Medical Discharge Questions?

I have been in the Army for over 9 years. I have had 4 knee surgeries in the past 2 and a half years. The first was a cyst in my left knee. The second was a torn ACL and meniscus from Afghanistan in my right. The ACL didn't take and ripped in half so the second ACL was done again using my left patellar tendon. Leaving the hospital my left knee split in half. So two days later my knee was put back together. I am considering a medical discharge but don't want to get screwed with the whole disability thing. Being a helicopter mechanic I can't perform my duties due to the fact that I have to walk with a cane. Can someone please give some advice or at least humor me with the whole medical discharge procedure?