Spasticity is a condition of excess tone in a body part. In this case, presumably in your leg. Spasticity may manifest as reduced function of an extremity or inability to get full range of motion at a certain joint, in this case your knee. Spasticity is considered a disorder of increase tone in muscle groups which is related to a dysfunction of the central nervous system, i.e., the brain or the spinal cord. In your case, there should not be any affliction of either, given than your problem area was the knee joint, that required replacement. In short, you should not have "spasticity" in your leg from knee joint replacement. Needless to say you should see your orthopedic surgeon and a physical therapist to convey your concern. Best wishes.