I had an unsuccessful PCL reconstruction many moons ago. The surgeon had to remove the medial meniscus (cartilage) so post-op I had very poor mobility. I have attended re-hab many times and have found that the one thing that seems to work is aqua-jogging. This is done with the asistance of a polystyrene belt (a must otherwise you'll probably drown). Put the belt on, go in the deep end, stay upright and run. You will not move very quickly but there is no impact on your knee, you are using the quads and hamstrings fully as well as having a cardio-vascular workout. This will improve the mobility greatly. Hope it works. Tony