I was doing pretty good keeping knee series before I started lower body.
But alas it don't take much... I had yoga mat folded 4 times for the elevated surface of my elevated Deck Squat. Usually works fine but it slipped on me when I went down this time and made uneven surface when I came up. Knee felt a tweak. I can Squat up and down and walk fine but it's tender on inner side and if I angle my leg. Gonna take it easy on my legs and see if I just bruised or strained it before I start to worry. Probably would be major pain if was worse.
Even though yoga mat comfortable to roll back on its not entirely safe. I'll look for a more stable elevated substitute. Or maybe vise grip it in place.