Sit up straight with your buttocks to the edge of the chair.
Lift your unaffected foot off the ground and keep it in front of you.
Try to do this exercise without using your hands.
Keeping your affected knee in line with your toes, stand up by pushing down through your foot until you are completely upright.
Hold this position and then gradually sit back down.
Control this movement and then repeat.
Make sure your knee always points directly in front of you.