If you receive a TKR( Total Knee Replacement) depending on your job you will probably be put in for an MEB. If you work in a career field where there are a lot of impact activities then you will surely go through an MEB. If you work something more like a desk job they may try and retain you depending on your job performance and see you as an asset. After a TKR you are not supposed to run or do impact activities. That doesn't necessarily stop some people. A lot also depends on which branch of service you belong to. Also if you do go through an MEB and are found unfit, a TKR is 100% for the first year and drops to a minimum of 30% after that, which means you will be medically retired. I have had 5 knee surgeries, 4 ACL replacements. I have been told by civilian doctors that I need a knee replacement because of the constant pain from repetitive surgeries which most likely caused severe nerve damage. The military says that as long as I can bend my knee to 90 degrees even though there is constant pain which worsens throughout the day and with daily activities. Also they say my age is a big factor, I'm 31. I hope I answered some of your questions.