bent left knee at impact

Hi,

So I have had this swing problem for as long as I can remember until last Fall I think I got it taken care of. I started swinging very very well in February, (left leg extended fully at impact and then hurt my lower left back somehow, then my swing went to crap from there. I was too shut at the top, and too flat. I am getting better with this but it took 6 weeks for my back to heal up. I don't know if the thing caused me to swing differently which introduced bad habits but now I am not nearly as fast as I was in CHS back in february, I am getting better, but not close yet. I am also hitting the ball with a low hook usually or just a low straight shot. I know I was doing this partially from being shot with the club at the top which I've pretty much fixed, and starting to hit a bit higher. But, I can see in my shadow that right at impact, my left knee goes foward to the target right at impact and collapses almost like I am not clearing my left side. In my practice swings I don't do it at all. But even with a pitch shot with a wedge it happens, and I have poor impact. I can sit there and hit for hours focusing on just extending the left leg at impact and make no progress. Febrary I was hitting a slight draw, 15 degree launch angle, good spin numbers and my BS average was about 172 and CHS 116mph. Flying it roughly 285 at sea level, now I am barely flying that at 4500feet elevation.

Any drills or what might be the cause?

Thanks

Thanks. The back gets sore lower left side after a while hitting balls. I am getting better with it but I still feel like I am lacking the speed I had a few months ago. One thing I've been trying is focusing on pulling my left shoulder up and back through the ball. My left knee is a tad more flexed towards target than those pics. But same idea. I just think there is something that causes me to do that, like maybe the shoulder thing.

I think I can get it worked out with time. Maybe I'll post a vid here. It stays flexed too long I know that too. There is power loss there and I am trying to make my swing as effecient as possible for higher launch and more speed.

Thank you for those pics too.