Both my knees have been shaky in the midrange squat position, just as I start to descend and until I get below parallel. They were feeling strained and weak in the dip before any jumps and while I would climb stairs. Even getting into a quarter squat position to deadlift was uncomfortable. I could squat fine, but my the knees themselves just didn't seem to be getting any more solid.
Since I was weak in the half and quarter squat positions, I figured I'd get strong in exactly those positions. I started doing heavy ass quarter squats to pins with knees way over toes. Escalating sets of five. Not to up my squat, but to condition my knee joints.
We're cautioned to avoid that movement and that position with load, but it did the trick. Knees snapped right back into shape. The effect was as immediate as when I started PVC pipe rolling my quads and IT band. Immediate improvement in function. This won't up my squat directly, but I suspect it will stop knee weakness from holding me back.
Interesting to note: the effusion I usually suffer from squatting is staying away since I did those heavy quarter squats.