The time to start knee flexion exercises after knee surgery varies from one week after surgery to six weeks after surgery, depending on the type of knee surgery. When a knee fracture is fixed with a secure fracture, functional exercises can be done the day after surgery. If the knee was a total knee replacement, passive knee flexion exercises can also be done the day after surgery. However, if the knee was operated on with ligamentous sutures, such as ligament rupture or ligament reconstruction, the knee needs to be immobilized in a cast for at least four weeks, and the cast should be removed before functional exercises can be performed. If the knee is fractured, the fracture is severely broken and the fixation is relatively poor, you may need a month and a half of fixation before you can do functional exercises.