Ouch, but on the other hand, good job it was only 4 not 400!
I hope the ACL isn't too bad - I did my ACL (a bit) and MCL (a lot) in my last ever rugby game at the age of 36. Surgeon said no more skiing, ever, but I have three kids and really wanted those memories, so I bought a brace and have skied every year since, often twice, and I'm now 55. I also did a lot of cycling which built up the quads and other things around the knee which, apparently, helped stabilise the knee area. It does get a bit sore after a few days but the brace does its job in stopping too much lateral movement and I have absolutely no regrets about ignoring the doc. I know quite a few people who have had ACL injuries and come back to skiing. All the best with the recovery.