I had ACL and meniscus repair in 2012, and was on crutches for a few weeks. I had to be especially careful on stairs. The two cats I had used to race by me like that, so I trained them by whacking them with my crutches, not too hard, but not a tap either. They learned! They wouldn't pass unless I looked back and stopped and told them it was ok to go. And for the rest of their lives, even when I didn't have crutches, they would pause behind me, and make a noise that they were coming by. Every time. Those two were great cats.