It sounds as if your between a rock and a hard place: both sports/exercise choices you want to do offer their own risks. But this is the same for everyone, the difference for you is that your probably more likely to fall ill to them then many others.
I think ultimately its your choice, its not something anyone on here can answer for you. Its something everyone could add their "if I were in your boots I'd do XXX" but at the end of the day, as Shelagh Lee has already said, its your body, and the same from me: your choice, not something anyone can advise fully for you.
You could weigh up the chances of things going wrong: how likely is it you will be knocked off your bike? (are competitions really that fierce that they have started shoving people off bikes now? (lol!)) but seriously, will you cope if you were to fall, would it be an instant "never able to cycle again" thing? How likely is it to happen anyway?
With regards to running, most if not all runners are at risk of osteoarthritis. I was told I have it beginning in my knees and that it will only get worse. I have cut back but I wont be stopping, not least of all because weight gain would apparently make it worse, keeping myself immobile would make it worse. I have tried to change HOW I do things: if I feel intense pain in my knees to be wary and if its possible, stop and to something else non knee irritating (hard to actually do being most cardio exercises require knees!) I have also tried to change my technique- though this for me is more to do with other issues I had been getting when running. I was already thinking about this a while before I was told about my knees. I took a more barefoot style and focused on form over distance and speed. I am not and never was running to win a race or compete, I do it for me, for my own PBs and changing my technique was not so much of a challenge but may be difficult for others. I have read that barefoot style running reduces impact when running and I have been told its the impact which itself brings about the osteoarthritis. I do have to wonder though as I was under the impression that cycling is just as likely to cause OA as running is due to the constant stressers on the joints and intensity of it all.
Maybe do a bit more research into how you can reduce the risks of either problem occuring, maybe think about the risks with either: if you fall off your bike again is that it and does it mean no more running no more anything? Can you work around there being another injury? Is it mainly fear of what happened before thats affecting you? And more importantly, maybe give it some real thought: whats really what you want to do and closer to your heart.