I had a conversation with a guy at the US Open. He was about 70 years old. He had had a meniscus operation which is usually a partial meniscectomy, or removal of a percentage of the damaged meniscus. He had had a very considerable percentage removed.
His Dr told him that for similar knee operations, because of the nerve locations in or near the knee joint, often one of two conditions results for exercises such as running or tennis:
1) either considerable pain, or
2) little pain.
In his case, he did not have much pain and could play.
- for articular cartilage
"As cartilage is aneural and avascular (lack of nerve and blood supply, respectively), shallow damage often does not trigger pain."
Painwise he was OK playing but because of his discussions with his Dr he knew that he was doing damage. He quit tennis after playing for a few/some months.