Stem cell therapy, particularly using mesenchymal stem cells (MSCs), is being researched for treating orthopedic conditions, most commonly osteoarthritis of the knee. This condition involves the breakdown of protective cartilage, leading to pain, stiffness, and reduced mobility. As a potentially less invasive alternative to joint replacement surgery, this therapy seeks to harness the body’s own regenerative capabilities. The goal is to alleviate symptoms and slow the progression of joint degeneration through biological repair.
How Stem Cells Are Supposed to Help Knee Joints
The therapeutic potential of mesenchymal stem cells injected into a knee joint centers on their ability to act as “medicinal signaling cells.” Their primary function is mediated by a paracrine effect, which involves the release of numerous bioactive molecules into the joint environment. These secreted factors include growth factors, anti-inflammatory agents, and specific proteins that modulate the activity of surrounding cells and tissues.
This signaling cascade helps to create a healthier microenvironment within the arthritic joint. MSCs demonstrate an anti-inflammatory effect by reducing destructive inflammatory cytokines like TNF-α, IL-1β, and IL-6, which are largely responsible for pain and cartilage breakdown. Through immunomodulation, the injected cells interact with local immune cells, promoting a shift toward an anti-inflammatory state that inhibits the activity of enzymes that degrade cartilage.
The growth factors released by the MSCs support the health of existing cartilage cells (chondrocytes) and the synovial tissue lining the joint. By stimulating the production of components like type II collagen and aggrecan, these factors work to maintain the integrity of the cartilage matrix. This trophic support mechanism is the core biological rationale for symptom relief and potential disease modification.
Sources of Cells and the Treatment Procedure
Stem cell therapy for the knee typically uses cells harvested directly from the patient’s own body, a method known as autologous transplantation, to minimize the risk of immune rejection. The two most common sources for obtaining mesenchymal stem cells are the bone marrow and adipose (fat) tissue.
Bone marrow aspirate concentrate (BMAC) is prepared after drawing a small amount of bone marrow, usually from the hip bone, using a specialized needle. Adipose-derived stem cells are collected through a minor liposuction procedure, often from the abdomen or flank, and are processed to isolate the stromal vascular fraction (SVF). Fat tissue offers the advantage of a larger cell reservoir and an easier collection process compared to bone marrow aspiration.
Regardless of the source, the collected tissue is processed quickly in a centrifuge to concentrate the beneficial cells and growth factors. Once concentrated, this final cellular product is immediately injected into the knee joint, most often guided by imaging techniques like ultrasound or fluoroscopy. This minimally manipulated, one-step procedure is performed in an outpatient setting and is generally completed within a single appointment.
What Clinical Evidence Says About Efficacy
The clinical evidence regarding the effectiveness of stem cell therapy for knee osteoarthritis is promising but remains complex due to the varying study designs and cell sources used. Many clinical trials and meta-analyses have reported that intra-articular injections of MSCs result in significant short-term improvements in pain and knee function. Patients frequently report pain reduction lasting between six and 24 months, with some studies showing sustained benefits over longer periods.
However, the question of whether this therapy works by truly regenerating lost cartilage is not definitively answered by the current data. While some advanced imaging studies, such as MRI, have occasionally shown an increase in cartilage thickness or density, the evidence for substantial, long-term cartilage regeneration remains limited. The observed clinical benefits are more consistently attributed to the anti-inflammatory and pain-relieving effects of the injected cells.
A significant challenge in interpreting the data is the heterogeneity among studies, which use different cell types, concentrations, and processing methods. Some randomized controlled trials have found that the pain and functional improvements achieved with stem cell injections were not significantly superior to those seen with a simple corticosteroid injection or a placebo injection at the 12-month mark. This suggests that while the therapy is safe and often beneficial, its superiority over conventional treatments is not yet universally established.
Regulatory Status and Patient Safety
In the United States, the regulatory landscape for stem cell therapy is managed by the Food and Drug Administration (FDA) to ensure patient safety. The FDA has not approved stem cell therapy for general orthopedic use, such as treating knee osteoarthritis, outside of approved clinical trials. The only stem cell products formally approved by the FDA are those used for specific blood cancers and immune disorders.
Clinics offering stem cell procedures often operate under a regulatory exception for “minimally manipulated” autologous tissue intended for “homologous use,” meaning the tissue is used in a similar manner to its original function. However, the FDA has issued warnings to many commercial clinics, clarifying that more than minimal manipulation of cells, or using them for a purpose not closely related to their original function, requires the product to undergo the rigorous drug approval process.
Patients must exercise caution, as the market is populated with commercial clinics offering unapproved products, such as those derived from umbilical cord blood or amniotic fluid, which may be heavily manipulated and carry risks. Serious adverse events, including infections, blindness, and even death, have been reported from unapproved procedures, often due to poor manufacturing standards or the use of contaminated products. A legitimate clinical trial will always be listed on a registry and will not charge patients for the experimental treatment, unlike unapproved commercial clinics that often charge thousands of dollars out-of-pocket.