ACL and shin pain

I had ACL reconstruction 18 mths ago and have made very slow progress to date,primarily due to poor range of movement,pain and stiffness.
Arthrofibrosis has been dismissed by the surgeon and after warm ups and exercises I can increase the ROM significantly, but it soon stiffens if I try and force flex it or rest or stand immobile for a while.

The pain is severe and goes down the front of my shin (along lateral dorsal aspect)and may extend behind the knee, slightly lateral to the midline and occasionally it goes up the hamstring and feels like my leg will snap beyond that point.The point at which pain arrives depends on wether I have warmed up with exercises and gradually increasing squats.If I try and squat or force flex without any warm up and stretching, the pain arrives with perhaps only 70 degrees of flexion but with the warm up ROM before pain, increases a great deal.

I have had Ant comp syndrome and the pathway of pain does seem to involve ant tibialis and possably the peroneal nerve pathway.

Appreciate your input
atb
H