What is happening here?

Here you go

Something like this I guess

That's called a kneel washout. It's a procedure to remove accumulated fluid in the kneel that is causing pain on movement to the patients.

I underwent this procedure a couple of days after injuring my Anterior Cruciate Ligament (ACL). It was necessary because I still had to wait a few more days for the surgery. After the injury, fluid built up in my knee, causing a lot of pain. Draining the fluid helped ease the pain and reduced the inflammation and risk of infection.

They are draining waste fluid?

Can someone tell us what this is really?

I believe they're removing liquid accumulation. I've seen it being done on someone with arthritis

I am trying to understand

What is he extracting 🥹

No idea