Don't judge a book (knee) by its cover (cartilage)

What is it about?

One of the enduring problems with osteoarthritis research is that many people appear to have osteoarthritic changes in their joints but yet they don’t experience major amounts of pain. Cartilage is lost from the osteoarthritic joint surface, which exposes the underlying bone (known as subchondral bone), which is a striking change in the appearance of the osteoarthritic knee, but is still not enough to cause pain by itself. To try and address this complex issue, this study has examined nerves that might be sending pain signals in the subchondral bone (called sensory nerves). We looked at the nerves growing through the subchondral bone and how they might be causing pain. We compared tissues from 2 groups of people who both appeared to have osteoarthritic changes in their knees. (1) 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 subchondral bone of people with painful osteoarthritis. We then looked at factors that might stimulate pain signals in nerves in the subchondral bone in osteoarthritis in rats. We blocked the action of one important molecule called nerve growth factor (NGF) which causes nerves to grow and can cause pain. Blocking NGF reduced the number of nerves growing within the subchondral bone and also improved pain levels. Blocking NGF did not change the appearance of the knees, showing that the visible osteoarthritic changes were not solely responsible for causing the pain.

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Why is it important?

This study showed 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.

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