Over the counter gravity- fed Cryo Cuff for post-surgery or as a general pressure cold pack.
I used this knee cooling compression system through both my knee replacements and it was great! Very simple; no motor. Ice and water go into the cooler (which also works fine as a small cooler to store food when not used for knees.) Wrap your affected knee in the sleeve. Raise the cooler a few inches, up to a foot. The higher you raise it the more pressure your knee will have. Lower it and raise the cooler again to refresh new cold ice water through the system. I used it a lot. Works fine, but fabric is a little worn.