On Instagram, Dr Victoria Tchaikovsky, sports doctor, recalls a key idea: in osteoarthritis, the pain does not come only from the cartilage. X-rays remain useful, but they cannot always explain the intensity of what a person is feeling.
Pain doesn’t just come from the cartilage
Osteoarthritis is often summarized as a story of “worn cartilage”. This is understandable, but too simplistic. As the video explains, healthy articular cartilage is not innervated : it does not have, in itself, the nerve endings capable of directly transmitting a painful message.
This does not mean that the pain is not real, nor that it is “in the head”. Rather, it means that osteoarthritis concerns the entire joint. Inserm now describes this disease as notably involving the cartilage, the synovial membrane and the subchondral bone, that is to say the bone located under the cartilage.
The expert cites several structures around the cartilage which are innervated: the synovium, the subchondral bone, the capsule, the ligaments, the periosteum or even certain parts of the meniscus. When the osteoarthritic joint changes, these tissues may be subjected to mechanical stress, local inflammation or remodeling. It is these changes that can activate nerve endings and contribute to pain.
Another important point taken up in the video: the chemical environment of the joint also changes. Inflammatory mediators and molecules like NGF, for nerve growth factor, can make certain nerve endings more reactive. In other words, the same movement or the same constraint can become more painful than before in some patients.
Why two similar x-rays can give different pain
Radiography plays an important role in diagnosis, particularly to characterize osteoarthritis of the knee. It may show narrowing of the joint space, bone changes or other suggestive signs. But it doesn’t tell the whole story of pain.
This is what is often called radio-clinical dissociation: severity visible on an x-ray does not mechanically predict pain intensity. Some people have very marked images and little embarrassment; others present less impressive images but significant pain. It is not a question of opposing the examination and the feelings: the radio helps with the diagnosis, but it is not always enough to measure the pain experienced.
To make this mechanism more concrete, Dr. Tchaikovsky uses the image of an alarm system. In an arthritic joint, certain nerves can become progressively more sensitive: the pain signal is then triggered more easily. Drchaikovsky summarizes this idea as follows:
“The alarm triggering threshold decreases.”
This phenomenon corresponds to a peripheral sensitization : the nerve endings present in or around the joint react more. Recent work also suggests, in certain pathological tissues, modifications of the innervation, but we must remain cautious: this is not presented as a systematic phenomenon in all people suffering from osteoarthritis.
In some patients, especially when pain persists, the nervous system that receives and processes these messages may also become more reactive. We then sometimes speak of central sensitization, involving the spinal cord and the brain. Here again, this notion does not mean that the pain is imaginary: it describes possible amplification of the pain signalwhich does not summarize all cases of painful osteoarthritis.
What this changes to understand its symptoms
This explanation helps to get away from guilt-inducing or overly simple reasoning. Significant pain with an unspectacular X-ray is not necessarily “exaggerated”. Conversely, a very marked X-ray does not automatically imply severe pain. Symptoms depend on several parameters: the affected tissues, local inflammation, mechanical stress, nerve sensitivity and the context specific to each person.
To better understand the mechanisms of osteoarthritis, it is therefore useful to keep in mind that cartilage is only one element of the problem. Pain, stiffness, inflammatory flare-ups or functional discomfort are part of a broader set, described in the pages devoted to the symptoms of osteoarthritis.
In practice, a few guidelines can avoid misunderstandings:
- An X-ray is not a “pain score” : it provides information on the lesions, not on the entire painful experience.
- Osteoarthritis pain can come from innervated structures around the cartilage, not just from the amount of cartilage remaining.
- Persistent, atypical or disabling pain merits medical advice, without changing current treatment or monitoring alone.
In the case of the knee, True Medical also points out the absence of perfect correlation between radiography and functional discomfort. It is precisely this point that allows us to better understand why two people with similar images can experience their osteoarthritis in very different ways.