Bullfrog, with 13 months left you might consider getting any health/dental needs taken care of while you're on the job. Coverage is usually better for current employees than it is for retirees.
If your knee is blown, torn ligaments, etc. requiring arthroscopic surgery you are not going to feel much like mowing the lawn or any other arduous task.
Do what you gotta do, don't bust your own chops, and don't jeapordize your retirement.
Be well, be safe,
Jim