Being able to stretch your knee again is one of the most important goals during the first phase of rehabilitation after anterior cruciate ligament surgery. This is often related to being able to properly tighten and use your upper leg muscles (quadriceps) If this is not successful in the first few weeks of your rehabilitation, it can be a predictor of further complications in rehabilitation such as a cyclops (scar tissue formation) in the knee. Read all about extension limitation after knee surgery here Stretch restriction after knee surgery - PhysioFitaal