Stem cell therapy for knees is an injection-based procedure that delivers concentrated stem cells into a damaged knee joint, aiming to reduce pain, slow cartilage loss, and improve function. It’s most commonly used for osteoarthritis but also marketed for meniscus tears and other cartilage injuries. The procedure typically costs $5,000 to $10,000 per knee, is not FDA-approved for this use, and is not covered by insurance.
How Stem Cells Work Inside the Knee
The stem cells used in knee injections are mesenchymal stem cells, a type found in bone marrow, fat tissue, and umbilical cord blood. Once injected into the joint, they appear to work through two main routes. First, they can differentiate into cartilage cells, directly contributing to tissue repair. Second, and possibly more important, they release tiny signaling packages called exosomes that influence the cells already in your knee.
These exosomes act like chemical messengers. They stimulate existing cartilage cells to multiply, recruit other repair cells to the area, and dial down inflammation. In lab and animal studies, they’ve been shown to protect cartilage by reducing the breakdown of collagen and other structural proteins that give cartilage its cushioning ability. They also appear to restore damaged energy-producing structures inside cartilage cells, which helps those cells survive longer rather than dying off prematurely. Separately, stem cell exosomes have reduced pain-signaling molecules in nerve tissue in animal models, which may explain some of the pain relief patients report.
Where the Stem Cells Come From
Most clinics use one of two sources, both harvested from your own body during the same visit as the injection.
- Bone marrow: A needle is inserted into the front of your pelvic bone (the iliac crest) under local anesthesia, and about 60 mL of bone marrow is withdrawn. This is then spun in a centrifuge to concentrate the stem cells into a small volume, roughly 8 mL, called bone marrow aspirate concentrate (BMAC). This is the most widely used approach in clinical practice.
- Fat tissue: A small liposuction procedure removes fat from the abdomen or thighs under local anesthesia. The fat is then processed, either by mechanical fragmentation or enzymatic digestion, to isolate the stem cells. Fat tissue contains a higher concentration of mesenchymal stem cells than bone marrow, is easier to collect, and may respond better in inflammatory environments based on preclinical data.
Some clinics use donor cells from umbilical cord blood or amniotic tissue, though these carry additional regulatory concerns. No randomized controlled trial has yet directly compared bone marrow and fat-derived approaches head to head, so neither has been proven superior.
What Happens During the Procedure
The entire process usually takes place in a single office visit, though some protocols culture and expand the cells over days or weeks before reinjection. After harvesting (from hip bone or fat tissue), the sample goes through lab processing to separate stem cells from red blood cells, fat cells, and debris. The cells are tested for viability, then concentrated into the final injection.
The injection itself is guided by ultrasound or real-time X-ray imaging so the needle reaches the correct spot inside the joint capsule. The imaging guidance is important because blind injections can miss the joint space entirely. The whole visit, including harvesting, processing, and injection, generally takes a few hours.
How Much Pain Relief to Expect
A meta-analysis of clinical trials found that patients receiving stem cell injections had significantly better pain scores than control groups at 3, 6, 12, and 24 months after treatment. Pain, measured on a visual analog scale, improved at each follow-up point. However, when researchers looked at more detailed measures of stiffness, physical function, and pain using a different scoring system (the WOMAC questionnaire), the differences between stem cell and control groups were not statistically significant. This suggests that stem cell therapy produces real but moderate improvements in overall pain, while its effects on stiffness and daily function are less clear-cut.
The stage of your arthritis matters considerably. A propensity-matched study of patients receiving fat-derived stem cell injections found that people with moderate osteoarthritis (where joint space is narrowed but cartilage isn’t completely gone) experienced significantly greater improvements in pain, daily activities, sports ability, and quality of life compared to those with severe, bone-on-bone arthritis. The improvements were most pronounced at 1 and 6 months after injection. The takeaway: stem cell therapy tends to work better when there’s still some cartilage structure left to work with. Patients with the most advanced joint damage see less benefit.
Risks and Side Effects
A systematic review of nearly 2,000 patients found an overall 12.3% rate of temporary side effects, almost entirely limited to swelling and pain at the injection site. The vast majority of these resolved within four weeks. A small number of cases, particularly with fat-derived and bone marrow approaches, had swelling lasting longer than a month. There were also occasional reports of soreness at the harvest site (the hip or abdomen).
Across all patients in that review, no cases of serious complications like sepsis, tumor formation, hospitalization, or death were reported. One isolated infection was documented. A separate report identified 14 patients across the U.S. who developed infections or sterile inflammatory reactions after injections, with umbilical cord blood products being the most common source of those problems. Overall, the safety profile appears favorable for a procedure of this type, though long-term data beyond a few years remains limited.
Recovery and Activity Restrictions
Recovery follows a gradual progression over about six weeks. For the first 24 to 48 hours, rest is recommended but you shouldn’t be completely sedentary. Physical therapy typically starts within four to six days.
During weeks one and two, activity is limited to light daily tasks. Stairs should be minimized, lifting kept under 10 pounds, and no running or weight training. Gentle stretching and range-of-motion exercises are fine. By weeks three and four, you can add a stationary bike, elliptical, swimming, pool walking, yoga, or easy walking, but all workouts should stay under 50% of your pre-injection capacity. Anti-inflammatory medications like ibuprofen should be avoided for at least four weeks, and ideally six, because they can interfere with the inflammatory signaling the stem cells rely on to do their work.
Weeks five and six allow a gradual return to resistance training, though high-impact and heavy compressive exercises (squats, leg press, box jumps, deadlifts) are still off-limits. Hiking on uneven terrain should also wait. Most patients are back to normal activity by around the two-month mark, with continued improvement in symptoms over the following months.
Cost and Insurance Coverage
Stem cell therapy for knees typically runs $5,000 to $10,000 per knee, making it one of the lower-cost stem cell procedures but still a significant out-of-pocket expense. Insurance does not cover it. Medicare covers established bone marrow transplant therapies for conditions like blood cancers, but does not cover unproven stem cell treatments for joints. This means patients bear the full cost, and some clinics offer payment plans to manage it.
FDA Status and Legal Landscape
No stem cell injection product is FDA-approved for treating knee osteoarthritis. The FDA regulates human cells, tissues, and cellular products on a tiered system, and the default position is that stem cell preparations require the same premarket approval as drugs, including clinical trial data proving safety and effectiveness.
This has been tested in court. In a case involving clinics that removed patients’ fat tissue, processed it to isolate stem cells, and reinjected the mixture into knees, the FDA argued the product was an unapproved drug. In September 2024, the Ninth Circuit Court of Appeals agreed, ruling that the stem cell mixture did not qualify for the “same surgical procedure” exception that some clinics had relied on. Despite this, hundreds of clinics across the country continue to offer these treatments, and regulators have been criticized for not doing enough to curb unapproved offerings. If you’re considering this treatment, it’s worth understanding that you’re opting into a procedure that has promising early evidence but has not cleared the standard regulatory bar for proven medical treatments.