Manipulation under Anesthesia (MUA):
When aggressive physical therapy fails, the next step is manipulation under anesthesia (MUA). It is preferably done under general anesthesia and muscle relaxation. Other types of anesthesia like regional anesthesia are infrequently used for manipulation. MUA is considered when the range of motion after knee replacement does not progress satisfactorily, reaches a plateau or deteriorates.
The timing of MUA is debated. Investigators have suggested that the MUA is effective when it is done between 6 and 12 weeks after knee replacement. MUA before 3 weeks has a higher risk of rupturing the surgical wound and opening the knee joint (traumatic arthrotomy). But, if the MUA is performed solely to improve flexion contracture, it may be done in the immediate post-operative period. The interval between two MUAs in patients undergoing more than one MUA is also controversial. The scar tissue progressively matures and becomes resistant to physical therapy with time. The benefit of MUA progressively declines and has a higher complication rate after 12 weeks.
The complications of MUA include rupture of ligaments and tendons, fracture of bones around the knee (femur, tibia, patella) and others.
Injecting medicine into the knee joint (intra-articular injection) at the time MUA has synergistic effect. The injection usually contains a mixture of long acting steroid and a long acting numbing medicine (local anesthetic).
Cast / Brace / Splint Application:
In patients with inability to bring the knee fully straight (flexion contracture), repeated MUA and application of a cast with the knee as straight as possible (serial manipulation and casting in extension) is helpful. Application of a cast with the knee fully straight for a prolonged period has a deleterious effect on the ability to bend the knee (range of flexion).
Braces are helpful in bringing the knee fully straight (extension). Braces could be removed at the time of physical therapy for range of flexion exercises and it can be worn at other times and at night (night extension splint). Various types of static and dynamic braces are available.