I blew out my knee badly skiing last April (complete obliteration of the ACL, partial tears of the MCL and LCL, and tear in the medial meniscus) and had surgery in May. Finally caught up on this thread, which has been very interesting to read given that so much of my past year has been taken over the injury, surgery and recovery, and I still have a ways to go until I'll feel like my old self again. First, I echo what others have said in that ACL reconstruction is MAJOR surgery, and is not to be taken lightly. This was unquestionably the most significant and humbling medical event in my life thus far (I realize that this makes me lucky), and I don't think I was fully prepared going in for just how painful, serious and difficult recovery would be. Every knee, every injury, and every personal circumstance is different, but I would counsel anybody dealing with a ACL, meniscus, or similar injury to get opinions from multiple surgeons and to do their own independent research before making any final decisions regarding whether to get surgery and, if so, which type. And regardless of whether you get surgery or not, physical therapy is paramount ("prehab" before surgery is important too!), and you should get started as soon as you are able post-injury.
In my case, I don't harbor serious doubts that surgery was the right option given the extent of damage to my ACL and my age/activity level, but I do still wonder at times if I should have opted for a less extensive surgery than the one I had, which included not just a quad graft to reconstruct my ACL, but also meniscus repair and an IT-band graft to reinforce my LCL (more on that below). I spoke to three surgeons after the injury (though only really seriously considered two of them, as the third was a friend who gave me some solid advice but who specializes more in hips in his everyday practice), and all of them told me that I would need surgery if I wanted to keep participating in high-level skiing and other rigorous sports and activities for decades to come. The consensus seemed to be that if I was a few decades older or if I was more sedentary, I could probably get by without repairing the knee, but that my knee wasn't going to be stable enough without surgery to withstand heavy use over time. Of course, not being a doctor myself, I'll never know for sure if this advice was true or not, but I did seem my MRI (looked like a bomb had gone off in my knee) and it was clear that the ACL was torn completely in half, and that scar tissue alone wasn't going to make up for that.
Where I have harbored some doubts is in whether I needed to get as complex and aggressive a surgery as I did. While all the surgeons I spoke to agreed that I needed ACL reconstruction, they were somewhat split on whether I needed meniscus repair given that the meniscus, while clearly torn, appeared to have stayed put in its proper place. Of the two surgeons I considered, one told me that he might need to operate on my meniscus, but that he wouldn't know for sure until he had my knee open in the OR. The second surgeon told me straight away that meniscus repair was necessary. I opted for the second surgeon (primarily because he was more experienced and comfortable with quad grafts, which my own research suggested had a better long-term success rate for female athletes than hamstring grafts, but also because he made better eye contact). In addition to the ACL and meniscus repair, he grafted a piece of my IT band to act as a sort of secondary LCL. He said that he did this because studies show that younger and active women who suffer secondary damage to the LCL show lower long-term rates of re-injury when this LCL operation is performed alongside the ACL reconstruction, but I don't think my LCL was sufficiently injured that it would have required surgery on its own. All this to say, while I probably did need the ACL reconstruction, it's possible that I would have been fine foregoing the work on my meniscus and LCL, and those extra aspects of my surgery have absolutely made recovery longer, more difficult, and more complex. This is particularly true with the meniscus repair, which required me to keep my knee locked in full extension and to avoid any weight-bearing for a full 6 weeks post-surgery (with ACL reconstruction, I could have begun bearing weight and working on ROM much sooner), which I think contributed quite a bit to the severe quad atrophy that I am still struggling to overcome.
At this point, I'm a little over eight months out, have decent ROM (though its not fully symmetrical with my good knee, and I still can't sit cross-legged or comfortably hang out in a deep squat), have minimal to no pain, and am finally noticing more steady increases in my ability to tolerate higher volume and intensity of weight and agility training. I've also been skiing some, though I've stuck to groomed blues and been keeping a firm check on my speed to avoid having to make any sudden movements that my knee won't like. My knee joint feels quite solid. My biggest issue now is the significant atrophy to and insufficient control of my affected quad, which is proving a stubborn impediment to my getting back to full activity. The atrophy and lack of complete muscle control also seem to be reinforcing each other, with the lack of control making it hard to find exercises that sufficiently isolate the quad to achieve hypertrophy and rebuild muscle, and the lack of muscle mass making it hard to work on stability and control. I spent the better part of my 20s and 30s building muscle tone and strength in my legs that is completely gone now, and I worry that I'll never quite rebuild what I lost.
On the arthritis issue, my understanding is that, once you have sustained major injury to the knee joint (whether that be a severe tear in one or more ligaments, meniscus damage, or both), you are are facing a significant possibility of future arthritis whether you have surgery or not. I both sprained and broke my right ankle in separate injuries years ago, neither of which needed surgery, and at 39 I am already starting to feel the beginnings of arthritis in the joint. With my knee, I was advised that, by limiting instability and helping to prevent future injuries and complications, surgery would actually decrease my chance of arthritis rather than increase it (though, again, the recommendation that I have surgery was based on the specifics of my injury as well as my age and fitness level, and so I don't think that the advise regarding surgery and arthritis is necessarily universally applicable to all). But basically everyone, including the (extremely lovely and competent) doctors and nurses at the Alta clinic who first examined my knee, multiple doctors, my physical therapist, and even the many random strangers who noticed my post-surgical brace and felt compelled to tell me their own knee-injury sagas, have told me that arthritis is a strong possibility in my future. Though neither both of my parents had bad arthritis without ever suffering serious joint injuries (my dad even had both knees replaced), so maybe I was doomed anyway.