Patients often are led to believe that a stem-cell injection used to treat moderate to severe knee osteoarthritis has the expectation of growing large amounts of new cartilage. This usually is not the case, but despite this many patients get prolonged relief. To understand why, we first have to understand why osteoarthritis hurts in the first place.

Based on what we can see on X-rays and MRIs, osteoarthritis is a progressive loss of cartilage that leads to changes in the bone. Physicians and patients alike have been lead to believe that osteoarthritis hurts because of lost cartilage. Like many messages in medicine, the simple ones are easiest to explain to patients, but the truth is often more complex.

Despite a multi-billion dollar industry that exists to try to diagnose and treat lost cartilage, the most recent high-level research shows that there is no relationship between lost cartilage and pain. Since this is a relatively new discovery, most medical providers haven’t yet gotten the memo.

So if cartilage loss doesn’t cause osteoarthritis pain, what does? That’s where the simple explanation gets more complex. We know that problems in the bone that are easily seen on MRI can cause pain. We also know that inflammatory chemicals in the joint are better predictors of pain. We know that patients with knee osteoarthritis have problems in the nerves from the spinal cord to the knee. Finally, we know that cells inside the osteoarthritic knee get activated and begin wrecking havoc.

In many types of orthopedic problems we commonly see big structural changes with stem-cell injections. A good example is a torn ACL ligament in the knee. In patients who have mild osteoarthritis with a pothole, we’ve seen evidence on MRI that stem-cell injections can help heal the defect. In patients with big-time cartilage loss and severe osteoarthritis, however, the changes we see on MRI are less dramatic, usually limited to improvements in the bone without evidence of widespread cartilage growth. Many of these patients with severe osteoarthritis do very well with treatment, so what explains the changes? Here’s what we know (each link below is to a short video explaining the concept):

Stem cells can block the cells that are literally eating away at the joint.
Stem cells release many helpful growth factors for the joint, essentially becoming tiny little medicine factories.
Stem cells can hijack the helpful protein making ability of other cells, getting them to become tiny little medicine factories.
Stem cells can revive the batteries (mitochondria) of dying cells by transferring some of their good batteries to the troubled cell. 
Lastly, stem cells can morph into cell types that are needed in the arthritic joint, a process called differentiation.

In short, stem cells can help severely osteoarthritic joints in many ways. The fact that they don’t regenerate large stretches of cartilage isn’t likely a big deal, since cartilage loss isn’t causing pain and lost function.

“Stem Cells for Arthritis” first appeared as a post on the Regenexx blog.

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