Physical therapy is usually the first line of treatment when stiffness after total knee replacement (TKR) occurs. Have you tried splinting of any kind? A dynamic splint applies a low load, prolonged stretch on contracted soft tissues. The goal is to promote long-term ROM gain.
If physical therapy and splinting don't reduce stiffness and improve motion, then surgery may be needed. There are several choices here. The first is the removal of scar tissue using an arthroscope. This long needle-shaped tool has a tiny TV camera on the end. It allows the surgeon to work inside the joint without making a large cut into the joint.
Manipulation of the joint is another option. Under anesthesia while the patient is relaxed, the surgeon moves the joint through all its motions. This breaks any adhesions holding the joint from gliding and moving.
The final choice is to replace the implant. This is called a revision. The surgeon
may replace part or all of the implant. It depends on how things look when the joint is examined from the inside.