Knee manipulation next week after patellar surgery in sept.

Hello dear Physiobob users. Mid-september I crashed my motorcycle and broke my patella into pieces. I had open patellar surgery that day and had wires/pins put into my patella. Luckily no ligaments were torn. I had a cast for 6 months and I have been doing physiotherapy for 4-5 weeks now. About 3 weeks ago I saw my Orthopaedic surgeon and was told by him that I would need a knee manipulation while under anestesia and a couple days in the hospital on a machine (to keep my leg bent/moving) to keep my leg from tightening up to the point where I would need surgery. When I saw my doctor I had only had about a week and a half of physio and because my insurance hadn't paid for the active therapy yet I wasn't getting any. At this time I had about 40 degrees of motion in my knee. A couple days later I started active therapy, and I've been seeing results that I think are very good since then. I've gained about 10 degrees of motion per week, but this week I have about 15 degrees over last week up to a total of 85-90 degrees. I have massage included in the physio and I think it is helping a whole lot and I want to think it is helping to keep my muscles/tendons/ligaments from tightening up as my surgeon had said would happen. I have the manipulation scheduled for next week wednesday and I'm curious as what to people have to say about me doing it. I really don't want to stay in the hospital again for even a day let alone 2 or 3 and even less so want to experience what I experienced coming out of anesthesia and having knee pains along with all kinds of problems. Should I do it? Or with my rate of progression is it likely I will gain back full range of motion within a couple months doing what I've been doing? Also I would like to know what kind of damage will be done to my knee. Will this set me back a couple weeks of strength training? Will it do any permanent damage? Will I even be able to do my regular stretches with the kind of pain and damage that will be done to my knee a couple days or a week after the op? My surgeon said the manipulation might not do a whole lot, and for some people it doesnt help, what should I expect as a young man of 21? And one final question which I don't want to ask but someone might have experience with this and I wan't to make sure I'm headed in the right direction: Is it possible at all that my surgeon doesnt really think the operation will help yet he still tells me to have it? What I don't like about the situation is that theres no pre-op testing a week before to examine a patient and see if they really still need the surgery at St Michaels hospital in toronto. Why is everything set in stone almost a month before a surgery like this? Because of this I question my own reasoning, I know nothing of knee mechanics. Thanks in advance for any responses. Be well.