Motorcycle. I already have a mountain bike. I still run on occasion but its getting to be less and less. The knee bears weight but It hurts like a mother when my knee cap pops out. I'm going to make an appointment with a specialist in the morning to see if they can fix it. I am guessing a partially torn meniscus.
You don't need a specialist. Suck it up and wrap it in duct tape. That'll keep that cap in place.
