I also know that in horses they routinely inject hyaluronic acid, which appears to be significantly beneficial. E.g. The horse limps in, and one day later the arthritis is gone. My mom always jokes that she should just do it for herself but it is not apparently approved for humans. She's been injecting many of he horses for 10+ years with it.
It is approved for humans actually. I had a hyaluronic acid injection my for knee injury. I didn't really notice that it did anything though. But I think it's generally supposed to help lessen the pain for cartilage damage that isn't a focal defect. Note that it doesn't do anything to improve the cartilage — it just helps the pain.
