As LFNS Resident Physical Therapist, I can concur - CPMs are great fun.....to administer
For those that haven't seen a Continuous Passive Motion Rig, they look like this.
They move the knee continuously for hours on end to stimulate healing and maintain optimal length-tension of any intact connective structures/musculature. This is done of course in addition to the actual physical work of rehab exercise and hydrotherapy.
One bit of advice... try remember to wear some underwear under your gown, once you're out of recovery. The amount of times I had to haul a knee onto a CPM and got an eyeful of furry mayhem is well into the thousands........
Good Luck Jae!