Hi guys (and gal), I hope everything is going splendid!!
Found an interesting article about leg extensions (well the article is older but I just found this recently) and how they lead to long-term knee problems. I strongly suggest you all remove leg extensions from your workout (if they are present) and replace them with squats or leg press to hit your quads.
http://www.t-nation.com/article/performance_training/the_truth_about_leg_extensions&cr=
Have a great week! May the gains be with you