I feel your pain on both counts--the knee and the dirty car.
Had reconstructive knee surgery about 20 years ago--ACL, MCL, meniscus, blah blah blah. Hurt like a sonofagun. Someone once told me there's not a heckuva lot you can go through that hurts more than knee surgery. To test that notion, I asked a female co-worker who'd gone through both childbirth and knee surgery which was worse. Far and away the knee surgery, she said.
So I wish you well, my friend. The pain will fade, your range of motion will come back and you'll be better off. You have an automatic, right? Be grateful (unless it was your right knee, of course, in which case the clutch is irrelevant).
Regarding the post-wash dirtying of your car, that sucks. The good part is that you can wash your car again. Be grateful that truck wasn't hauling gravel or something damaging. I've had to do a lot of freeway driving this week, which I hate, and I keep hearing crap pinging off my car. I just know that when I wash it this weekend, I'll have nicks to touch up. Grrr.