Anyone ever do an IM or HIM without an ACL?

How did you find out your ACL graft has failed?  if it was by MRI I wold submit they are not 100%.  If it was by exam which is typically more accurate than MRI in the hands of an experienced examiner then maybe but if you had residual laxity it may just be a loose graft.  If it was by arthroscopy to address your meniscal issues then its gone.  Int eh face of some arthritis get tehmeniscus taken care of at least if you have not already. You should be OK for straight ahead things (like SBR) but I would wear a brace for skiing soccer basketball etc.  Get the meniscus cleaned up tho

Yup.  HIM last summer, no ACL in my right knee for 10 years.  I was originally misdiagnosed as LCL and told to strengthen.  I re-injured, saw a surgeon and was told it was ACL.  MRI showed my meniscus is ok though.  The surgeon said he could do surgery, but I would be a year out of my sport (hockey at the time) and there were no guarantees.  He said if I have been playing hockey without it, I was likely ok .  I have occasional pain in the knee, and it will click and give out here and there, but I managed the HIM.  And plan to do an IM in 2014.  Strengthen, and listen to your body, rest when needed.  Good luck!!

Two years ago I attempted IMLP without an ACL.

I tore mine skiing late December. After talking to my doctor we decided to push surgery until after IMLP. It had no effect on my swim or bike training, but I did limit my running(essentially I didn't do any real speed work). Other than immediately after the injury I never wore a knee brace. 

Long story short I DNFed Lake Placid 3.5 miles into the run due to sever dehydration (>10% bodyweight loss). However my knee was fine for everything.

My biggest fear was during training was if a stray dog would run out at me or if I would have to hop quickly to avoid an obstacle that I would do more damage to my knee.

I will say that there are some issues with prolonged training without an ACL(or any knee ligament). It changes the way your muscles in the leg respond to stresses and loads. However the fact of how well trained I was before my surgery did make for a speedy recovery in other areas, so it's a give and take.

EDIT: I just reread your post and saw that you have some meniscus damage. That could affect things more. Depending on the severity of the damage the high impact of running _may_ lead to further tears and more damage. Really you should just pay close attention and if you have any strange or elevated levels of pain stop and take some time to rest, but I still think it should be possible.

Thanks every one for the answers, nice to know I'm not the only one that has attempted it.  My ACL tear (the 2nd) was dx on MRI and through direct visualization during an arthroscopy.  Since I had the scope done my knee feels pretty good overall.  I'm an Orthopedic PA and spend long hours standing in the OR, it can get sore and swollen from that but generally feels OK.  Running feels great while I'm doing it but I pay for it afterwards.  I know that part of my problem is a weight issue.  I've gained quite a few pounds since the injury and my knee certainly knows the difference.  I've started a new training plan 2 weeks ago and have already lost 7lbs and hope to lose A LOT more by next tri season.  Basically, I'm going to go somewhat slower than I want but I just going to go for it and see what happens.

Since you are an ortho PA you have lots of good info at your finger tips. I am a sports trained orthopedist and a 2 time loser with my ACLS (tore both sides).  Even tho you work in ortho I will assume no knowledge RE ACLs

1-Strengthen the heck out of it.  Give yourself a hamstring strong leg as your hamstrings do, dynamically, what you ACL does statically
2-I would be worried about how much DJD you may have.  If it is unicompartmental consider an unloader brace which will also help stabilize your knee
3-Work with a PT in addition to the hamstring strong leg you also really need to work on balance and proprioception
4-Some people do fine without an ACL and we call them copers.  Others are having a lot of instability.  Unfortunately we have no way to say YOU are going to do fine and cope and the next person will not
5-If you are falling down every time someone gets too close to you, you might need to have it fixed again however I would give the PT a good try first if you don't want to have it re-done
6-In general you should be OK for straight ahead sports....swimming biking and running.  This is not the time to take up a cutting sport like Soccer

good luck. Feel free to PM me if you have any questions