We know that the knee is capable of some degree of self-repair because patients with small tears in the cartilage or meniscus can experience spontaneous healing of these injuries. The question is how?
The answer. according to one recent study, appears to be through knee stem cells that live in the synovial tissues. The synovial membrane is a spongy tissue that lines the inside of the joint capsule of the knee. We’ve known for some time that knee stem cells live in these tissues. Other studies have observed that these knee stem cells can help to repair injuries in the knee meniscus.
In this new study, the researchers created small cartilage injuries and then observed what happened to labeled knee stem cells that lived in the synovial membranes. They observed a specific knee stem cell type grow more of itself and then migrate from the synovial membrane into the cartilage defect and demonstrate clear signs of cartilage repair. We’ve had similar observations with the use of an older regenerative medicine technique known as prolotherapy (aka prolo). Prolo involves injecting substances into a tendon, ligament, or other area in need of healing. These injected substances cause a brief inflammatory response, which helps recruit cells to the area to help the damage heal.
In our unpublished study, we injected prolo solution into 6 knees (using a usual treatment) vs. placebo and then took samples of the synovial fluid. Knee stem cells were then isolated in the synovial fluid and cultured in our medical practice’s advanced stem cell lab to determine their final number. We saw more knee stem cells in the prolo treated knees compared to knees injected with saline, which is consistent with the results of this new study. While the knee stem cells we detected were of a greater number in the prolo knees, we felt that for most purposes of knee cartilage or meniscus repair, they wouldn’t be enough to get the job done. This fits with our clinical experience that prolotherapy works best with damaged ligaments and tendons (easier to repair), and doesn’t work as well for things like meniscus or cartilage repair. This would also explain why in most patients, bigger injuries don’t heal naturally as there simply aren’t enough knee stem cells to get the job done. As a result, we use the patient’s own stem cells to treat knee meniscus or cartilage problems.