratory processing. Animal model research has documented cases in which injected cells produced bone tissue rather than the intended cartilage.

Current evidence does not support the use of stem cell injections to prevent joint degeneration in otherwise healthy individuals. Existing clinical data relate exclusively to joints already affected by disease. Given that no intervention is entirely without risk, preventive use is not recommended.

Because younger cells retain greater regenerative potential, interest has grown in banking umbilical cord blood stem cells at birth for potential future use. Public and private cord blood banking facilities exist and may provide value for certain blood-related conditions such as lymphoma or myeloma. However, the practical benefit of private cord blood banking for future orthopedic or degenerative disease applications remains unestablished, and it is not currently recommended as a standard practice. Private banking involves an initial fee typically ranging from $500 to $2,500, with annual storage costs of $100 to $300 thereafter.