Lower the bar down to the knees, as if you were doing a Romanian deadlift.
Explode into a vertical jump while holding the bar. Do not pull the bar. The arms stay straight.
Don't lower the bar too slowly. Just keep it under control. Be sure to finish the hip extension; make yourself "tall." Don't be surprised if you jump backward a bit when you get it right.
Forget everything your gym teacher taught you about rehabbing an injury. Here are some controversial approaches to healing fast, starting from the bottom up.
Learn to apply force quickly and it'll make you stronger. That's what speed training is all about: power, explosiveness, and strength. Try this before you plateau.