Home › Blog › Are there stem cells in my knee? Stem Cell Number in the Synovial Fluid Increases after Knee Meniscus Injury

Are there stem cells in my knee? Most patients seem surprised that there are stem cells in their knees. We did a study many years ago where we injected a pro-inflammatory agent into the knee joint and drew off the swelling in the joint. What was in the fluid? When compared to the other knee we didn’t treat, the fluid had many more stem cells. So it’s not a surprise today to see a recent study that shows that the natural stem cell number in the knees is higher when someone tears a meniscus. It’s also fitting that this study comes on the heels of new research showing that surgical treatment for knee meniscus tears doesn’t work.

Why are we seeing more stem cells in knees where the meniscus has been injured? Because these cells normally live in the synovial membrane, the inside lining of the knee joint. When there is an injury, they mobilize from there to the fluid so they can hitch a ride to the injury site (in this case the knee meniscus). This is why younger patients who injure their knees tend to heal more often, they simply have more stem cells that are available in the synovial membrane. I call this the “stem cell reserve”, which naturally declines as we age. Now this process of getting stem cells from the knee joint lining to the injured site (like a meniscus) isn’t that efficient. Many will end up somewhere else in the knee and some won’t attach to the right portion of the meniscus tear. Hence, when performing knee stem cell therapy, this is why exact placement becomes so important. You want to make sure you get the maximum number of cells where they are needed. For example, for a meniscus tear, this takes a high level of expertise in ultrasound guidance of the injection, so the stem cells make it to the parts of the tear where they’re needed. In addition, early studies showing that stem cell injections into the knee may help reduce the progression of arthritis, likely give credence to this concept of replenishing a worn out stem cell reserve with new cells.

The upshot? There are stem cells in your knees and they’re important in helping you heal. So the next time you tweak your knee, know that it’s mobilizing an army of repairmen into the spot. However, because of your age or the size of the injury, this army of cells may need some reinforcements!

Chris Centeno, MD is a specialist in regenerative medicine and the new field of Interventional Orthopedics. Centeno pioneered orthopedic stem cell procedures in 2005 and is responsible for a large amount of the published research on stem cell use for orthopedic applications. View Profile