I will have to study these threads... but my first thoughts are
Did your friend (with serious arthritis and meniscus tear) have surgery to repair the meniscus? or for the articular cartilage damaged by arthritis? or both?
When the Doctor advised him that he would likely need surgery again in a few years, what specific surgery is he referring to? to repair the meniscus again?
How long had your friend with serious arthritis and meniscus tear wait before having the surgery? Is it possible that physical therapy would have resulted in the same outcome had he given it enough time?... That seems to be what these studies of meniscal tears and concomitant arthritis are suggesting?
Also note the quote from Ollinger in the other thread:
You may have seen in some newpapers or magazines reports of a pretty good study recently published on this topic. Conclusion was that if you have any evidence of arthritis in the knee, a meniscus procedure is worthless."
If the surgery enabled your friend to play tennis for additional time -- something that would've been impossible with non-surgical
treatment -- it sounds like the surgery was successful.
But the successful surgery would seem counter to what Ollinger is saying...