If a skier is tired or not going into the bump and absorbing it with their legs and core then knee injuries and soreness is an issue. I did about 8 solid bump runs yesterday and don't notice my knees at all but it feels like I did a few hundred sit-ups and squats today lol.
The knee injury concerns in my head are more about the DIN setting. It's a balancing act between pre-releasing or saving a knee. I keep the DIN on my bump/hard pack skis relatively low (10) and if I release it is because I have lost some control and am hot-dogging it, rather just release and save my knees. I have my DIN higher on my powder skis because I'd rather not release out of them because chances are that is a recipe for a head/neck injury and I would rather a knee injury. Would love to hear other views on this.
Hit Magic yesterday and the bumps and some of the woods (e.g., east side stuff) were fun and could get a good edge in. Did a few laps with the Freeride Team on Broomstick - Black Line and lower sections of Red Line. Pretty amazing to watch 6-10 year-olds just flying through bumps and throwing 360s off rocks and ledges.
Got to love Magic! This is a pic Kinderspeil my buddy took, "a beginner trail." Pretty good spacing so you could really zip them.