O/T The rehab motivation is the key, IMO. When I was running after 6-weeks, the people who were doing the rehab and those familiar with the procedure thought it almost impossible. This was 17-years ago when an ACL usually meant 6-months before running. It's more common now to come back after a couple of months, although it is still a very aggressive schedule.
Surgeon skill is also a factor in coming back from the surgery. The extent of the injury is as well. Mine was very extensive.
I'm not sure about scar tissue being a factor with Tiger. Every surgery you do to clean up cartilage causes more tearing of cartilage later on. All that cutting to clean up cartilage leaves small tears in remaining cartilage from the instrument blades. Those pieces later fray and tear. It's a downward spiral that eventually will lead to arthritis, or bone on bone due to lack of cartilage.
The main factors in Tiger's comeback will be his tolerance of pain and the swelling. Some people swell at the slightest joint irritation, either a ligament sprain/tear or cartilage tear. Some people don't swell much at all. Tiger seems to have the pain under control, so it will be mostly about the swelling. He will need to strengthen the joint to keep new damage to a minimum.
If he rehabs like I did, that knee will end up being his good one for some time because of the intensity of the rehab and the focus on that leg.
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