One way to avoid prolonged period of rest is to undergo an operation for fixation of your fracture and that way you can move your knee sooner.
If you have been treated by plaster cast, then there would be a tendency for quadriceps atrophy - thigh getting thinner.
You should start on quadriceps isometric exercises. Also you should start with gentle range of motion otherwise you might end up with a stiff knee. You should do physical therapy under supervision, so that adequate program is initiated.
Once stretching is done and you have attained a good range of motion, then strengthening with weights should be initiated. Thus, there has to be a phasic rehabilitation program to get you going.