The best low-risk options are TKE's (as mentioned), Peterson step-ups, and sled dragging. Also VERY effective if you're an experienced lifter and have good form are full squats, full front squats, and split squats (especially with the bar racked in front squat position). Leg extensions will do the job for the VMO, but there's just better options.
Lunges are actually not that effective at preferentially recruiting the VMO. Good exercise, just not for that goal.
Have a good one,