New nerves growing through the bone and cartilage might be causing osteoarthritic knee pain
Full reference: Aso K, Shahtaheri SM, Hill R, Wilson D, McWilliams DF, Nwosu LN, Chapman
V, Walsh DA, Contribution of nerves within osteochondral channels to osteoarthritis knee pain in
humans and rats, Osteoarthritis and Cartilage, https://doi.org/10.1016/j.joca.2020.05.010.
One of the enduring problems with osteoarthritis is that many people appear to have osteoarthritic changes in their joints but yet they don’t experience major amounts of pain making research targets difficult to identify. We know cartilage is lost from the osteoarthritic joint surface, which exposes the underlying bone causing a change in the appearance of the osteoarthritic knee but this change has not been found to cause pain by itself. To try and address this complex issue and identify the cause of pain, this study has examined nerves, that might be sending pain signals, for an answer.
We compared the nerve tissue from 2 groups of people who both appeared to have osteoarthritic changes in their knees and were undergoing total knee replacement therapy. We were able to collect tissue from the following two groups.
(1) people with painful knee osteoarthritis
(2) people with osteoarthritic changes within their knee who had not reported knee pain
We found more sensory nerves growing within the knee tissue of people with painful osteoarthritis.
We then looked at factors that might stimulate pain signals in nerves in a pain model. We blocked the action of one important molecule called nerve growth factor (NGF) which causes nerves to grow and can cause pain. Blocking NGF improved pain levels but did not change the appearance of the knee.
This study found that the appearance of the joint is not always the cause of pain and that joints that look like they will be troublesome might not be problematic. Blocking the actions of NGF might be an important way to improve osteoarthritis pain; and several drugs targeting NGF are being developed and tested by researchers.