Any condition of the knee that causes swelling or loss of range of motion in the knee will have a knock on effect to the strength of your knee muscles. No-one is entirely sure why but the knee particularly if swollen causes wasting of the Quadriceps which are the main knee muscles.
If you have stiffness and loss of full range this is also very important for the function of the knee.
These simple exercises will help you regain full range of motion.
Extension
1. Place a rolled up towel or a pilates roll under your heel. Then push down hard with your muscles then let the knee bent slightly and then push down again. You can also help push down a bit with your hands.
2. When sitting you can pop your ankle up on a stool and let the knee sag down and encourage it with your hands pressing down.
If you are lacking extension you can sit in this position( as above) and place a weight over the knee to stretch it out.
Use a pair of oven gloves and put a weight in each glove. Sit in this position for 20-30 minutes.
Flexion/Bending the Knee
If your knee is not bending fully depending on what age you are and what positions you can adopt there are a variety of exercises you can do.
1. Lie flat on the bed and slide your heel up the bed towards your buttocks.
You can then try and pull it further in with your hands.
2. Lie on your tummy and bend the stiff knee as far as you can. Then with the other foot push it further.
3. Sit in a chair- slide your bad leg back under the chair as far as you can and then use the heel over the other foot to push it back further.
4. This exercise can only be done in those agile enough to get down on to all fours.
From this position slowly move your trunk and hips backwards i.e towards sitting on your heels to stretch the knees into further flexion.