First of all - I expect this question to get very little attention: It's amazing how little attention people who work out seem to give to joint health.
Anyway, it seems that moving the joint "passively" (which seems to vary in definition from the joint being moved through ROM by a machine to moving the joint on you own with very little resistance). There is a study of rabbits that shows that rabbits with damaged cartilage healed faster when the injured joint was put through passive motion:
At three weeks this assessment revealed that in the adolescent rabbits, healing of the defects by hyaline articular cartilage was present in 8 per cent of forty defects in ten animals whose knees were immobilized, in 9 per cent of forty defects in ten animals whose knees were permitted intermittent active motion, and in 52 per cent of forty defects in ten animals whose knees were managed immediately after operation by continuous passive motion.
So - two things from this study:
- The idea that cartilage can heal, which most surgeons will vehemently deny.
- The idea that a joint put through "CPM" is 5 times more likely to heal than a joint that is not.
However, if we look at a summary of studies, the results seems more vague:
The reported clinical results, combined with the existing basic science evidence, suggest that there may be an ideal combination of all 3 treatments—CPM, AROM, and early weight bearing—that is most advantageous for both quality of life and quality of healing. Appropriate basic science research and focused clinical research are needed to generate postoperative rehabilitative protocols that will maximize benefits of articular cartilage repair and restorative procedures as they continue to advance and gain popularity.
There is also an article by some guy named Doug Kelsey that stipulates that:
Injured joints like movement, generally, and dislike being still. For an injured knee, I suggest things like a furniture slider, or even a paper plate to place your foot on and slide the foot forward back while in a sitting position. You can do this for 5-10 minutes a few times a day and most people find it quite helpful.
His example of AROM (basically moving joint lightly with no resistance) is shown in this picture:
It seems to me that he is just jumping on the "synovial fluid circulation promotes healing via nutrient delivery since blood flow is poor" idea. Edit: Also seems that his book isn't on sale on Amazon, so there aren't any real reviews, which makes me skeptical.
TL;DR: Is there any conclusive reason to believe that motion with no resistance heals joints? If so, how much and what kind?