How are you going? I’m just back from a camping holiday in the Australian outback, it was very relaxing.
Yes, CPM is often not prescribed. The few good quality clinical studies that examine its use do so in the general surgical population, and not in arthrofibrosis patients, so the beneficial effects are washed out by the large numbers of people who don’t need to use it. In addition, I believe that CPM is not used frequently enough, or for long enough, in these studies for sustained benefits.
I need to clarify that “passive stretching” is stretching that does not activate the muscles of the limb being treated. If the muscles are activated this is active stretching (equals exercise), and unfortunately exercise is well known to generate inflammation. However, each person’s inflammatory status will be different, and given your medical history, your AF drivers may be different to the typical inflammatory drivers that involve chronic inflammation. The amount of pain is a guide to this. Perhaps your AF drivers are more to do with collagen production or turnover and you might be able to exercise more than many people with AF are able to.
In any case, I suggest that you take the bike riding very slowly and carefully. It is very easy to overdo exercise and end up worse off. However, if you find that your pain and ROM are not negatively affected by your bike riding, then that’s terrific! The riding most likely won’t improve your ROM unless you are stretching the knee to the maximum (pain-free) amount on every cycle, and gradually increasing this degree of ROM, but movement is healthy. For those in the situation where they can safely ride a bike there is another pedal arm available called the Orthopedal, see https://www.orthopedal.com/
If you find that your knee is worse after riding then you should still be able to exercise the rest of your body safely to gain the benefits that brings.
It will be good to hear how you’re getting on.