Been off MT for a while...hanging mostly over at Kenpotalk, and not even there that much. I've been spending my time reviewing my Goju and Shotokan forms with Kenpo eyes and just working on getting back into something that resembles "in-shape."
Providing there was no significant soft tissue damage, distraction through normal full range of motion is a very effective way to treat cases of traumatic hyperextension. My recommendation would be to find a physician/therapist that knowledgeable in extra-spinal traction techniques. The stiffness that you are experiencing is likely due to inflammation of the soft tissue within the knee joint, and distraction through full range of motion helps to "milk" the fluid accumulation out of the knee.
MT1, I study Moo Duk Kwan Taekwondo, and have done so for the past 25 years. I have trained with martial artists from other styles (Bando, Silat, Shorei-ryu, Shorin-ryu, Isshinryu, Yoshikai, Shotokan, Aikido, and Jujutsu) but I have never studied any art in depth other than Moo Duk Kwan TKD.