What was the underlying condition that was fixed. That may also need to be reported. There had to be an issue with your knee that prompted the cleaning / surgery. Did anything change to what you answered to these questions.
53. Have or ever had: Any bone or joint problem, injuries, surgery or medical treatment.
76. Had or been advised to have, any surgical operation.
I believe you have knee pain to report, unless you already reported it, and the surgery. You may be required to have 6 months recovery, before you are qualified and you may need a medical opinion that states you are fully recovered with no restrictions.
If the surgery was this year (2017) I would be worried.