I am 45 with normal BMI. Played badminton till 2 years ago, when knee swollen after game.
Went to KLSMC, consulted Dr Tan ( not Dr Saw or Dr Tay).

Diagnosis was torn meniscus and damaged cartilage. I asked him how severe, he said category 3. Luckily no need surgery. Just physio, supplement and hyaluronic injection. Dr said shouldn't play badminton or go hiking anymore and avoid stairs if possible. First 9 months I couldn't sit cross legged (maybe due to knee mechanism problem) but now ok. After doing physio for a while, I felt fine and good for normal function like walking. However, I could no longer do squat hold or squat jump without feeling pain afterwards...which would last 5 min or so. I tested and tried jogging on treadmill, next day a little sore but nothing so severe.

Had tried physio, supplement (Projoin, Excel product), acupuncture, and injection (now maybe once a year). Only surgery or stem cell haven't tried. Now i had stopped all supplements and physio occasionally only as condition never improve but doesnt get worse also.

Can't get back to old life.
Do you guys have any suggestion?

This may sound weird ... try 48 - 72 hour fast. It works wonders on your body, think of it as a reset button to your body.
I have shoulder pain that never went away no matter what I did, but after a 48-hour fast, the pain reduced very significantly. No medication, no treatment. Just simple fast. Look up YouTube.

Same situation. Knee pain very complicated. Depending on where the tear located. There are certain angle or force that can cause irritation.

I still squat heavy, jogging, hiking and badminton. Depending on the intensity then next day will swell.

Its better to avoid at lot of impact / twisting move especially badminton, steep down hill. More controlled movement like squatting is okay.

Practice how to use ur hamstring more by moving the weights more to heel.

Lastly, just know that we're old already.

Old =/= Fragile!

You mentioned that you're doing physio occasionally but your condition isn't improving.
My question is if your physio is challenging you enough? Are they progressing your exercises? For example, squatting more in terms of intensity as weeks passes?

Most importantly, you need to manage the volume. If you feel pain after, probably your activity was too much for your current situation. But that is ok & normal.
Example, knee pain after squat hold for 1 minute.
Try breaking them up into several repetitions.. 3x20s
Monitor the next day. Still pain? Change. No pain? Increase

This is interesting and new. I have researched the video and seen it. So far haven't decided to try it yet. But thanks.

I see what you mean. Yes, it does seem more aggravated at certain angles. That is why I was advised no more breaststroke kicking motion and only swim freestyle. But I dare not do those high impact activities like before. As I really do not want any operation, especially the knee replacement as I dreaded it. Just hope it doesn't become necessary some 10 or 20 years later.

Guess not as I wasn't doing enough. Getting back into it now, as I felt niggling discomfort on the knee after some inactivity. At this age, muscle bone maintenance is becoming important. Need to be disciplined and can't lax with the physio. Will keep in mind the frequency, intensity and monitoring as per your suggestion. thanks.

Remember, physio is there to guide you.
Ultimately you need to do your homework to get better.