Scar Tissue after Knee Replacement

My father (age 58) has continued pain and inflexibility after a total knee replacement last spring.  He has underwent manipulation under anesthetic to break up the scar tissue and is currently undergoing intensive therapy.

The problem seems to be the continued build-up of the scar tissue. At times the knee is hot and swollen, and he is always in pain.

Any suggestions for what can be done? He, his doctor and his therapist all are becoming frustrated. He has been in therapy for months now. Additionally, he is overweight, has diabetes, and has arthritis in the knee.  He has also had the other knee partially replaced and it is now starting to give him pain as well.

We would greatly appreciate any advice anyone may have. Thank you