Is there such a thing as knee nerve pain? Your joint pain due to arthritis is caused by lost cartilage, right? Likely wrong. There’s been a mounting body of evidence that arthritis itself doesn’t cause pain, and in fact the pain of arthritis (and perhaps arthritis itself in some cases), is caused by nerves.
The scientific research world studying arthritis has been all abuzz these past few years with more and more studies showing the nerve related origins of arthritis. I’ve blogged on one of my favorite of these papers that posits that irritated nerves dump bad chemicals into the joint which lead to the cartilage breakdown of arthritis. A new study shows us a little more about how this works. This group noticed that sympathetic nerves grew in the skin over an arthritic joint. These are nerves that maintain many of the automatic functions of the body and they also act as the braking system for pain. The researchers wanted to know if the same thing was happening inside an arthritic joint. So they made one in an animal model and went looking for these nerves. They found new sympathetic nerves sprouting in the joint and again concluded that arthritic joint pain is a nerve phenomenon.
Another study from Paris determined that Osteoarthritis pain originates in the free axonal nerve endings in the synovium, the tendons, and the periosteum (dense irregular connective tissue covering the bone rich in blood vessels and nerve endings), not the cartilage. They found that OA, or Osteoarthritis pain is a complex issue involving several different types of neuromediators and nerve signals, and is not correlated with joint degradation. Let me restate that – this is one of a bevy of studies where the degree of arthritis on imaging is not related to the amount of pain that patients report. Hence severe arthritis on x-ray doesn’t mean severe pain. The study concluded that because of it’s complex nature, treatment approaches to treat OA pain should be carefully chosen (i.e. not determined by solely looking at an x-ray or MRI image and a quick exam).
The upshot? We doctors may need to spend a lot more time looking for nerve issues in our arthritis patients than staring endlessly at MRI images!