First off, where are you based?? I am guessing the UK like myself?
Anyway.....I am staggered by the "protocol" that your surgeon has used.....is he a general orthopaedic surgeon (NHS?).....as this seems very likely?
What exactly was his thinking behind keeping your leg bent at 10 degrees in a cast for three weeks??
Most surgeons are keen for ACL recon patients to regain full ROM ASAP. Also, a knee surgeon that I know personally has his patients up and weightbearing a few days after the ACL operation (or as soon as they are able).
Passive motion of the joint is VITAL in order to keep it from "seizing up" and developing other complications like flexion contractures and so forth...
Also...it's rather strange that you can only extend to 10 degrees from being straight ....adn you were made to wear a pot for three weeks at 10 degrees off full extension
I had a similiar problem though for a different operation. I tore my lateral meniscus big time playing football and it displaced into the intercondylar notch in my knee. This meant PAIN and that my leg was totally locked between -30 degs extension and a max of 90 degs flexion.... Unfortunately as as I am UK based the NHS took 4 weeks of visits, persuasion etc to actually do the "emergency" operation as they put it
End result......a load of sutures to repair my meniscus and a Looong recovery!
It took me 6 weeks to be able to fully turn a stationary bike pedal and a bit longer to get full extension back as my leg had been locked essentially (No way could I walk etc) except for 60 degs. 7 months on I STILL have some stiffness at FULL extension (postero lateral corner eg/ back right side of my knee!) which my surgeon believes is tethering of the structures near the op site due to minor scar tissue from the op.
It is unfortunately quite possible that you have arthrofibrosis (even if not very severe?)
As ACL recons are known common causes for this condition due to bleeding into the joint from the op and general trauma. This is why nearly ALL surgeons encourage even just Passive ROM exercises (some a lot more than this) to try and keep the joint moving freely......so I can see why you have lost faith in your surgeon....
If I were you I would do some serious reading on the "soft tissue" section of this site (in addition to this "cruciates" section) to find out more about arthrofibrosis.There are some great posts on the subject that will help you learn a lot about it (HeatherM has some VERY informative posts).....as it's not something to be trifled with or left alone unchecked as it can irreperably alter the fundamental mechanics of the knee joint if it's not treated correctly and in time.
The fact that your muscles and other structures may have contracted somewhat during the time you were in a cast after the op is quite likely so could be a partial or even total cause of your extension problems??
Rolfing (a very specialist technique for bodily structure realignement and integration) might be well worth a try to see if it helps your leg. Check this link out below and if you decided to do just locate a QUALIFIED practitioner in your area.http://www.rolf.org/about/
Hope this helps you out a bit
All the best