Two years ago I had open heart surgery as a precaution since my mitral valve was leaking. I was then age 85 and always fit. The operation was successful with no complications. At the time, and during rehabilitation which included supervised walking at normal pace for two kilometres around the hospital block, my left knee was playing up. Not seriously painful but slowed up my walking pace. Been like that for a year before my operation and it didn't go away. As a simulator instructor I had to demonstrate various sequences to students and the left knee pain restricted my movement . One of my students was a doctor who owned a farm with horses. He noticed me limping because of the inside of my left knee was a bit painful at times. On our next sim session he gave me a large tube of horse liniment under the trade name Rapigel. At least that is the trade name in Australia. It specifically states for animals only. Nevertheless my student says it is widely used on humans and so did my own doctor and chemist.
I rubbed the liniment on the inside of my knee twice a day for a month and very soon the knee pain vanished. I could not believe how effective the Rapigel was. That was two years ago and so far so good. No re-occurrence of the ailment and I discontinued use of the Rapigel about a month after the knee pain disappeared. My medical doctor attended a conference where Rapigel was discussed and many doctors swore by its effectiveness. Even though it is labelled for legal reasons, only to be used on animals who have sore limbs.