2000 mg in 24 hrs is the maximum dose for Tylenol. More than that risks liver damage, especially if you drink alcohol, too. That's 2000 mg from all sources. Pain meds that end with "---cet" have Tylenol in them: Percocet, Lorcet, Darvocet, etc. That is where people get into trouble. Some of those combo drugs have 500 mg of Tylenol per pill. That means TWO doses per day if you're taking two at a time. Neither Tylenol nor narcotics work very well for nerve pain--- that burning, shooting, electric pain that goes with sciatica. The sciatic nerve emerges from the lower spine and goes down the buttocks and then down the outside back of the leg to the feet. If the swelling in the knee were pinching the sciatic nerve, the sciatic pain would normally be from the knee down. It might go the other way, but that would be unusual. The back pain is more likely caused by the slipped disk(s). An inversion table will help that. Ask your doc about injections of collagen, or even silicon for the knee joint as an alternative to surgery. If they give you any grief, look for another doctor. The Sportsman's Guide has inversion tables for less than $160. I'm sure other places have them, too.