Re: What's the ROM after a full knee-replacement
It really is an individual difference in the absolute ROM end. Most likely with as old as his is, swelling is no longer a limiting factor, most likely the limiting factor is muscle length and strength. Your brain and the muscles will not move a joint beyond what it is strong enough to control. You constantly need to be lengthening the muscle and also strengthening the muscle within the range you have available. Now depending upon the type and amount of therapy he had, and his pain tolerance and his personal physiology scar tissue may also be a limiting factor.
Another possible limiting factor is the type of knee that they put in. Just like everything else there are several models and depending on how bad his knees were, his expected activity type and level after surgery, and the surgeons preference the type of knee put in might be a limiting factor.
If he were my patient/client, I would work the squat, but I would not be as aggressive about getting it as low as possible. I would allow his natural physiology and strength determine how low he went on his squats, but as I said before parallel depth is not usually an unreasonable expectation. If you are working with him you should be able to teach him body awareness enough to tell you where and what is his limiting factor and work on that.