Would a preexisting knee injury be permanently disqualifying me from enlisting?

Talk to a recruiter. It depends on the medical exam at MEPS.

If you have not already talked to a recruiter, that is the best place to get this answer. I will tell you that you are going to have an up hill battle, but not impossible. Have all your medical documents with you when you got to see the recruiter and be honest with them. I had a knee injury and it required a waiver to get back in, however my injury was service related so it was a different process to re-enlist. It will take longer to get signed up, but when you get the waiver approved, and put the uniform on for the first time it is all worth it! Best of luck!

So this is where you need to weigh options very carefully and specifically. I was medically retired following multiple attempts at reconstructive intervention of my right knee. I destroyed the entire medial femoral condyle and was running around with impingement and bone to bone contact. So with your current knowledge of your condition and it being documented; any following injury during training will be most likely considered EPTS (existing prior to service) and will not receive evaluation for a disability rating. The VA also only rates knees at a 10 percent disability unless there has been a total replacement which increases the rating to 40 percent.

I admire your patriotism and say talk to a recruiter. The worst that can happen is being told no.