Where does a pain in soft tissues come from when a joint is affected by osteoarthritis?

Pain is a frequent companion of osteoarthritis, and this pain becomes such that it greatly worsens the patient’s quality of life. Hence, at a minimum: to reduce pain, and at a maximum: to eliminate pain completely – this sometimes becomes almost the main task in the treatment of osteoarthritis.

The first among the drugs that are prescribed for pain in this disease are NSAIDs. I wonder how justified this is? There are many cases when there is severe pain in osteoarthritis, but the use of NSAIDs practically does not relieve pain. Let’s consider the mechanism of pain reduction with NSAIDs in a simplified form. NSAIDs, as a rule, reduce pain if this pain arose from inflammation. This means that if any disease is accompanied by inflammation, then NSAIDs can somehow reduce pain. But what about inflammation in osteoarthritis? Osteoarthritis is predominantly a degenerative disease. There is an inflammatory component in osteoarthritis, but not to the same extent as in, say, rheumatoid arthritis. And if it is there (inflammation), then to a small extent and it is mostly aseptic (that is, non-infectious; small fragments of articular cartilage begin to be perceived by immune cells as “foreigners”, hence aseptic inflammation occurs).

And what then generates pain in osteoarthritis, if there is no inflammation as such? Here it is necessary to determine where the pain receptors are located. They are mainly located in the joint capsule, ligaments, nearby muscles, fascia. It is these anatomical formations that give pain. And why can they give pain if there is no inflammation? The causes of osteoarthritis are still not fully understood. But it can be assumed that, most likely, improper use of the body leads to degenerative changes in the soft tissues of the joint and nearby structures. For example, muscle spasms lead to compaction in them, the formation of trigger points, as well as to shortening of muscles, which ultimately leads to fibrosis of some areas of muscle fibers. And this again, in turn, worsens the supply and nutrition of the joint, which in the future can lead to degenerative processes of intra-articular structures. By the way, there are no pain receptors in articular cartilage, as there are no blood vessels.